by Jon Solberg, MD, FACEP, FAWM

With adventurers pushing the extremes of geographical and seasonal exploration, a thorough understanding of cold weather illness is paramount. For a good review of frostbite, reference Overland Medicine, Winter 2012. For an overview of hypothermia, and to discover why Polar explorer Scott’s choice in skivvies may have lead to his death, read on! 

Physiology

Hypothermia is a medical condition characterized by a core body temperature of less than 35°C. A patient’s degree of hypothermia is difficult to define, and the disorder should be understood as a progression of symptoms over a range of temperatures.  

 Mild hypothermia (34-36°C) symptoms can easily be mistaken for other illnesses: dysarthria (slurred speech) mimics alcohol intoxication and stroke, nausea and vomiting mimic carbon monoxide poisoning and gastroenteritis, and ataxia (difficulty with balance) mimics high altitude cerebral edema. Irritability may be attributed to lack of personal constitution. Surface blood vessels constrict to conserve heat and blood is forced back to the body’s core. The kidneys respond by producing more urine, known as cold induced diuresis (urination), a phenomenon well known to scuba divers (who hasn’t peed in his/her wetsuit?). Hypothermic victims initially develop a shivering reflex that generates heat 2-5 times faster than normal and burns up to 1000 Calories per hour until short-term fuel supplies are exhausted.

 Moderate hypothermia(30-33°C) is characterized by mental status changes. Paradoxical undressing may occur and unmonitored victims may erroneously strip off insulating layers. The shivering reflex is extinguished, which may dangerously lead rescuers to believe that a victim is not hypothermic. Urine production stops, breathing shallows, and the heart struggles to pump, leading to hypotension (low blood pressure) and bradycardia (slow pulse rate).

 Severe hypothermia(less than 30°C) leads to coma and pulmonary edema (build up of fluid in the lungs). Now, the cold heart becomes irritable and is prone to developing rhythm disturbances that can render it completely unable to function. 

Treatment

Passive rewarmingis the first step for all hypothermia and it augments the body’s own thermoregulatory response. Remove cold, damp clothing, and place the victim on an insulated sleeping pad to minimize conduction and evaporation. Convection and respiratory heat losses can be minimized by seeking shelter from the wind in a tent, bivy sack, or nearby vehicle. Application of appropriate clothing, blankets, and sleeping bags combat losses from radiation heat loss. Because of cold induced diuresis, even minimally hypothermic patients are dehydrated, and a victim should be encouraged to consume warm liquids until urination ensues. Warm soup provides calories, heat, and fluid, and avoids the urination and blunted shivering that are associated with caffeine and/or alcohol. Do not attempt rehydration with fluids of less-than ambient temperature, as the risks of worsening the hypothermia outweigh the benefits of fluid resuscitation.

Active rewarmingis necessary for more severely hypothermic patients and provides direct transfer of heat utilizing all available means: hot water bottles, warmed blankets, air-activated charcoal heat packs at the groin and axilla (armpits) where large blood vessels carry heat directly to the core. Hypothermic skin is less able to discern surface temperature, so be extra careful when placing hot items next to a victim’s skin; burns have been known to occur. Some criticize out-of-hospital active rewarming, citing a concept termed core temperature after-drop, which suggests that warmth provided only to extremities causes dilated blood vessels to carry icy blood directly to the core, further chilling the vital organs. This phenomenon is not well understood and it should not prevent attempts to rewarm a hypothermic patient in the wilderness. 

 Despite the hypothermic heart being extremely irritable, The American Heart Association recommends CPR be given to all pulseless patients. Experts endorse starting CPR after carefully verifying the complete absence of a pulse. Remember the frequently taught anecdote “no one’s dead until they’re warm and dead,” and efforts at resuscitation should continue until the victim can be adequately rewarmed. Consider one of several rescue stories of late: Anna Bagenholm, a Swedish physician, went on to almost complete recovery after a 1999 skiing accident left her submerged in freezing water for 80 minutes.  She received CPR for over one hour and at the hospital had a core temperature of 13°C, one of the coldest ever recorded. 

