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259 Clinical The recognition and management of body temperature disturbances in Royal Navy personnel Surg Lt Cdr DJC Angus, Dr EHN Oakley Abstract This article discusses hypothermia and hyperthermia, described together as thermal illness. These conditions are seen within the United Kingdom (UK) Armed Forces population at home and abroad and may endanger life, with significant implications for both the individual and the chain of command. Recognition and management from initial presentation to return to duty is discussed and guidance given on occupational considerations. Introduction In the summer of 2013, three Service personnel died from heat illness during a training exercise in Wales (1). This highly publicised event on UK soil reminds us of the risk to Service personnel from thermal illness, even in relatively benign conditions. In the United States of America (USA), heat illness claims an average of 448 lives a year and contributes to the deaths of a further 240 individuals, whilst hypothermia results in 1,301 deaths per year (the USA has around 2.5 million deaths per year) (2). Review of the Naval Service Incident Notification Cell database reveals that between June 2012 and June 2013, there were ten reported thermal illness cases in the Royal Navy (RN) alone, distributed evenly between hypothermia and hyperthermia. These occurred on board ships and submarines, and in the field. Extremes of heat and cold can be fatal, but survivors can also suffer significant long-term problems, even from a single incident and despite optimal management. Prevention is therefore preferable and the chain of command must be given robust advice from the medical branch, which has a key role. Individuals can also help protect themselves both by preparation and discipline in the field. Detailed advice on prevention is beyond the scope of this article, but is available in Joint Service Publication (JSP) 539 (3). While thermal illness may result in mortality, it has arguably a greater impact on operations through associated morbidity. Extremes of temperature cause impairment in the ability to reason and perform, and irrational decisions in the field may endanger the individual and colleagues. Additionally, others may follow one case of thermal illness and operations may have to be delayed or altered in order to maintain the health of those at risk. While on board a ship or submarine, sailors are generally protected by a controlled climate. However, emergencies including fire, man overboard or failure of heating or air-conditioning units can cause thermal problems. More routine activities can also pose a risk: fitness test candidates, upper deck sentries and weapons aimers, for example, can be at risk. The early recognition and management of thermal illness maintains our fighting effectiveness, reduces or prevents long-term illness, and saves lives. Clinical picture and diagnosis Hypothermia Environmental hypothermia follows exposure to cold, but individuals are affected differently by the same exposure. The unwell, poorly fed, or dehydrated sailor will be much less able to stay warm than his or her colleagues. Hypothermia should always be suspected when there is a suggestive history of circumstances such as: • Immersion. Exposure to cold or cool water, classically following a man overboard. The initial overwhelming cold stimulus to the peripheral thermoreceptors will produce immediate ‘cold shock’ with difficulty controlling breathing and keeping the airway clear of water. Following this, rapid heat loss to the water can cause early signs of hypothermia within minutes and unprotected lean individuals may be unconscious after as little as half an hour. • Exposure. Typically outdoors in wet, windy, cool or cold environments. Symptoms may even develop J Royal Naval Medical Service 2014, Vol 100.3 in still air temperatures above 5 degrees C, especially in wet clothing. While possible on ship, this would most likely be seen in a land-based operation or exercise, particularly within the UK, when clothing, shelter and physical activity may be insufficient to stay warm. Evaporating water from skin and clothing can be an even more potent means of heat loss than immersion, so cases are common in those who have become drenched from immersion or precipitation. Other scenarios include disaster relief operations, Pre-hypothermia Mild hypothermia temperature between 32˚C and 35˚C) Moderate hypothermia (core temperature <32˚C) and severe (<30˚C) 260 both in survivors and those rendering assistance. • Urban. Typically a gradual onset in compromised people such as the elderly in poorly heated houses. The formal diagnosis of hypothermia requires a core temperature below 35 degrees C as measured with a rectal thermometer. Several other forms of temperature measurement (including aural, particularly infra-red tympanic membrane, axillary and oral thermometers) are not reliable in this These subtle symptoms occur in individuals at high risk of developing hypothermia. Their mood may change, they may lose coordination or feel overly tired, and