Heat Stroke - Environmental Emergencies

Environmental Emergencies

HEAT STROKE

Heat stroke is an acute medical emergency caused by failure of the heat-regulating mechanisms of the body. It usually occurs during extended heat waves, especially when they are accompanied by high humidity. People at risk are those not acclimatized to heat, elderly and very young people, those unable to care for them-selves, those with chronic and debilitating diseases, and those taking certain medications (eg, major tranquilizers, anticholiner-gics, diuretics, beta-adrenergic blocking agents). Exertional heat stroke occurs in healthy individuals during sports or work activ-ities (eg, exercising in extreme heat and humidity). Hyperthermiaresults because of inadequate heat loss. This type of heat stroke can also cause death. See Chart 71-7 for prevention strategies.

Gerontologic Considerations

Most heat-related deaths occur in the elderly, because their cir-culatory systems are unable to compensate for stress imposed by heat. Elderly people have a decreased ability to perspire as well as a decreased thirst mechanism to compensate for heat.

Assessment and Diagnostic Findings

Heat stroke causes thermal injury at the cellular level, resulting in widespread damage to the heart, liver, kidney, and blood coagu-lation. Recent patient history reveals exposure to elevated ambient temperature or excessive exercise during extreme heat. When as-sessing the patient, the nurse notes the following symptoms: profound central nervous system (CNS) dysfunction (manifested by confusion, delirium, bizarre behavior, coma); elevated body temperature (40.6°C [105°F] or higher); hot, dry skin; and usually anhidrosis (absence of sweating), tachypnea, hypotension, and tachycardia.

Management

The primary goal is to reduce the high temperature as quickly as possible, because mortality is directly related to the duration of hyperthermia. Simultaneous treatment focuses on stabilizing oxy-genation using the ABCs of basic life support.

After the patient’s clothing is removed, the core (internal) temperature is reduced to 39°C (102°F) as rapidly as possible. One or more of the following methods may be used as directed:

·      Cool sheets and towels or continuous sponging with cool water

·      Ice applied to the neck, groin, chest, and axillae while spray-ing with tepid water

·      Cooling blankets

·      Iced saline lavage of the stomach or colon if the temperature does not decrease

·       Immersion of the patient in a cold water bath (if possible)

During cooling, the patient is massaged to promote circulation and maintain cutaneous vasodilation. An electric fan is positioned so that it blows on the patient to augment heat dissipation by convection and evaporation. The patient’s temperature is constantly monitored with a thermistor placed in the rectum, bladder, or esophagus to evaluate core temperature. Caution is used to avoid hypothermia and to prevent hyperthermia, which may recur spontaneously within 3 to 4 hours.

Throughout treatment, the patient’s status is monitored care-fully, including vital signs, ECG findings (for possible myo-cardial ischemia, myocardial infarction, and dysrhythmias), CVP, and level of responsiveness, all of which may change with rapid alterations in body temperature. A seizure may be followed by re-currence of hyperthermia. To meet tissue needs exaggerated by the hypermetabolic condition, 100% oxygen is administered. The patient may require endotracheal intubation and mechanical ven-tilation to support failing cardiopulmonary systems.

Intravenous infusion therapy of normal saline or lactated Ringer’s solution is initiated as directed to replace fluid losses and maintain adequate circulation. Fluids are administered carefully because of the dangers of myocardial injury from high body tem-perature and poor renal function. Cooling redistributes fluid volume from the periphery to the core.

Urine output is also measured frequently, because acute tubu-lar necrosis is a complication of heat stroke from rhabdomyolysis (myoglobin in the urine). Blood specimens are obtained for ser-ial testing to detect bleeding disorders, such as disseminated intra-vascular coagulopathy, and for serial enzyme studies to estimate thermal hypoxic injury to the liver, heart, and muscle tissue. Permanent liver, cardiac, and CNS damage may occur.

Additional supportive care may include dialysis for renal fail-ure, antiseizure agents to control seizures, potassium for hypo-kalemia, and sodium bicarbonate to correct metabolic acidosis. Benzodiazepines or chlorpromazine may be prescribed to sup-press seizure activity. Patient education regarding the prevention of heat stroke (ie, adequate fluid intake, staying out of the sun es-pecially between 10 AM and 2 PM) is also important to prevent a recurrence of heat stroke.