Pathophysiology And Clinical Features

The response of various organ systems to lowered temperature varies widely among individuals.34 and 5 In general, however, body temperatures from 32 to 35°C (89.6-95°F) constitute "mild" hypothermia. In this temperature range, the patient is in an excitation (responsive) stage, in which physiologic adjustments attempt to retain and generate heat.

When temperature drops below 32°C (89.6°F), general excitation gives way to the slowing (adynamic) stage, in which there is a progressive slowdown of bodily functions. Metabolism slows, causing a decrease in both oxygen utilization and CO 2 production. Shivering ceases when body temperature falls below 30 to 32°C (86-89.6°F).

In the initial excitation phase, heart rate, cardiac output, and blood pressure all rise. With decreasing temperature, these all decline. Cardiac output and blood pressure may be markedly depressed by the negative inotropic and chronotropic effects of hypothermia and further depressed by concomitant hypovolemia.

Hypothermia causes characteristic ECG changes and may induce life-threatening dysrhythmias (T§bIe...l8.6.-2). The Osborn (J) wave, a slow, positive deflection at the end of the QRS complex (Fig 1.86-1), is characteristic, though not pathognomic, of hypothermia.

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