Answer

C. Hypothermia

Cases figure 2This patient was diagnosed with hypothermia. His ECG demonstrated classic abnormalities of hypothermia (most notably, profound sinus bradycardia); additionally, all leads showed the classic Osborne waves (J waves) at the junction of the QRS complex and the ST segment (see Figure 2) representing alterations in ventricular repolarization. Classically, Osborne waves do not affect the ST segment; however, an ECG must be interpreted within the clinical context.

This case is an example of primary hypothermia. This occurs when an unprepared individual faces unanticipated environmental exposure. Primary hypothermia must be distinguished from secondary hypothermia, in which a medical illness causes the body's temperature set-point to be reduced.

Mild hypothermia is a core body temperature of 90–95°F (32.2–35.0°C); patients may initially show signs of shivering, tachycardia, vasoconstriction and tachypnea. Later signs include apathy, ataxia, impaired judgment and diuresis. Moderate hypothermia is a temperature of 82.4–89.9°F (28.0–32.2°C), with signs of dysrhythmia, bradycardia, hypotension, Osborne waves on ECG, diminished reflexes, dilated pupils and decreased consciousness. Severe hypothermia is a core body temperature of 82.4°F (28°C), at which point apnea, decreased electroencephalographic activity, nonreactive pupils, oliguria, pulmonary edema, coagulopathy, hemoconcentration and more severe arrhythmia are seen. Mild or moderate hypothermic patients have an excellent chance of recovery, but patients with severe hypothermia have a mortality rate of roughly 50 percent.

Initial stabilization begins with an accurate, continuous means of measuring the core body temperature to detect the degree of hypothermia and the response to therapy. Patients may need a rectal, esophageal or bladder thermometer for continuous measurements. Wet clothing should be removed immediately. Patients in respiratory failure should be intubated, mechanically ventilated, and given warmed, humidified, supplemental oxygen. Volume resuscitation should be initiated with warmed (104–113°F, or 40–45°C) normal saline. Cardiac reserve is decreased in hypothermic patients and, therefore, judicious volume resuscitation is advised. Cardiac arrhythmia can occur, the management of which may differ in hypothermic patients. Rewarming the patient is typically sufficient to regain normal myocardial contractility and rhythm.

There are three general types of rewarming techniques: passive external, active external and active internal. Passive external rewarming is for mildly hypothermic patients and involves insulating the patient to allow the intact thermoregulatory mechanisms to reheat the body. Having patients inspire humidified air allows for slow but steady increases in the core body temperature. Active external rewarming includes warm-water immersion, forced-air warming systems or placement in a heat cradle; a major complication is core temperature after drop, in which cold peripheral blood rapidly returns to the heart leading to inappropriate temperature readings and subsequent inappropriate management. Active internal rewarming is reserved for severe hypothermia or for patients who do not respond to less aggressive measures. It can be either minimally invasive (e.g., heated, humidified air and warm intravenous fluids) or more invasive (e.g., body cavity lavage, hemodialysis, cardiopulmonary bypass and extracorporeal blood warming). The least invasive means of adequate rewarming is generally best.

This patient had moderate hypothermia and was immediately stripped of his clothes. He was given warm intravenous fluids and a mask with warm, humidified air to breathe. A forced-air blanket was used on his torso, and warmed blankets were wrapped around his extremities. With these measures, the patient's core body temperature began to rise and his symptoms resolved. He was admitted for monitoring and treatment of his pneumonia. Eventually, the patient was discharged without any major disabilities.