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HYPOTHERMIA: PART I Jassin M. Jouria, MD Dr. Jassin M. Jouria is a medical doctor, professor of academic medicine, and medical author. He graduated from Ross University School of Medicine and has completed his clinical clerkship training in various teaching hospitals throughout New York, including King’s County Hospital Center and Brookdale Medical Center, among others. Dr. Jouria has passed all USMLE medical board exams, and has served as a test prep tutor and instructor for Kaplan. He has developed several medical courses and curricula for a variety of educational institutions. Dr. Jouria has also served on multiple levels in the academic field including faculty member and Department Chair. Dr. Jouria continues to serves as a Subject Matter Expert for several continuing education organizations covering multiple basic medical sciences. He has also developed several continuing medical education courses covering various topics in clinical medicine. Recently, Dr. Jouria has been contracted by the University of Miami/Jackson Memorial Hospital’s Department of Surgery to develop an emodule training series for trauma patient management. Dr. Jouria is currently authoring an academic textbook on Human Anatomy & Physiology. ABSTRACT When the human body becomes too cold to spontaneously rewarm itself through normal metabolic procedures, hypothermia occurs. Hypothermia can range from mild to severe and its symptoms include mental confusion, slow heart rate, and even death. Since an extreme low core body temperature can suppress heart and brain function, hypothermia treatment protocols vary from the treatment of other heart- and brain-related incidents. This course, Part 1 of a 2-part series, provides a detailed explanation of hypothermia and field treatment protocol. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 1 Continuing Nursing Education Course Planners William A. Cook, PhD, Director, Douglas Lawrence, MA, Webmaster, Susan DePasquale, MSN, FPMHNP-BC, Lead Nurse Planner Policy Statement This activity has been planned and implemented in accordance with the policies of NurseCe4Less.com and the continuing nursing education requirements of the American Nurses Credentialing Center's Commission on Accreditation for registered nurses. It is the policy of NurseCe4Less.com to ensure objectivity, transparency, and best practice in clinical education for all continuing nursing education (CNE) activities. Continuing Education Credit Designation This educational activity is credited for 4 hours. Nurses may only claim credit commensurate with the credit awarded for completion of this course activity. Statement of Learning Need Hypothermia is a leading cause of death in several United States regions. Cases of profound hypothermia and devastating consequences have been well documented in the pre-hospital setting. New criteria to determine exposure, prognosis, even death, and critical treatment modalities is important for nurses to know when dealing with life-threatening situations. Course Purpose To provide professional nurses with advanced learning of hypothermia and critical interventions to support survival. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 2 Target Audience Advanced Practice Registered Nurses and Registered Nurses (Interdisciplinary Health Team Members, including Vocational Nurses and Medical Assistants may obtain a Certificate of Completion) Course Author & Planning Team Conflict of Interest Disclosures Jassin M. Jouria, MD, William S. Cook, PhD, Douglas Lawrence, MA Susan DePasquale, MSN, FPMHNP-BC – all have no disclosures Acknowledgement of Commercial Support There is no commercial support for this course. Activity Review Information Reviewed by Susan DePasquale, MSN, FPMHNP-BC Release Date: 7/18/2016 Termination Date: 7/18/2017 Please take time to complete a self-assessment of knowledge, on page 4, sample questions before reading the article. Opportunity to complete a self-assessment of knowledge learned will be provided at the end of the course. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 3 1. The normal adult temperature ranges from 36-38°C, depending on many internal factors such as: a. b. c. d. Wind movement Circadian rhythm Humidity Nature of surrounding environment 2. Which of the following neuronal effector mechanisms activated by cold stimuli increase heat production? a. b. c. d. Shivering Cutaneous vasodilation Piloerection Humidity Sweating 3. Which clinical findings can be seen in patients with mild hypothermia? a. b. c. d. Diminished shivering Slow stretch reflexes Stiff muscles and joints Cold-induced diuresis 4. Which mechanism of environmental heat loss is exemplified by the dissipation of up to 50 percent of the body’s heat through an uncovered head? a. b. c. d. Convection Conduction Radiation Evaporation 5. Which mechanism of environmental heat loss is exemplified by excessive sweating? a. b. c. d. Convection Conduction Radiation Evaporation nursece4less.com nursece4less.com nursece4less.com nursece4less.com 4 Introduction Hypothermia is defined as a pathologic condition wherein the core body temperature is less than 35°C. It is the opposite of hyperthermia, wherein the body experiences elevated core temperature due to failed thermoregulation. Hypothermia is due to a cold stressor that overwhelms the body’s thermoregulatory mechanisms and represents a potential medical emergency. It may be classified by its degree, mild, moderate or severe; or, by its cause, accidental or intentional (therapeutic). In this course, accidental hypothermia is the focus of discussion. There is always a greater incidence of hypothermia in cooler climates; however emergency medical service providers and other health professionals must be able to recognize it even in patients on ambient temperatures. Early recognition of hypothermia and treatment is very critical. Patients with signs and symptoms of hypothermia must be brought to the hospital as soon as possible. Here, the pathophysiology of hypothermia is discussed as well as its field assessment, pre-hospital management and treatment measures, and possible complications. It is important for nurses and paramedics to be able to identify the signs and symptoms of hypothermia and treat it accordingly prior to the arrival of the patient in the hospital or during the pre-hospital care of hypothermic patients. Background In the United States., hypothermia is often caused by prolonged exposure to external cold temperatures, especially in the winter. The reported cases of hypothermia reflect those that have resulted in emergency room visits, although this is not the true number. Nevertheless, the number of reported cases for hypothermia is increasing, due to growing interest in winter activities, as well as personal issues with alcoholism, mental illness, and homelessness. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 5 The Centers of Disease Control and Prevention (CDC) published statistics of reported hypothermia cases in areas that experience severe weather, although other areas with milder winter climates also experience such cases regularly.1 This is particularly true in milder areas that are subject to rapid weather changes on a daily basis. Based on the latest U.S. data, the highest rates of hypothermia occurred in the Midwest and Northwest regions with Alaska, Maine and Montana having the highest annual rates of hypothermia cases requiring hospital treatment.2 In urban areas, hypothermia rates are highest among those that are overly exposed to external cold due to alcoholism, illegal drug use, or psychiatric illness, combined with homelessness. On the other hand, hypothermia also occurs a lot among those who frequently engage in outdoor activities such as climbers, swimmers, rafters, hunters, and campers. Although they happen, deaths due to hypothermia are relatively uncommon. The report of one study found that the total inpatient of hypothermic individuals occurring in the coldest regions of the U.S. is about 12 percent.2 Deaths tend to result from moderate and severe hypothermia, with significant mortality rates despite hospital-based treatments. Hypothermia-related deaths for the U.S. in the most recent CDC report indicated annual rates ranging from 0.3 to 0.5 per 100,000 persons, which represented a significant increase of reported cases.1 The majority of people can tolerate mild drops in core body temperature (i.e., less than <95°F or 35°C core body temperature) relatively well, which do not result in significant morbidity or mortality. On the other hand, moderate hypothermia has been found to be associated with a higher patient mortality rate. As mentioned previously, deaths are more likely to occur with severe hypothermia. This is especially true for patients with comorbid illness, advanced age or with positive blood alcohol levels. Other risk factors for deaths due to moderate and severe hypothermia are also due to homelessness and mental illness and addiction disorders.1,2 nursece4less.com nursece4less.com nursece4less.com nursece4less.com 6 According to latest estimates in the U.S., between 2003–2013, there was a total of 13,419 hypothermia-related deaths with unadjusted annual rates ranging from 0.3 to 0.5 per 100,000 persons. During the ten-year period, male victims accounted for 67%; and both males and females aged ≥65 years accounted for 1.8 and 1.1 per 100,000 population, respectively. Ten percent of reported deaths from hypothermia had alcohol or drug poisoning as a contributing factor.1 Pathophysiology In order to understand the pathophysiology of hypothermia, one must understand the thermoregulatory mechanisms of the human body. This section discusses physiological processes and external factors influencing how individuals respond to freezing conditions.1-4 Thermoregulation ensures that the body maintains its normal core body temperature of about 37°C. This temperature is also the set point, which means that temperatures below or above 37°C can seriously harm the body by affecting its physiological mechanisms. The normal adult temperature ranges from 36-38°C, depending on many internal factors, such as: Circadian rhythm Monthly menstrual cycle (females) Exercise Area of measurement (oral, esophageal, maxilla, rectal) The core body temperature, such as esophageal and rectal, is normally 0.5°C greater than the oral temperature. Due to the circadian rhythm, it also fluctuates more or less 0.6°C between the morning and evening. The core temperature is highest during the evenings and lowest during the mornings. Women also experience core body temperature changes during their monthly menstrual cycle. It increases by 0.5°C during ovulation and falls back to nursece4less.com nursece4less.com nursece4less.com nursece4less.com 7 normal when menstruation begins. It also increases during exercise, rising to as high as 40°C and falling back to normal after exercise. When an individual is exposed to cold air in the external environment, the rate and degree of decrease in the body temperature depends on the following external factors: Wind movement of the air Humidity The nature of the surrounding environment This means that generally speaking, a nude individual exposed to dry air between 13-54°C can maintain a normal body temperature ranging from 3637.7°C. This is only true for dry air since greater wind movement and humidity can exacerbate the sensation of coldness in the air. Physiological functions including metabolism dependent, which means that and thermoregulation are temperature they only occur when the core body temperature is at its set point or normal level. The balance between heat loss and heat production (thermogenesis) determines the normal level of body temperature or set point. Two regions of the hypothalamus, the posterior region and the anterior region, control thermoregulation. These regions play a unique but mutually coordinated role through a feedback mechanism. The posterior pituitary region is concerned with heat maintenance. It contains a large number of cold-sensitive nerve cells. These cells act as cold sensors and are stimulated by the brain cortex when the body comes into contact with a cold stimulus. Once the cold sensation is registered, neuronal effector mechanisms that produce heat and reduce heat loss are activated. One example is the increase in firing rate of these neurons. Other examples are outlined in the table below. