The effects of cold and heat

  • Maintaining body temperature
  • Core temperature
  • Alcohol
  • Recognition of hypothermia
  • Management of hypothermia
  • Vapour barrier principle
  • Prevention of cold injury
  • Other cold-related conditions
  • Heat illness
  • Heat-related conditions

In the outdoors, death or serious illnesses or injuries are relatively uncommon. The frequency of encountering a seriously injured or very ill person in the bush is low, so few outdoor leaders have good hands-on experience in managing medical emergencies. However, conditions arising from extremes of cold and heat are relatively common, and are potentially life threatening. Hence, a knowledge of effective techniques to prevent heat and cold related injuries and conditions, and the correct treatments to apply, can be life saving.

Heat and the body

Heat flows to and from the body are determined by the amount of heat produced by the body from metabolic processes, and heat gain or loss to and from the environment. The body loses and gains heat through conduction, convection, radiation and evaporation. Understanding these processes is necessary to understand heat or cold injury, and how they should be managed.

Conduction
Conduction is the transfer of heat between objects by direct contact. Heat flows from higher temperature to lower temperature. In this way, heat may be lost from the body when a person is placed on the snow with little insulation, or heat may be provided to a hypothermic patient by contact with a warming device. Contact with clothing that has been cooled by evaporation of water or sweat is another example of heat loss by conduction. The well, alert person usually protects themselves from these heat losses by wearing insulating clothing and footwear and using appropriate equipment. The person who is injured, ill, intoxicated or has an altered conscious state is at risk of significant heat exchange when lying uninsulated on hot or cold ground for prolonged periods.

Convection
Convective heat exchange occurs when heat is transferred between the body and air. Increasing air movement will increase transfer by convection; for example, fanning a patient suffering a heat illness will facilitate heat loss from the body.

Radiation
Radiation is the transfer of heat through space, by electromagnetic radiation, without any intervening medium. Radiation is a major source of heat gain to the body in hot climates. Protection from direct sunlight and the wearing of light coloured clothing reduces absorption of solar radiation.

Evaporation
Evaporative heat loss occurs when water vaporises from the body surface. This occurs with sweating and with breathing, because the air we breathe out contains water. The scalp, face and upper torso are the most important sites for cooling from sweating. The capacity for sweat to evaporate varies with humidity, ambient temperature and wind velocity. High ambient temperature, high humidity and low wind velocity minimises evaporative heat loss from the body and results in an increased risk of heat illness. When sweating is minimal, evaporative heat loss accounts for only 15% of total body heat loss. However, with maximal sweating, evaporative heat loss can increase to around 70% of body heat loss. Evaporative heat loss through breathing can be reduced by breathing warm, moist air. Loose fitting clothing increases both convective and evaporative heat losses.

Maintaining body temperature

The body responds to heat and cold stress by changing blood flow quantities and patterns around the body, modifying sweating, adjusting metabolism and changing behaviour. Blood flow to the superficial vessels (those just beneath the skin) is reduced in cold conditions to conserve heat, and is increased in hot conditions to aid heat loss. Sweating facilitates heat loss by evaporative cooling, and increases in response to exertion and rises in body temperature. Shivering, which can increase the body’s heat production five-fold, and muscular activity, which can increase heat production tenfold, are the main means by which the body generates metabolic heat in cold environments.

Shivering and deliberate activity to keep warm have high energy demands and are limited in duration by energy availability. People in normal states of consciousness automatically modify their behaviour to cope with heat and cold stress, for example, by seeking shelter or shade, curling up in a ball or lying spreadeagled, depending on the need to gain or lose heat.

Core temperature

The normal body temperature is 37.0°C (range 36.6–37.4°C). Core temperature refers to the temperature of blood supplying vital organs, such as the brain, heart and lungs and is the most reliable and generally used measure in clinical settings. Core temperature is measured deep within the body (e.g. rectum, bladder) and requires special thermometers. It is generally impractical to measure core temperatures in the field, so heat or cold illness should always be considered when a person displays relevant symptoms and signs in a setting where heat or cold injury could occur.

