The Basics
- On average, approximately 1300 Americans die of hypothermia each year
- These don’t all occur in cold mountain regions. Homelessness, mental illness and substance abuse are important risk factors, particularly in urban areas.
- Not all hypothermia cases are related to exposure! Other causes include hypoglycemia, hypothyroidism, hypoadrenalism, hypopituitarism, CNS dysfunction, drug intoxication, sepsis and dermal disease
- Hypothermia = core body temperature < 35 degrees C (95 degrees F)
- Mild hypothermia (32-35 degrees C): present with shivering, tachycardia, tachypnea and hypertension
- < 32 degrees C: shivering stops and HR and BP decrease; patients become confused, lethargic and then comatose; Reflexes are lost, RR increases; bronchorrea occurs; aspiration is common; cold diuresis and hemoconcentration occur
- As temp lowers, sinus bradycardia develops into atrial fibrillation with slow ventricular response to ventricular fibrillation to asystole. At temps < 30 degrees C, the risk for dysrhythmias increases
Rewarming and Management
- Type of rewarming is based on cardiovascular status, NOT temperature
- Passive rewarming: removal from cold environment and wet clothes, insulation
- Active external rewarming: warm water immersion, heating blankets set at 40 degrees C, radiant heat, forced air
- Active core rewarming at 40 degrees C: Inhalation rewarming (warm air via the vent), heated IV fluids, GI tract lavage, bladder lavage, peritoneal lavage, pleural lavage, extracorporeal rewarming, mediastinal lavage by thoracotomy
- Remember to handle these patients gently to avoid precipitation of ventricular fibrillation!
ECMO in Hypothermic Arrest
- The use of ECMO has been recommended as the rescue therapy of choice for hypothermic cardiac arrest for its ability to rapidly rewarm patients (8-12 degrees/hour) and provide complete cardiopulmonary support
- Studies have shown that patients with cardiac arrest have a rate of survival of 50% with the use of ECMO, whereas, at centers without ECMO, these same types of patients have a survival rate of only 10%
- Cases of survival with a good clinical outcome have been reported with core temperatures as low as 13 degrees Celsius and in cases requiring long transport with more than 5 hours of CPR!
Risk Factors for Poor Prognosis Despite Aggressive Therapy (ECMO, etc):
- Clear history of cardiac arrest before cooling
- Obvious signs of irreversible death
- Core body temperature higher than 32 degrees Celsius with asystole
- Potassium greater than 12 mEq/L