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 8 Posterior hypothalamic lesions can severely interfere with thermoregulation. For example, a patient can become severely poikilothermic (temperature tends to fluctuate), which is followed by a very low body temperature. On the other hand, the anterior pituitary region is concerned with heat loss. It contains a greater number of heat-sensitive neurons which also act as sensors. An elevated blood temperature above the set point is what stimulates these cells. Once an abnormally high intravascular heat level is registered, neuronal effector mechanisms that increase heat loss and decrease heat production are activated. One example is the two- to ten-fold increase in the firing rate of these nerve cells. Other examples are outlined in the table below. Anterior hypothalamic lesions can also severely interfere with thermoregulation. For example, a patient can become severely warm, with a core body temperature reaching up to 43°C. Activated Mechanisms in Response to Cold Stimuli ↑ Heat production Shivering Increased muscular activity Hunger Increased TSH release Increased epinephrine release Increased norepinephrine release ↓ Heat loss Cutaneous vasoconstriction Piloerection Behavior modification (i.e., building fire) Thermoreceptors Aside from the hypothalamus and the sensory neurons in the brain, there are also other thermoregulatory parts of the body. The most notable of these are thermoreceptors found in the skin. The skin contains both cold and warmth receptors. The number of cold receptors is ten times more than the warmth or nursece4less.com nursece4less.com nursece4less.com nursece4less.com 9 heat receptors. As a result, peripheral recognition of temperature is primarily focused on detecting cool and cold instead of warm temperatures. When the cold stimulus is encountered, immediate reflex effects are stimulated and initiate the increase in body temperature through: Provision of a strong stimulus to cause shivering to increase body heat production. Inhibition of sweating. Promotion of cutaneous vasoconstriction to reduce heat loss from the skin. Other body thermoreceptors are located primarily in the spinal cord, abdominal soft tissues, and in or around the major veins in the upper abdomen and thoracic cavity. These receptors help to regulate body temperature differently from the skin receptors. Essentially, they detect cold stimuli within the internal body instead of the body surface. Neuronal effector mechanisms activated by cold stimuli are outlined in the table below. Activated mechanisms in response to heat stimuli ↓ Heat production Decreased activity Anorexia Decreased TSH release Decreased epinephrine release Decreased norepinephrine release ↑ Heat loss Cutaneous vasodilation Sweating Behavior modification (i.e., take off clothing) The blood vessels just below the surface of the skin dilate in response to heat stimulation. Vasodilation is caused by inhibition of the sympathetic centers in the posterior hypothalamus, which is the same center that nursece4less.com nursece4less.com nursece4less.com nursece4less.com causes 10 vasoconstriction. Complete vasodilation speeds up the rate of heat transfer to the skin by about eight-fold. Sweating is the response to increased body temperature above the critical level of 37°C in an effort to speed up the rate of evaporative heat loss. A 1°C increase in body temperature is enough to cause profuse sweating to eliminate 10 times the basal rate of body heat production. A decrease in heat production is the result of the inhibition of the mechanisms that cause excess heat production, such as shivering and chemical thermogenesis. Heat production and loss is further illustrated below. Shivering The major motor center for shivering is found in the dorsomedial area of the posterior hypothalamus close to the wall of the third ventricle. The region is inhibited by warmth signals from the heat center in the anterior hypothalamicpreoptic area and excited by cold signals from the skin and spinal cord. In fact, the region is very sensitive to temperature depressions that are easily activated when the temperature drops even a fraction of a degree below the critical temperature level. Once activated, it relays signals that cause shivering through bilateral tracts on the brain stem, into the lateral columns of the spinal cord, and finally to the anterior motor neurons. These signals increase the tone of all skeletal muscles of the body by facilitating the activity of the anterior motor neurons. When the tone rises above a certain critical level, shivering begins. During severe shivering, thermogenesis can increase up to four to five times the normal. Chemical Thermogenesis Greater sympathetic stimulation or number of the chemical neurotransmitters norepinephrine and epinephrine in the circulation can trigger an instantaneously speed up cellular metabolism. This is called chemical thermogenesis. Its occurrence is a partial result of the uncoupling of oxidative phosphorylation by these two neurotransmitters. This means that surplus nursece4less.com nursece4less.com nursece4less.com nursece4less.com 11 foodstuffs are converted and released into energy in the form of heat without causing adenosine triphosphate (ATP) to be formed. High levels of circulating thyroxine may also stimulate chemical thermogenesis. Set Point for Temperature Control The intensity of chemical thermogenesis that happens in the body is approximately directly proportional to the amount of brown fat in the tissues. Brown fat is heavily populated with special mitochondria, the cellular organelle where uncoupled oxidation takes place. Brown fat also has a rich supply of sympathetic nerves, which secrete norepinephrine, in turn triggers the expression of thermogenin and increases thermogenesis. Acclimatization has profound effects to the degree of chemical thermogenesis. For example, a rat that has been exposed to a cold environment for long periods show a 100 to 500 percent increase in thermogenesis when severely exposed to cold. In contrast, a rat that is unacclimatized and exposed to the same cold stimuli responds with only one-third increase in thermogenesis. Consequently, the animal also experiences an increase in food intake. Adult humans, on the other hand, have almost no brown fat. Therefore, it is exceptionally uncommon for chemical thermogenesis to speed up the rate of heat production more than 10 to 15 percent. However, infants have a small amount of brown fat in the interscapular space. Because of this, chemical thermogenesis can speed up heat production to as much as 100 percent. This is a significant factor in keeping normal body temperature in neonates. Effects of Thyroxine Output on Heat Production As mentioned previously, thermogenesis is triggered by the presence of cool stimuli. A cool stimulus stimulates activity within the anterior hypothalamus, increasing the production of the metabolic hormone thyrotropin-releasing hormone (TRH) in the region. Once produced and released nursece4less.com nursece4less.com nursece4less.com nursece4less.com by the 12 hypothalamus, it is transported to the anterior pituitary gland via the hypothalamic portal veins. There, the hormone stimulates the secretion of thyroid-stimulating hormone (TSH), which speeds up cellular metabolic activity. Thyroid-stimulating hormone (TSH) speeds up metabolic activity by increasing the thyroxine secretion by the thyroid gland. The large number of circulating thyroxine activates uncoupling protein and speeds up metabolism in all cells of the body. This mechanism is also called chemical thermogenesis. However, the increase in cellular metabolic activity does not happen instantaneously, rather, it requires long periods of exposure to cold. Usually, several weeks of exposure to cold stimuli results in thyroid gland hypertrophy, allowing for greater secretion of the thyroxine hormone. However, since humans have the natural instinct to avoid this degree of cold exposure, the quantitative extent to which the increase in the thyroid gland size contributes to the human adaptation to cold remains uncertain. Other animals that are exposed to extreme cold for several weeks also experience a 20-40 percent hypertrophy of their thyroid glands. Studies have found that military personnel assigned to the Arctic for a period of several months develop increased metabolic rates. Inuit-Yupik (Eskimos) have also been found to have unusually elevated basal metabolic rates. Additionally, it is believed that the effects of constant cold stimulation to the thyroid gland are partially responsible for the greater frequency of toxic thyroid goiters in such individuals and others who reside in cold climates. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 13 As explained previously, a body core temperature of above or below 37.1°C can result in severe alterations to the thermoregulatory mechanisms, affecting both heat loss and heat production. Temperatures above this level result in rapid heat loss that is greater than heat production, which eventually leads to its decline until it reaches the set point again. Alternatively, temperatures below this level result in rapid heat production that is greater than that of heat loss, which eventually leads to its elevation until it reaches the set point again. Ultimately, the thermoregulatory mechanisms in the body continually attempt to bring the body core temperature back to this set-point level. Feedback Gain Feedback gain is used to measure the effectiveness of the thermoregulatory system. It is crucial for the internal core temperature to remain constant at all times amid fluctuations in the temperature of the external environment. The feedback gain of the thermoregulatory system is equal to the ratio of the change in environmental temperature to the change in body core temperature minus 1.0. The formula for feedback gain is given below: Feedback gain = ∆ environmental temperature -1 ∆ body core temperature Results of experiments involving humans show that body temperature changes about 1°C for every 25-30°C change in the temperature of the external environment. Effects of Internal Temperature The temperature set point in the hypothalamus is determined mainly by the intensity of activity of the heat thermoreceptors in the anterior hypothalamus. However, temperature signals from other parts of the body, such as the skin and spinal cord tissues and abdominal viscera also contribute partially to body nursece4less.com nursece4less.com nursece4less.com nursece4less.com 14 temperature regulation by altering the set point of the hypothalamic thermoregulation center. The set point increases as the skin temperature decreases. This means that when the skin temperature is high, sweating begins at a lower hypothalamic temperature compared to when the skin temperature is low. This is especially important to prevent excessive loss of body heat. A similar effect happens in shivering. When the skin encounters cold stimuli, the hypothalamic centers are activated towards the shivering threshold even when the hypothalamic temperature may be normal. This is especially important because a cold skin temperature can result in severely depressed body temperature unless heat production is increased. Local Cutaneous Temperature Reflexes When an individual puts a foot under a hot lamp and leaves it there for a few minutes, local capillaries dilate and mild local sweating occurs. Alternatively, when a foot is placed in cold water, local vasoconstriction and local cessation of sweating occur. Both reactions are caused by local effects of temperature changes directly on the blood vessels and also by local cord reflexes that run from skin receptors to the spinal cord and back to the same skin cutaneous region and the sweat glands. The intensity of these local effects is, in addition, controlled by the central brain temperature controller, so their overall effect is proportional to the hypothalamic heat control signal times the local signal. Such reflexes can help prevent excessive heat exchange from locally cooled or heated portions of the body. Behavioral Modification Aside from the autonomic mechanisms in thermoregulation, the body can also control body temperature through behavioral modification. When the internal body temperature increases significantly, signals from the anterior and posterior hypothalamus sends out a psychic sensation of overheat. On the other hand, when the body temperature drops too low, signals from the skin nursece4less.com nursece4less.com nursece4less.com nursece4less.com 15 and visceral tissue receptors draw out the feeling of cold discomfort. Consequently, the individual makes proper environmental adjustments to restore comfort, such as building a fire, turning on the heater, or putting on warmer clothing in cold weather. This voluntary behavior modification is a powerful mechanism of thermoregulation that most physiologists believe to be an evolved human survival response. In fact, this is the only effective mechanism that retains body heat in extremely cold environments. Classification of Hypothermia Hypothermia is defined as a core body temperature below 35°C. Traditionally, it’s been classified as discussed below:1 Mild hypothermia: a body core temperature between 32-35°C, Moderate hypothermia: a body core temperature between 28-32°C, and Severe hypothermia: a body core temperature below 28°C. Mild Hypothermia When the core temperature drops by 0.7°C, mild hypothermia ensues and is manifested by shivering. It also results in the increase of the metabolic rate by up to 5 times. When the core temperature drops down further to 32°C, the individual may shiver uncontrollably. The severe fall of core temperature also produces cutaneous vasoconstriction, tachycardia, greater cardiac output, increased plasma catecholamine levels, cold-induced diuresis and hyperglycemia. If glycogen stores in the liver are exhausted, hypoglycemia may occur which inhibits shivering. In addition, the plasma levels of thyrotropin releasing hormone (TRH), triiodothyronine (T3), L-thyroxine (T4), growth hormone, thyroid-stimulating hormone (TSH) and adrenocorticotropic hormone (ACTH) stimulation tests remain normal, all of which indicate a normal pituitary, adrenal and thyroid function during mild hypothermia. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 16 Moderate Hypothermia When the core temperature drops below 33°C, shivering slowly diminishes, replaced by stiff muscles and joints and a delayed relaxation phase of the stretch reflexes. If left untreated, the individual exhibits signs of lethargy and drowsiness. Unconsciousness rarely happens at temperatures greater than 28°C, which is why other potential causes of coma should be investigated if coma exists. The pulse, blood pressure and respiratory rate are usually low. Severe Hypothermia When the core temperature falls below 30°C, the individual becomes poikilothermic and it is unable to spontaneously return to the set point. In these cases, active re-warming must be initiated. At temperatures below 28°C, the patient loses consciousness and reflexes, and there is a faint pulse. The patient may also exhibit with fixed and dilated pupils. Bradycardia and atrial fibrillation occur at temperatures below 30°C and ventricular fibrillation can occur at temperatures below 28°C. At 20°C, asystole is seen more than ventricular fibrillation. Respiratory depression may occur along with bronchorrhea. Pulmonary edema is uncommon. Circulatory arrests for 10 minutes at 30°C, 25 minutes at 25°C, 45 minutes at 20°C and 60 minutes at 16°C are the frequently used limits for cerebral function to return to normal; although, studies suggest that these limits can go higher. Outlined in the table below is the summary of the traditional classification of hypothermia and their characteristic clinical findings and vital signs. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 17 Degree of Core Temperature Clinical Findings and Vital Signs Hypothermia Uncontrolled shivering Mild 32°C to 35°C Cold-induced diuresis Hyperglycemia Tachycardia Diminished shivering Moderate 28°C to 32°C Stiff muscles and joints Slow stretch reflexes Lethargy and drowsiness Unconsciousness Ventricular and atrial fibrillation Lost reflexes Severe -28°C Fixed and dilated pupils Bradycardia Asystole Respiratory depression Bronchorrhea The classification of hypothermia has recently been revised using the Swiss staging system. Its classification is based on vital signs. Outlined in the table below is the Swiss staging system of hypothermia and their corresponding clinical findings and vital signs. Staging Core Temperature Range Clinical Findings and Vital Signs HT I 35°C to 32°C HTII <32°C to 28°C Impaired consciousness, not shivering HT III <28°C to 24°C Unconsciousness, not shivering, vital signs Conscious, shivering present HT IV <24°C No vital signs nursece4less.com nursece4less.com nursece4less.com nursece4less.com 18 Mechanism of Environmental Heat Loss As mentioned previously, cellular metabolism is primarily responsible for heat generation. The metabolism of food and water, muscular activity, and biological chemical reactions all contribute to thermogenesis. Environmental heat loss occurs via several different mechanisms, which include: Radiation: Radiation accounts for more than 50 percent of heat loss. It occurs under dry conditions. A good example of heat loss through radiation is the dissipation of up to 50 percent of the body’s heat through an uncovered head. Conduction: Conduction accounts for about 15 percent of heat loss. The direct transfer of heat to a nearby object that is cooler than the body is a very common cause of accidental hypothermia. The heat lost is only a small fraction but wet clothing causes a twenty-fold increase in heat loss. Conversely, submersion in cold water increases heat loss by as much as thirty-fold. In fact, conduction is an important mechanism of heat loss in drowning or immersion accidents. Convection: Convection also accounts for approximately 15 percent of heat loss. The heat transfer occurs when the air movement creates loss of the warm layer of heat near the body; and, the degree of heat loss is dependent on the speed of the wind. A good example is a wind traveling 12 mph, which increases heat loss by as much as five-fold. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 19 Evaporation: Evaporation accounts for approximately 20 percent of heat loss. Heat is lost when liquids are converted into gas. One good example is sweating and respiration wherein the consequent evaporation of water will cool the body at the rate of 0.6 kcal per gram. Hypothermia also causes cellular membrane disruption, allowing intracellular fluid to leak out, and enzymes to start malfunctioning. Consequently, electrolyte imbalance occurs, particularly hyperkalemia. The intra- and extracellular water begins to crystallize resulting in cellular death, if not alleviated in time. During hypothermia, the hypothalamus tries to stimulate thermogenesis through shivering and chemical means (i.e., increase catecholamine secretion and adrenal activity). To minimize heat loss, blood flow to the peripheral tissues is reduced through vasoconstriction. Hypothermia has profound effects on almost all organ systems. These effects are particularly significant in the cardiovascular system and the central nervous system (discussed later in the course). Hypothermia results in reduced depolarization of cardiac pacemaker cells, resulting in bradycardia. Because the vagal nerve does not mediate it, this form of bradycardia can be refractory to standard therapies such as atropine. In addition, mean arterial pressure and cardiac output decline, and an electrocardiogram may exhibit the characteristic J or Osborne waves. Although the wave is especially seen in hypothermic individuals, it may be a normal variant as seen sometimes in sepsis and myocardial ischemia. Causes And Risk Factors Of Hypothermia The external environment presents with several precipitating factors such as an acute exposure to cold in an otherwise previously fit individual, a relatively brief exposure to mild cold during an ongoing illness such as sepsis, or nursece4less.com nursece4less.com nursece4less.com nursece4less.com 20 inactivity after a fall. A previously fit and young individual with hypothermia generally has a good prognosis in the absence of circulatory arrest. Factors and predisposing causes mentioned in preceding sections are outlined in the table below and discussed in more detail here.1-5 FACTORS EXAMPLES Environment Time of the year Ambient temperature Wind chill Water chill Humidity Behavior Inadequate or wet clothing Immersion Prolonged exposure Fatigue Lack of physical fitness Inadequate shelter and heat Drugs Alcohol Nicotine Opiates Barbiturates Benzodiazepines Tricyclic antidepressants Phenothiazines Impaired hypothalamic thermoregulation Very old age CNS trauma Stroke Wernicke’s encephalopathy Burns Sepsis Acute myocardial infarction Chronic renal failure Neoplasms Pancreatitis Decreased heat production Hypothyroidism Hypoglycemia Anorexia nursece4less.com nursece4less.com nursece4less.com nursece4less.com 21 Adrenal insufficiency Hypopituitarism Older age Reduced lean body mass Impaired mobility Reduced shivering mechanism Inadequate diet Comorbidities such as sepsis, diabetes mellitus In a study of 85 consecutive hypothermic patients at San Francisco General Hospital, it was found that a coexisting infection was the primary cause in 33 of them, and alcohol ingestion in 27 of them. In fact, environmental exposure accounted for only 9 cases. About 50 percent of these hypothermic patients died. As already mentioned, hypothermia is a failure of thermoregulatory control. Several factors and predisposing causes are attributed to its development including the external environment, old age, acute and chronic diseases and disorders, and pharmacological agents. Decreased Heat Production Endocrine dysfunctions are known causes of decreased heat production. These include hypopituitarism, adrenal insufficiency, and hypothyroidism. These endocrine disorders must be considered in patients presenting with unexplained hypothermia who fail to rewarm with conventional treatment modalities. Other causes may also play a role such as severe anorexia, hypoglycemia and neuromuscular degenerative disorders such as Parkinson’s disease. Increased Heat Loss Increased heat loss can result from behavioral, iatrogenic, and other etiologic factors. These factors contribute to the severity of accidental hypothermia caused by immersion and non-immersion etiologies. Both these types of nursece4less.com nursece4less.com nursece4less.com nursece4less.com 22 hypothermia are the two most commonly encountered in the emergency department. Skin disorders and injuries such as psoriasis and burns decrease the body's ability to preserve heat. Cold infusions, rapid treatment of heat stroke, and emergency deliveries can all cause hypothermia due to increased heat loss. Drugs as a Cause of Heat Loss Drugs can also facilitate heat loss by causing thermoregulatory failure. Patients who are on opioids and psychotropic drugs may present with induced vasodilatation. Alcohol and phenothiazines decrease the body’s ability to respond to low ambient temperatures. Alcohol is especially dangerous because it not only changes the perception to cold and impairs judgment, but also causes peripheral vasodilation that boost the loss of heat. Alcohol can also cause impaired shivering and hypoglycemia. In addition, it can also lower the core temperature by exerting direct effects on the hypothalamus. Phenothiazines can cause central thermoregulation dysfunction and inhibition of peripheral vasoconstriction in response to cold through their blockade of alpha-receptors. Other alpha-blockers such as prazosin have also been reported to cause hypothermia, with the elderly being more susceptible to their alpha blocking activity. Lithium overdose and valproic acid at therapeutic doses have been reported to cause a drop in core temperature. Impaired Hypothalamic Thermoregulation Disorders affecting the hypothalamus can impair its ability to perform its thermoregulatory function. Examples include central nervous system (CNS) nursece4less.com nursece4less.com nursece4less.com nursece4less.com 23 trauma, strokes, toxicologic and metabolic derangements, intracranial bleeding, CNS tumors, Wernicke’s encephalopathy, and multiple sclerosis. Older Age Older aged people are especially more prone to accidental hypothermia of progressively impaired thermoregulatory function. The elderly usually have decreased ability to produce heat due to decreased lean body mass, impaired mobility, inadequate diet, and reduced shivering mechanism. As mentioned previously, sympathetically activated thermogenesis in brown adipose tissue only occurs among infants, not the elderly. In fact, older adults have very little, if at all, brown adipose tissue. Additionally, the elderly are more likely to sustain heat loss because of their impaired ability to: Vasoconstrict properly Discriminate changes in temperature Adapt normal behavioral responses to cold The elderly also have greater exposure to cold through falls or comorbidities. This is especially true for those who have predisposing socioeconomic factors. In fact, some elderly people are more likely to experience recurring hypothermia, which may suggest that they may have a specific predisposition to thermoregulatory failure that may be precipitated by a relatively minor insult. Among the elderly, the most common precipitating factor is sepsis brought on by severe and unresolved infection. In fact, a study found that approximately 80% of elderly patients with hypothermia have a comorbid systemic infection. Sepsis predisposes the elderly to hypothermia by either of the following: Causing vasoconstriction failure nursece4less.com nursece4less.com nursece4less.com nursece4less.com 24 Inducing an abnormal hypothalamic response. The mechanism by which it stimulates an abnormal hypothalamic response remains unclear; however, study reports have found an abnormally increased inflammatory response, with elevated levels of tumor necrosis factor alpha (TNF‐α) and interleukin‐6, and increased prostacyclin and thromboxane B2 metabolites. Inflammation of the pancreas and diabetic ketoacidosis are also precipitating factors that can cause hypothermic episodes, even if they are not clinically noticeable. This is especially true for people with diabetes and malnutrition. Complications And Related Dysfunctions Mild hypothermia usually does not cause any permanent damage. People with mild hypothermia usually recover easily. However, people with moderatesevere hypothermia may suffer from serious complications and even death. Children have greater chances of recovery from severe hypothermia compared to adults. In fact, the death rate for hypothermia in the elderly is about fifty times more than in children. The following discussion highlights complicating and other related factors or dysfunctions occurring during exposure to freezing conditions and resulting hypothermia.1-3,5,6 Complications There are several possible complications from hypothermia, classified as mental and physical. The mental complications include paradoxical undressing and terminal burrowing. Physical complications include frostbite, frostnip, trench foot, and chilblains. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 25 Mental Complications The mental complications are the so-called paradox reactions of hypothermia by victims prior to their deaths. Paradoxical undressing is a dangerous state of hypothermia and occurs before terminal burrowing. It is a term used to describe the final undressed state of the victims of hypothermia. Just before death, they remove all their clothes (as if burning up), in an effort to cool down despite their severely hypothermic state. Consequently, they are often found naked and frozen to death. The reason for this paradoxical reaction may be due to the cold-paralysis effect of the nerves in the blood vessels, leading to reflexive vasodilation, which in turn results in the false sense of warmth. Another theory suggests that the reflex vasoconstriction that occurs during the first stage of hypothermia cause paralysis of the vasomotor center, also leading to a false sense of warmth despite the lethal hypothermic state of the body. Terminal burrowing occurs after these victims have undressed. This type of behavior refers to their attempts at crawling into small and enclosed spaces. This is why victims of lethal hypothermia are not only often found naked; they are often huddled and squeezed into cupboards and shelves, garbage cans, underneath beds, and behind wardrobes. The discovery positions of their bodies are akin to protective burrowing-like or hiding-like behaviors.9 The clothes of the victims are almost always scattered on the ground in front of their final position, suggesting the occurrence of paradoxical undressing before terminal burrowing. Also, these victims are often found with abrasions and hematomas on their knees, elbows, feet and hand, suggesting movement on all fours (crawling) after undressing and just before terminal burrowing. In 1995, an article published in the International Journal of Legal Medicine told the story of German researchers who studied and described hypothermia nursece4less.com nursece4less.com nursece4less.com nursece4less.com 26 victims in a position which indicated a final mechanism of protection. Although terminal burrowing is a behavior that isn’t understood well by the scientific community, the German researchers described it as an autonomous process of the brain stem, triggered in the final state of hypothermia; it produces a primitive and protective burrowing-like behavior akin to conduct found in hibernating animals. Physical Complications Frostbite and Frostnip Frostbite is a term used to refer to local tissue (nerves, muscles, blood vessels) damage and injury due to severely cold temperatures. Frostnip is a mild degree of frostbite and usually only involves the surface of the skin. It is characterized by tingling sensations and numbness due to severely cold temperatures. Frostbite generally affects the tissue extremities, with the hands and feet being the most common sites of tissue damage and injury. Other extremities vulnerable to frostbites are the ears, nose, cheeks, and penis. Because hypothermia affects the elderly and pediatric populations more than any other population group, it stands to reason that they are also the group most susceptible to frostbites and frostnips. However, frostbite is also fairly common in adults between 30-50 years of age. Numerous studies from the Scandinavian countries found that frostbite is frequently linked with wet and improper winter clothing, history of previous hypothermia or frostbite, wound infections, diabetes, and smoking. These factors are also frequently seen in homeless individuals necessitating health authorities to be vigilant for frostbite during the cold weather. