Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Hyperthermia and Hypothermia Back to Basics April 2011 Dr. J. Clow, ER Case 1: 22 y.o. female Out with friends celebrating her birthday (February 19th) Dropped off at her front door by friends Found by her parents in the morning, passed out just inside the screen door Unable to wake her… call 911 Case 2: 85 y.o. male Mid-August, during heat wave Son goes to apartment and finds patient confused and lethargic Patient unable to give history Heat Regulation Four mechanisms of heat loss/dissipation: Radiation Convection Conduction Evaporation Radiation Physical transfer of heat between the body and the environment by electromagnetic waves 65% of heat transfer under normal circumstances Modified by insulation (clothing, fat layer), cutaneous blood flow Convection Energy transfer between the body and a gas or liquid Affected by temperature gradient, motion at the interface, and liquid Not usually a major source for heat loss or dissipation, but this increases with wind and body motion Conduction Direct transfer of heat energy between two surfaces Responsible for only a small proportion of heat loss under normal circumstances Increases significantly with immersion in cold water Major cause of accidental hypothermia Evaporation Most important source of cooling under extreme heat stress; important for hypothermia when in wet environment 25% of heat loss in temperate/cool conditions… may be increased significantly by sweating, increased respiratory rate Affected by relative humidity and clothing Hypothermia… Definition Core body temperature less than 35oC Mild: 32.2 - 35oC Moderate: 28 - 32.2oC Severe: < 28oC Causes… Decreased heat production Increased heat loss Endocrine, insufficient fuel, neuromuscular inactivity Accidental/immersion hypothermia, vasodilatation, skin disorders, iatrogenic Impaired thermoregulation Central (metabolic, drugs, CNS) Peripheral (spinal cord injury, neuropathy, diabetes, neuromuscular disorders) Predisposing Factors Risk Factors for Hypothermia Age extremes Elderly Neonates Outdoor exposure Occupational Sports-related Inadequate clothing Drugs and intoxicants Ethanol Phenothiazines Barbiturates Anesthetics Neuromuscular blockers Others Endocrine-related Hypoglycemia Hypothyroidism Adrenal insufficiency Hypopituitarism Neurologic-related Stroke Hypothalamic disorders Parkinson's disease Spinal cord injury Multisystem Malnutrition Sepsis Shock Hepatic or renal failure Burns and exfoliative dermatologic disorders Immobility or debilitation Signs and Symptoms Clinical Manifestations of Hypothermia System Mild Hypothermia Moderate Hypothermia Severe Hypothermia CNS Confusion, slurred speech, impaired judgment, amnesia Lethargy, hallucinations, loss of pupillary reflex, EEG abnormalities Loss of cerebrovascular regulation, decline in EEG activity, coma, loss of ocular reflex CVS Tachycardia, increased cardiac output and systemic vascular resistance Progressive bradycardia (unresponsive to atropine), decreased cardiac output and BP, atrial and ventricular arrhythmias, J (Osborn) wave on ECG Decline in BP and cardiac output, ventricular fibrillation (< 28°C) & asystole (< 20°C) Respiratory Tachypnea, bronchorrhea Hypoventilation (decreased rate and tidal volume), decreased oxygen consumption and CO2 production, loss of cough reflex Pulmonary edema, apnea Signs and Symptoms, cont’d TABLE 110-2. Clinical Manifestations of Hypothermia, cont’d System Mild Hypothermia Moderate hypothermia Severe Hypothermia Renal Cold diuresis Cold diuresis Decreased renal perfusion and GFR, oliguria Hematologic Increased hematocrit, decreased platelet & white blood cell counts, coagulopathy, DIC GI Ileus, pancreatitis, gastric stress ulcers, hepatic dysfunction Metabolic Increased metabolic rate, hyperglycemia Decreased metabolic rate, hyper- or hypoglycemia Musculoskeletal Increased shivering Decreased shivering (< 32°C, 90°F), muscle rigidity Patient appears dead, "pseudo-rigor mortis" History Often from bystanders/medics Circumstances surrounding