CHAPTER 61

establish the diagnosis. Keep in mind that the majority of

standard ED thermometers will not record temperatures

below 34.4°C (94°F).

Physical exam findings frequently vary based on the

degree of hypothermia. It is imperative to immediately and

completely undress the patient to remove any wet clothing

and identify any signs of coexisting frostbite, trauma, sepsis,

hypothyroidism, adrenal crisis, toxidromes, or cardiac dysfunction. Refrain from any unnecessary movement of the

patient to avoid precipitating life-threatening dysrhythmias, as hypothermic myocardium is exceptionally irritable.

Finally, perform a comprehensive neurologic exam including an evaluation for level of consciousness, pupillary

reactivity, and focal deficits. The following describes findings specific to varying degrees of hypothermia.

Mild Hypothermia

Patients tend to present with shivering, tachycardia, tachypnea, and hyperventilation. As their core temperature

approaches 33°C (9 1.4°F), ataxia and apathy b egin to develop.

Moderate Hypothermia

Patients with moderate hypothermia develop hypoventila ­

tion, hyporeflexia, and an altered sensorium or stupor.

Shivering typically disappears once the core temperature

drops below 32°C (89.6°F), and this should be considered an

ominous finding. As the temperature approaches 30°C

(86°F), the risk for dysrhythrnias increases significantly.

Severe Hypothermia

Patients with severe hypothermia may present with pulmonary edema, areflexia, hypotension, and apnea and are

extremely susceptible to ventricular fibrillation and cardiac

arrest. Nearly all patients with a core body temperature

below 27°C (80.6°F) are comatose.

DIAGNOSTIC STUDIES

� Laboratory

Obtain a STAT bedside glucose level on all hypothermic

patients to rule out concurrent hypoglycemia. Serum

hyperglycemia is actually more common secondary to a

cold-induced inhibition of insulin secretion. Avoid treatment with supplemental insulin in these patients, as this

may precipitate iatrogenic hypoglycemia on rewarming.

Check a metabolic panel to assess electrolyte status and

renal function. Hypothermia can impair the concentrating

ability of the renal tubules, leading to a "cold-diuresis" with

secondary dehydration and hypovolemia.

Hypothermia impairs both platelet aggregation and the

coagulation cascade, and patients may become profoundly

coagulopathic. In spite of this, the laboratory measurement

of the prothrombin time and partial thromboplastin time

will be normal as blood samples are warmed to physiologic

temperatures before running these tests. In addition,

hypothermia classically induces hemoconcentration with

an expected increase of the hematocrit by 2% for every 1 °C

drop in core temperature.

� Electrocardiogram

An electrocardiogram is critical for all moderately to

severely hypothermic patients to assess for potentially lifethreatening cardiac dysrhythmias. Sinus bradycardia and

QT prolongation are the most common early findings.

Although not specific for hypothermia, Osborn J waves,

wide positive deflections at the junction of the QRS complex and ST segment, can be seen once the core temperature drops below 32°C (89.6°F) (Figure 61-1). As the

hypothermia worsens, atrial fibrillation and eventually

ventricular fibrillation often develop.

� Imaging

Imaging studies should be dictated by the clinical

presentation. Obtain a head computed tomography in

patients who exhibit persistent alterations in mental status

despite adequate rewarming and in those with any signs of

cranial trauma.

MEDICAL DECISION MAKING

The history and physical examination, coupled with a

known environmental exposure, are typically adequate to

establish the diagnosis of hypothermia. The absence of a

known environmental exposure or any concern for

secondary hypothermia should prompt an active search for

potential etiologies. That said, treatment should not be

delayed while awaiting the diagnostic work -up (Figure 61-2).

TREATMENT

Passive rewarming is typically adequate for patients with

mild hypothermia (35°-32°C). This technique uses the

body's inherent heat production mechanisms to restore a

normal core temperature. To be successful, the patient

needs an intact shivering response and sufficient energy

stores. Remove any wet clothing and wrap the patient in

warm blankets. Passive rewarming usually raises the core

temperature by < 1 °C per hour.

Most patients with moderate hypothermia (32°-30°C)

require active external rewarming. This includes the infusion of intravenous (N) fluids warmed to 42°C, administering humidified supplemental 0 2 warmed to 46°C, and the

placement of forced-air rewarming blankets (eg, Bair

Hugger). Taken as a whole, these methods can rewarm

patients at a rate of approximately 3.SOC per hour. These

measures are usually adequate for patients with severe hypothermia ( <30°C) as well, provided they exhibit no evidence of

cardiac instability. Those who do demonstrate signs of myo ­