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 27 Trench Foot Trench foot is also known as immersion foot. The term refers to an injury of the feet due to prolonged exposure to wet and cold terrains. It can happen at temperatures as high as 16°C given the feet are continuously exposed to a wet environment. This happens because wet feet lose heat 25-times faster than dry feet. In response to that, the body attempts to inhibit peripheral blood circulation in the feet by constricting their blood vessels in order to preserve heat and avoid its loss. Consequently, the skin tissue undergoes necrosis due to lack of oxygen and nutrients and accumulation of toxic products. Chilblains Chilblains refer to capillary injuries to the cheeks, ears, fingers and toes due to their repeated exposure to temperatures as high as 16°C. The cold exposure permanently injures the capillary beds in the skin. The redness and itching are usually felt with additional exposure. The signs and symptoms of all four physical complications are summarized in the table below. Frostbite/Frostnip Trench foot Chilblains Fingers/toes reduced blood flow Reddening of the skin Redness Numbness Numbness Itching Tingling sensations Leg cramps Possible blistering Aching or stinging sensations Swelling Inflammation Bluish, waxy skin Tingling pain Possible ulceration (severe case) Blisters or ulcers Bleeding under skin Gangrene nursece4less.com nursece4less.com nursece4less.com nursece4less.com 28 Mechanism of Injury in Frostbites There are three processes that occur simultaneously in frostbites, and these include the following. 1. The freezing of the tissue is accompanied by the formation of ice crystals that damage the cell membranes. Water then leaks out of the cells, leading to cellular dehydration and death. 2. Peripheral blood vessels constrict in response to the cold, depriving the tissue of oxygen. The flow of blood in the capillaries ceases, leading to clotting or thrombosis within small arterioles and venules. This further exacerbates the hypoxia in the tissue. 3. Inflammatory mediators are released in response to all of these insults: local tissue damage, hypoxia, and thrombosis. The most potent are the prostaglandins PGF2 and thromboxane A2. These cause further vasoconstriction, depriving the tissue of yet more oxygen, and also cause platelet aggregation, exacerbating the thrombosis. The peak time for the release of these mediators is during the rewarming process. The goal of treatment is to reverse or limit each of these processes. Rewarming can stop the tissue from freezing and reverse the vasoconstriction, while medications can block the release of the inflammatory mediators. Related Dysfunctions Other complications of hypothermia include renal, metabolic, cardiovascular, hematologic, neuromuscular, respiratory, and gastrointestinal dysfunctions. Each one is discussed in detail below. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 29 Renal and Metabolic Dysfunctions As mentioned previously, a mild decline in body temperature (mild hypothermia) can result in a cold-induced diuresis. This is originally caused by the enhanced renal blood flow following vasoconstriction, then with declining temperature, the decrease in distal tubular reabsorption of water and the resistance to the effects of the anti-diuretic hormone (ADH). The cold-induced diuresis occurs together with enhanced urinary electrolyte excretion, which may be attributed to decreased tubular sodium reabsorption. In moderate hypothermia, the glomerular filtration rate (GFR) declines together with cardiac output, resulting in declining renal blood flow by as much as half at temperatures between 27–30 °C. In addition, this is accompanied by declining tubular function and renal clearance of glucose. When the core temperature falls below 27°C, the tubular capacity for hydrogen ion secretion decreases, thus, further aggravating the acidosis. In the clinical setting, acute renal failure is seen in more than forty percent of patients with accidental hypothermia who were admitted to the intensive care unit. Tissue examination has revealed ischemic damage to the kidneys, which may have occurred during the rewarming phase, after a period of relative protection at lower temperatures. Total body metabolism declines in response to worsening hypothermia, as measured by a decline in oxygen consumption, which is about six percent for every degree Celsius fall in temperature. Consequently, the basal metabolic rate declines by 50% at 28 °C. Conversely, pituitary, adrenal and thyroid functions remain normal. However, some researchers have observed a depressed cortisol response to stimulation of the adrenocorticotropic hormone. Although TSH and thyroxine plasma concentrations tend to remain at normal levels, they should still be assessed in order to rule out hypothyroidism as an underlying cause. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 30 Hypothermia can also cause hyperglycemia. Elevated corticosteroid levels, accompanied by direct cooling of the islets of Langerhans, repress the release of insulin release and impair insulin uptake at the peripheral tissues. There is also an increase in sympathetic activity, accompanied by elevated plasma norepinephrine and free fatty acid concentrations. Due to the elevated levels of catecholamine, glycogenolysis and gluconeogenesis ensues contributing to the hyperglycemia. Likewise, glucagon concentrations rise. The plasma cortisol concentrations correspond to lactate and glycerol concentrations, suggesting an active stimulation of glycogenolysis and lipolysis. In situations where hypothermia has progressed gradually or chronically, glycogen reserves may be exhausted, and leading to greater likelihood of the development of hypoglycemia. Shivering may also contribute to the depletion of glycogen reserves and chronically contribute to hypoglycemia. Hypokalemia is caused by the movement of extracellular potassium into the cells, stimulated by alterations in cell membrane permeability and the activity of the sodium-potassium pump. Conversely, hyperkalemia indicates acidosis and necrosis, all of which are signs of poor prognosis. Cardiovascular Dysfunctions In cases of mild hypothermia, tachycardia and peripheral vasoconstriction is seen initially followed by an increase in cardiac output and slight increase in blood pressure. Moving onto situations of moderate hypothermia, bradycardia ensues as a result of reduced spontaneous depolarization of the pacemaker cells. An increase in systemic vascular resistance brought on by autonomic reflex response and catecholamine secretion can balance the reduced cardiac output. Additionally, the increase in systemic resistance may be attributed to hemoconcentration, greater viscosity and local vasomotor responses. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 31 Osborn or J-waves on the electrocardiogram are evidence of repolarization abnormalities in hypothermic patients. The waves increase proportionally in amplitude with declining temperature, but remain unaffected by electrolyte disturbances. It must be remembered though that J waves are not exclusively seen in hypothermia; they are also present in patients who sustained myocardial ischemia, subarachnoid hemorrhage and other head injuries. Hence, they are not diagnostic for hypothermia. Additionally, broad QRS complexes also develop, suggesting a slower pace of myocardial electroconduction. This is usually accompanied by notable ECG changes such as elevated or depressed ST-waves and inversed T-waves, all of which may be attributed to the developing acidosis. The slowed electroconduction of the myocardial muscles may be attributed to decreased and late activation of the inward sodium current. There is also greater PR interval and second or third degree atrioventricular block suggesting a prolongation of systole, and conduction delay. QT prolongation may appear at lower temperatures and is evidenced by delayed repolarization. At a temperature of 28°C, the heart rate drops to 30–40 beats per minute. At even lower temperatures (i.e., 20°C), the bradycardia may worsen, with rates falling dangerously low to 10 beats per minute. Systemic vascular resistance reduces as catecholamine release and cardiac output decreases. At temperatures below 24°C, the risk of asystole increases. There have been suggestions that asystole is a primary symptom of hypothermia, whereas ventricular fibrillation develops secondary to re-warming, hypocapnia, or alkalosis. Ischemia, amplified adrenergic activity and electrolyte imbalance help lead to myocardial instability such as arrhythmias in cases of moderate hypothermia. Ventricular fibrillation is frequently seen at temperatures below 27°C. Its likelihood of occurrence is greater with sudden alterations, such as: nursece4less.com nursece4less.com nursece4less.com nursece4less.com 32 Physical movement pO2 or pCO2 Myocardial temperature Biochemical or acid/base status Serum levels of hydroxybutyrate dehydrogenase and creatine kinase are sometimes slightly greater than normal, but may not necessarily suggest cold-induced ischemic myocardial damage. This is because creatine kinase serum levels rise independent of temperature, and do not occur with concurrent ECG changes or histological proof of myocardial infarction at postmortem exams. Another, more reliable marker of cardiac damage is troponin measurements. Hematologic Dysfunctions Hypothermia cause hematological disturbances such as increases in: Blood viscosity Fibrinogen Hematocrit These disorders are the primary underlying cause of many of the dysfunctions of other organs. Altered vascular permeability leads to loss of plasma to extravascular compartments, resulting in hemoconcentration, and consequently, worsened hypovolemia (due to cold-induced diuresis). A 2% increase in hematocrit levels is seen for every 1°C decline in temperature. However, a normal hematocrit level in moderate or severe hypothermia is suggestive of pre-existing anemia or hemorrhage. In addition, hypothermia has also been found to be associated with marrow suppression and progressive marrow failure, and induction of erythroid hypoplasia and sideroblastic anemia. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 33 Cold stimuli directly prevent the enzymatic reactions in the intrinsic and extrinsic pathways of the clotting cascade, leading to a coagulopathy. The prothrombin time and partial thromboplastin time may remain normal when the measurements are taken at 37°C, but, may significantly increase if measured at lower temperatures, even with normal clotting factor levels. Reports of a disseminated intravascular coagulopathy may be attributed to the release of tissue thromboplastin from ischemic tissue, or its circulatory collapse itself. Hypothermia can also interfere with endothelial synthesis of prostacyclin (PGI2) and its inhibitory action on platelet aggregation, triggering platelet activation and thrombosis. Conversely, thrombocytopenia may also develop. This frequently results from any of the following three causes: sequestration in the liver and spleen, or disseminated intravascular coagulation, or bone marrow depression. Additionally, the synthesis of thromboxane B2 by platelets is dependent on temperature, thus, promoting a fall in platelet activity with declining temperature. Above normal cryofibrinogen concentrations can sometimes occur in situations of hypothermia. This is responsible for dramatically elevating the blood viscosity, in response to progressively cold temperatures; and, interfering with the microcirculation and, possibly, leading to the commonly found tissue micro-infarcts. Greater incidence of purpura is suggestive of cryofibrinogenemia, and is linked to increased mortality. The exhaustion of leukocytes can happen due to hypothermia. It is therefore important to consider sepsis in elderly patients with hypothermia to be a predisposing cause of thermoregulation failure. Consequently, antibiotic coverage should be seriously considered in this patient population. