Hypothermia and Frostbite

HYPOTHERMIA

Hypothermia is defined as a core body temperature of _35_C and is classified

as mild (32.2_–35_C), moderate (28_–32.2_C), or severe (_28_C).

ETIOLOGY Most cases occur during the winter in cold climates, but

hypothermia may occur in mild climates and is usually multifactorial. Heat is

generated in most tissues of the body and is lost by radiation, conduction, convection,

evaporation, and respiration. Factors that impede heat generation and/

or increase heat loss lead to hypothermia (Table 30-1).

CLINICAL FEATURES Acute cold exposure causes tachycardia, increased

cardiac output, peripheral vasoconstriction, and increased peripheral

vascular resistance. As body temperature drops below 32_C, cardiac conduction

becomes impaired, the heart rate slows, and cardiac output decreases. Atrial

fibrillation with slow ventricular response is common. Other ECG changes include

Osborn (J) waves. Additional manifestations of hypothermia include volume

depletion, hypotension, increased blood viscosity (which can lead to thrombosis),

coagulopathy, thrombocytopenia, DIC, acid-base disturbances, and

bronchospasm. CNS abnormalities are diverse and can include ataxia, amnesia,

hallucinations, delayed deep tendon reflexes, and (in severe hypothermia) an

isoelectric EEG.

DIAGNOSIS Hypothermia is confirmed by measuring the core body temperature,

preferably at two sites. Since oral thermometers are usually calibrated

only as low as 34.4_C, the exact temperature of a patient whose initial reading

is _35_C should be determined with a thermometer reading down to 15_C or,

ideally, witha rectal thermocouple probe inserted to _15 cm. Simultaneously,

an esophageal probe should be placed 24 cm below the larynx.

TREATMENT

Cardiac monitoring should be instituted, along with attempts to limit further

heat loss. Mild hypothermia is managed by passive external rewarming and

insulation. The pt should be placed in a warm environment and covered with

blankets to allow endogenous heat production to restore normal body temperature.

Active rewarming is necessary for moderate to severe hypothermia,

cardiovascular instability, age extremes, CNS dysfunction, endocrine insufficiency,

or hypothermia due to complications from systemic disorders. Active

rewarming may be external (forced-air heating blankets, radiant heat sources,

and hot packs) or internal (by inspiration of heated, humidified oxygen

warmed to 40_–45_C; by administration of IV fluids warmed to 40_–42_C;

or by peritoneal or pleural lavage withdialysate or saline warmed to 40_–

45_C). The most efficient active internal rewarming techniques are extracorporeal

rewarming by hemodialysis and cardiopulmonary bypass. External

rewarming may cause a fall in blood pressure by relieving peripheral vasoconstriction.

Volume should be repleted with warmed isotonic solutions; lactated

Ringer’s solution should be avoided because of impaired lactate metabolism

in hypothermia. If sepsis is a possibility, empirical broad-spectrum

antibiotics should be administered after sending blood cultures. Atrial arrhythmias

usually require no specific treatment. Ventricular fibrillation is often

refractory. Only a single sequence of 3 defibrillation attempts (2 J/kg)

should be attempted when the temperature is _30_C. Since it is sometimes

difficult to distinguish profound hypothermia from death, cardiopulmonary

resuscitation efforts and active internal rewarming should continue until the

core temperature is _32_C or cardiovascular status has been stabilized.

FROSTBITE

Frostbite occurs when the tissue temperature drops below 0_C. Clinically, it is

most practical to classify frostbite as superficial (without tissue loss) or deep

(withtissue loss). Classically, frostbite is retrospectively graded like a burn

(first- to fourth-degree) once the resultant pathology is demarcated over time.

CLINICAL FEATURES The initial presentation of frostbite can be deceptively

benign. The symptoms always include a sensory deficit affecting light

touch, pain, and temperature perception. Deep frostbitten tissue can appear waxy, mottled, yellow, or violaceous-white. Favorable presenting signs include

some warmthor sensation with normal color.

TREATMENT

A treatment protocol for frostbite is summarized in Table 30-2. Frozen tissue

should be rapidly and completely thawed by immersion in circulating water

at 37_–40_C. Thawing should not be terminated prematurely due to pain from

reperfusion; ibuprofen, 400 mg, should be given, and parenteral narcotics are

often required. If cyanosis persists after rewarming, the tissue compartment

pressures should be monitored carefully.