Alcohol and cold and heat injury

There is the incorrect impression that alcohol has a warming effect on the body. This is partly due to the ‘flushing’, which causes increased blood flow to the skin and gives a false perception of body warmth, when actually there is increased heat loss. Alcohol increases the risk of inappropriate behaviour in adverse environments, including failure to take usual precautions to protect against cold or heat, and engaging in risk-taking behaviour. Alcohol increases blood flow to the skin, impairs body heat production and impairs shivering, all of which are undesirable in the face of cold injury and may result in lowered body temperature. Alcohol directly impairs the body’s ability to regulate body temperature at both high and low temperatures, and should be avoided in situations of heat and cold stress.

Cold injury—hypothermia

Hypothermia is defined as a fall in core body temperature to below 35°C. Predisposing factors for the development of hypothermia include:

  • hunger
  • fatigue
  • exertion
  • low body fat (e.g. thin, male etc)
  • low ambient temperature
  • high wind chill
  • inadequate clothing (ineffective insulation, unprotected head)
  • wet clothes (rain, sweat)
  • inadequate equipment (protection from cold, wind, wet)
  • alcohol
  • underlying disease or illness (e.g. diabetes, dehydration)
  • underlying debility (e.g. elderly, frail, anorexic)
  • injury (blood loss, head injury, immobilisation from any cause).

Some people who may be more susceptible to hypothermia include those who are lean, male, young or elderly, or undereating, unfit teenagers. If coupled with adverse environmental conditions and or underlying illness or injury, the risk increases significantly.

Prevention of cold injury

Humans' responses to cold are to reduce heat loss, increase body heat production and seek external heat. The prevention of hypothermia focuses on ensuring these processes can operate effectively.

Trip planning
A key part of prevention is adequate trip planning, party preparation and sound leadership. Party members should be fit for the trip and should have adequate rest and nutrition. Dehydration should be avoided. It is preferable to drink cold water than ingest snow or ice, as the conversion of ice to water uses a large amount of body energy. Appropriate clothing is essential. There should be insulation worn over areas with large blood vessels close to the surface, such as the head and neck, which have a high heat loss potential. Wet inner garments should be changed, conditions permitting. Clothing should be varied according to the weather conditions and exertion levels to stay warm and dry. The effectiveness of clothing in the cold depends on its insulating properties, including when wet. Parties should be well equipped for shelter in cold or wet conditions. Over exertion should be avoided, as cold and exhaustion in combination predispose hypothermia.

Clothing
Clothing should be layered to avoid both cooling and over-heating. Water conducts heat around 30 times faster than air at the same temperature, so wet clothes, including those wet from perspiration, must be avoided. Keeping clothes dry reduces heat loss by evaporation and conduction. Ventilation is important to allow evaporation of sweat and to keep clothing dry. Windproof outer shells reduce heat loss by evaporation and convection.

Windchill
The cooling effect of wind combined with cold should be understood. Windchill charts demonstrate that the rate of cooling ('windchill') increases as the wind rises, as shown in Figure 21.1. This is not a linear relationship - an increase in wind chill approximates the square root of the wind speed. There is no change in actual temperature, but the effect of wind velocity on the rate of cooling for a given temperature is significant.

Recognition of hypothermia

Recognition is based on knowing the signs and observing the patient. The signs may be subtle, so there should be a high level of suspicion of hypothermia in any person behaving abnormally in likely conditions. Patients of hypothermia cannot recognise their own impairment, and so recognition must be done by others. Response cannot be delayed; failure to implement appropriate measures immediately risks the life of the patient.

All party members should be observed, remembering that the occurrence of hypothermia in one member of a party suggests that others may be susceptible. While the body can acclimatise to heat, there is no clear evidence that the body can acclimatise to cold to any significant degree. The combination of exertion and the need to maintain body temperature in a cold environment places a large demand on body energy stores, requiring frequent carbohydrate snacks. Fitness alone does not improve the ability to withstand cold stress, but physical fitness and good nutrition may reduce fatigue or exhaustion when activity and shivering are required for heat generation, and increase the margin of safety in the cold.

Classification of hypothermia
Hypothermia is considered mild if core temperature lies between 35°C and 32°C and profound at core temperatures below 32°C. In most cases of mild hypothermia, the patient is able to rewarm themselves by shivering, provided proper first aid measures are instituted, with prevention of further heat loss being the most important. However, in severe hypothermia, the patient loses the ability to rewarm themselves, there is significant impairment of brain, heart and other bodily functions, and there is grave threat to life. It is virtually impossible to rewarm such a patient in the field, but further heat loss can be minimised by first aid measures. Evacuation should be arranged urgently. While the lowest recorded adult accidental hypothermia survival temperature to date is 16°C, the risk of death is high once core temperatures fall below 32°C.