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 34 Neuromuscular Dysfunctions Hypothermia causes clinically apparent central neurological effects, which are listed below: Initial confusion Amnesia (mild hypothermia) Apathy Impaired judgment Paradoxical undressing Terminal burrowing Dysarthria Coma Severe hypothermia (25°C) also results in loss of cerebrovascular autoregulation and reduction in cerebral blood flow by six to seven percent for every 1°C drop in temperature. However, there is also an apparent decrease in metabolic rate, thus, relatively increasing to cerebral ischemia. At temperatures below 20°C, ischemic tolerance is ten times the normothermic. This is evident in a flat electroencephalogram reading. Shivering increases in cases of mild hypothermia but then decreases as the temperature drops further. However, the temperature at which shivering is lost varies greatly, from as low as 24°C to as high as 35°C. There is also an increase in viscosity of synovial fluid at lower temperatures, which explains the symptoms of stiff muscles and joints in moderate hypothermia. Neurological deficits such as ataxia and loss of fine motor control develops during the initial stages of hypothermia, then followed by hyporeflexia, and extensor plantar response and delayed pupillary response in moderate hypothermia. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 35 Rigidity, pupillary dilatation and areflexia develop when temperatures drop below 28°C. The stiff muscles and joints may deceptively look like rigor mortis, although the stiffness may paradoxically diminish as the temperature declines further. These can be explained by animal studies in peripheral nerve conduction. There is a progressive decrease in conduction velocity with declining temperatures, which may be attributed to a reduced movement of potassium and chloride ions across the axon membrane. The delay in synaptic transmission is also aggravated due to a cooled neuromuscular junction. Muscle contraction is, to some extent, temperature-dependent; decreased tension development and maximal shortening velocity occurs at lower temperatures. At skin temperatures as low as 12°C, the pre-capillary sphincters do not contract, resulting in vasodilatation and increased blood flow. The latter may then lead to sufficient warming to restore capillary function and restoration of local vasoconstriction. The shift between dilatation and constriction is referred to as the Lewis Hunting Reaction and affects primarily the peripheries such as the fingertips, toes, ears and face. Respiratory Dysfunctions Mild hypothermia also has several respiratory effects. For instance, in mild hypothermia, an initial tachypnea is seen followed by decreased minute volume and oxygen consumption, leading to bronchospasm and bronchorrhea. In moderate hypothermia, there is a decrease in protective airway reflexes due to impaired ciliary function, predisposing the patient to aspiration and pneumonia. In addition to reduced oxygen consumption, there is also a marked decrease in carbon dioxide production by about 50 percent at 30°C. Core temperature control is especially dependent on pCO2 level, identified by the carotid bodies, nursece4less.com nursece4less.com nursece4less.com nursece4less.com 36 which in turn act on sources of heat production and thermal decomposition. The ventilatory drive is depressed by the direct cooling effect at the respiratory centers. At temperatures less than 34°C, there is greater sensitivity to pCO2 stimulation despite the maintenance of the hypoxic drive to deeper levels of hypothermia. Physiological and anatomical respiratory dead spaces rise due to bronchodilation, however, alveolar dead space remain normal. Hypothermia does not affect the local gas exchange but it does cause greater pulmonary vascular resistance and ventilation-perfusion mismatch. Severe hypothermia causes chronic hypoventilation, apnea, and rarely, pulmonary edema. In addition, there is an initial shift to the left of the oxyhemoglobin dissociation curve due to declining temperature. This leads to a dysfunctional oxygen delivery and tissue hypoxia, although this is balanced to some extent by the consequent lactic acidosis and other respiratory and metabolic factors causing the acidosis. Shivering can also contribute to the increase in lactate production, and its subsequent impaired hepatic clearance. Most often, the metabolic acidosis aggravates during re-warming efforts as the products of anaerobic metabolism are brought back into the blood, which can compound the risk of arrhythmias. In severe hypothermia, there is a corresponding severe resulting in an overall shift to the right of the oxyhemoglobin dissociation curve. The impediment to the delivery of oxygen to the hypoxic tissues is not as significant due to the fall in oxygen requirement at lower temperatures. Gastrointestinal Dysfunctions Intestinal movement is compromised at temperatures less than 34°C, leading to ileus when the temperature falls even further at less than 28°C. There may nursece4less.com nursece4less.com nursece4less.com nursece4less.com 37 also be punctate hemorrhages seen all over the GI tract. In addition, it is not uncommon for gastric erosions and submucosal hemorrhages to occur, although they are not clinically significant. The superficial gastric ulcers called Wischnevsky's ulcers are found in many cases during autopsy investigations. A characteristic linear pattern is usually present which is commonly found in patients who succumbed to acute cold stress. In addition, liver function is affected, possibly due to decreased blood flow brought on by reduced cardiac output. Consequently, the metabolic clearance of lactic acid is reduced contributing to the existing acidosis. The pancreas is also affected by hypothermia. Its resulting inflammation is found during postmortem exams in more than one-fourth of cases. There is also a mild increase in serum amylase in the absence of clinical evidence of pancreatitis in half of the patients studied. There is no clear explanation for this but studies suggest that it is due to the thrombosis in the microcirculation, and consequent ischemia and perilobular necrosis in the organ. Some studies thought this occurrence share a similar underlying process to that which causes tiny infarcts in the stomach, liver, brain, myocardium, and many other organs. Portal vein thrombosis may also be seen together with hemorrhagic pancreatitis. Assessment And Treatment Of The Hypothermic Patient There are several factors to consider when assessing patients suspected of hypothermia. These include: 1) A history of cold exposure, 2) A history of predisposing disease, 3) Presence of a cold trunk, and 4) Core body temperature below 35°C. As mentioned previously, hypothermia can be staged clinically on the basis of vital signs. This is preferred over the traditional staging system in cases when the core temperature cannot be accurately measured. The following discussion details aspects of assessing and treating a hypothermic patient.5,7-13 nursece4less.com nursece4less.com nursece4less.com nursece4less.com 38 Accurate Temperature Determination Core temperature measurement is required to confirm staging of hypothermia and consequently, help emergency responders arrange for appropriate transport and management decisions. In order to get an accurate reading, properly calibrated, low-reading thermometers must be used, although these may not always available in the pre-hospital setting. As mentioned previously, body temperature varies between body sites, present degree of perfusion, and temperature of the surrounding environment. A thermistor probe inserted into the lower third of the esophagus is preferably used to obtain the core temperature in patients who are intubated. There is a risk of obtaining a falsely elevated temperature if the probe is inserted proximally, due to its exposure to warmed gases. The temperature obtained by a probe in touch with the tympanic membrane is an accurate reflection of the brain temperature, given the ear canal is not contaminated with snow and cerumen, and shielded from the cold environment. Caution should be taken when using IR cutaneous, aural, bladder, rectal and oral thermometers to measure core temperatures since these often offer inaccurate readings in patients with hypothermia. The bladder temperature can rise during diagnostic peritoneal aspiration (DPA). Thermistor probes measuring rectal temperatures should be inserted into a depth of 150 mm. However, these readings may reflect a delayed core temperature during rewarming. It is important to remember that a reliably accurate measurement is not always feasible, such as occurs in various field settings. Initial rescue and prehospital treatment decisions should be based on the current Swiss staging system of hypothermia. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 39 Physical Examination The physical examination of hypothermic patients is challenging, especially in moderate to severe hypothermia. These patients can appear dead or comatose, with very faint and hard-to-hear blood pressure, shallow to absent respirations, non-palpable pulse, dilated pupils, absent deep tendon reflexes, and increased muscle tone deceptively similar to rigor mortis. Assessing the core temperature of hypothermic patients requires nurses and emergency responders to basically look, listen and feel for vital signs and other clues that can help guide management decisions. They may find it useful to follow the steps outlined below in assessing patients who are conscious and able to talk. 1. Look at the patient, talk and ask questions when assessing the airway. Listen for sounds of noisy breathing since it is a strong indication for airway obstruction. 2. Gather as much information as to how they are feeling. Some patients may feel shivery, and sometimes hot, and then cold. This subjective information actually gives clues to changes in core temperature of the patients. 3. Observe the skin color. Determine whether it is pale, cyanosed, pink or flushed. Determine the skin integrity, whether it is intact, bruised or burnt. 4. Touch the skin and feel its temperature. Determine whether it is hot to touch, sweaty or clammy. A skin that’s hot to touch is suggestive of infection or dehydration. 5. Assess circulation by looking at the skin color again. Also, perform capillary refill time (CRT) and look manually for the pulse. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 40 Laboratory Testing White Blood Cell (WBC) Count Hypothermia can affect the white blood cell (WBC) count. A rise in WBC count in hypothermia may be attributed to leukocyte demargination, which happens during shivering. Conversely, reduction in WBC count in hypothermia may be due to splenic sequestration during the physiologic stress. Hemoglobin Count The hemoglobin and hematocrit levels may rise as a result of hemoconcentration secondary to cold diuresis (increased urine production on exposure to cold). Electrolyte Concentrations Electrolyte concentrations are altered often during re-warming efforts. The most affected electrolyte is potassium; with levels fluctuating frequently in response to alterations in the acid-base balance. Mild hypothermia can cause hypokalemia, while severe hypothermia can trigger hyperkalemia secondary to hypoxic and traumatic cell death. In fact, severe hyperkalemia is associated with non-survival and is considered a strong indicator of hypoxia before cooling. The greatest recorded concentrations of serum potassium in victims of accidental hypothermia who were successfully revived are: 11.8 mmol per liter in a 31-month-old child, 9.5 mmol per liter in a 13-year-old child, 7.9 mmol per liter in a 34-year-old adult, and 6.4 mmol per liter (in an adult who survived burial in an avalanche). Other electrolytes such as sodium, magnesium, calcium, and chloride levels are not affected significantly. However, sodium levels may become elevated at the onset of coexisting dehydration. Consequently, serum osmolality may also rise. Studies have found that almost half of all patients admitted into the ICU nursece4less.com nursece4less.com nursece4less.com nursece4less.com 41 for hypothermia have an abnormal renal function. In addition, creatine kinase levels must be measured to assess or rule out renal failure secondary to rhabdomyolysis or acute tubular necrosis. This is especially important in hypothermic patients who are unconscious and do not have a medical history on file. Lastly, hypothermic patients present with abnormal liver function tests and decreased lactic acid elimination because of reduced cardiac output. Microbiological Tests Blood cultures are performed, as septicemia is a common cause of hypothermia, particularly in the cirrhotic patient. Depending on the clinical circumstance, urine, sputum, cerebrospinal fluid and ascitic fluid may also be taken for culture. Blood Gas Analysis The blood gas values of hypothermic patients are hard to interpret and its method of assessment is controversial. Blood gas analyzers heat the blood sample to 37°C which results in the elevation of partial pressure of the gases tested. The elevated pressure increases the hydrogen ion concentration of the sample. The result of the analysis is a corrected value with deceptively elevated CO2 levels and decreased pH levels. As a result, some hospitals and medical practitioners prefer to use uncorrected arterial blood gas values to direct clinical management decisions. The correction of an impaired acid-base balance based on corrected arterial blood gas values can potentially aggravate an existing acidosis and worsen overall prognosis by interfering with both cerebral and coronary circulation, and potentiating arrhythmic disorders. Hypothermic patients are especially prone to acid-base disorders. Examples of these include: Metabolic acidosis due to lactate Respiratory alkalosis from the cold blood nursece4less.com nursece4less.com nursece4less.com nursece4less.com 42 Respiratory acidosis from the hypoventilation A combination