AVOIDING THE BIG CHILL
Heat Production and Conservation
Treating Hypothermia and Frostbite
INTRODUCTION
All homeotherms face the same dilemma, how to maintain a constant body temperature in a varying environment. When human body temperature exceeds 37°C (98.6°F) the body must cool itself to prevent hyperthermia. When it is below 37°C, the body must produce heat to avoid hypothermia. The first paper in this section will discuss maintenance of body temperature in winter and strategies to avoid hypothermia. The second paper will discuss winter clothing and the third will deal with the treatment of hypothermia if, in spite of all attempts to avoid the problem, it still arises. All three papers should be studied and the importance of preparing for winter weather should be stressed to the students. All members of a winter outing should understand the basics of prevention and treatment of hypothermia since the teacher or leader could be unavailable in an emergency. The teacher and leader of an expedition must be thoroughly informed of all aspects of dealing with all possible weather conditions which could be encountered and should review the clothing and provisions of each member of the group. The teacher and/or leader should carry a pack (day pack or book bag is fine)--on all outings which will occur more than 100 yards from a heated, open building--containing extra wool or insulated gloves, hat, socks, and a sweater or sweatshirt big enough to fit anyone--man's L or XL. Each student should carry an emergency snack such as a candy bar or dried fruit and nuts and the leader should carry a couple extras. If the outing involves more than a mile away from shelter or will be in an isolated area near shelter each member should carry 1 quart of water or a sugared drink. "Wine skins" are very convenient and can be worn under the jacket to keep thawed. For extended periods outdoors as many students as possible should carry packs containing extra gloves, socks and sweater. No overnight camping or extensive day outings should be done unless all members are fully informed of winter survival and an experienced leader who is familiar with the area involved in winter is along for the trip. Sudden storms have stranded many a group which anticipated a few hour hike in mild winter weather. Emergencies arise suddenly and hypothermia can occur in an injured person waiting for aid or in the companions left behind when one group goes for help even in relatively mild weather. At least four people should be involved in any outing more than 100 yards from shelter and no member of a party should ever be left alone or go off alone.
HEAT PRODUCTION AND CONSERVATION
A dry healthy body in a 22-27°C (~70-80°F) environment can maintain temperature easily. Below 22°C or wet below 37°C cooling occurs and energy must be expended to maintain the temperature of the internal organs (core temperature). Heat flows from a warmer object to a cooler. The difference in temperature between two objects divided by the distance between them is the temperature gradient this and the thermal conductivity of the material between the objects determines the efficiency of heat transfer. Heat loss increases as the temperature gradient increases and as the thermal conductivity increases. Air is a poor conductor and thus a good insulator. Water is a good conductor and metal is an excellent conductor. The sensation of "cold" is experienced when heat is lost by the body to the environment. Four physical processes are involved: conduction, convection, radiation, and evaporation. When mammals are discussed one sometimes sees respiration listed as a fifth process, but respiration really is a combination of the other four occurring internally.
Heat will be lost through conduction whenever an object is in direct contact with an object colder than itself. Solids are the best conductors and gasses are the poorest.
Heat will be lost through convection if the contacting substance is a fluid such as air or water. Continual movement of the fluid accelerates the transfer of heat (bellows effect) by carrying the warmed fluid away and replacing it with cool fluid. Convection is the basis of the concept of "wind chill". If air is cooler than skin temperature, heat will be removed from the body. The faster the air is moving in relation to the body, the more rapidly cooling will occur. For example at 4°C (39°F) with a 15 mile per hour wind, the cooling effect on the skin equals that of a person walking on a calm day at -4°C (25°F).
Radiation is the transfer of heat from a warm object to a cooler one by means of electromagnetic waves. The rate of radiative loss increases as the temperature difference increases.
Evaporation losses occur when liquid on the surface is vaporized--a process which utilizes heat from the surface. Humidity is the main determiner of the rate of evaporation. Humid days seem warmer in the summer because evaporation is less and this reduces the cooling ability of the body. Winter is dry and evaporation is increased in winter.
The human body loses heat through conduction whenever it is in direct contact with colder objects. Since air is a poor conductor, providing a layer of air between the body and the environment reduces this loss. Feet are a major source of loss, especially on pavement and thick, non-compressible soles are essential to minimize this loss.
