Heat stroke: first aid

Heat stroke is hyperthermia accompanied by a systemic inflammatory response that causes multiple organ failure and often death. Heat stroke is characterized by a rise in body temperature above 40 °C and a disturbance in mental state; sweating is often absent. The diagnosis is established based on clinical data. First aid for heat stroke includes rapid external cooling of the body, intravenous fluids, and supportive measures necessary for organ failure.

Heat stroke occurs when thermoregulatory mechanisms stop functioning and body temperature rises significantly. Multiple organ failure may develop as a result of activation of inflammatory cytokines. Gastrointestinal endotoxins may play a role. Functional failure of the central nervous system, skeletal muscles (rhabdomyolysis), liver, kidneys, lungs (acute respiratory distress syndrome) and heart is possible. The coagulation cascade is activated, sometimes causing disseminated intravascular coagulation syndrome. Hyperkalemia and hypoglycemia may develop.

There are two types of heat stroke: classic and due to overexertion. Classic heat stroke develops over 2-3 days, is more common in summer, in hot weather, usually in elderly, sedentary people living without air conditioning, often with limited access to water. Classic heat stroke caused many deaths during the unusually hot summer in Europe in 2003.

Heatstroke due to overexertion occurs suddenly in healthy, active people (e.g., athletes, military recruits, factory workers). Heavy physical work in hot conditions results in a sudden, massive heat load that the body cannot compensate for. Rhabdomyolysis often develops, and severe coagulopathy and renal failure are possible.

A syndrome similar to heatstroke may occur with the use of certain drugs (e.g., cocaine, phencyclidine, amphetamines, monoamine oxidase inhibitors). In most cases, this requires an overdose; additional physical exertion or environmental conditions may cause the stroke without it. Malignant hyperthermia (see the relevant section) may occur in response to the administration of certain anesthetics and neuroleptics. This is a genetically determined disease with a high fatality rate.

Symptoms of heat stroke

The main symptom is dysfunction of the central nervous system, ranging from confusion to delirium, convulsions and coma. Characteristic are tachypnea, even in the supine position, and tachycardia. In classic heat stroke, the skin is hot and dry, and in the second variant, increased sweating is noted. In both cases, the body temperature is >40 °C, may exceed 46 °C.

Diagnosis of heat stroke

The diagnosis is usually obvious, especially if there is a history of physical exertion and fever. However, if it is known that the situation is not extreme, acute infectious diseases (e.g. meningitis, sepsis) and toxic shock should be excluded. The possibility of taking drugs that can cause such a condition should also be clarified.

Laboratory testing includes a complete blood count, prothrombin time, partial thromboplastin time, electrolyte levels, urea, creatinine, CPK, and liver function profile to assess organ function. A urinary catheter is placed, urine is tested for occult blood, and a drug test may be helpful. A urine myoglobin test is not necessary. Body temperature should be monitored continuously, preferably with a rectal or esophageal probe.

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Prognosis and first aid for heat stroke

Heatstroke has a high mortality rate, varying with age, comorbidities, maximum body temperature, and most of all with the duration of hyperthermia and rate of cooling. Approximately 20% of survivors have residual CNS dysfunction. Renal failure may persist in some patients. Body temperature remains unstable for several weeks.

Rapid recognition and effective, aggressive cooling are essential. Methods that do not cause shivering or vasoconstriction of the skin are preferred, although ice packs or immersion in ice water are effective. Evaporative cooling is comfortable for the patient, convenient, and considered by some to be the fastest. It involves continuously wetting the patient with water, blowing air onto the skin, and vigorously massaging the skin to increase blood flow. A spray hose and large fan are ideal, and can be used for large groups of casualties in the field. Warm water (around 30°C) is sufficient, since evaporation itself causes cooling; cold or ice water is not needed. Placing the patient in a regular body of water can be used for on-site care. Ice packs on the groin and axillary areas can be used, but only as a supplement. In life-threatening cases, literally “packing” the patient in ice can reduce body temperature rapidly while closely monitoring the patient.

Intravenous rehydration with 0.9% sodium chloride solution (as described in the relevant section), treatment of multiple organ failure and rhabdomyolysis are initiated. Injectable benzodiazepines (lorazepam or diazepam) may be used to prevent agitation and convulsions (which increase heat production); convulsions may occur during cooling. Measures must be taken to protect the airway, as vomiting and aspiration of vomitus are possible. In cases of severe agitation, muscle relaxants and artificial ventilation are indicated.

Platelet transfusions and fresh frozen plasma may be required in severe disseminated intravascular coagulation. Intravenous sodium bicarbonate may be given to alkalinize the urine and prevent nephrotoxicity in myoglobinuria. Intravenous calcium salts may be needed to treat hyperkalemic cardiotoxicity. Vasoconstrictors, commonly used to treat hypotension, may decrease cutaneous blood flow and slow cooling. Hemodialysis may be required. Antipyretics (eg, paracetamol) are of no use. Dantrolene has been used to treat anesthetic-induced malignant hyperthermia but has not been shown to be effective in other forms of heat illness.

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