Hypothermia is a condition in which the core (internal) temper-ature is 35°C (95°F) or less as a result of exposure to cold. Hy-pothermia occurs when a patient loses the ability to maintain body temperature. Urban hypothermia (extreme exposure to cold in an urban setting) is associated with a high mortality rate; elderly people, infants, people with concurrent illnesses, and the homeless are particularly susceptible. Alcohol ingestion increases susceptibility because it causes systemic vasodilation. Trauma vic-tims are also at risk for hypothermia resulting from treatment with cold fluids, unwarmed oxygen, and exposure during exam-ination. The patient may also have frostbite, but the hypothermia takes precedence in treatment.
Hypothermia leads to physiologic changes in all organ systems. There is progressive deterioration, with apathy, poor judgment, ataxia, dysarthria, drowsiness, pulmonary edema, acid-base ab-normalities, coagulopathy, and eventual coma. Shivering may be suppressed below a temperature of 32.2°C (90°F), because the body’s self-warming mechanisms become ineffective. The heart-beat and blood pressure may be so weak that peripheral pulses become undetectable. Cardiac irregularities may also occur. Other physiologic abnormalities include hypoxemia and acidosis.
Management consists of continuous monitoring, rewarming, removal of wet clothing, insulation, and supportive care.
The ABCs of basic life support are a priority. The patient’s vital signs, CVP, urine output, arterial blood gas levels, blood chem-istry determinations (blood urea nitrogen, creatinine, glucose, electrolytes), and chest x-rays are evaluated frequently. Body temperature is monitored with an esophageal, bladder, or rectal thermistor. Continuous ECG monitoring is performed, because cold-induced myocardial irritability leads to conduction distur-bances, especially ventricular fibrillation. An arterial line is in-serted and maintained to record blood pressure and to facilitate blood sampling.
Rewarming methods include active core (internal) rewarming, active external rewarming, and passive or spontaneous rewarming.
Core rewarming methods include cardiopulmonary bypass,warm fluid administration, warm humidified oxygen by venti-lator, and warmed peritoneal lavage. Core rewarming is recom-mended for severe hypothermia. Monitoring for ventricular fibrillation as the patient passes through 31° to 32°C (88° to 90°F) is essential.
Passive external rewarming includes the use of warm blankets orover-the-bed heaters. Passive rewarming of the extremities increases blood flow to the acidotic, anaerobic extremities. The cold blood with high lactic acid levels returning to the core has significant effects on the core temperature and metabolic response, possibly causing cardiac dysrhythmias and electrolyte disturbances.
Supportive care during rewarming includes the following as directed:
· External cardiac compression (only as directed in the very cold patient)
· Defibrillation of ventricular fibrillation. Patients whose temperature is less than 32°C (90°F) will experience spon-taneous ventricular fibrillation if moved or touched. Defib-rillation is ineffective in patients with temperatures lower than 31°C (88°F).
· Mechanical ventilation with positive end-expiratory pres-sure (PEEP) and heated humidified oxygen to maintain tissue oxygenation
· Administration of warmed intravenous fluids to correct hy-potension and maintain urine output and core rewarming, as described previously
· Administration of sodium bicarbonate to correct metabolic acidosis if necessary
· Administration of antiarrhythmic medications
· Insertion of an indwelling urinary catheter to monitor fluid status
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