Mild hypothermia
Early signs of mild hypothermia are forgetfulness, loss of judgement and loss of coordination, particularly of fine movements (e.g. use of fingers). There may be some abnormal behaviour, such as lack of cooperation and apathy. Shivering will occur and may be uncontrollable. Other signs of impaired brain function may occur, such as slurred speech and stumbling gait. The appearance of hypothermia can cover a wide spectrum, ranging from mild, insidious loss of judgement, which may not be immediately apparent, to the obviously stumbling, forgetful person. ‘Paradoxical’ undressing may occur; the inappropriate undressing in a hypothermic patient indicates loss of normal protective behavioural responses. The signs of mild hypothermia may be subtle and easily missed when the party is battling adverse conditions, unless vigilant observation of all party members is maintained.

Profound hypothermia
Profound hypothermia should be suspected when there is marked loss of coordination and marked change in mental function (such as confusion, reduced level of consciousness or coma). Shivering stops and the patient loses the ability to rewarm themselves. The patient will be cold to touch. Breathing becomes shallow and the pulse becomes faint and slow. In very severe cases the patient may have fixed, dilated pupils, be rigid and unresponsive, and without obvious breathing or pulse; they may appear lifeless. Signs of life must be carefully checked for, as they may be present but very hard to detect, as discussed later. The cause of death in hypothermia is cardiac arrest; that is, the heart stops.

Management of hypothermia

Hypothermia is a life-threatening condition. Mild hypothermia alone should not result in death when treated appropriately, but the mortality rate from severe hypothermia is very high. The prime aim in the management of hypothermia in the field is the prevention of further heat loss. Patients with mild hypothermia can usually rewarm themselves if further heat loss is prevented. Even with special equipment it is virtually impossible to rewarm the profoundly hypothermic patient in the field, and prevention of further heat loss is the prime treatment, while awaiting urgent evacuation.

If hypothermia is suspected, commence treatment immediately. Do not continue to shelter. Shelter from cold, wind, rain, and snow should be provided by whatever means possible (e.g. tent, snow wall, bivvy bag). The patient must be kept as dry as possible. Attempt to provide a warm environment. Placing several rescuers inside the tent with the patient may help raise the air temperature.

If the patient is sufficiently alert to assist in the process, wet clothing can quickly be removed and replaced with dry, provided that this does not expose the patient to further heat loss. Cutting off clothing may speed this process. This may only be achievable in an environment of warm, still air. Gentle handling of the patient at all times is extremely important. With more severe hypothermia, or in adverse conditions, removal of wet clothing is usually too risky, in which case the use of a vapour barrier is recommended.

The vapour barrier principle
This is the accepted treatment for severe hypothermia in the field, and involves enclosing the patient, complete with all clothing, in waterproof material (e.g. Gore-Tex, plastic garbage bags), and then in a sleeping bag. Remember to cover the head and neck (keeping the face clear), as these are sites of high heat loss; up to 80% of total body heat loss may occur from the head and neck regions.

Ground insulation is essential, and improvisation to increase insulation with clothing or newspapers may be possible. The patient should be placed in a single prewarmed sleeping bag, or two bags zippered together, with one or two other rescuers dressed lightly in thermal underwear. The awake patient may be rehydrated with warm sweet drinks and high energy foods if they are able to swallow.

Heat sources such as chemical heat packs or hot water bottles may be applied to the patient's neck, armpits and groin. These are sites where large blood vessels lie close to the surface of the body, the aim being to provide heat to the body's core, rather than the surface. The heat source must be adequately wrapped in clothing or padding so as not to be too hot and not in direct contact with the skin, which risks burning the patient. Particular care must be taken in the semi-conscious or unconscious patient. The patient should be kept horizontal, as the hypothermic patient is prone to a fall in blood pressure (leading to fainting) if they are placed in an upright position. Exertion or massage of the extremities must not be allowed, as these increase heat loss.

