Chapter 118. Frostbite and Hypothermia

Trench foot is a direct soft tissue injury that results from prolonged exposure to nonfreezing cold and moisture. The foot is initially pale, mottled, pulseless, and anesthetic and does not improve quickly with rewarming. Several hours after rewarming, the foot becomes hyperemic and painful and perfusion returns after 2 to 3 days. Bullae and edema are late findings. Chilblains (pernio) are painful inflammatory lesions typically affecting the ears, hands, and feet caused by chronic exposure to intermittent damp, nonfreezing conditions. Localized edema, erythema, and cyanosis appear up to 12 hours after the exposure and are accompanied by pruritis and burning paresthesias. Tender blue nodules may form after rewarming. Treatment of trench foot and chilblains include elevation, warming, and bandaging of the affected body part. Nifedipine 20 milligrams PO 3 times daily, pentoxifyline 400 milligrams PO 3 times daily, or limaprost 20 micrograms PO 3 times daily, as well as topical corticosteroids, such as 0.025% fluocinolone cream or a brief burst of oral steroids may be added.

Clinical Features

Freezing of the tissue causes frostbite. Patients initially complain of stinging, burning, and numbness. Frostbite injuries are classified by the depth of injury and amount of tissue damage based on appearance after rewarming. First-degree frostbite (frostnip) is characterized by partial thickness skin freezing, erythema, edema, lack of blistering, and no tissue loss. Second-degree frostbite is characterized by deeper skin freezing and results in the formation of clear bullae. The patient complains of numbness, followed by aching and throbbing. Deep cold injury, third-degree frostbite, involves freezing of the skin and subdermal plexus leading to hemorrhagic bullae and skin necrosis. Fourth-degree frostbite, extends deeper to muscle, tendon, and bone with mottled skin, nonblanching cyanosis, and eventual dry, black, mummified eschar formation. Because it is difficult to initially evaluate the depth of injury, early injuries are better classified as superficial or deep. Laboratory testing or imaging is not needed to diagnosis frostbite.

Treatment

1. Provide rapid rewarming in circulating water at 40°C to 42°C (104.0°F to 107.6°F) until tissue is pliable and erythematous.

2. Debridement of clear blisters and aspiration of hemorrhagic blisters are controversial. Consult with a surgeon for local preference.

3. Apply topical aloe vera every 6 hours.

4. Provide pain management, local wound care and dressing. Splint and elevate affected extremities. Patients may require parenteral opioids initially, followed by oral NSAIDs.

5. Update tetanus immunoprophylaxis.

6. Patients with superficial local frostbite may be discharged home with close follow-up arranged.

7. Patients with deeper injuries require admission for ongoing care.

8. The use of prophylactic bacitracin ointment, prophylactic antibiotics, and silver sulfadiazine is controversial.

Hypothermia, a core body temperature of <35°C (95°F), results from heat loss due to conduction, convection, radiation, or evaporation.

Clinical Features

Patients with mild hypothermia (32°C to 35°C [90°F to 95°F]) present with shivering, tachycardia, tachypnea, and hypertension. When core temperatures fall below 32°C (90°F), shivering ceases and heart rate and blood pressure decrease. As temperature falls, patients become confused, lethargic, and then comatose. Pupillary reflexes are lost. Respiratory rate decreases, gag and cough reflexes are diminished, bronchorrhea occurs. Aspiration is common. Impaired renal concentration results in a cold diuresis and hemoconcentration. As temperature decreases, the typical progression is from sinus bradycardia, to atrial fibrillation with slow ventricular response, to ventricular fibrillation, to asystole. At temperatures <30°C the risk for dysrhythmias increases.

Diagnosis and Differential

The diagnosis of hypothermia is based on core temperature and may not be initially obvious, especially in cases where a history of prolonged environmental exposure is missing. Low reading thermometers are required to measure and monitor temperature. Laboratory investigation is directed at determining the underlying cause and complications and includes glucose, CBC, electrolytes, clotting profile, blood gas and EKG. Acid-base disorders are common, but do not follow a predictable pattern. Intravascular thrombosis, embolism, and DIC may occur. Electrocardiographic changes include PR, QRS, and QT prolongation, T-wave inversion, and a slow positive deflection at the end of the QRS (Osborn J wave). In addition to environmental exposure, causes of hypothermia include hypoglycemia, hypothyroidism, hypoadrenalism, hypopituitarism, CNS dysfunction, drug intoxication, sepsis, and dermal disease.

Emergency Department Care and Disposition

1. Place patient in a warm environment. Initiate continuous monitoring of vital signs, pulse oximetry, and core temperature (rectal, bladder, or esophageal thermometer). Indications for intubation are similar to those for normothermic patients. Initiate warmed crystalloid intravenous fluids. Remove wet clothing, dry, and cover patients.

2. Handle patients gently to avoid precipitation of ventricular fibrillation.

3. Attempt to palpate a pulse and detect respirations for 30 to 45 seconds. If none is detected, initiate CPR.

4. Sinus bradycardia, atrial fibrillation, or flutter usually requires no therapy and will resolve with rewarming. Ventricular fibrillation is typically refractory to therapy until the patient is rewarmed, but a single defibrillation is recommended.

5. Rewarming techniques include passive rewarming, active external rewarming, and active core rewarming (Table 118-1). Choice of technique depends primarily on cardiovascular status. Temperature is a secondary consideration. Patients with a stable cardiovascular status (including sinus bradycardia and atrial fibrillation) and temperature above 30°C may be passively rewarmed. All patients with cardiovascular instability require rapid core rewarming; extracorporeal circuit rewarming is the technique of choice for these patients. Invasive rapid core rewarming in patients without cardiac instability is controversial.

6. Continue resuscitative efforts until core temperature reaches 30°C to 32°C.

7. Address and treat underlying causes (eg, dextrose 50 mL IV for hypoglycemia, thiamine 100 milligrams IV/IM in thiamine deficient alcoholism; treat suspected hypothyroidism and hypoadrenalism with hormone replacement).

8. Admit all patients with symptomatic hypothermia. Healthy patients with mild environmental hypothermia that resolves quickly may be discharged home if social circumstances allow.