Hot on the inside

When a disease process becomes life-threatening, it is termed to be malignant. Hyperthermia is a heat illness that arises from one of two basic causes: 1) the body's normal thermoregulatory mechanisms are overwhelmed by the environment (an exogenous heat load) or, more commonly, by excessive exercise in a moderate-to-extreme environment (an endogenous heat load); or 2) failure of the thermoregulatory mechanisms, such as those encountered in the elderly or debilitated patient. Either cause can lead to heat illnesses such as heat cramps, heat exhaustion or heatstroke. Heat cramps are brief, intermittent and often severe muscular cramps that frequently occur in muscles fatigued by heavy work or exercise. They are believed to be caused by a rapid change in the extracellular fluid osmolarity resulting from sodium and water loss. Heat exhaustion is a more severe form of heat illness characterized by minor changes in mental status (poor judgment, irritability), dizziness, nausea and headache. In severe cases, the patient may have an altered LOC. Just as with heat cramps, profuse sweating is present. Removing the patient from the hot environment and administering fluids will usually result in a rapid recovery. [table: see text] Left untreated, heat exhaustion may progress to heatstroke. Heatstroke results when there is a complete collapse of thermoregulatory mechanisms. This will lead to a rise in body core temperature in excess of 105.8 degrees F (41 degrees C), which will produce multisystem tissue damage and physiological collapse. Severe cases can cause death. The patient in this case had an axillary temperature taken and recorded at 101.4 degrees F. Typically, axillary temperatures are one degree cooler than oral temperatures, which are one degree cooler than core temperatures. This patient, then, had a core temperature of 103 degrees F or higher. There are two types of heatstroke: classic and exertional. Classic heatstroke occurs during periods of sustained high ambient temperatures and humidity. Exertional heatstroke more often occurs in athletes, military personnel and people who work strenuosly in the environment. In these situations, endogenous heat accumulates more rapidly than the body can dissipate it in the environment. Although sweating is usually absent in the classic form of heatstroke, 50% of exertional heatstroke cases have persistent sweating as a result of catecholamine release. The presence of sweating does not preclude the diagnosis of heatstroke, and cessation of sweating is not the cause of it. As the illness progresses, peripheral vasodilation occurs, resulting in hypotension and shunting. As internal temperatures rise, myocardial contractility begins to decrease, manifested by bradycardia and irritability of the myocardium. No matter the age group, the presence of hypotension and decreased cardiac output indicates a poor prognosis for the patient.