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 increas

Rewarming and Managment:

• 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 Cardiac 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

References:
1. Ginty C, Srivastava A, Rosenbloom M, Fowler S, Filippone L. Extracorporeal membrane oxygenation rewarming in the ED: an opportunity for success. Am J Emerg Med. 2015 Jun:33(6):857.
2. Tintinalli, J. E., Stapczynski, J. S., Ma, O. J., Yealy, D. M., Meckler, G. D., & Cline, D. (2016).Tintinalli's Emergency Medicine: A Comprehensive Study Guide. Chapter 18: Frostbite and Hypothermia. New York: McGraw-Hill Education.