they are often slow and the last in a moving group. Spotting these symptoms in someone exposed to cold should raise suspicion and prompt core temperature assessment. This patient will probably be conscious and feeling very cold, shivering uncontrollably and have cold hands and feet. They may have a rapid heart rate and a cold diuresis can result in dehydration and other changes in fluid balance. While this helps the body preserve warmth, it sacrifices the extremities and should be borne in mind during re-warming. Distinguishing these clinically is difficult and rather unhelpful. Both are lifethreatening emergencies and generally develop as shivering wanes with falling core temperature. Patients are likely to have stiff limbs (increased muscle tone which changes to flaccidity as death approaches) with reduced consciousness, vital signs that are difficult to detect (including pupillary reflexes) and have ‘marbled’ skin. This means they may appear dead even on careful examination, so all profoundly hypothermic casualties should be assumed to be revivable until attempts to re-warm them (preferably in hospital) have proven unsuccessful. Table 1. Stages of hypothermia. Investigation(s) Blood sugar level Electro-Cardiogram (ECG) blood pressure Full Blood Count (FBC) Urea and Electrolytes (U&Es). Coagulation screen Amylase Blood cultures Arterial Blood Gas (ABG) Explanation Hypoglycaemia may present with very similar symptoms to early hypothermia and is treated by replacing sugar either orally or intravenously. A Boehringer-Mannheim (BM)TM device will suffice pre-hospital. Hypothermia may trigger changes that can be life threatening: immersion and casualties can be in profound hypothermic bradycardia, asystole, or ventricular fibrillation, and there are characteristic changes seen in many hypothermic casualties including J waves, prolonged PR and QT segments and a widened QRS complex. Anaemia and infection predispose to hypothermia. Exclude acute kidney injury secondary to dehydration. Hypothermia can produce clotting disorders, which may need careful correction. Pancreatitis is more common in hypothermic patients and sub-acute fulminating pancreatitis does sometimes cause unexpected death in those who may not have appeared to be particularly hypothermic. To exclude sepsis as a cause of the hypothermia. Monitoring of the effectiveness of gas exchange, particularly in those who may have aspirated water, and in differential diagnosis. Table 2. Suggested investigations for the hypothermic patient. 261 Clinical scenario and should never be used for diagnosis (3, 4). Although most commonly associated with cold and wet environments, patients may present with hypothermia from the same event that has rendered other participants hyperthermic, and they can be hard to distinguish from symptoms alone. A reliable estimate of core body temperature is therefore important and it may be helpful to consider three levels or stages of progression (Table 1). Symptoms and signs may appear in any order and inconsistently (Box 1). Pulse, respiratory rate and level of consciousness should always be recorded. When able, perform a standard panel of investigations (Table 2). Pulse, respiratory rate and level of consciousness should always be recorded and investigations performed if possible (Box 2). Hyperthermia Similarly, raised core temperature may cause a wide variety of illness of varying severity. Classification and terminology can be confusing, but effective early management is essential in all cases. As the symptoms are often non-specific, the history is important and should prompt formal assessment. Commonly, symptoms will develop in individuals after a period of exercise in a warm environment while wearing excessive clothing. Acclimatisation is an important protective factor, but raised environmental heat stress or additional occlusive clothing, which challenges individuals beyond their acclimatised condition, are frequent causes of hyperthermia (3, 5). Cases are also common in those required to undertake physical work shortly after arriving in a warm theatre of operations, before any effective acclimatisation can take place (3, 5). Dehydration may be evident from the history, perhaps the result of prior alcohol consumption, and there are strong associations with drug use, both prescribed and illegal (5, 6). Neurological Headache, Weakness, Confusion, Loss of co-ordination and/or dizziness, Disturbed vision, Collapse, Loss of consciousness, Agitation, which may progress to aggression and violence. Other systems Feeling hot, tired, exhausted, Hyperventilation, which often results in further symptoms including tetany, Cramps, Diarrhoea, nausea or vomiting, resulting in dehydration and worsening illness if untreated. Box 1. Symptoms of hyperthermia. Individual variation is an important consideration. Differences in body mass index, clothing, physical exertion, hydration, and microclimate, can produce both hypothermic and hyperthermic casualties on the same day. This means that reliable measurement of core temperature is crucial. • • • • • • Rectal temperature. Temperature measured