Convective losses are best minimized through prevention of convection--snug but not tight collars, cuffs and waist bands reduce the movement of air and trap warmed air near the skin. Wet (or the newer dry) suits serve the same purpose in water.
Radiation heat loss can be minimized by covering the body. As much as 50% of radiation loss occurs from the head because scalp skin is richly supplied with warm blood. The importance of covering the head cannot be overemphasized.
Evaporative losses occur when the surface of the body is moist. Perspiration is a continuous process. Insensible (not noticeable) perspiration is responsible for the dispersion of 710 ml (24 oz) water per day which is the by-product of metabolism. Since fluid production cannot be prevented, provisions must be made to allow evaporation to occur. Wicking (the transfer of fluid from one place to another via capillary action) allows the fluid on the skin to be transferred to the surface of the clothing. There is some heat loss involved because the skin surface must heat the clothing surface, but since the temperature gradient between clothing and air is less than between skin and air, the heat loss is reduced. Failure to wick allows moisture to buildup and replace the air space next to the skin allowing conductive heat loss to occur which is an efficient heat robber. Also evaporation at the outside garment surface reduces the temperature of that surface thus the temperature gradient between skin and that outside surface. Respiration necessitates the contact of cold dry air with the warm moist surface of the respiratory tract and heat loss to the body core does occur. Face masks and scarves which cover the mouth reduce this loss by using exhaled air to humidify and warm the air being inhaled.
The human body evolved to maintain core temperature over a moderate temperature range through systems of heat production, conservation and dispersion. An understanding of all three is essential to preventing and treating hyperthermia.
Heat dispersion is important because it can contribute to excess perspiration which can lead to excess heat loss. Perspiration is the body's main cooling method and should be minimized. When the body is warm because the air temperature has increased, the wind has decreased or strenuous activity is occurring a hat should be removed (to rapidly cool through radiation) or collar and waist loosened (to increase convection), or a layer of clothing removed (to increase conduction). All these steps can be rapidly reversed whereas clothing wet through perspiration will cool the body until it dries and can lead to hypothermia.
Heat is produced through metabolism and production can be increased through increase metabolism. Caloric needs are increased during heat production and these needs must be met. All participants in outdoor activities should bring high caloric easy to digest snacks and appropriate meals should be provided. No one should diet when out in the cold. Chocolate bars are a standard item of survival kits, because they can make the difference between life and death. People with diabetes and hypoglycemia should discuss with their doctor which snacks should be available and what emergency methods can be employed and the teacher and/or leader should have a written sheet of instructions from the doctor before a student or adult with either condition participates on a trip or outing more than 100 yards from shelter. Emergency winter conditions are not normal and normal diets should not be depended upon. Cold liquids must be warmed internally and can lead to considerable heat loss. Eating snow as a liquid source can be especially dangerous and can lead to gastric bleeding as a stress response to excessive stomach chilling.
Increased metabolism can be recognized by increasing respiration (which increases heat loss) and increasing heart rate. Increased activity increases metabolism and leads to increased cooling through respiration (unpreventable) and perspiration (preventable) in response to increased heat production. It is important to understand this cycle.
It is dangerous to try to minimize heat loss by minimizing calories. Ideally avoiding increasing metabolism by perfect clothing and an activity level perfectly matched to body condition would obviate the need for extra calories, but such an ideal is not possible even in the best conditions and should not be the anticipated reality.
Heat preservation mechanisms also exist in humans, but since man has evolved depending on external aids (i.e. clothing, fire) they are not as efficient as they are in other homeotherms. When heat production fails to keep pace with heat loss, body temperature drops. The hypothalamus responds to cooler blood passing through it by signalling the body to reduce heat loss and increase heat production simultaneously. To prevent damage to vital organs, the core temperature is preserved at the expense of the extremities. Preservation of brain temperature used to be thought to be essential, but now we know that a cooled brain has reduced oxygen and other metabolic needs and can survive reduced or even absent blood flow. This heat conservation is accomplished by constriction of surface and extremity blood vessels reducing blood flow to these areas and reducing the temperature gradient between the body surface and environment. If the surface of the body is cooled until sensory nerve fibers become less excitable, frostbite can occur.
