by Dick Hurd, MD
Cool weather is just around the corner, so it is appropriate to take a refresher course on hypothermia,which is defined as a drop in the body's core temperature to less than 95 F. I will discuss the physiology, recognition, practical treatment, and prevention. Much of this information was provided at the recent annual meeting of The Wilderness Medicine Society.

First, I want to emphasize that hypothermia is not confined to cold weather. I am a summer paddler, and have seen lots of paddlers shivering after an unintended swim. All we need is cold water, prolonged or repeated immersion, or rain, a little wind, overcast skies, wet clothing, and we have the ingredients for hypothermia.We should have some dry clothes in a waterproof container with us whenever we are on a river, regardless of season.

Second, it is an interesting fact that our perception of being hot or cold is more related to skin temperature than core temperature. This has a curious connection to hypothermia: if you try to externally warm (heating pad, hotwater bottles) a hypothermia victim who is vigorously shivering, you may turn off the shivering, making matters worse. Also, you have all heard of hypothermia victims discovered in various stages of undress: the explanation seems to be that in the terminal stages of hypothermia,vasoactive chemicals are released causing constricted blood vessels at skin level to dilate, in turn causing the victim to feel very warm — like a permanent hot flash —and remove their clothes.

PHYSIOLOGY:Hypothermia occurs when there is excess heat loss to the environment. For paddlers, this can be by convection(wind or cold moving water) or conduction. Conductive heat loss is hastened by wet clothes (5x)or being in the water (25x).Once core temperature drops below 95 F, shivering begins, which is the body's attempt to increase metabolic heat production. If heat loss continues to below 90 F, shivering ceases and the body begins a slow downward spiral that can result in death. Below 80 F is considered severe hypothermia; the lowest recorded adult survivor of accidental hypothermia reached 56.8F.

RECOGNITION:Hypothermia is classified as mild, moderate, and severe, based on core (rectal) temperature readings. Most GCA trips do not have a thermometer along, so there are some practical things you can look for. The following 'rule of thumb' scheme was developed by the Swiss: Mild victim alert, shivering 95-89.6O F Moderate victim drowsy, nonshivering 89.6-82.4O F Severe victim unconscious 82.4-75.2O F victim not breathing <75.2O F

Besides shivering, note that change of mental status and muscular coordination is the next thing to look for; this person may exhibit poor judgment, unsteady gait, slurred speech, and apathy. This is a person you may have to take charge of and convince they are in trouble!

TREATMENT:Remembering that we are on ariver somewhere with 'field' conditions, I am going to focus only on MILD hypothermia, because anything beyond that requires urgent evacuation to a medical facility.

1. Prevent further heat loss: get victim out of water and wind, replace wet clothes with dry clothes, and insulate with a tarp, plastic garbage bag, sleeping bag, leaves, pine straw, etc. This needs to be top and bottom: laying a victim on cold ground allows continued heat loss. A pullover hat should be placed on the head.

2. Facilitate rewarming, of which shivering is the best mechanism. Warm food or warm sugar containing drinks will provide energy needed to maintain shivering. A hot drink is not helpful — pour a cup of hot coffee in a 10 gal. container of water and see how much the temperature rises! As mentioned earlier, external heat may actually turn off the shivering mechanism. However,inhalation of steam from boiling water may help, as may a fire to create a warmer environment.

Given what we usually carry on a GCA trip, other than canoe camping, item #1 may be our only resource. If a victim is moderate or severe, get help fast! PREVENTION:This should be pretty obvious. Be aware of weather and water conditions when you paddle, and remember they can change. You canput some dry clothes, a "watch"hat, a large industrial size trash bag, a pack of matches,and a votive candle in a pretty small bundle. If you don't need it, maybe someone else will. Because the onset of hypothermia can be subtle, be aware of how you feel, and be aware of others in the group:shivering, altered mental status, and altered muscular coordination are the things to look for. Finally, if you suspect this problem, bring it to the attention of others in the group, because the time to begin treatment is when you suspect the diagnosis.

Good luck, and see you on the river.

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