Ongoing care
The patient's condition may deteriorate in the first few hours following commencement of treatment due to shock or a further fall in body temperature. Excessively rough handling in treating hypothermic patients is a suspected cause of death. The comatose hypothermic patient must be handled extremely carefully because the heart is very sensitive; rough handling may precipitate cardiac arrest and death. The gentle, vigilant care of the semi-conscious or comatosed patient is a very taxing task, requiring the assistance of several rescuers.

Once a mildly hypothermic patient is rewarmed, well hydrated and has returned to normal function, then there is no need for evacuation, although care must be taken to prevent recurrence. If circumstances are such that adequate first aid measures cannot be delivered to the patient with mild hypothermia, then great care must be taken to monitor the patient for further deterioration while walking out.

Any patient who does not respond to the rewarming measures, who deteriorates or who has profound hypothermia must be treated with maximum first aid measures and evacuation arranged urgently.

Resuscitation of hypothermic patients
If breathing is absent, initiate mouth-to-mouth resuscitation immediately. For hypothermic patients it is wise to feel for a pulse at the carotid pulse for at least one minute, before declaring the patient pulseless. This is because in severe hypothermia the pulse may be slow, faint and very difficult to feel. CPR should not be undertaken in hypothermia if:

  • there are obvious lethal injuries present
  • chest wall depression is not possible (due to a rigid, frozen chest)
  • any signs of life are present (e.g. pulse, breathing, movement)
  • if there is danger to rescuers.

Management of the hypothermic patient

  • Prevention.
  • Observe all party members.
  • Treat as an emergency.
  • Stop at the suspicion of hypothermia in any party member.
  • Reassure victim and check whole party.
  • Shelter from cold, wet, wind.
  • Handle extremely gently at all times.
  • Insulate from the cold, including the ground.
  • Remember head insulation.
  • Replace wet clothing with warm and dry clothing, but only if patient's state of consciousness and risk of further heat loss is minimal.
  • Apply vapour barrier principle to retain warmth.
  • Use prewarmed sleeping bags, with warmth from other bodies.
  • Warming devices (e.g. hot water bottles) should be carefully applied to neck, armpits and groin.
  • Wrap the patient in layers (e.g. clothing, vapour barrier, sleeping bag, insulation, tent or other shelter).
  • Warm the air around the patient if possible (e.g. inside the tent).
  • No alcohol.
  • No activity.
  • No rubbing or massaging.
  • Monitor and record your management and the victim's condition.
  • Seek urgent rescue and evacuation if severe hypothermia is suspected.

Ensure that other party members are not placed at risk of hypothermia during care of the first patient. Maintain the morale of the patient and other party members (including self!). It may be useful to delegate providing reassurance, explanation and comfort to a specific team member not involved in other aspects of patient care.

Summary of management of the hypothermic patient
In the hypothermic patient always consider that there may be other injuries present, particularly if the circumstances are not clear (e.g. finding an unconscious skier). Care of the unconscious patient should follow standard practice.

Other cold-related conditions

Frostbite
Frostbite is the localised injury or death of tissue due to cold exposure. Factors which predispose to frostbite injury are:

  • alcohol intake
  • type of cold contact (especially contact with cold metal, water or fuels)
  • duration of cold exposure
  • ambient temperatures below –2°C
  • high winds
  • humidity and skin wetness
  • inadequate protective clothing (e.g. wet clothes, poorly fitting boots or gloves)
  • impaired circulation (e.g. constrictive clothing, smoking)
  • fatigue, over-exertion
  • previous frostbite
  • long periods of immobility.

Frostbite often occurs in the setting of a sudden storm, accident, fatigue or alcohol intoxication. Avoid tight clothing and ensure that shoes and socks fit well, with no pressure areas. Keep the hands and feet dry. Wet skin is more likely to become cold or damaged, and is more susceptible to frostbite. Similarly, modify dress and activity to minimise perspiration. In extreme cold, unless dexterity is required, mittens are preferable to gloves. Take care handling equipment, particularly wet metal objects and fuel. Party members should have up-to-date tetanus immunisation.

Frostbite occurs on the extremities, such as toes, fingers, nose and ears, with the toes being the most common. The frostbitten part feels very cold and is usually numb. The area is painless until rewarming. The extremity appears pale, white or mottled blue. In superficial frostbite, tissues below the skin remain soft to touch. In deep frostbite, the deeper tissues appear frozen solid, and are hard to touch. Following thawing, there may be a few clear fluid-filled blisters in superficial frostbite and many clear or purple blisters in deep frostbite. The initial treatment of frostbite is the same regardless of the severity.