If body temperature continues to drop after vaso constriction, the skin muscles tense raising the body hairs. In man these "goose bumps" have no effect, but in other homeotherms the fluffed up fur or feathers increase their insulative values considerably. Further cooling triggers involuntary muscle contractions, shivering, (remember--increased activity leads to increased metabolism leads to increased heat production) which is extremely effective for a short time. It can increase core temperature by about 4°C in a healthy well nourished person, but it is extremely costly to the body in energy needs and is often the last step before succumbing to hypothermia. It has been estimated that man becomes incapable of life saving actions by the time core temperature has dropped about 4°C (7°F) but by a 2°C drop 100% of his time is devoted to self survival and he cannot help others or avoid dangers; judgment is impaired and disorientation is common. As shivering ceases muscles stiffen and the person looses consciousness. Death will occur when core temperature drops to 26°C (78°F) although revival has been possible with a core temperature as low as 18°C (64°F) under very sophisticated medical care.
Since man has evolved in non tropical zones with clothing, clothing is essential to survival in winter. To be effective clothing must complement and enhance the bodies own heat conservation mechanisms. The surface blood will cool first and cooled blood will signal initiation of heat conservation. When the surface blood is warm heat conservation ceases. Hands and feet have a high surface to volume ratio and cool quickly. If excessive gloves or socks are worn the signal to the body is stop conserving heat and core temperature continues to decrease because blood flow to the surface is not reduced. This explains why some people who pile on gloves and footwear freeze outside while a companion is comfortable. Since shivering is triggered by a continued decrease in core temperature enhancing core heat preservation is desirable. Kaufman's rule suggests three layers of clothing on the torso--two on the extremities and one on hands and feet as a good rule of thumb. He has demonstrated that in extreme conditions a person whose hands and feet are cold to the point of pain maintains core temperature most efficiently. Under favorable conditions, keeping hands and feet warmer than the "pain point" is adequate. If hands and feet are maintained in a warm state core temperature decreases even under moderate conditions. Remember conductive loss through the soles of the feet must be minimized and thick soles will do that without warming the whole foot.
Understanding heat conservation also helps prepare one to deal with emergencies. Here are a couple of examples to demonstrate how the principles involved are translated into action.
These scenarios are presented to demonstrate the kinds of decisions that have to be made in emergency situations and to show how important is knowledge of the physiology of cold, the area visited and possible complications. Part of trip preparation is to review all imaginable problems and their possible solutions. Including students in this review is essential if a long or potentially dangerous trip is anticipated.
Trips planning winter camping require a lot more expertise than this manual is able to provide and should only be lead by someone with demonstrated experience. But in the event that a day trip becomes an overnight a few words will be said about emergency shelters. Part of this manual will discuss Quinzhee construction and its potential as an emergency shelter is discussed. Considerable energy is required to build a Quinzhee and in an emergency it may be too costly. Shelters should be thought of as group clothing and should reduce conduction, convection and radiation. Snow is an excellent insulator and snow caves can often be dug into drifts or shelter found under pine trees or in the pit around tree trunks. Remember to line snow with bark and pine and keep the shelter small--allow a small vent hole and stay put. Ration energy expenditure and never, repeat never move when visibility is reduced. Keeping calm, recalling what is known about preventing hypothermia and conserving energy can allow one to survive potential disasters and enjoy the adventures of winter. But good judgment depends upon knowledge and a leader is responsible for acquiring that knowledge.
The effectiveness of clothing depends upon the degree to which it facilitates the body's own heat conservation methods. To do this it must insulate the torso and head to prevent heat loss while allowing the extremities to remain cooler than the torso. If the extremities are too warm the hypothalamus won't signal the body to reduce circulation to the limbs and heat will be continuously lost from the core. For this reason vests are particularly effective in very cold weather. Important to this conservation of heat is the rate of heat transfer across the space between the skin and the outside environment. If no space exists, heat loss is rapid in a cold environment. If air, a poor heat conductor, is trapped between the skin and environment by clothing the heat loss is reduced. If the environment is cold water, heat loss is very rapid because water is a much better heat conductor than air. If clothing is wet, water replaces air between the body and environment and heat loss is almost as rapid as in immersion. Therefore the most effective clothing will trap air and keep it dry.
