Surviving hypothermia after being left for dead in the wilderness makes an interesting story line in the movies. In real life, hypothermia kills over a thousand people each year in the United States alone. Knowing how to recognize it and treat it (or better yet, prevent it) can save lives.
Systemic hypothermia involves a core body temperature below 35 degrees Celsius. Accurate measurement is crucial and the core temperature probe must be able to measure as low as 25 degrees Celsius. Resuscitative measures must always be continued until the patient’s core temperature is clearly over 32 degrees Celsius (unless there are obvious fatal injuries). As every physician, nurse, and first responder has been taught, “you’re not dead until you’re warm and dead.”
Susceptibility to hypothermia is increased by extremes of age, heart disease, exhaustion, hunger or malnutrition, dehydration, hypoxia, immobility, intoxication with drugs or alcohol, low body mass, contact with moisture or metal, and loss of consciousness. Even in the movies, victims of hypothermia try desperately to stay awake and keep moving.
Clinical signs and symptoms of hypothermia vary based on the patient’s underlying status. In general, however, there are four stages:
- Stage I- CBT (core body temperature) is between 32 degrees Celsius and 35 degrees Celsius. The patient is shivering and may be losing good judgement and coordination; still conscious and hemodynamically stable.
- Stage II – CBT is between 28 degrees Celsius and 32 degrees Celsius. Shivering stops, pulse slows, and pupils dilate. Reflexes slow and “cold diuresis” develops as a result of renal dysfunction and low levels of ADH (antidiuretic hormone). Eventually, this will lead to hypovolemia and shock. The patient becomes increasingly confused and lethargic.
- Stage III-CBT is between 24 degrees Celsius and 28 degrees Celsius. Vital signs may still be present, but the risk of cardiac arrest increases dramatically, and the patient is now unconscious.
- Stage IV – CBT is less than 24 degrees Celsius. Vital signs are absent. There is coma, loss of reflexes, asystole or ventricular fibrillation and rigor mortis. The patient appears dead but may still be salvageable.
The cornerstone of treatment in hypothermia is rewarming. Rapid assessment with support of airway, breathing, and circulation must occur almost simultaneously. All cold, wet clothing should be removed and replaced with warm, dry clothing and blankets. The patient’s head should be covered and every effort must be made to prevent additional heat loss. In general, raising core body temperature by 1 degree Celsius per hour is safe. Giving warmed IV fluids (normal saline at 45 degrees Celsius) may be helpful.
Great care and caution must be used when moving or transporting a hypothermic patient. The combination of vasoconstriction, hypovolemia, and return of cold peripheral blood to the central circulation can cause ”core temperature after drop.”
This phenomenon, combined with lactic acidosis, can precipitate potentially fatal arrhythmias known as “rescue collapse.” This is where real life must break with the movies. Dramatic scenes where the rescuer frantically rubs and massages the victim’s extremities may be riveting, but they’re also wrong.
Preventing hypothermia is much easier than treating it. When in doubt, rely on the old adage: Keep warm, keep dry, and keep moving.