Management of frostbite
Replace wet and constrictive clothing on the affected limb with loose, dry clothes (e.g. socks and mittens). Remove jewellery or other items that are restrictive or cause pressure on the skin. Cover any blisters or wounds with dry, sterile dressings, and apply padding and a splint to the area. Remember to check for the presence of hypothermia and provide all possible shelter.

There are a number of actions that are definitely not helpful in managing frostbite:

  • do not prick blisters
  • avoid smoking and alcohol
  • do not apply snow or cold water
  • do not apply direct heat to the area
  • do not rub or massage the part as this is potentially harmful.

Evacuation should be undertaken as soon as possible if blisters have formed. Self evacuation may be possible if the hands are involved but frostbite on the feet may render the patient unable to walk. If deep frostbite is suspected then medical care should be sought urgently.

Field rewarming may be precluded by adverse conditions or lack of appropriate equipment, such as an adequately sized container to provide a bath for the affected part. Rapid rewarming is undertaken by immersing the affected part in gently circulating, warm water at 40–42°C. (The rescuer should test the water with an elbow if a thermometer is not available.) Rewarming usually takes 30 minutes, and the whole of the thawed part, including the tip, should appear soft and red. Pain may be very severe, and is difficult to manage with oral medications. Blisters may appear after thawing and should be kept intact. The parts should be gently dried, sterile gauze placed between the toes or fingers, then the part padded, wrapped and insulated to prevent injury or refreezing. Elevation will help reduce swelling.

The damage caused by refreeze after the thawing of a frostbitten part is much greater than the damage caused by delayed thawing. Therefore, if the patient must evacuate by walking through snow, then that is best undertaken before thawing frostbitten feet, rather than risk refreezing after thaw. In addition, extreme pain may occur during rewarming, which may render a person previously capable of walking on frozen feet incapable of self evacuation on thawed feet. Spontaneous thawing may occur during evacuation depending on the conditions. The decision to undertake rewarming in the field needs to consider:

  • the expected time until evacuation or rescue
  • the likelihood of spontaneous thawing
  • the rendering of an ambulatory patient incapable of walking by rewarming
  • the ability to rewarm in the field, given the equipment needed.

Snow blindness
Snow blindness is not a cold or heat injury, but is included in this chapter because it is a highly debilitating but entirely preventable injury associated with altitude and snow.

Snow blindness is the burning of the front surface of the eye (the cornea) from exposure to ultraviolet (UV) radiation, rather like sunburn damage to the skin. Exposure to UV radiation is increased with altitude and in snow conditions, and reflection of UV radiation onto the eyes from the snow can greatly increase exposure.

Although damage can occur from a short period of exposure (e.g. 60 minutes), symptoms do not occur until 8 to 12 hours after the actual injury, so will not become apparent until later in the day or the following day. Snow blinded eyes are very painful, feel irritated and gritty, and are sensitive to light. The eyes may water profusely, have swollen lids and the surface of the eye may be red and swollen. Without treatment, the eyes will usually heal themselves over the following 24–36 hours or so. However, the discomfort experienced in the meantime may be severe and render the patient quite incapacitated.

Resting with eyes closed and in a dark environment will give some relief. Cold compresses applied gently to the closed eyes may also help relieve discomfort. Contact lenses should be removed while recovery occurs, and the patient discouraged from rubbing their eyes, which may cause additional irritation. Painkillers (e.g. paracetamol) or anti-inflammatory drugs (e.g aspirin) may assist. Snow blindness is a very distressing condition for the patient and reassurance and explanation should be provided. Full recovery is normal.

Snow blindness is entirely preventable with effective eye protection. Snow goggles and sunglasses should have an Eye Protection Factor (EPF) of at least 10. Protection can be improvised by cutting narrow viewing slits in an opaque piece of foam, cardboard or cloth, and securing it around the eyes. Even on overcast days, UV exposure can be high and eye protection should be worn.

Heat illness

The spectrum of heat-related illness ranges from mild heat cramps, to life-threatening heat stroke. Regardless of ambient temperature, situations where body heat production is high, such as vigorous exercise, and where evaporative heat loss is limited (e.g. high humidity, impermeable garments) place people at risk of heat illness.