Air can be trapped between layers (as in the typical ski jacket) or can be trapped between fibers (as in knits). Cold weather clothing is composed of combinations of fibers and fabrics designed to conserve body heat by maximizing air entrapment, thus insulating the body from the cold.
Each of these fibers and fabrics has its own properties, advantages and disadvantages. Some of the more important ones will be discussed in this paper.
Wool is the traditional "warm" fiber. It sets the standard by which all other fibers are judged. Because it is naturally curly and scaly, it traps lots of air between fibers. Lanolin -- an oil found in wool inhibits water absorbency -- and the tiny air pockets are not easily penetrated by water droplets. Tightly woven fabrics have smaller air spaces between threads (threads are made up of many fibers) than knits; so loose, thick knits trap more air than tight woven fabrics. But air is easily moved between the larger air pockets and the environment, so loose fabrics are much less effective in windy conditions than are tight. Felting -- a method of layering fibers -- is tight like woven fabric, but because of the increased thickness is more insulating. Because water does not penetrate wool easily wool retains most of its insulating properties even when wet. Bulky knits will compress when wet and resemble felt in insulating qualities. Wool wicks well -- that is, it transfers moisture from the skin to the surface through capillary action along the surfaces of the fibers. Air moving across the outside surface of the fabric evaporates moisture. This evaporated moisture is replaced by skin moisture and the surface of the skin remains relatively dry. Wicking requires maximum surface area for capillary action and a steady evaporation of surface moisture. Evaporated heat loss to the skin is minimal because of the non-conductive barrier of trapped air held by the fabric's fibers. Since wool does not get saturated it does not freeze solid. Wool blends (i.e. 85% wool, 15% nylon) retain most of the advantages of wool but increase wool's durability and shape retention dramatically.
Acrylic is a synthetic fiber designed to simulate wool. It does well, but since it lacks the natural crimp of wool it does not trap quite as much air. It is a hydrophobic fiber (as are most synthetics) so does not allow capillary action, but it dries very quickly.
Cotton has smooth straight fibers which are very absorbent woven or knit as a tight, flat material it traps little air. Air within fibers is quickly replaced by water so cotton becomes saturated, can freeze solid and dries slowly. But cotton can be knit in patterns -- thermal knits -- which trap air and enhance evaporation of moisture from fibers. It is comfortable next to the skin and makes a good first layer of clothing. Cotton can also be napped (flannel) on one or both sides, napping "loosens" individual fibers from the thread and combs them to stand perpendicular to the fabric. These fibers trap air and since they increase the surface area of the fabric they enhance evaporation of moisture and wicking. Even bulky cottons saturate with water and most insulation is lost when it is wet. Denim which is a tight, heavy, smooth fabric can be lethal when wet since it clings to the skin, has no air pockets and holds a layer of water against the skin.
Nylon, like acrylic, is a synthetic fiber which is non-absorbent. It is usually woven as a tight smooth fabric which is water repellent and wind tight. It can be napped and loose fibers be used as insulation, but it is not designed to be an insulating fiber and is most effective when used as an outer layer. It does not wick and can trap moisture beneath it but garment design can minimize heat loss from that.
Polyester is also a synthetic, hydrophobic fiber. It can be used as a fabric for outerwear or near the skin. Dacron™ shirts and pants don`t breathe -- but blended with cotton, dacron™ can improve cotton's characteristics as an inner garment. Knit dacron pants can be okay under not too severe conditions -- certainly far superior to denim because air is trapped (heavy "tweedy" knits are better than fine smooth ones) and they dry very quickly.
Polyester's primary value is as an insulator which will be discussed below.
Polypropylene is a synthetic that was designed to be extremely durable. It is not hydrophobic -- though it does not absorb moisture. Moisture is attracted to fibers and held there until it evaporates or is drawn off through capillary action of an overlayer. It's use in clothing is primarily as "fishnet" underwear where the loose knit allows lots of perspiration to be held and a shirt -- usually cotton can wick it away -- the relatively large diameter of the threads hold the cotton away from the skin and prevent it from becoming saturated. Non polypropylene fishnet appears fashionable but does not wick and really serves no purpose. Recently polypropylene has been used as insulation where it is effective in thin layers (Thinsolate™).