exposure Where, submersion, ambient temperature? Length of exposure Mental status changes Any predisposing illness – acute/chronic? Alcohol/drugs? Physical Exam Vitals… Temperature – want a core temperature Where do we take it? Signs of other injuries? Can you find the cause of hypothermia? Any focal findings? Esp. neurologic, cardiovascular, respiratory Diagnositics ECG (always), CXR (most patients) Other tests depend on the clinical scenario Any signs of trauma? May need imaging… Are you able to take a history? Past medical history? Labs for all: CBC, electrolytes, glucose, renal function, toxicology, coags, ABGs, LFTs, lipase/amylase, cultures ECG Changes May see J waves late, terminal upright deflection of QRS complex; best seen in leads V3-V6 Multiple arrhythmias Heart block Atrial fibrillation Ventricular fibrillation ECG Changes, cont’d Management… Interventions Airway: need for intubation? Breathing: spontaneous respiration? Warmed humidified oxygen – either through an ETT, or via mask Circulation: pulse? BP? Large IVs – warmed IV fluids Arrhythmias – when do we treat? CPR? Interventions, cont’d Disability GCS Glucoscan, narcan, thiamine C-spine immobilization prn Exposure Undress, assess for trauma Re-cover quickly Rewarming Rewarming Techniques Passive rewarming: Removal from cold environment Insulation, Warm blankets (e.g. Bair hugger) Active external rewarming: Warm water immersion Heating blankets set at 40°C Radiant heat Forced air Active core rewarming at 40°C: Inhalation rewarming Heated IV fluids GI tract lavage Bladder lavage Peritoneal lavage Pleural lavage Extracorporeal rewarming Active Rewarming When? Cardiovascular instability Temp less than 32oC Concominant illnesses Extremes of age Failure of passive rewarming Active external or internal? Rewarming - Extracorporeal Options for Extracorporeal Rewarming Extracorporeal Rewarming (ECR) Technique Considerations Venovenous (VV) Circuit — CV catheter to CV or peripheral catheter No oxygenator/circulatory support Flow rates 150-400 mL/min ROR 2°-3°C/h Hemodialysis (HD) Circuit — single-or dual-vessel cannulation Stabilizes electrolyte or toxicologic abnormalities Exchange cycle volumes 200-500 mL/min ROR 2°-3°C/h Continuous arteriovenous rewarming (CAVR) Circuit — percutaneous 8.5 Fr femoral catheters Requires BP 60 mmHg systolic No perfusionist/pump/anticoagulation Flow rates 225-375 mL/min ROR 3°-4°C/h Cardiopulmonary bypass (CPB) Circuit — full circulatory support with pump and oxygenator Perfusate-temperature gradient (5°-10°C) Flow rates 2-7 L/min (ave. 3-4) ROR up to 9.5°C/h Note: BP, blood pressure; CV, central venous; ROR, rate of rewarming. Hyperthermia… Definition Core body temperature > 38oC Caused by a failure of thermoregulation Contrast with fever – cause is cytokine activ’n Spectrum of heat-related illnesses Heat cramps Heat exhaustion Heat stroke Spectrum Heat cramps Cramps in big muscles – spasms Normal temperature, mentation Caused by dilutional hyponatremia (hypotonic fluid replacement) Spectrum, cont’d Heat exhaustion Weakness, dizziness, headache, syncope Nausea, vomiting Temperature 39-41.1oC Normal mentation Profuse sweating Spectrum, cont’d Heat Stroke Temperature >41.1oC Coma, seizures, confusion No sweating Classic triad: hyperpyrexia, CNS dysfunction, anhidrosis Mortality of 10-20% with treatment Classic vs. Exertional Spectrum, cont’d Heat Stroke: Classic (non-exertional): Persistent environmental exposure Impaired thermoregulation Exertional: Heavy exercise in setting of high temperature and humidity Causes of Hyperthermia Increased heat load Heat absorption from environment Metabolic heat Diminished heat dissipation Heat stroke (exertional, classic) Obesity, anhidrosis, drugs Sepsis Predisposing Factors… Predisposing Factors for Heat Stroke Increased Heat Production Decreased Heat Loss Environmental heat stress Environmental heat stress Exertion Cardiac disease Fever Peripheral vascular disease Hypothalamic dysfunction Dehydration Drugs (sympathomimetics) Anticholinergic drugs Hyperthyroidism