1) DEFINITION AND DESCRIPTION
Hypothermia: From “Hypo” meaning: Low, lowered, lowering or below. And “Thermia” meaning temperature, so: Lowered (body ) Temperature.
Hypothermia Is a state of low body temperature, specifically low body core temperature. When the core temperature of the body drops below 97º (36º C) an individual is considered to be in a hypothermic state. Hypothermia can be attributed to either: a decrease in heat production (perhaps due to illness or injury, dehydration, or lack of food); or an increase in heat loss (perhaps due to; lack of adequate clothing for the temperature, wet, windy conditions.); or a combination of both.
2) HYPOTHERMIA vs FROSTBITE
Years ago you heard of people dying of “exposure.” What we used to call exposure is hypothermia. This is different from frostbite, which can only occur below freezing. Frostbite is freezing of an exposed part of the body. With frostbite the cells in the affected area freeze and the cell walls burst actually killing the tissue in that area, like nerves, skin, muscle, and capillaries. This is why you see severe frostbite areas turning black from the dead tissue. Serious frostbite can be extremely painful and require months of recovery with possible loss of fingers, limbs, etc.. Contrary to popular old wife’s tales an area of frostbite should not be rubbed as this will just cause more damage. The treatment of frostbite is similar to that of burns. With hypothermia there is no tissue damage.
It is amazing how misunderstood hypothermia is. Basically, the human body functions over a very narrow internal temperature range. The loss of core temperature, or losing heat faster than it can be generated by the body, results in hypothermia. The body’s normal temperature is 98.6°F and a drop of under 2°F will start this process. Note that hypothermia is caused only by loss of core temperature and you could have frostbite on your hands and still not be hypothermic. Hypothermia also doesn’t require near freezing temperatures, in fact, a person with low body fat and a low metabolic rate could easily get hypothermic sitting in a swimming pool or bath at 75°F. Your body’s ability to generate heat depends on health, level of fitness, proper hydration, food, etc. Alcohol consumption will make you FEEL warm, when in reality the alcohol, in addition to clouding your judgment further (see “97°F” above), dilates the blood vessels in your skin thereby increasing heat loss (& causing that flushed feeling/look). Coffee and some other drinks are also diuretics and can cause dilation of blood vessels in the extremities and accelerate heat loss. Most cases of hypothermia associated with hiking occur in the summer months when the temperature is 40°F-50°F and you have wet, windy conditions.
Hypothermia victims can be divided into three main categories According to Core Body temperature range: mild, moderate & severe:
A core temperature between 94º and 97º F (34 – 36 C) is considered mild hypothermia.
A core temperature between 86º and 94º (30 – 34 C) is Moderate Hypothermia.
A core temperature less than 86º F (30 C) is Severe Hypothermia.
So let’s see what happens as you lose core temperature:
98.6°F- your brain functions normally
97°F - judgment starts to go; as temperature decreases so does mental ability
96°F - you begin shivering, there is loss of fine motor skills like tying shoes
94°F - coordination is failing, you start stumbling; shivering increases
92°F - shivering is severe; you will be unable to walk
90°F - shivering is convulsive; you are unable to talk; you assume the fetal position
88°F - shivering stops because the body is giving up on that method of re-warming itself
86°F and below -you are in what is referred to as a “metabolic icebox” where you may appear dead. You are unconscious, ashen gray, no perceivable pulse or breathing.
3) SYMPTIONS -WHAT TO LOOK FOR
Although the “umbles” (grumble, mumble, stumble, tumble) have been mentioned as telltale symptoms of hypothermia, keep in mind that these aren’t necessarily obvious or occur in exact order. Also, these symptoms are generally not obvious to the person who is getting hypothermic because of their depressed brain function. Almost always it will be a fellow hiker that recognizes the symptoms.
Grumble The grumbling occurs when we get irritable, but some people start out that way. What you should be looking for in your fellow hikers is a change from what is normal for them. A lot of people who grumble aren’t hypothermic, that’s just normal for them. However, if it is cold and wet and someone starts to grumble, try to figure out the cause. If it is the onset of hypothermia, take corrective measures.
Fumble As your hands get cold, there is loss of fine motor skills like those required to tie shoes. This may also be caused by localized cooling and not hypothermia.
Mumble Contrary to popular belief, this doesn’t have a lot to do with the brain. There are facial muscles that move the jaw and when they get cold and stiffen up we have trouble forming words. If you start talking nonsense then it probably is the brain that is involved.
Stumble Again, the brain is not the only thing that could cause this problem. If your legs get really cold there are two big nerve bundles in your legs that control things like foot drop, etc. If you’ve ever watched a drunk, you can recognize this staggering, flatfooted foot slapping on the floor type of gait. The inability to send and receive nerve messages from the feet are one thing that causes this problem. This could occur alone or in combination with the brain having problems because of hypothermia.