There are many new fabrics on the market - usually a synthetic fiber is woven into a fabric which is laminated with one or more coatings. Gortex™ is coated to allow the small droplets from perspiration to pass from inside out, but not to allow larger droplets to pass from outside in and is an example of high-tech fabrics. It allows excellent breathability with effective water repellency.
Insulating fibers are an important component of cold weather garments. The two most common are down and polyester.
Down has an excellent weight/loft ratio and has become the standard by which other fibers are measured. The loft or thickness of the garment determines the amount of air trapped -- the greater the thickness the greater the insulation provided. The fine fibrils of down trap a great quantity of air and since down remembers its shape it fluffs up quickly after being compressed. But down mats completely when wet -- becomes thoroughly saturated and loses most of its insulating abilities. It dries extremely slowly and the weight of wet down can tear the fabric separating compartments.
Modern polyesters such as Dupont Quallofil™ and Hollofil™ consist of short hollow fibers which loft almost as well as down. Since polyester is hydrophobic, water does not adhere to the fibers; thus little air is displaced and there is little loss of insulating ability. Wet garments can be shaken to remove much moisture without damage and dry quickly. Long fiber, spun polyester, monofilament fills do not loft well, but do dry relatively quickly. They can be found in cheaper garments and garments designed to look fashionable, but not meant for long term use in extreme cold.
Polypropylene has an extremely low thermal conductivity and does not depend upon air for insulation as much as down or polyester. Therefore, it can be used in thin, non bulky layers. Since it wicks so well it does not trap moisture and maintains its insulating properties even when wet. Wicking depends upon evaporation; it is not effective in rain or extremely damp conditions. But since the insulation has less volume, less water can be trapped than in polyester or down; it also resists saturation like wool.
Effective clothing must prevent moisture from perspiration from accumulating next to the skin, provide adequate insulation against the cold and provide protection from wind and rain. Wool can be used by itself. Although the addition of a layer of nylon improves wind and water resistance substantially. A layer of cotton or cotton over polypropylene can contribute to comfort.
Clothing must be chosen for the purpose for which it is to be used. When most cold weather exposure is limited to short trips between heated buildings and heated vehicles, any winter wear will suffice and cheap copies of "good" clothing are adequate. When much time is spent outdoors, either for work or leisure more attention needs to be paid, though since a warm, dry place is usually very near, poor choices need not have serious consequences. But if time is to be spent under a variety of weather conditions away from immediate safety, care needs to be taken to dress for all expected contingencies. Layering is a necessity and Kaufman's "rule of thumb" for preserving core temperature must be followed (see previous article on Heat Conservation). The first layer -- underwear -- should wick moisture away from the skin and trap a layer of air next to the skin. This thin layer of air is the primary insulator -- all other layers are designed to protect this layer. If it becomes replaced by water, the other layers function only to keep that water warm and much of the heat conservation of the whole outfit is lost. Flat weaves or knits of anything with the possible exception of wool are less effective then bulky fabrics. The best choice is polypropylene fishnet for tops and bottoms though thermal knit wool/cotton/polyester/nylon blends are okay. Some people use a flat silk under wool for socks and gloves to improve the comfort of wool, but polypropylene wicks and the fishnet design traps more air than silk.
Wool is excellent for the next layer. It is durable and rugged. Wool socks (over silk, bulky orlon, or bulky cotton, if sensitivity is a problem) are the best footwear. Tightly woven, loosely cut, wool slacks are absolutely the best if no other insulating layer is worn. Denim should be avoided at all costs -- even if waterproof outer slacks are to be worn. It is still, heavy and tight fitting and can be lethal when wet. Other weaves of cotton and/or synthetics are acceptable under insulated clothing. Since the torso has more layers than the limbs, a cotton or blended t-shirt or turtle neck can be worn over the underwear followed by a wool shirt, synthetic fleece sweatshirt or sweater as an extra insulating layer. If two layers of slacks are worn over underwear, at least three layers should be worn over the torso -- a vest, knitted or down or synthetic filled should be worn. Wool gloves and/or mittens are good. Mittens keep fingers warmer and if dexterity is important, additional warm gloves can be worn underneath and mittens removed as needed. Filled ski gloves or mittens can be used, mittens being preferred, but the advantages of layering are lost unless a change of handwear is provided. A close-fitting wool hat or other warm hat should be worn.