Important factors in preventing heat illness are route planning, including the consideration of the availability of ample water supplies, modifying activity to the cooler morning and evening, and considering humidity and exposure when planning distances and length of days.

Heat illnesses are preventable. Party leaders should be aware of risk factors in the group that predispose to heat illness, adapt activity according to risk factors and environmental conditions, and ensure adequate fluid intake while exercising. Regardless of preparation, training and acclimatisation, no person is immune from heat illness. Prevention of heat illness requires an awareness of the following:

  • Dress in light coloured, loose garments to facilitate sweat evaporation, which is the main means used by the body to dissipate heat. Excess body fat provides insulation which reduces heat loss. The face, scalp and upper torso are the most important areas to provide cooling through sweating, so prudent removal of headgear and towelling off improves heat loss.
  • Modify the level of physical activity according to the heat and humidity, taking frequent rests in the shade.
  • Physical fitness results in improved exercise tolerance in the heat, but even fit individuals may lack conditioning for a particularly strenuous activity or adverse environmental conditions.
  • Acclimatisation, improving the body’s response to heat, occurs with gradual increase in time and intensity of exercise in the heat, usually requiring about 1 hour of exercise per day over a period of 8–10 days. Once acclimatised, the body sweats sooner and in greater volumes, facilitating body cooling. Loss of acclimatisation to heat takes about 1–2 weeks. Acclimatisation is not improved by restricting fluid intake.
  • Fluid intake must be adequate. Remember to be well hydrated before commencing activity, and that relieving thirst alone is not a good marker of sufficient fluid intake. Sweat losses in an acclimatised person can reach up to 1.5 L per hour during exertion. About 250–500 mL water should be drunk 10 to 15 minutes prior to commencing exercise, followed by 250–350 mL every 20–30 minutes during exercise. Deliberate restriction of fluids while exercising in hot conditions is a very hazardous practice.

Susceptible candidates for a heat-related illness are the young or elderly, unfit, obese, exercising in hot, humid conditions, inappropriately dressed, unacclimatised to the heat and with an insufficient fluid intake. Dehydration from any cause, such as inadequate fluid intake during exercise, diarrhoea or vomiting is another a risk factor for heat illness. Nevertheless, remember that healthy young adults exercising strenuously in hot conditions, may be susceptible to heat stroke in the absence of other risk factors. Note that alcohol, which impairs body temperature control, and certain drugs which increase body heat production or impair sweating, predispose to heat illness. Examples include antihistamines, and stimulants such as amphetamines.

Fluids in heat illness
Remember that a person exercising in the heat can readily lose over 1 L of water per hour, and ensuring sufficient fluid replacement may be difficult. Cold oral fluids are absorbed more quickly than warm. Drinking smaller volumes of fluids (e.g. 150–250 mL) is less likely to cause abdominal discomfort or nausea, especially if exercising. The concentration of carbohydrates in fluids should not exceed 6% or absorption from the gut is delayed, and diarrhoea may occur.

Heat-related conditions

Heat cramps
Heat cramps are brief muscle spasms that may cause severe pain and usually involve heavily exercised muscles, with legs and abdomen most commonly affected. Cramps usually follow several hours of sustained exercise of involved muscle groups, and are not solely due to heat exposure. Heat cramps are associated with heavy sweating in a hot environment and the consumption of large volumes of water. Cramps in the abdominal muscles may be hard to differentiate from gastrointestinal upset. Although this is a distressing condition, it is not life threatening.

Management of heat cramps
Heat cramps resolve with rest in a cool environment and with oral fluids containing sodium, such as common salt. Gentle stretching or massage of the involved muscles may help. Once recovery occurs the patient may resume activity, but if cramps return then they should rest for 24 hours.

Heat exhaustion
Heat exhaustion occurs from loss of salt and or water from the body, usually by significant sweating. The presentation of heat exhaustion covers a broad range of symptoms, including headache, dizziness, nausea, vomiting, weakness, heat cramps, ‘goose bumps’, chills, faintness, mild confusion or drowsiness. The skin may be warm or cool, with sweating. Pulse and respiration are rapid. Core temperature is normal or moderately elevated. Early symptoms may go unrecognised, or may not be recognised as heat related, as the body retains the ability to lose heat and brain function is intact.