Obesity Skin disease Ethanol β Blockers Causes of Hyperthermia… Causes of Hyperthermia Syndromes HEAT STROKE Exertional: Exercise in higher-than-normal heat and/or humidity Nonexertional: Anticholinergics, including antihistamines; antiparkinsonian drugs; diuretics; phenothiazines DRUG-INDUCED HYPERTHERMIA Amphetamines, cocaine, phencyclidine (PCP), methylenedioxymethamphetamine (MDMA; "ecstasy"), lysergic acid diethylamide (LSD), salicylates, lithium, anticholinergics, sympathomimetics NEUROLEPTIC MALIGNANT SYNDROME Phenothiazines; butyrophenones, including haloperidol and bromperidol; fluoxetine; loxapine; tricyclic dibenzodiazepines; metoclopramide; domperidone; thiothixene; molindone; withdrawal of dopaminergic agents SEROTONIN SYNDROME Selective serotonin reuptake inhibitors (SSRIs), monoamine oxidase inhibitors (MAOIs), tricyclic antidepressants MALIGNANT HYPERTHERMIA Inhalational anesthetics, succinylcholine ENDOCRINOPATHY Thyrotoxicosis, pheochromocytoma CENTRAL NERVOUS SYSTEM DAMAGE Cerebral hemorrhage, status epilepticus, hypothalamic injury Differential Diagnosis Differential Diagnosis of Heatstroke Drug toxicity: anticholinergic toxicity, stimulant toxicity (phencyclidine, cocaine, amphetamines, ephedrine), salicylate toxicity Drug withdrawal syndrome: ethanol withdrawal Serotonin syndrome Neuroleptic malignant syndrome Generalized infections: bacterial sepsis, malaria, typhoid fever, tetanus Central nervous system infections: meningitis, encephalitis, brain abscess Endocrine derangements: diabetic ketoacidosis, thyroid storm Neurologic: status epilepticus, cerebral hemorrhage History Circumstances (as per hypothermia) Exertion? Fluids? Past medical history – any acute or chronic illnesses that may worsen situation Medications/Drugs Trauma? Physical Examination Temperature Where do we take it? And how? Vitals! Look for complications or other causes of the patients symptoms Respiratory, cardiac, neurologic examination Signs of bleeding Diagnostics ECG (all), CXR (most) Imaging guided by history CBC, electrolytes, renal function, LFTs, Ca, Mg, PO4, coags, CK Urine – myoglobin Pan-cultures Poor prognostic factors Temperature > 41.1oC AST > 1000 Coma Rhabdomyolysis Renal Failure Hypotension Treatment ABC’s!!! Remove to cool environment! Active cooling Correct fluid and electrolyte imbalances Supportive care Treatment Comparison of Cooling Techniques Technique Advantages Disadvantages Evaporative (i.e. wet the patient’s gown, sheets then use fan) Simple, Readily available Noninvasive Easy patient access Relatively effective Shivering Difficult to maintain monitoring electrodes in position Immersion (in cold/ice water) Noninvasive Relatively effective Shivering, Cumbersome Poorly tolerated Logistically difficult to access Difficult to maintain monitoring Ice packing (cover w/ ice) Noninvasive Readily available Shivering Poorly tolerated Strategic ice packs Noninvasive Readily available Combined with other techniques Shivering Poorly tolerated Medium efficiency Cold gastric lavage Generally available Invasive Labor intensive Potential for water intoxication May require airway protection Limited human experience Cold peritoneal lavage Theoretically beneficial Invasive Limited human experience Complications of Heat Stroke Complications of Heatstroke Immediate Delayed Vital signs Hypotension Hypothermia overshoot Hyperthermic rebound Muscular Shivering Rhabdomyolysis Neurologic Delirium Seizures Coma Cardiac Heart failure Pulmonary Pulmonary edema Acute respiratory distress syndrome Renal Oliguria Renal failure Gastrointestinal Diarrhea Hepatic necrosis Mucosal gastrointestinal hemorrhage Metabolic Hypokalemia Hypernatremia Hyperkalemia Hypocalcemia Hyperuricemia Hematologic Cerebral edema Thrombocytopenia Disseminated intravascular coagulation Back to the cases… Case 1: Hypothermia What do you want to know? Physical Exam? Labs? Any imaging? How are you going to treat her? Case 2: Hyperthermia What do you want to know? Physical Exam? Labs? Any imaging? How are you going to treat him?