The outerwear chosen should meet the expected conditions of the trip. Waterproof boots are a must. Rubber bottom, nylon topped boots with a felt or foam liner are best. If available, felt is better than foam since it works better when wet from perspiration and remains thick under foot. For very long or overnight use a spare liner is nice to have so that there is time to dry out a damp one. More thickness should be on the sole than sides, since a major source of conductive heat loss is through the sole of the foot. Boots and socks should not be tight since tight covering inhibits circulation and feet will get colder. Too much insulation covering the feet will violate Kaufman's rule but thick insulation under foot is a necessity. Properly waterproofed leather shoes or boots can be used especially when the snow is cold and dry, or when cross country skiing. Plastic boots or shoes should be avoided unless they have a thick felt liner to absorb moisture and insulate. The winter boots designed for short term wear with light fleece linings could be very dangerous if depended upon for long term exposure.
If conditions are expected to be very wet, coated nylon or Gortex™ or Klimate™ pants and parkas and mitten shells are highly recommended. Gortex™ and Klimate™ allow the body to wick perspiration moisture away when it isn't raining keeping the inner layers dryer than urethane coated nylon, but in continuous rain with lots of under layers they offer little advantage. Under less wet conditions there are more options. Tightly woven nylon is quite water resistant even uncoated and is wind resistant. Parka and pants made with a nylon outer layer can be filled with down or synthetic. Since some moisture can seep through from sitting on snow, good synthetics such as Hollowfil™ or Quallofil™ may offer an advantage. If it is raining, they are a must. A wool jacket or sweater is also good and improved by the addition of a nylon shell if it is windy. The hood of a jacket or parka can be worn over the hat for extra warmth and neck protection if necessary. Face masks, scarves and fur trimmed hoods can offer protection in extreme mold or high winds. Although not clothing, sunscreen can also protect the face from a real winter hazard. Goggles protect the eyes from sun and the drying effects of wind.
Construction details of clothing is as important as fiber and fabric in determining effectiveness. Fashion may dictate the clothing of short term exposure but the basic design of clothing designed for extreme conditions has changed little since primitive times. No clothing should be skin tight. Remember it is the layer of air next to the skin that is the primary insulator. No clothing should bind and compromise circulation. All clothing should allow complete freedom of movement. But clothing should prevent the dispersion of the critical air layer next to the skin since movement of air (bellows effect) can cause rapid cooling. Snug cuffs at wrists, and ankles (tucking underwear or slacks into socks works) are essential. A drawstring waist on parkas or shells reduces torso losses and the collar should be snug. If over-heating occurs the collar can be opened in any or all layers. No gaps should occur at wrists, waist or ankles. Shirts should have long tails and jackets with enough of an extension to sit on them can make a big difference when sitting down on snow or cold surfaces. Drawstring boots are nice because they also allow venting when conditions permit. Hats should cover the ears and a scarf worn if there is no hood. If the person is overheated that hat can be rolled up and scarf removed. Completely removing a hat should be avoided because too much core heat can be lost too quickly. Though on a calm, sunny day when it has warmed up to near freezing that may not be a danger.
Overheating should be avoided because it leads to excess perspiration which leads to wet clothing which leads to excess heat loss. A thorough understanding of the body's mechanisms for heat production and conservation, knowledge of the function of various types and articles of clothing and an awareness of the environmental conditions which might be encountered on an outing are all essential to a safe enjoyable experience in the outdoors in winter. Nothing can replace common sense and judgment when based on knowledge and experience. Use them both and you will have a good time.
TREATING HYPOTHERMIA AND FROSTBITE
Hopefully one can avoid hypothermia and frostbite. But anyone who leads a group out of doors in winter needs to know what to do should the necessity arise: The first thing is to recognize impending frostbit or hyperthermia.