of the metabolic acidosis, respiratory alkalosis, and respiratory acidosis Thus, there is greater preference for directly treating the actual uncorrected ABG, with a goal of an uncorrected pH of 7.35 and a pCO2 of 40 mm Hg. Coagulation Studies Severely hypothermic patients may also have severely impaired clotting functions because clotting enzymes are temperature dependent. A study by Rohrer et al. showed that both prothrombin time (PT) and partial thromboplastin time (PTT) rise in response to temperature reduction. Fifteen samples of pooled plasma were investigated at varying temperatures, 37°C, 34°C, 31°C, and 28°C, and showed a statistically significant elevation in both the PT and PTT (p< 0.001) in response to declining temperatures. The mean prothrombin time at 37°C was 11.8 seconds compared to a mean of 16.6 seconds at 28°C. Another comparable study by Felfernig, et al., investigated the partial thromboplastin time of in vitro plasma and found a 10 percent rise in plasma less than 35°C compared to plasma at 37°C. In this study, the obtained values were normal since the blood was heated to 37°C before analysis. The results of these studies imply that both values must be considered in severely hemorrhaging trauma patients despite seemingly normal coagulation values. Impaired coagulation is self-limiting and eventually resolves with rewarming. Alcohol Intoxication Level Usually, patients presenting with altered mental status are tested for blood alcohol levels, particularly if they are also hypothermic. This is because both nursece4less.com nursece4less.com nursece4less.com nursece4less.com 43 alcohol and drug intoxication are causative and aggravating factors to hypothermia. In fact, about 90 percent of deceased victims of hypothermia have detectable blood alcohol levels. Urine Toxicology As mentioned above, drug intoxication is both a causative and contributing factor to hypothermia. Patients who present with altered mental status should undergo urine toxicologic screening. This is especially useful in detecting or ruling out suspected specific drugs. The clinician needs to remember that urine toxicology reports may appear positive even after the intoxication has been resolved. Diagnostic Imaging Studies Diagnostic imaging studies that may help pinpoint underlying contributing factors to hypothermia or help guide management decisions include x-rays, ultrasound, CT scan, and electrocardiogram. X-ray Chest x-ray (CXR) should be considered for hypothermic patients with altered mental status since they are particularly at greater risk for aspiration pneumonia. Ultrasound Currently, ultrasound is not specifically indicated in hypothermic patients. However, an emergency department bedside ultrasound has a recognized role in assessment for contributing factors of altered mental status: A Focused Assessment with Sonography in Trauma (FAST) examination assesses for free fluid, which is indicative of trauma or eroding intra-abdominal processes. In addition, ultrasound can also be used to assess for pericardial effusion, contractility, and dysfunctional wall motion. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 44 CT Scan Like ultrasound, a CT scan is not clearly indicated for hypothermic patients, although it can be particularly considered in those who continue to experience altered mental status after re-warming to above 32°C. Once patients with severe hypothermia has been stabilized, directed CT imaging, based on patient signs and symptoms, may be initiated to find any underlying infection or trauma. Electrocardiography (ECG) As mentioned previously, a hypothermic patient will have a reduced spontaneous depolarization of pacemaker cells, prolonged action potential, and slowed electroconduction of impulses in the myocardium. These abnormalities are evident in ECG results, such as those listed below: Prolonged intervals (PR, QRS, and QT) Premature beats Atrioventricular (AV) blocks ST depressions and elevations Bradycardia, and Atrial and ventricular arrhythmias Also, as mentioned previously, the characteristic ECG finding called the Osborn wave or J-wave occurs in about 80 percent of hypothermic patients. The J-wave is a positive deflection at the QRS-ST junction. There is no clear evidence on what specifically triggers the electrocardiographic formation of the J-wave (Osborn wave). One hypothesis suggests that hypothermiainduced ion changes cause delayed depolarization or early repolarization of the left ventricle. Another hypothesis suggests an unidentified hypothalamic or neurogenic factor. The characteristic J-wave is seen in the majority of hypothermic patients, regardless of the degree of hypothermia. Some studies nursece4less.com nursece4less.com nursece4less.com nursece4less.com 45 have found proof that the absolute size of the J-wave is associated to the temperature as hypothermia slowly resolves during the period of time that the patient is rewarmed. Other Studies Patients who have no clear source of cold exposure and remain unresponsive to rewarming efforts should be considered for testing for underlying etiologies such as hypothyroidism and adrenal insufficiency. Common Situations Resulting in Hypothermia Trauma Shock and cerebrospinal injury can destabilize thermoregulation. This is why patients with multiple traumas or with CNS trauma are prone to hypothermia. As mentioned previously, hypothermia exacerbates bleeding and increases transfusion demands. It may also increase mortality. Coagulation factor activity and platelet function decrease in response to declining temperatures, leading to critical coagulopathy below 34°C. A combination of coagulopathy, acidosis and hypothermia is often known as the death triad. Burial Avalanche About 150 people die due to being buried in avalanches each year in North America and Europe. Fatalities are alleged to be greater in developing countries. There are four major factors that affect survival of victims of avalanche burial: 1. Grade of burial 2. Duration of burial 3. Presence of an air pocket or patent airway 4. Degree of trauma nursece4less.com nursece4less.com nursece4less.com nursece4less.com 46 Based on the Swiss report, the overall mortality rate with avalanche burial is 23%, although this number primarily is dictated by the grade of burial. The mortality rate for victims who are completely buried in snow is 52.4%, while those who are partially buried only have a 4.2% rate. Avalanche victims pulled from underneath deep snow has greater likelihood of survival if burial time is no more than 35 minutes because the risk of developing severe hypothermia is unlikely. This is because there is inadequate cooling time. Individuals buried in snow can lose heat (cool down) at a maximum rate of 9°C per hour. If such patients present with absent vital signs, trauma and hypoxia should be highly suspected. If the burial time is more than 35 minutes, the airway is obstructed with snow, and the patient is asystolic, there is good chance that hypoxia occurred prior to hypothermia. On the other hand, if the burial time exceeded 35 minutes and the airway remained unobstructed, severe hypothermia should be highly suspected and the patient should be treated accordingly. In cases where the burial time is unknown, the core temperature can be used to estimate it. A core temperature below 32°C is associated with a burial time exceeding 35 minutes. Cold Water Submersion Cold-water submersion offers better outcomes than warm water submersion. If the patient’s body was exposed to cold water with breathing intact, there is great likelihood that the core temperature declined prior to the onset of hypoxia and cardiac arrest (stage HT IV). Survival is also possible without neurologic impairment. Conversely, if the patient’s body was exposed to cold water and the breathing compromised prior to cooling, the prognosis may be worse. The maximum-recorded time of nursece4less.com nursece4less.com nursece4less.com nursece4less.com 47 cold water submersion correlated with survival without neurologic impairment was 66 minutes in a child who was two and a half years old. Frostbites The American College of Surgeons (ACS) classifies frostbite based on the severity of tissue injury. It is important to note that this classification cannot be made until after re-warming efforts have been initiated, and in certain cases, it may take up to 14 days for the severity of damage to be completely revealed. Regardless of the severity of the tissue injury, the majority of patients with frostbite exhibit comparable initial symptoms. The area of the affected tissue feels cold and numb, and prone to poor motor coordination. Rewarming the affected area can lead to agonizing throbbing pain that may persist for several weeks. Another symptom is electric shock sensations running through the area of tissue injury. The frostbitten area may also develop sensory loss and greater sensitivity to cold, which may persist for years. It is not uncommon for arthritis and chronic neuropathic pain to develop in the affected area. First-degree Frostbite First-degree frostbite is shallow, involving the epidermis of the skin. It does not affect the deeper tissues. Also known as frostnip, it is characterized by skin accompanied numbness, swelling, and stiffness. The underlying tissue is warm and soft. The skin may also appear mottled, red, white or yellowish. Second-degree Frostbite Second-degree frostbite is also superficial. It is characterized by white or bluish skin that feels hard and frozen to touch. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 48 Clear or milky blisters usually develop within 24 hours of exposure to cold stressors. These blisters are often surrounded by reddened and swollen skin. The tissues beneath the injury remain. Third degree Frostbite Third degree frostbite involves the underlying tissues of the epidermis. Bloodfilled blisters that turn to black thick scabs and shed off spontaneously about two weeks after the injury characterize this injury. The skin appears white, blotchy or blue. The injured area feels hard and cold to touch. Fourth degree Frostbite Fourth degree frostbite is the most serious kind of frostbite. It affects the underlying muscles, tendons, and bones, leading to tissue necrosis, gangrene, and eventual loss of tissue. It causes severe pain deep in the joints. The skin appears red or bluish which transforms into black. Upon inspection, the affected area will not present with swelling, rather the skin over it feels rubbery. Treatment Field Treatment Field (pre-hospital) management measures for hypothermia are focused on the following treatment priorities: Inhibiting further heat loss Re-warming the core temperature Preventing the onset of fatal complications such as ventricular fibrillation (VF) or other forms of arrhythmias The cardiovascular consequences of hypothermia should be the top priority to address. Mentally alert hypothermic patients can develop ventricular nursece4less.com nursece4less.com nursece4less.com nursece4less.com 49 fibrillation suddenly with jerky and sudden movements. This is why prehospital rescue workers, especially those involved in remote search-andrescue operations should take care not to unnecessarily move these patients, or if they must, must do so gently and carefully. Patients who develop arrhythmias due to hypothermia in the field may become unresponsive to resuscitation efforts. This is especially true among those who were rescued from cold-water submersion. Rescuers are correct in instructing such patients to reduce movements while waiting for careful extrication. The widely circulated anecdotal reports of sudden cardiac death linked with tracheal intubation do not warrant attention, especially in cases of adequately pre-oxygenated patients. The anticholinergic drug, atropine, and cardiac pacing are not useful in managing bradyarrhythmias in hypothermic patients. Likewise, lidocaine is also not useful in preventing hypothermia-induced ventricular arrhythmias. Anecdotal reports and several animal studies have found bretylium to be effective in preventing sudden ventricular fibrillation in severely hypothermic patients. In fact, some clinicians use the drug for that very same reason under the following conditions: Ventricular fibrillation developed at a core temperature of 30°C. When the core temperature of the patient reached below 22°C since this is the temperature which ventricular fibrillation is most likely to develop. An initial dose of 5 mg/kg bretylium is recommended for all hypothermic patients exhibiting apparent novel ventricular arrhythmias. The drug is currently unavailable in the U.S. market. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 50 Rewarming efforts should be initiated in the field prior to hospital arrival by rescuers and emergency responders to prevent the development of cardiac arrhythmias with continued hypothermia. However, an exception to this recommendation is in cases of frostbite injuries wherein rewarming efforts directed towards the affected would rule it out because of pain. The following are general rapid pre-hospital management and treatment guidelines of hypothermic patients. Gentle placement of patients in safe environments that prevent and/or reduce further heat loss through evaporation, radiation, conduction, or convection. Removal of wet clothing, and securely placing patients within dry blankets or sleeping bags. Initiation of active external rewarming with heat packs such as chemical packs and hot water bottles appropriately placed in the axillae, and on the groin and abdomen. Careful administration of rewarming techniques, with special caution towards causing body surface burns from energetic active external rewarming efforts. In situations where heat packs are unavailable, rescuers and emergency responders can provide skin-to-skin contact with patients to facilitate rewarming using body heat. Ventricular fibrillation presents a poor prognosis for hypothermic patients. Generally, defibrillation is not effective when hypothermia has already set in and when resuscitation equipment is unavailable. In cases like these, rescuers or emergency responders should try a round of chemical conversion using bretylium administered intravenously (if available), followed by extended cardiopulmonary resuscitation (CPR) until such time that active re-warming can be initiated and defibrillation performed successfully. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 51 Observing Vital Signs Hypothermic patients need to be checked for vital signs including: Temperature Heart rate Blood pressure Respirations Temperature The majority of conventional clinical thermometers do not measure temperatures less than 34°C. Esophageal thermometers can measure very low core temperatures and may be employed to accurately assess the patient. Another option is the use of a pulmonary catheter, which is partially invasive, but very accurate since it is closest to the core. Its efficacy is superior compared to rectal or bladder thermometers. Heart Rate Heart rate is usually fast in uncomplicated accidental hypothermia. It usually persists until such time that the core temperature goes down below 29°C (84.2°F) at which point, it slows down. Blood Pressure Blood pressure elevates in response to progressive hypothermia, at temperatures as low as 27°C.89 This is a result of sympathetic stimulation by the catecholamines released, which in turn cause greater vasoconstriction and cardiac output. Patients with severe hypothermia often exhibit low blood pressure due to volume alterations, cold diuresis, and dehydration.91 However, this is true for all patients, since hypothermic patients without complications can maintain normal blood pressure even at temperatures as nursece4less.com nursece4less.com nursece4less.com nursece4less.com 52 low as 25°C.90 It is critical to constantly monitor blood pressure levels to prevent cardiovascular collapse during rewarming. Respirations Rapid breathing is usually present in mild and early hypothermia during the sympathetic stimulation that occurs. This is often accompanied by severe shivering. Conversely, the respiratory drive decreases, leading to slower respiratory rate and shallow breathing once temperatures drop to less than 33°C. Other respiratory consequences are bronchorrhea and non-cardiogenic pulmonary edema. Oxygen Perfusion Oxygen perfusion may be measured accurately using pulse oximetry, although this may be difficult in patients with severe hypothermia due to the consequent vasoconstriction. In these cases, measuring the arterial blood gases (ABGs) may be the only way to evaluate oxygen perfusion. Summary This Part I Hypothermia course has discussed how individuals exposed to freezing conditions become mild to profoundly hypothermic. Nurses and rescue teams need to be educated and to be able to educate the public to the signs and symptoms of the degrees of hypothermia that can occur, and the prognosis based on the time exposed to or submerged in freezing conditions. Thermoregulation involves transmission of cold sensation to hypothalamic neurons through the thalamus and various nervous system tracks. Alterations in the core temperature and impulses from nerves originating in the skin directly affect temperature sensitive hypothalmic neurons. Both physiological nursece4less.com nursece4less.com nursece4less.com nursece4less.com 53 biochemical factors and behavioral responses affect body temperature and responses to adverse internal and external conditions. While it’s important to understand the setting and history of the patient and the condition when they are rescued, it’s also just as critical to intervene with the right decision-making and rescue methods. Hypothermia Part II covers more specific modified and advanced rescue measures. Definition of Terms Adrenal insufficiency: An endocrine disorder wherein the adrenal glands do not produce adequate amounts of steroid hormones such as cortisol and aldosterone. Anoxic: An abnormal condition characterized by low amount of oxygen in the body tissues. Arteriovenous anastomoses: A blood vessel that connects an arteriole directly to a venule. Asystole: A cardiac standstill with no cardiac output and no ventricular depolarization. Bradycardia: A slow heart rate of less than 60 beats per minute. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 54 Chilblains: These are small, itchy, painful lumps that develop on the skin due to capillary injuries. They develop as an abnormal response to cold. Circadian rhythm: The body’s natural clock which dictates the patterns of physiological and behavioral processes over a 24-hour period. Core temperature after-drop: Refers to the phenomenon of continuous core temperature decline despite re-warming efforts. Debridement: Refers to the surgical removal of unhealthy tissue from a wound to promote healing. Eschar: Refers to dead tissue that sheds off from healthy skin following injuries such frostbites, burns and pressure wounds. Frostbite: A medical condition wherein peripheral tissues (i.e., foot, fingers, toes) sustain localized damage due to severe cold. Frostnip: An initial stage of frostbite characterized by a reddish and very cold skin due to its frozen surface. Gangrene: Refers to a type of tissue death which occurs due to loss of blood supply. Hyperkalemia: Refers to condition wherein the potassium level in the blood which higher than normal. Hypocapnia: It refers to a condition wherein the level of carbon dioxide in the blood is lower than normal which can result from acapnia. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 55 Hypokalemia: Refers to a condition wherein there is lower than normal level of potassium in the bloodstream. Hypothermia: A medical emergency that happens when the body loses heat faster than it can produce it, causing a dangerously low core temperature. Hypopituitarism: An endocrine syndrome characterized by inadequate pituitary hormone production. It usually is a result of disorders involving the pituitary gland, hypothalamus, or surrounding structures. Ischemia: Refers to a condition wherein the blood flow (and thus oxygen) is restricted or reduced in a part of the body. Normothermia: A condition of normal body temperature. Paradoxical undressing: It refers to the phenomenon of removing all articles of clothing shortly before death due to severe hypothermia. Poikilothermic: An organism having a body temperature that fluctuates with the temperature of its surroundings. Set point: The temperature level at which there is a balance between heat loss and heat production. Terminal burrowing: It refers to the phenomenon of crawling into small confined spaces after removing all articles of clothing (paradoxical undressing) shortly before death due to severe hypothermia. Thermoregulation: Also known as temperature homeostasis. It refers to the process that allows the human body to maintain its core internal temperature. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 56 Thoracotomy: Refers to a surgical incision into the pleural space of the chest to access the lungs, heart and other adjacent organs or insertion of mechanical ventilation. Trench foot: Also known as immersion foot. It refers to an injury of the skin, blood vessels, and nerves of the feet due to prolonged exposure to cold and wet terrains. Please take time to help NurseCe4Less.com course planners evaluate the nursing knowledge needs met by completing the self-assessment of Knowledge Questions after reading the article, and providing feedback in the online course evaluation. Completing the study questions is optional and is NOT a course requirement. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 57 1. The normal adult temperature ranges from 36-38°C, depending on many internal factors such as: a. b. c. d. Wind movement Circadian rhythm Humidity Nature of surrounding environment 2. Which of the following neuronal effector mechanisms activated by cold stimuli increase heat production? a. b. c. d. Shivering Cutaneous vasodilation Piloerection Humidity Sweating 3. Which clinical findings can be seen in patients with mild hypothermia? a. b. c. d. Diminished shivering Slow stretch reflexes Stiff muscles and joints Cold-induced diuresis 4. Which mechanism of environmental heat loss is exemplified by the dissipation of up to 50 percent of the body’s heat through an uncovered head? a. b. c. d. Convection Conduction Radiation Evaporation 5. Which mechanism of environmental heat loss is exemplified by excessive sweating? a. b. c. d. Convection Conduction Radiation Evaporation 6. True or False: The presence of the characteristic J-wave or Osborne wave on the ECG is diagnostic for hypothermia. a. True b. False nursece4less.com nursece4less.com nursece4less.com nursece4less.com 58 7. Which of the following disorders is caused by impaired hypothalamic thermoregulation and predispose individuals to hypothermia? a. b. c. d. Acute renal failure Wernicke’s encephalopathy Hypothyroidism Hypoglycemia 8. Which of the following complications of hypothermia is characterized by the victim’s removal of clothes just before death? a. b. c. d. Voluntary behavior modification Involuntary behavior modification Terminal burrowing Paradoxical undressing 9. Which of the following cold injuries refers to an injury of the foot/feet due to prolonged exposure to wet and cold terrains? a. b. c. d. Second degree frostbite Frostnip Trench foot Chilblains 10. The cold-induced diuresis, which occurs during mild hypothermia, is due to which of the following physiological mechanisms? a. b. c. d. Enhanced renal blood flow following vasoconstriction Inhibition of ADH Enhanced urinary electrolyte excretion Increased distal tubular reabsorption of water 11. _________________ is a pathologic condition wherein the core body temperature is less than 35°C. a. b. c. d. Thermogenesis Failed thermoregulation Hyperthermia Hypothermia nursece4less.com nursece4less.com nursece4less.com nursece4less.com 59 12. True or False: The core body temperature, such as esophageal and rectal, is normally 0.5°C greater than the oral temperature. a. True b. False 13. Due to the circadian rhythm, body temperature fluctuates more or less 0.6°C a. b. c. d. between meals. between the morning and evening. during exercising. between body organs and the skin surface. 14. Women experience core body temperature changes during their monthly menstrual cycle: It _____________________ during ovulation and returns to normal when menstruation begins. a. b. c. d. increases by 0.5°C decreases by 0.6°C rises as high as 40°C falls to less than 35°C 15. The posterior pituitary region is concerned with heat maintenance. It contains a large number of ____________ nerve cells. a. b. c. d. hot- and cold-sensitive heat-sensitive cold-sensitive poikilothermic-sensitive 16. True or False: The skin contains both cold and warmth receptors. The number of cold receptors is ten times more than the warmth or heat receptors. a. True b. False nursece4less.com nursece4less.com nursece4less.com nursece4less.com 60 17. Piloerection, which produces “goose bumps,” is caused by sympathetic stimulation of the _____________________ attached to the hair follicles. a. b. c. d. neurotransmitters sympathetic nerves arrector pili muscles brown fat cells 18. The increase in cellular metabolic activity, caused by the thyroid-stimulating hormone (TSH), a. b. c. d. results instantaneously in thyroid gland hypertrophy. causes “goose bumps.” happen instantaneously. does not happen instantaneously. 19. Toxic thyroid goiters is found more frequently in individuals who a. b. c. d. change climates often. reside long periods in cold climates. live long periods in hot climates. often have a body core temperature above 37.1°C. 20. The temperature set point in the hypothalamus is determined mainly by the intensity of activity of the heat thermoreceptors a. b. c. d. in the anterior hypothalamus. in the skin. in the spinal cord tissues. hypothalamic thermoregulation center. 21. When the skin temperature is high, ____________ begins at a lower hypothalamic temperature compared to when the skin temperature is low. a. b. c. d. shivering sweating excessive heat loss activity nursece4less.com nursece4less.com nursece4less.com nursece4less.com 61 22. True or False: When the skin encounters cold stimuli, the hypothalamic centers are activated towards the shivering threshold even when the hypothalamic temperature may be normal. a. True b. False 23. When an individual puts a foot under a hot lamp and leaves it there for a few minutes, local capillaries __________ and mild local sweating occurs. a. b. c. d. slow constrict dilate reflex 24. Sweating starts and stops due to temperature changes directly on the blood vessels and also by local cord reflexes that run first from skin receptors to a. b. c. d. the the the the hypothalamic center. sweat glands. brain. spinal cord. 25. When the internal body temperature increases significantly, signals from the _________________________ sends out a psychic sensation of overheat. a. b. c. d. skin visceral tissue receptors anterior and posterior hypothalamus anterior hypothalamus 26. The only effective mechanism that retains body heat in extremely cold environments is a. b. c. d. local capillary dilation. the activity of the individual’s heat thermoreceptors. the body’s involuntary mechanism of thermoregulation. the individual taking action to warm his or her body. nursece4less.com nursece4less.com nursece4less.com nursece4less.com 62 27. Traditionally, hypothermia has been classified into three categories. A person classified as moderate hypothermia has a body core temperature between a. b. c. d. 28-32°C. 32-35°C. 35-40°C. 25-29°C. 28. True or False: Skin disorders and injuries such as psoriasis and burns decrease the body's ability to preserve heat. a. True b. False 29. If glycogen stores in the liver are exhausted, hypoglycemia may occur which inhibits a. b. c. d. sweating. shivering. vasoconstriction. capillary dilation. 