in other areas may be misleading. Blood pressure. Low pressure is a late sign of suboptimal hydration and imminent circulatory collapse. Arterial oxygenation using a pulse oximeter. Give supplemental oxygen if <94% in an otherwise healthy individual. Blood sugar level. Give sugar by an appropriate route if low. Urine dip. Look for protein as a sign of renal failure, specific gravity to monitor hydration and “blood” which may indicate myoglobinuria, a sign of extensive muscle damage. Fluid balance monitoring on an In/Out chart such as the FMed 100. Box 2. Observations suggested for hyperthermic patients. With such vague symptoms there is a very broad differential diagnosis. Paradoxically, consumption of excessive fluid may cause overload with similar symptoms to hyperthermia, but rectal temperature may appear normal, and in hot environments some individuals may become profoundly hyponatraemic. Although this may resolve spontaneously, the risk of pulmonary oedema and serious sequelae of hyponatraemia should promote hospital admission during which other potential causes may be excluded (3). Infection commonly causes pyrexia (which may be apparent from the history) and this independently predisposes to heat illness (5). Acute neurological events such as stroke or epilepsy should be considered, especially if rectal temperature is normal. Other, non-environmental causes of hyperthermia include thyroid storm, phaeochromocytoma, malignant hyperthermia, neuroleptic malignant syndrome, and hypothalamic haemorrhage. Clinical management Confused patients may temporarily lack capacity and be unable to consent to, or refuse, treatment. There is detailed J Royal Naval Medical Service 2014, Vol 100.3 guidance available from the General Medical Council but in short, when a patient cannot “…understand, retain, use and weigh up the information needed to make a decision, and communicate their wishes”, then healthcare workers must act in the best interests of the patient (7). Hypothermia The aim of management is to restore the core temperature to normal as safely as possible. Importantly, this does not necessarily require the fastest re-warming possible because rapid heating of a profoundly hypothermic patient risks arrhythmia, collapse and rapid changes in fluid balance, making successful management more difficult. Passive methods are normally used in the field to avoid these problems, and generally, the rate of warming should not exceed the original rate of cooling (5). While at the site, assess for catastrophic haemorrhage, a patent airway, effective breathing and adequate circulation (<C>ABC). The normal rules of first aid apply, and serious injuries should be treated before, or ideally while, rewarming the patient. Cardio-Pulmonary Resuscitation (CPR), however, should only be started if it can be maintained effectively until delivery to a place of definitive care. JSP 539 Chapter 5 includes a modified algorithm (Figure 5.1) which considers the actions required for patients in whom signs of life are absent in remote locations where maintaining effective life support may not be feasible (Figure 1) (5). 262 incorporating metallic sheeting seldom seal the internal environment properly, meaning additional insulation is beneficial, particularly if a water-tight layer is included (9). Those who are only very mildly hypothermic and fully conscious can be offered hot and sweet, but non-alcoholic, drinks. Continue to monitor the patient (Figure 1). Once inside shelter, a patient who has been rapidly cooled but has remained conscious (typically seen in immersion incidents) can be rapidly re-warmed in a warm bath at no more than 40 degrees C. However, this must be avoided where hypothermia is profound or prolonged, and is inadvisable if there is a concomitant risk of non-freezing cold injury, which would be worsened by rapid re-warming (3). Once in hospital, further interventions and monitoring may be appropriate (Box 3). • • • • • • • • • • • • • • Humidified oxygen warmed to 42-46˚C. ECG monitoring to detect arrhythmias. Continuous monitoring of rectal temperature until >36˚C. Where available, extra-corporeal rewarming using cardio-pulmonary bypass may be the method of choice for rewarming the profoundly hypothermic, and those apparently dead. Avoid giving any drugs until core temperature is >30˚C and then prolong the intervals between doses. Consider a Central Venous Pressure (CVP) line and urinary catheterisation for monitoring fluid balance. Record an ECG as high core temperature can cause cardiac damage and metabolic disturbances can cause dysrhythmias. Continuous rectal temperature monitoring. Consider intubation or ventilation to reduce effort and therefore heat generation by the patient. Blood tests including FBC, U&Es, Liver Function Tests (LFT), calcium, magnesium, creatinine kinase (CK), coagulation screen, myoglobin clearance, lactate and serum osmolality. Arterial blood gases if indicated. Consider a urinary catheter, giving fluids by nasogastric tube, central venous pressure line or arterial line for accurate fluid balance monitoring. Consider Dantrolene (2.5-3 mg/kg) in exertional illness administered by an anaesthetist/intensivist (3). At 24 hours, repeat at least the U&Es, CK, LFT and coagulation to monitor for deterioration. Seek shelter where available. This would ideally be indoors or within the ship’s superstructure, but in the field a cave or tent would suffice. Because of the risk of circumrescue collapse, anyone suspected of being hypothermic should rest in a recumbent position until thoroughly rewarmed (8). This is most important in immersion casualties as the pressure of the water around the legs and a roughly horizontal position helps return blood to the heart. If removed from the water in an upright posture, the loss of this pressure along with the increased circulatory demand of this position may cause excessive cardiac strain upon an already ‘irritable’ heart and may precipitate atrial and ventricular arrhythmias. In an attempt to avoid this postimmersion collapse, the Royal Navy now uses two strops to rescue a casualty, one under the arms and one behind the knees to keep the patient close to a horizontal position (Figure 2). Box 3. In-hospital monitoring and treatment of hypothermia. Dry clothes, if available, should be worn by an otherwise well casualty. Otherwise, a wind- and water-proof bag will stop evaporative heat loss and make wet clothing less thermally disadvantageous. Specialist re-warming and recovery bags are available, although their most important property is stopping evaporative heat loss; thin, flimsy bags Significant heat illness may result in cardiac arrest, convulsions and other central nervous damage, hypoglycaemia, hyperkalemia, renal failure, and rhabdomyolysis. The most severe cases may have overt evidence of single or multi-organ failure, which can also 263 Figure 1. Management of hypothermia (5). Clinical J Royal Naval Medical Service 2014, Vol 100.3 Figure 2. Taken during a man overboard exercise, a rescuer is lifted with one strop (left) and a dummy casualty with two (right). 264 265 Figure 3. Management of hyperthermia (3). Clinical J Royal Naval Medical Service 2014, Vol 100.3 266 result in cardiac muscle damage, liver failure and clotting disorders. If present, these conditions should be treated while continuing to cool the patient concomitantly. Occupational considerations in the RN/UK Armed Forces At the site, stop physical activity as soon as possible and consider stopping and cooling other personnel if present, in order to prevent further casualties. Assess <C>ABC and treat any life-threatening injuries or illnesses, then lie the patient down in the shade or, ideally, in an air-conditioned space. If conscious, raise the patient’s legs, or place them in the recovery position if unconscious. The patient should be stripped to their underwear and then sponged or sprayed with cool (not cold) water and their skin fanned. Commercially available garden sprays with a capacity of several litres are ideal. This should be stopped if the patient starts to shiver and can be restarted when shivering stops. Keep a careful temporal record of their level of consciousness using a recognised scoring system such as Alert, Voice, Pain, Unresponsive (AVPU) or the Glasgow Coma Scale (GCS). Give sips of water if conscious and arrange urgent medical evacuation (3). Following complete recovery from hypothermia, potential causes or contributing factors such as hypothyroidism should be considered. In the absence of these, and assuming there were no significant sequelae such as pancreatitis, a patient can be returned to full duties when fit. Even relatively brief periods of mild hypothermia can leave personnel feeling physically exhausted for some days. Patients who have been hypothermic may have also sustained local cold injury, so it is important to question or examine them for possible symptoms including numbness, discolouration or swelling of an exposed body part. In a pre-hospital setting, administer 100% inspired oxygen if this is available. Continue to give oral fluids if the patient is conscious; oral fluid may be supplemented with intravenous fluids. A suggested regimen is to give one litre of crystalloid fluid over 30 minutes, followed by 2.5 ml/kg/hr (i.e. the second litre over four to six hours). If hospital admission is not indicated, the patient should be removed from duties and rested for 24 to 48 hours. Blood investigations should be performed after 24 hours if available (Box 4) and Medical Officer review arranged on at least days three, five and seven (4). The individual should then re-undertake the local acclimatisation protocol as if newly arrived from the UK. Patients who do not respond within 30 minutes of treatment or who suffer seizures, have a GCS<8 at any stage or have a rectal temperature persistently >40C despite active cooling should be evacuated to a Role 2 or 3 facility where they should be comprehensively re-assessed (Box4) (3). JSP 539 Chapter 4 Annex A details management strategies of such patients in this setting (Figure 3). Reporting There are statutory and single Service requirements to report thermal illness. Cases should also prompt a Significant