Definition:
Hypothermia is defined as a core body temperature lower than 35°C (95°F).
Pathophysiology:
Cold stress causes the hypothalamus to stimulate the sympathetic nervous system to release catecholamine, causing peripheral vasoconstriction and shunting of blood centrally. The metabolic rate and muscle tone (shivering) increase to prevent further heat loss. As the temperature decreases, the body’s metabolic rate slows, causing a decrease in cardiac output, respiratory effort, and central nervous system function.
Clinical Presentation:
- Mild — bradycardia, bradypnea with few alterations in sensorium; 32°-35°C or 89.5°-95°F
- Moderate — confusion, combativeness, ataxia, pallor, 28°-32°C or 82°-89.6°F
- Severe — Comatose, cool skin, <28°C or <82°F
Standard Management Approach:
During the rewarming process, consideration should be given to avoid the four mechanisms of heat loss:
- radiation (warm environment);
- evaporation (keep the patient dry);
- conduction (do not place cool objects on or near patient);
- convection (remove obvious sources of circulatory air).
Active external rewarming techniques are numerous and should be tailored to the individual patient, the risk of adverse effects, and the practicality and availability of these techniques in individual emergency departments and during transport.
Mild to Moderate — External warming techniques include warm baths, thermal blankets and pads, heat lamps, hot packs, radiant warmers, and maintenance of a high ambient air temperature.
Severe — Require one or more core rewarming techniques, which include: warm humidified oxygen (42°- 48°C) inhalation, peritoneal dialysis hemodialysis, mediastinal irrigation, and gastric or bladder lavage with warmed fluids. Extracorporeal blood rewarming is considered the ultimate therapy for arrested hypothermic patients:
- Provide supplemental oxygen.
- Watch for arrhythmias on electrocardiogram monitor (watch for arrhythmias).
- Monitor airway, breathing, and circulation, and history of trauma cervical-spine immobilization.
- Monitor vital signs including blood pressure, rectal temperature.
- Remove wet, cold clothing and blankets.
- Maximize temperature in transport vehicle.
- Avoid excessive movement.
- Raise body temperature 1°C/hour — slow rewarming.
- Never place intravenous in frozen extremities.
- Labs: Arterial blood gas, Chem 7 (hypoglycemia is common in infants and children), complete blood count, amylase, liver function tests, blood cultures, and urinalysis.
- Fluids: Normal saline or lactated Ringer solution warmed through a blood-warming coil (45oC). 10-20 ml/kg increments.
- Use pharmacologic agents cautiously as drug metabolism is unpredictable. Exceptions include glucose, lidocaine, and bretylium.
- Antibiotics should be considered in neonates and in all children with nonexposure hypothermia.
Considerations:
- Arrhythmias — particularly ventricular fibrillation.
- "After-drop" or "rewarming shock," defined as the maximum drop in temperature and pH that occurs with rewarming, particularly with external rewarming. With after-drop, peripheral potassium-laden blood moves into the central circulation and can cause hyperkalemia.
- Infants are susceptible to hypothermia because of a large surface area-to-weight ratio, a lack of subcutaneous fat, and a failure to produce heat by shivering.
- Children may become hypothermic during near-drowning events, even in water of 70°F.
- Other predisposing conditions for hypothermia include age, environmental extremes, alcohol and drug consumption, endocrinopathies, head and spine trauma, and infection.
Source: Children’s Hospital, Columbus, OH.
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