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.