30. Active re-warming must be initiated when the core temperature falls below _____ because below that temperature, an individual cannot spontaneously return to the set point (the normal core body temperature of about 37°C). a. b. c. d. 28°C. 30°C. 34°C. 25°C. 31. ___________________ accounts for about 15 percent of heat loss. a. b. c. d. Conduction Radiation Sweating Thermogenesis nursece4less.com nursece4less.com nursece4less.com nursece4less.com 63 32. Evaporation accounts for approximately ___ percent of heat loss. a. b. c. d. 50 15 20 40 33. Hypothermia also causes cellular membrane disruption, allowing intracellular fluid to leak out, and ultimately leading to electrolyte imbalance, particularly a. b. c. d. hypertrophy. poikilothermia. hyperglycemia. hyperkalemia. 34. True or False: Cold infusions, rapid treatment of heatstroke, and emergency deliveries do NOT cause hypothermia. a. True b. False 35. Endocrine dysfunctions, such as __________________, are known causes of decreased heat production. a. b. c. d. severe anorexia poikilothermia Parkinson’s disease adrenal insufficiency 36. In patients presenting with unexplained hypothermia who fail to re-warm with conventional treatment modalities, causes may include a. b. c. d. severe anorexia hypoglycemia Parkinson’s disease All of the above nursece4less.com nursece4less.com nursece4less.com nursece4less.com 64 37. Therapeutic doses of ______________ have been reported to cause a drop in core temperature. a. b. c. d. valproic acid lithium antidepressents All of the above 38. True or False: Phenothiazines can cause central thermoregulation dysfunction and inhibition of peripheral vasoconstriction in response to cold through their blockade of alpha-receptors. a. True b. False 39. Among the elderly, the most common precipitating factor for hypothermia is a. b. c. d. presence of brown adipose tissue in the elderly. increased lean body mass. sepsis (systemic infection). hypothyroidism. 40. Trench foot occurs in part because wet feet lose heat _________ faster than dry feet. a. b. c. d. 25-times twice 10% three-times 41. True or False: Numerous studies from the Scandinavian countries found hypothermia may be delayed by the victim smoking. a. True b. False nursece4less.com nursece4less.com nursece4less.com nursece4less.com 65 42. ______________ is caused by the movement of extracellular potassium into the cells, stimulated by alterations in cell membrane permeability and the activity of the sodiumpotassium pump. a. b. c. d. Hypertrophy Poikilothermia Hypokalemia Hypothyroidism 43. Ischemia, amplified adrenergic activity and electrolyte imbalance help lead to myocardial instability such as arrhythmias in cases of ____________ hypothermia. a. b. c. d. moderate severe mild All of the above 44. Hypothermia can also interfere with endothelial synthesis of prostacyclin (PGI2) and its inhibitory action on platelet aggregation, triggering platelet activation and a. b. c. d. anemia. hypokalemia. thrombosis. alkalosis. 45. Hypothermia, postmortem patients who showed evidence of a mild increase in serum amylase, which means that the ___________ is/are also affected by hypothermia. a. b. c. d. kidneys capillaries liver pancreas nursece4less.com nursece4less.com nursece4less.com nursece4less.com 66 Correct Answers: 1. The normal adult temperature ranges from 36-38°C, depending on many internal factors such as: b. Circadian rhythm 2. Which of the following neuronal effector mechanisms activated by cold stimuli increase heat production? a. Shivering 3. Which clinical findings can be seen in patients with mild hypothermia? d. Cold-induced diuresis 4. Which mechanism of environmental heat loss is exemplified by the dissipation of up to 50 percent of the body’s heat through an uncovered head? c. Radiation 5. Which mechanism of environmental heat loss is exemplified by excessive sweating? d. Evaporation 6. True or False: The presence of the characteristic J-wave or Osborne wave on the ECG is diagnostic for hypothermia. b. False 7. Which of the following disorders is caused by impaired hypothalamic thermoregulation and predispose individuals to hypothermia? b. Wernicke’s encephalopathy 8. Which of the following complications of hypothermia is characterized by the victim’s removal of clothes just before death? d. Paradoxical undressing nursece4less.com nursece4less.com nursece4less.com nursece4less.com 67 9. Which of the following cold injuries refers to an injury of the foot/feet due to prolonged exposure to wet and cold terrains? c. Trench foot 10. The cold-induced diuresis, which occurs during mild hypothermia, is due to which of the following physiological mechanisms? a. Enhanced renal blood flow following vasoconstriction 11. _________________ is a pathologic condition wherein the core body temperature is less than 35°C. d. Hypothermia 12. True or False: The core body temperature, such as esophageal and rectal, is normally 0.5°C greater than the oral temperature. a. True 13. Due to the circadian rhythm, body temperature fluctuates more or less 0.6°C b. between the morning and evening. 14. Women experience core body temperature changes during their monthly menstrual cycle: It _____________________ during ovulation and returns to normal when menstruation begins. a. increases by 0.5°C 15. The posterior pituitary region is concerned with heat maintenance. It contains a large number of ____________ nerve cells. c. cold-sensitive 16. True or False: The skin contains both cold and warmth receptors. The number of cold receptors is ten times more than the warmth or heat receptors. a. True nursece4less.com nursece4less.com nursece4less.com nursece4less.com 68 17. Piloerection, which produces “goose bumps,” is caused by sympathetic stimulation of the _____________________ attached to the hair follicles. c. arrector pili muscles 18. The increase in cellular metabolic activity, caused by the thyroid-stimulating hormone (TSH), d. does not happen instantaneously. 19. Toxic thyroid goiters is found more frequently in individuals who b. reside long periods in cold climates. 20. The temperature set point in the hypothalamus is determined mainly by which of the following intensity of activity of the heat thermoreceptors a. in the anterior hypothalamus. 21. When the skin temperature is high, ____________ begins at a lower hypothalamic temperature compared to when the skin temperature is low. b. sweating 22. True or False: When the skin encounters cold stimuli, the hypothalamic centers are activated towards the shivering threshold even when the hypothalamic temperature may be normal. a. True 23. When an individual puts a foot under a hot lamp and leaves it there for a few minutes, local capillaries __________ and mild local sweating occurs. c. dilate nursece4less.com nursece4less.com nursece4less.com nursece4less.com 69 24. Sweating starts and stops due to temperature changes directly on the blood vessels and also by local cord reflexes that run first from skin receptors to d. the spinal cord. 25. When the internal body temperature increases significantly, signals from the _________________________ sends out a psychic sensation of overheat. c. anterior and posterior hypothalamus 26. The only effective mechanism that retains body heat in extremely cold environments is d. the individual taking action to warm his or her body. 27. Traditionally, hypothermia has been classified into three categories. A person classified as moderate hypothermia has a body core temperature between a. 28-32°C. 28. True or False: Skin disorders and injuries such as psoriasis and burns decrease the body's ability to preserve heat. a. True 29. If glycogen stores in the liver are exhausted, hypoglycemia may occur which inhibits b. shivering. 30. Active re-warming must be initiated when the core temperature falls below _____ because below that temperature, an individual cannot spontaneously return to the set point (the normal core body temperature of about 37°C). b. 30°C. 31. ___________________ accounts for about 15 percent of heat loss. a. Conduction nursece4less.com nursece4less.com nursece4less.com nursece4less.com 70 32. Evaporation accounts for approximately ___ percent of heat loss. c. 20 33. Hypothermia also causes cellular membrane disruption, allowing intracellular fluid to leak out, and ultimately leading to electrolyte imbalance, particularly d. hyperkalemia. 34. True or False: Cold infusions, rapid treatment of heatstroke, and emergency deliveries do NOT cause hypothermia. b. False 35. Endocrine dysfunctions, such as __________________, are known causes of decreased heat production. d. adrenal insufficiency 36. In patients presenting with unexplained hypothermia who fail to re-warm with conventional treatment modalities, causes may include d. All of the above 37. Therapeutic doses of ______________ have been reported to cause a drop in core temperature. a. valproic acid 38. True or False: Phenothiazines can cause central thermoregulation dysfunction and inhibition of peripheral vasoconstriction in response to cold through their blockade of alpha-receptors. a. True 39. Among the elderly, the most common precipitating factor for hypothermia is c. sepsis (systemic infection). nursece4less.com nursece4less.com nursece4less.com nursece4less.com 71 40. Trench foot occurs in part because wet feet lose heat _________ faster than dry feet. a. 25-times 41. True or False: Numerous studies from the Scandinavian countries found hypothermia may be delayed by the victim smoking. b. False 42. ______________ is caused by the movement of extracellular potassium into the cells, stimulated by alterations in cell membrane permeability and the activity of the sodiumpotassium pump. c. Hypokalemia 43. Ischemia, amplified adrenergic activity and electrolyte imbalance help lead to myocardial instability such as arrhythmias in cases of ____________ hypothermia. a. moderate 44. Hypothermia can also interfere with endothelial synthesis of prostacyclin (PGI2) and its inhibitory action on platelet aggregation, triggering platelet activation and c. thrombosis. 45. Hypothermia, postmortem patients who showed evidence of a mild increase in serum amylase, which means that the ___________ is/are also affected by hypothermia. d. pancreas nursece4less.com nursece4less.com nursece4less.com nursece4less.com 72 References Section The reference section of in-text citations include published works intended as helpful material for further reading. Unpublished works and personal communications are not included in this section, although may appear within the study text. 1. Centers of Disease Control and Prevention (2015). Hypothermia-Related Deaths — Wisconsin, 2014, and United States, 2003–2013. 64(06);141-143. Retrieved online at https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6406a2.htm. 2. Noe, Rebecca S., et al. (2012). Exposure to Natural Cold and Heat: Hypothermia and Hyperthermia Medicare Claims, United States, 2004–2005. American Journal of Public Health: April 2012; Vol 102, No. 4. 3. Hall, J. (2011). Regulation of body temperature: role of the hypothalamus. Guyton and Hall Textbook of Medical Physiology. 4. Brown, D.J.A., Brugger, H., Boyd, J. & Paal, P. (2012). Accidental hypothermia. New England Journal of Medicine, 367;20. Retrieved from http://www.uphs.upenn.edu/ppmc_emergency/PPMC%20Bookmarks/2015%2 0LLSA%20Articles/Accidental%20Hypothermia.pdf. 5. O’Connell, J., Petrella, D., & Regan, R. (Accidental hypothermia and frostbite: cold-related conditions. The Healthcare for Homeless Persons. Retrieved from http://www.bhchp.org/BHCHP%20Manual/pdf_files/Part2_PDF/Hypothermia.p df. 6. Lallanilla, M. (2013). Get naked and dig: The bizarre effects of hypothermia. Retrieved from http://www.livescience.com/41730hypothermia-terminal-burrowing-paradoxical-undressing.html 7. Danzl, D.F. Accidental hypothermia. In: Auerbach PS, ed. Wilderness medicine. 6th ed. Philadelphia: Mosby, 2012:116-42 8. Putzer, G., Schmid, S., Braun, P., Brugger, H., & Paal, P. (2010). Cooling of six centigrades in an hour during avalanche burial. Resuscitation, 81:1043-4 nursece4less.com nursece4less.com nursece4less.com nursece4less.com 73 9. Vanden-Hoek, T.L., Morrison, L.J., & Shuster, M. (2010). Part 12: cardiac arrest in special situations: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation, 122:Suppl 3:S829-S861. [Errata, Circulation 2011;123(6):e239, 2011;124(15):e405.] 10. Soar, J., Perkins, G.D., Abbas, G. (2010). European Resuscitation Council Guidelines for Resuscitation 2010 Section 8: cardiac arrest in special circumstances: electrolyte abnormalities, poisoning, drowning, accidental hypothermia, hyperthermia, asthma, anaphylaxis, cardiac surgery, trauma, pregnancy, electrocution. Resuscitation, 81:1400-33. 11. Brugger, H., Paal, P., & Boyd, J. (2011). Prehospital resuscitation of the buried avalanche victim. High Altitude Medicine and Biology, 12:199-205. 12. Boyd, J., Brugger, H., & Shuster, M. (2010). Prognostic factors in avalanche resuscitation: a systematic review. Resuscitation, 81:645-52. 13. Tipton, M.J, & Golden, F.S. (2011). A proposed decision-making guide for the search, rescue and resuscitation of submersion (head under) victims based on expert opinion. Resuscitation, 82:819-24. 14. Perlman, R., et al. (2016). A recommended early goal-directed management guideline for the prevention of hypothermia-related transfusion, morbidity, and mortality in severely injured trauma patients. Critical Care (2016) 20:107 DOI 10.1186/s13054-016-1271-z. The information presented in this course is intended solely for the use of healthcare professionals taking this course, for credit, from NurseCe4Less.com. The information is designed to assist healthcare professionals, including nurses, in addressing issues associated with healthcare. 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