Tumble This one is pretty obvious and almost always comes after some combination of the previous three “umbles”. This is when you are getting into a really serious stage of hypothermia.
Some of the other symptoms that you may notice are the hypothermic person becoming combative, or even taking off clothing. Even well prepared hikers suffering from hypothermia have died despite having everything they needed to survive right in their pack. Don’t expect rational thought processes from someone who is hypothermic.
4) TREATMENT –HOW DO I TREAT SOMEONE WHO IS HYPOTHERMIC?
The first thing to do is to recognize a person who is hypothermic, remove the cause, and take corrective measures. The only true way is to measure core temperature is with a special low-reading rectal hypothermia thermometer. A friend of mine who trains EMTs and is an expert in cold weather related injuries claims if you are willing to let him take your rectal temperature, you ARE truly hypothermic.
If the hypothermia is mild and the person can still walk, the best course of action is to remove the cause. If the clothes are wet, strip the person and put on dry warm clothes. If they haven’t been eating or drinking, feed them. And, most important, keep them moving. It is easier to keep them producing their own heat than for you to try to warm them by other means. This works only if the hypothermia is mild and the person can still walk. Always ambulate before carry if possible because any backcountry litter carry involves a large group of rescuers and many hours.
If the hypothermia is more moderate, keep this one thought in mind: never strip them and put them in a sleeping bag with a functioning warm person. Almost always you will succeed in creating two hypothermic people. This is a very bad idea. What you need to do is to remove the cause of the hypothermia, like their wet clothes, and put them in a hypothermia wrap or sleeping bag (see link for details). You should try to warm the core and not the extremities. Warming the arms and legs can “fool” the body into thinking it is warmer and flushing the warmer blood from the core to the extremities, further cooling the core. The last reference below shows how to create this “human burrito,” as it is sometimes called, to re-warm a hypothermic person.
If a hypothermic person is conscious and is capable of drinking (after removing the cause of the heat loss and protecting them), be very careful that the drinks you give them aren’t too hot. Because the sensation of touch and warmth is so depressed it is very easy for a hypothermic person to be burned by steaming hot liquids that a normal person could not drink. Any drinks should be tested or measured by thermometer to be no more than 105°F. Never try to give drinks or food to an unconscious person.
One last thing. Never assume that if there are no visible signs of life in a severly hypothermic person that it is too late. The experts in this field of medicine say they aren’t dead until they are warm and dead. Respiration can be near zero and the pulse rate could be 6 per minute. Because the blood supply to the extremities is basically shut down, you will get no distal pulse. The muscles stiffen up with the cold and the heart is a muscle. A severe hypothermic person who appears to be dead may just be in this “metabolic icebox.” The severely hypothermic person's heart is extremely susceptible to ventricular fibrillation, which even the slightest jolt can cause. A severely hypothermic person should never be re-warmed in the field. They must be protected from further heat loss and carefully transported to a hospital as soon as possible.
5) PREVENTION –FUEL FOR THE BODY
I know some of you are saying: “Hey, that doesn’t sound like any fun, how to I prevent it?” Well, to prevent it you have to know a little bit about thermodynamics, fortunately, very little. You have to understand how the body generates heat and distributes it through the body as well as how the body loses heat. Metabolism, level of conditioning, illness, drugs, alcohol, and fatigue also can play a big role in hypothermia.
First of all, the body can be thought of as a furnace, burning the fuel (food) that you feed it. The blood forms an important part of this system sending the processed fuel to the cells. Anything that compromises this flow (even restrictive clothing) will cause problems. As you get dehydrated the blood becomes more viscose, or thicker, and its ability to transport oxygen and fuel to the cells decreases. The sensation of thirst isn’t a good indication of when to drink. When you “feel” thirsty, you are already down a quart or so. The sensation of thirst is also depressed by the cold affecting the brain. This is why it is so important pay attention to staying hydrated.
Not all foods are created equal and not all fluids are either. Sugars give you a quick shot of energy but pastas, potatoes, and fats are slower burning and are best to eat before bedtime to help keep your furnace going through the night, but they require more water to digest as well. The problem with fruit juices and some energy drinks is they are too concentrated and are absorbed by the body slowly. Juices diluted about 2 to 1 are absorbed faster. Alcohol, coffee and some other drinks should be avoided. Coffee is a diuretic and can cause dilation of blood vessels allowing the extremities to radiate more heat. The effects of drinking coffee could be thought of like taking off an insulation layer.
