Hypothermia: It’s Cold Out There

shutterstock_171146414I credit the information that I’ve learned and posted here to Eric Weiss, MD who is an international expert in Wilderness Medicine and Hypothermia.

Patients with accidental hypothermia come to medical providers year-round and in all climates.  Hypothermia is defined as a decrease in core body temperature below 95 degrees F (35 degrees C).

For purposes of emergency management and resuscitation, hypothermia can best be characterized as either mild or severe.  In mild hypothermia (core temperature 87.8-95 degrees F), the victim is conscious, still shivering and generally not prone to developing abnormal heart rhythms.  In severe hypothermia (core temperature below 87.8 degrees F), the patient has altered level of consciousness, diminished or absent shivering and is prone to abnormal heart rhythms.

Mild hypothermic victims can still generate heat through shivering so they generally do well without intensive rewarming.  In severe hypothermic patients, active rewarming techniques such as extracorporeal blood rewarming, inhalation therapy, peritoneal lavage, thoracic cavity lavage or thoracotomy with mediastinal irrigation may be needed.

Pre-hospital Treatment of Mild Hypothermia:  Preventing further heat loss and facilitate rewarming are the goals.  The rescuer should remove all wet clothing and replace it with dry clothing, insulate the patient with sleeping bags, blankets, extra clothing or other suitable material.  Use insulation underneath the patient as well as on top.  Encourage drinking of warm fluids and sugary drinks if they can swallow without aspirating (inhaling the drink into their lungs).  It is not uncommon to observe a continued decline in core temperature after a hypothermic patient is removed from the cold environment and external warming is initiated.  This phenomenon is called core temperature afterdrop.

Pre-hospital Treatment of Severe Hypothermia:  Careful handling is necessary because these patients are prone to develop abnormal heart rhythms through rough handling.  If in the backcountry, consider helicopter transport to prevent jostling that might occur with an overland evacuation.  Keep them horizontal when possible to minimize orthostatic hypotension.  Provide oxygen if you have it.  Administer a minimum of 500ml of heated (98.6-105.8 degrees F) IV normal saline or D5NS.  Lactated ringers should be avoided because when the liver is cold, it poorly metabolizes lactate.  Consider intraossious (I/O) infusion for alternative pathway for fluid replacement for a dehydrated patient who you cannot get IV access. Hot water bottles or heat packs can be placed in the axillae and groin area and along the neck where large blood vessels course near the surface.  Hot water bottles should be wrapped with insulation to prevent thermal burns.

In a severely hypothermic patient, they may feel/look clinically dead. Breathing may be difficult to detect if the breathing rate is significantly depressed. The rescuer should listen to the chest and palpate over carotid or femoral arteries for at least 1 minute to detect a pulse.   If the patient has any sign of life, chest compressions should not be initiated as they may precipitate ventricular fibrillation (abnormal heart rhythm). At a core temperature of 20 degrees C, cardiac arrest is tolerated for up to 30 minutes without clinically significant neurologic or neuropsychological deficits.  This knowledge and the fact that a dead victim may be clinically indistinguishable from one that is severely hypothermic and alive has lead to the adage that “No one should be pronounced dead, until they are warm and dead.”

A serum potassium greater than 10mmol/L in a non-hemolyzed specimen however has been proposed as a reasonable ceiling for viability.

Negative Pressure Rewarming (Thermarescue):  A non-invasive way of creating a direct thermal pipeline between the skin and body core.  The patients forearm is fitted through an acrylic sleeve with an air tight seal around the arm.  Vacuum pressure of -40 mm Hg is established and the thermal load is applied via a chemical heating pad.

If you are interested in learning more about wilderness medicine, a great resource for information is the wilderness medicine society:  http://www.wms.org/

This document is for informational purposes only, and should not be considered medical advice for any individual patient.  If you have questions please contact your medical provider.


I hope that you have found this information useful.  Wishing you the best of health,

Scott Rennie, DO

Blog: https://doctorrennie.wordpress.com


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