Frostbite is the term given to frozen tissue. Although under careful conditions of quick freezing scientists can freeze cells, thaw them later and have living cells, frostbite is not laboratory science. Freezing expands the water in cells and breaks cell membranes. Cells are killed and dead cells begin to decompose which is what gangrene is. Mild cases, caught before tissue dies is reversible and serious cases can often be treated but prevention is, as usual, the best medicine. Frost bitten tissue appears yellow or grayish white and will appear first on areas farthest from the core and/or exposed to air--nose, cheeks, ears, fingers and toes--and will spread. Tissue is cooled beyond the excitability threshold (the point at which nerve fibers respond to a stimulus) so pain and cold is not felt. Cessation of pain is an important signal that frost bite is imminent and action should be taken. The affected area must be immediately, but gently rewarmed. Body temperature is best: under an armpit, against a stomach, wherever it can be arranged. Since we are talking about day trips, a sleeping bag won't be available but extra clothing should be. Extra food and warm drinks should be provided if possible. Never use liquid above 41øC (105øF) (experiment at home to know how hot this is!); never rub the affected tissue with anything and never allow the rewarmed area to cool again. Surviving tissue is very fragile at this point.
Any tissue which does not "pink-up" within minutes and look normal within hours should be seen by medical personnel as soon as possible.
Hypothermia occurs when the body temperature falls below normal and can be a serious problem when it falls as little as 2øC. Frostbite may or may not be present at this stage so is not a reliable signal of hypothermia. The first symptoms include muscle weakness, a feeling of extreme cold and a stiffening of muscles. Shivering may have preceded these symptoms and is an important signal when it does occur. Everyone has experienced a "frozen face" when speech is affected because face muscles stiffen. When hypothermia occurs all of the body muscles stiffen. Speech may become slurred (if no one is speaking this won't be a clue) and judgment will be impaired. The person may discard items of clothing, appear dazed, be incoherent when confronted. At the first hint of a problem immediate action should be taken. The group should stop--preferably in a sheltered location. Extra clothing should be wrapped around the person--all wet clothing should be removed. Bundling one or two people with the victim is very beneficial--preferably with maximum skin contact. Under these conditions sexual fantasies will not immediately spring to mind. The person should be fed as much as possible--slowly and warm drinks (remember a canteen can be warmed a lot tucked under a jacket next to the skin) provided. Cold drinks will further cool the body core. Help should be sought as soon as possible. If the victim comes around rapidly the group should return to the starting point as quickly as possible keeping a close eye for further problems. If conditions are threatening the group should stay put and seek shelter. One weakened member stresses the rest and could be the downfall of all unless everyone immediately conserves and pools all available energy resources. Exercise generates heat and moderate exercise can rewarm a person by 4ø/hr so the victim can be walked or the group can do easy exercises--avoid perspiration at all costs and keep calorie intake high while awaiting rescue. If hypothermia is caught early while the rest of the group still has plenty of energy reserve the victim can usually be re-warmed in the field and walk out but the group must be ready to act promptly and return to "civilization" immediately. Do not decide the victim is okay and the trip con continue. And do not send one or two people back with the victim while the rest continue. If one person becomes hypothermic all are at risk and the entire group's resources must be pooled to maximize survival. Remember prevention is the best medicine. One case in a group caught early may be an accident--two cases is stupidity. Severe hypothermia leads to death. It can occur if the person is wet, injured or if the group is stranded for a period of time. It should not occur at all in a well run group on a day trip. If the person is unconscious--do not feed. Passive exercise may be done after bundling the dry person with someone else. Immediate rescue is important, but care should be taken before sending out a group to seek help. Remember survival often depends upon numbers.
BIBLIOGRAPHY
Cena, K. & Clark, J. A. (1978). Thermal insulation of animal coats and human clothing. Physics in Medicine & Biology, 23(4), 565-591.
Fear, E. H., Simac, J., Lasher, E., Cashman, G., Tegner, L. & Haneline, J. (1975). Outdoor Living: Problems, Solutions, Guidelines. 105 pp. Tacoma Mountain Reserve Unit, P. O. Box 696, Tacoma, WA 98401.
Kaufman, W. C. (1982). Cold weather clothing for comfort or heat conservation. Physician & Sports Medicine, 10(2), 71-75.
Kaufman, W. C. (1983). The hand and foot in the cold. Physician & Sports Medicine, 11(2), 156-168.
Kaufman, W. C., Bothe, D. & Meyer, S. D. (1982). Thermal insulating capabilities of outdoor clothing materials. Science, 215, 690-691.