Event report where appropriate, and a Defence Lessons Implementation and Management System (DLIMS) submission (3). All moderate and severe cases should be reported, but even milder cases should be reported when the risk assessment had deemed them unlikely. Instructions for reporting are in JSP 539 paragraphs 106-114 (3). Hypothermia Hyperthermia Any significant central nervous system (CNS) derangement, seizures, or significant biochemical disturbance should prompt referral for follow-up in the Heat Illness Clinic at the Institute of Naval Medicine (INM) (3). The occupational impact will depend on severity and may be ultimately determined by the Heat Illness Clinic. As a guide: • Mild heat illness. Where there was no need for hospital admission and no evidence of biochemical abnormality, patients may be restricted to light physical exercise only for seven days followed by gradual supervised return to activity over the next seven days (3). • Moderate heat illness. These patients will probably have required hospital admission and should be restricted from exposure to excessive heat and made unfit for any physical training until INM review. Using the current UK Joint Medical Standards (JMES), this is P7 Medically Non Deployable (MND) L4, 214 (Unfit exposure to excessive heat), 103 (Unfit physical training). They can, however, start a gradual, supervised return to exercise before attending INM, starting no sooner than fourteen days after biochemical recovery (3). Recurrence of a mild heat illness should be managed similarly. • Severe heat illness. Patients who require intensive care admission should all be discussed with INM and referred for review. The likely recommendation is for restricted duties as for moderate illness (above) for at least three months, and until INM review. Gradual, supervised return to exercise is recommended from at least one month after biochemical recovery and resolution of any complications (3). Return to exercise should be part of a structured regime developed with an Exercise Rehabilitation Instructor (ERI) in a Primary Care Rehabilitation Facility (PCRF). This 267 should start before an INM appointment, if needed. If the creatinine kinase (CK) was markedly raised, a baseline and 8-24 hour post-exercise CK should be compared after the first fifteen-minute treadmill session. Significant elevation requires a further two weeks of rest, and this should be repeated until the CK is normal (3). Water-based exercise is ideal, otherwise only Physical Training (PT) kit should be worn and intensity should not exceed 60% of the patient’s maximum heart rate. Initially limited to fifteen minutes, sessions should be gradually extended to 30 minutes, twice daily, with the aim of avoiding delayed onset muscle soreness, which contraindicates further exercise until resolved (3). Clinical Conclusion Thermal illness poses a significant threat to RN personnel and other members of the Armed Forces both during training and while on deployed operations. While these conditions would ideally be prevented by preparation and protection, early recognition and management will reduce the risk to the individual and facilitate a prompt return to duty. Unfortunately, these conditions tend to develop in remote and environmentally adverse areas, which may make management more difficult. Adhering to the advice in this article as far as practicable will help provide the best available care for the patient. References 1. http://www.bbc.co.uk/news/uk-wales-23311651 accessed Apr 14. 2. www.cdc.gov accessed Apr 14. 3. Headquarters of the Surgeon General, Head of Strategic Medical Policy. Joint Services Publication 539: Climatic illness and injury in the Armed Forces: force protection and initial medical treatment. London: Ministry of Defence; 2012. 4. Lt Col R Russell RAMC, Miss A Bess MIPA, editors. Joint Service Publication 999: Clinical Guidelines for Operations [Internet]. Royal Centre for Defence Medicine; Sep 2012 [cited 2014 Jan 4]. Available from: https://www.gov.uk/government/uploads/system uploads/attachment_data/file/79106/20121204-8-AVB-CGO_Online_2012.pdf accessed Jan 14. 5. Pandolf KB & Burr RE. Medical Aspects of Harsh Environments, Vol 1. Virgina: Office of the Surgeon General US Army 2001. Available from: www.cs.amedd.army.mil/borden/Portlet.aspx?ID=eebb9338-2027-46d5-a5f2-f245e2019b6c accessed Jun 14. 6. Seedat YK, Aboo N, Naicker S et al. Acute renal failure in the “Comrades Marathon” runners. Renal Failure 1990;11(4):209-12. 7. http://www.gmc-uk.org/guidance/ethical_guidance/consent_guidance_endnotes.asp accessed Apr 14. 8. Golden FStC, Hervey GR, Tipton MJ. Circum-rescue collapse: collapse, sometimes fatal, associated with rescue of immersion victims. J R Nav Med Serv 1991;77:139-149. 9. Light IM, Dingwall RHM, Norman JN. The thermal protection offered by lightweight survival systems. Aviat Space Environ Med 1980;51(10):1100. Authors Surgeon Lieutenant Commander DJC Angus, MB ChB RN General Practice Specialty Trainee Year 2 Dr EHN Oakley Physician Former Head of Survival and Thermal Medicine Institute of Naval Medicine Gosport ,Hampshire PO12 2DL