Failure to appreciate the presence of heat exhaustion may place the patient at risk of ongoing heat stress and the development of life-threatening heat stroke. The clinical presentation of heat exhaustion may be very difficult to distinguish from heat stroke, particularly in the field, so immediate management is required. The suspicion of heat stroke, for instance the presence of a marked alteration in level of consciousness, should mandate immediate treatment for heat stroke, and medical care sought as an emergency. Classic heat exhaustion, possibly leading to heat stroke, may develop slowly over hours or even days.

Management of heat exhaustion
The focus in management is on cooling and rehydration. The patient should cease all activity and rest in a shaded, cool environment. They should be given oral fluids, ideally cool, lightly salted water or an oral electrolyte solutions prepared according to manufacturer’s instructions. Initial fluid replacements of 1–2 L over 2–4 hours is generally recommended. Cool the skin by wetting and fanning. The patient should rest over the next 24 hours, although full recovery may take up to 36 hours. The patient may resume activity when recovered, but not before a full night’s rest.

Heat stroke
Heat stroke is a true medical emergency with a mortality rate of around 80% if not promptly and effectively treated. In heat stroke, body systems lose their ability to regulate body temperature, and elevation of the core temperature follows, resulting in damage to many body systems, including the brain, and ultimately death from multiorgan failure.

The collapse of a previously healthy person associated with physical exertion in a hot environment should be regarded as heat stroke unless there is another obvious cause.

Any of the symptoms and signs of heat exhaustion described above may be present. Heat stroke can be regarded as a progression from heat exhaustion. The key findings in heat stroke are markedly elevated body temperature and altered conscious state. The skin looks red, feels hot and may be dry or sweaty. The altered conscious state may range from irritability, confusion, hallucinations, poor coordination, aggression or bizarre behaviour to seizures and coma. There is a rapid pulse and breathing.

Management of heat stroke
Rapid cooling must be undertaken immediately. The chance of serious injury or death from heat stroke increases with the duration and height of elevated body temperature, so the more rapid the cooling, the lower the mortality rate. Cooling should include as many of following measures as possible:

  • immediate rest
  • shade from sunlight
  • loosen restrictive clothing
  • remove excess clothing
  • sprinkle the patient with cool or tepid water
  • fan aggressively
  • periodic towelling off of skin improves evaporative cooling
  • apply cold packs (ice if available!) to the neck, armpit and groin, where large blood vessels lie close to the skin, to facilitate cooling
  • allow the air to circulate around the patient, while providing shade (e.g. tent flaps open).

Cooling measures should be tapered off once the patient feels cool. Evaporative cooling is more effective with tepid water rather than cold, and this also reduces shivering, which is undesirable in heat illness as the muscle spasms produce heat. Watch for any return of high temperature, which would warrant renewed cooling.

Shock may develop in heat stroke due to heart failure or dehydration, and should be treated with standard patient stabilisation measures (danger, response, airway, breathing, circulation). Most patients with heat stroke are initially unconscious or semi-conscious and should not be given oral fluids.

Water is a key component to the management of heat stroke; lack of water greatly reduces the ability to cool the patient. Unfortunately, if trip planning and party preparation is poor, heat stroke may occur in circumstances where there is a lack of water. Further, exhausting water supplies to treat the patient with heat stroke places the remainder of the group at risk. Again, the emphasis is on the need for planning and prevention. Urine may be used to moisten the patient and facilitate cooling. Do not give medications used to treat fever (such as aspirin or paracetamol) as these are not effective in heat stroke. Heat stroke is an indication for urgent evacuation or rescue.

Further reading

Wilderness Medical Society. 1995. Practice Guidelines for Wilderness Emergency Care. ICS Books.
Proceedings of the Stanford Symposium on Emergency Medicine and Acute Care. May 1–4, 1996. Division of Emergency Medicine, Stanford University School of Medicine.
Auerbach PS. ed. 1995. Wilderness Medicine. Management of Wilderness and Environmental Emergencies. St Louis: CV Mosby.
Winter Sports and Expedition Medicine. Proceedings of the 1997 Winter Meeting of the Wilderness Medical Society. February 1–5, 1997.
Brookes J, Dunn R, Rogers I. 1997. Environmental Medicine. In: Dunn R. ed. The Emergency Medicine Manual.