Winter Travel

While growing up in rural North Dakota, we traveled frequently despite winter weather advisories. I remember my dad driving in a blizzard, using his left arm to remove snow from the windscreen when the wipers were inadequate. My dad was always prepared, however, and in addition to driving a well maintained vehicle, he always packed survival gear consisting of sleeping bags, a homemade, coffee-can sized candle which he swore would produce enough heat for a small motorhome, granola bars, water bottles, a snow shovel, and a tow strap. He always called ahead to let my grandparents know our plans and we could count on Grandpa to come looking if we were late. Similar advice should be followed by all winter travelers and can be found by searching for “winter” on the North Dakota Department of Transportation website: www.dot.nd.gov

Gear

Space blankets come in a variety of shapes and sizes, and a recent military study concluded that the Blizzard Emergency Survival Blanket (The Tactical Medic, $37) was a reasonable compromise between cheap, flimsy units, and the more superior yet costly Gortex versions. I have personal experience with Blizzard brand blankets, gained during deployment to Afghanistan with the US Army. They are a reasonable, space saving addition to a vehicle’s first aid kit, no matter the season or forecast.

When monitoring a victim’s temperature, mercury thermometers are prone to breakage and have a dismal range of accuracy. Instead, get a new and improved digital one (Veridian V Temp 10-second Hypothermia Digital Thermometer, $8.20, 26°-50°C).  Of note, tympanic (ear scanner) thermometers and forehead strips are for rookies and, like dashboard inclinometers, should be left at home. “I can tell when a patient is cold,” you say? I diagnose and treat patients with altered mental status every single day and I can assure you, differentiating mild hypothermia from altitude sickness, carbon monoxide poisoning, intoxication, or stroke is not easy, except when the thermometer gives you the answer. Face the same situation in the wilderness and you too will be wishing for that thermometer, in which case by the way, the only accurate temperature is a rectal temperature, obtained by sticking a well-lubricated thermometer probe an inch or two into the rectum. At $8.20 apiece, you may want to bring two.

Clothing

Cold weather clothing is beyond the scope of this article, but an interesting historical perspective is the work of George Havenith, PhD, professor of Environmental Physiology and Ergonomics at Loughborough University.  He has studied the clothing worn by Scott’s and Amundsen’s competing teams during their 1911 race to the South Pole.  While all teams wore layered clothing (still the gold standard), Scott’s team wore layers of coarse fabric like wool, and Amundsen’s team wore layers of slippery fur.  The difference in friction, Havenith concludes, lead to the Amundsen team’s 20% smaller energy requirement: an interesting factoid considering Amundsen’s team was successful and all of Scott’s team perished.

Also recently examined for historical and scientific purposes was the clothing worn by George Mallory, who disappeared on Mt Everest in 1924.  After his body was finally recovered in May 1999, his clothing was sampled, studied, and reproduced in the “Mallory Clothing Replica Project” (http://www.derby.ac.uk/news/george-mallorys-everest-clothes-learning-from-the-past).  Their research determined that Mallory was sufficiently well-insulated to operate effectively in the mountains, in good weather, while sporting “a hand-knitted jumper, two other hand-knitted fragments, three pairs of socks, a blue and white shirt, a vest that is in a fibre blend with silk, and his puttees, which might be cashmere rather than sheep wool.” Nothing says c-o-z-y like cashmere puttees!

Conclusion

While cold weather shouldn’t deter anyone from heading outside for good adventure, it’s best to check the forcast and pack for the worst-case scenario. No matter where your adventures take you, check your first aid and survival gear and ensure it contains equipment to diagnose and treat hypothermia: a quality digital thermometer plus batteries, and a Blizzard Blanket.  These items are worth way more than they cost in money and weight and they will convey the presence of a true professional if you’re called upon to render aid. Doctor’s orders

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