Signs and Symptoms

Hypothermia affects almost every organ system.

Learning bite

All systems respond with an initial increase in activity (compensation), followed by a decrease and then eventual loss of activity (decompensation).

1. Cardiovascular system

Tachycardia and vasoconstriction, the initial response to cold stress, result in an increase in blood pressure and cardiac output.

With worsening hypothermia, bradycardia occurs, oxygen demand decreases and cardiac output falls.

Eventually, severe bradycardia, ventricular fibrillation or asystole ensues.

2. Coagulation system

Patients with moderate-to-severe hypothermia may develop a coagulopathy.

Lower temperatures adversely affect enzymes responsible for the coagulation cascade. This will not be reflected in laboratory studies such as PT or APTT, which may be normal.

Hypothermic patients will also be thrombocytopenic and may develop physiological hypercoagulability similar to DIC.

3. Central nervous system

The response to mild hypothermia starts with impaired judgment and memory.

As the severity of hypothermia worsens, slurred speech, ataxia and drowsiness develop. Patients may exhibit foot stomping and paradoxical undressing.

Finally, in severe hypothermia, coma and death result.

4. Renal system

Initially, peripheral vasoconstriction leads to relative central hypervolemia, leading to a diuresis.

More severe hypothermia results in renal failure and renal shutdown.

5. Respiratory system

The initial response to hypothermia is an increase in respiratory rate and a resultant respiratory alkalosis.

As the body cools, the respiratory rate falls and the patient develops carbon dioxide retention, respiratory acidosis and ultimately respiratory arrest.