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Heat-Related Illnesses


Heat Cramps

Heat Cramps are seen both in unconditioned persons just beginning a strenuous exercise in hot temperatures and in acclimatized individuals that have been sweating profusely while working out (particularly when rehydrating only with unsalted fluids). The cramps are usually found in the muscle groups that were exercised but may occur in any muscle. The spasms may occur during the activity period or hours later. Replacement of fluid losses with hypotonic solutions may contribute to the cramping.

Management - Remove the patient from the hot environment. Mild dehydration can be managed with oral replacement of fluids i.e. 1 tsp of NaCl mixed with 500 ml of water or a stock electrolyte solution given over 1 - 2 hours. Severe dehydration should be treated with a bolus of 20 ml/kg of NS given over an hour.


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Heat Exhaustion

Heat Exhaustion is a vague clinical syndrome characterized by headache, nausea, vomiting, lethargy, irritability, thirst, and anorexia. Exposure to high temperatures, excessive sweating, and inadequate replacement of salt and water are the chief causes. Two types of heat exhaustion can be seen. Most patients experience a combination of both types. Water depletion heat exhaustion results from exposure to high temperature and insufficient fluid intake with onset of symptoms occurring over a few hours. Salt depletion heat exhaustion usually develops over several days; usually in people that replace the fluid loses adequately, but fail to replace salt loses.

Diagnostic Findings- thirst, headache, nausea and vomiting, irritability are common. The temperature may be normal or elevated usually < 40 degrees. Tachycardia and tachypnea are present. Complications of heat exhaustion include impending heatstroke and shock.

Management - Remove the patient from the hot environment. Mild dehydration can be managed with oral replacement of fluids i.e. 1 tsp of NaCl mixed with 500 ml of water or a stock electrolyte solution given over 1 - 2 hours. Severe dehydration should be treated with a bolus of 20 ml/kg of NS given over an hour followed by a rehydration protocol.


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Heatstroke

Heatstroke - is a medical emergency characterized by temperature > 40 degrees, neurological dysfunctioning, and often a lack of sweating. Heatstroke occurs when the body is unable to dissipate heat with resultant loss of temperature control. The rapid rise in the core temperature is injurious to cells and organs throughout the body. Renal failure, rhabdomyolysis (breakdown of muscle cells), hepatocellular necrosis (liver cellular damage), myocardial damage, cerebral edema, and various metabolic abnormalities can occur. A profound respiratory alkalosis coupled with a metabolic acidosis is common. Hyperventilation and tachycardia are present.

Heatstroke can be divided into two forms;

  • Classic heatstroke (nonexertional) - is more commonly seen in infants, children, and the elderly. It develops over a period of days (usually coinciding with a heat wave) and typically presents with nausea, vomiting, headache, and a deteriorating mental status.
  • Exertional heatstroke- usually develops rapidly in a young, vigorously exercising individual who have not acclimatized to a hot environment. A dramatic presentation is seen with central nervous system changes ranging from severe headache to seizures and collapse. Rhabdomyolysis and disseminated intravascular coagulation are often prominent. Marked lactic acidosis may develop early but it is not the grave prognostic indicator when noted in classic heatstroke.

Diagnostic Findings - Rectal or core temperatures greater than 104 degrees; hypotension; mental changes, severe headache, bizarre behavior, ataxia, seizures, and coma; tachycardia; tachypnea; and profuse or absent (usually) sweating can all be seen. In severe heatstroke disseminated intravascular coagulation may occur.

Ancillary Data - Numerous lab studies are warranted; the arterial blood gas typically indicates a respiratory alkalosis and a metabolic acidosis; electrolytes can reveal either a hypo or hyper kalemia, a hypo or hyper natremia and the BUN and Glucose levels will be elevated. An increased hematocrit, decreased platelets, elevated AST, lactate dehydrogenase, creatinine phosphokinase can be seen.

Management - Heatstroke is potentially life threatening and requires ICU admission. The patient requires removal from the heat, clothing removed and if possible should be immersed in cool water. If immersion is impossible the patient should have ice packs applied to the groin, axilla, and neck area and the patient should be fanned. Fanning the patient while sprinkling with water may increase evaporative losses until the patient's temperature is below 39 C (102.2 F). Massaging the extremities may be helpful. These patients are severely dehydrated and should be bolused with 20 mg/kg of NS. Further replacement of fluids and monitoring should reflect the patient's condition.


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References

  1. Barkin RM, Asch SM, Caputo GL, Jaffe DM, Knapp J, Schafermeyer RW, Seidel JS. Pediatric Emergency Medicine: Concepts and Clinical Practice. 1992, Mosby - Year Book Inc., p 432 - 433
  2. Howell JM, Altieri M, Jagoda AS, Prescott JE Scott JL, Stair TO. Emergency Medicine, 1998 W.B. Saunders p1567-1573