6) PREVENTION –CLOTHING AND THERMOREGULATION
There are several ways the body can lose heat. The main ways are:
Conduction One way is by direct contact like lying on the ground. If you and your clothing are wet the loss of heat is up to 25 times greater than if you are dry.
Convection is heat loss due to a breeze and is known as “wind chill.” Again, if you are in damp or wet clothing, the problem is much worse. Although fleece is a good insulation layer, it is very porous and is next to useless in a wind. One way to improve fleece is to add a wind block layer. Another way is to wear a thin wind shirt over the fleece. A tent, or an enclosed hammock, would be warmer than an open-faced shelter by blocking wind and adding some insulation.
Respiration A lot of heat is lost during respiration as a combination of conduction and evaporation. Inhaled cold air is warmed by contact with the upper airway & lungs and the warm exhaled air has moisture from evaporation in the lungs if the inhaled air is dry. The drier the air, the more respiration also contributes to dehydration. Higher altitude, colder and drier air, and rapid breathing all contribute to higher heat loss and dehydration.
Radiation The rate of radiation increases as the difference in temperature between you and the air increases. Like convection, this form of heat loss can be lessened considerably by adding a layer of insulation.
Evaporation Sweating is the body’s natural way of trying to regulate our temperature when we get too hot. The amount of sweat produced by a body at rest could be about 100ml per day. With heavy exercise this could climb to 5000ml or 5 liters per day. If this moisture can’t pass through your clothing to the outside, you will get soaked.
The materials used for your clothing layers are important. Remember cotton absorbs water, loses its insulation ability, gets heavy, and should not be used as a layer. The phrase "cotton kills" says it all. The base layers should be hydrophobic, i.e., not absorb or attract water, the synthetic base layer should freely pass sweat to the outer layers and keep your body as dry as possible. Any of the layers you use should not be constrictive as this will restrict blood flow and make you feel colder. Always think of your layers as part of a “system” that has to fit together properly. When you buy your outer rainproof layer, make sure it is large enough to fit over all the other layers you could be wearing underneath it. Added features like full front zippers and "pit-zips" in jackets and full-length side zippers in rain/wind pants can make them much more versatile and easy to put on or take off. Check the references on layering for a more complete description of material options and layering.
Putting on or taking off layers of clothing allows you to bring your body’s temperature back closer to the normal range under widely varying conditions which could include wind, sun, rain, snow, or your differing levels of exertion. If you do not have the proper clothing for the conditions you are in, you are at risk of hypothermia. A popular belief is that the body tries to “protect” the core organs by shunting blood flow away from the extremities. While this is the effect, the reason is simply to prevent heat loss from the extremities. Not as much heat is radiated from the head as is commonly believed but a hat is an important part of a clothing system. Gloves are also important to prevent your hands from getting wet and cold, which could lead to loss of coordination.
Trying to prevent having to go pee in the middle of a cold night by not drinking (hydrating) properly before bed isn’t wise and can cause you to sleep colder. The old wife’s tale about it taking energy to keep the water in your bladder warm defies logic and science. One practical suggestion to add warmth is to fill a water bottle with hot water and take that to bed with you. This should be done with care because if the water leaks, then you are in trouble. My personal feeling is that you should be carrying enough clothing and a warm enough sleeping bag so this isn’t necessary for warmth.
Also, the air in the sleeping bag doesn’t hold some mystical property that make you sleep warmer when naked. The bottom line is more insulation equals more warmth. If you put on a layer of dry clothing, you will sleep warmer. One footnote should be that an equal sized volume filled with down (or any other type of sleeping bag insulation) is warmer than an equal sized volume filled with air. The reason is convection currents in the larger air areas allows heat flow. The down actually doesn’t have any insulation properties itself, it does, however, break up the possibly convection current heat losses by creating many micro pockets of air, and it is very light and compressible. Keep in mind that if down gets wet, it is useless as an insulator, and is very heavy. Synthetic insulation (like Primaloft) is much better in this regard.
-Hypothermia is sneaky and can kill. The hypothermic victim is generally not the person who notices their problem.
-Hypothermia (lowered core temperature) should not be confused with frostbite (localized freezing of tissue). These are two different things. Both are serious and require immediate attention.
-If you are hypothermic, or find someone who is hypothermic, remove the cause and prevent further heat loss. Take corrective measures as described above depending on the severity and level of consciousness of the person.
-Alcohol and any diuretics are to be avoided; they will cause the blood vessels to dilate, especially in the skin, causing you to feel warm but in fact accelerating the heat loss.
-Cotton clothing is totally inappropriate for hiking: The saying “Cotton Kills” may seem over used, but cotton & cold, wet weather do not mix. Always carry extra appropriate clothing, raingear, and shelter. Be prepared.