Its not really something you look into through your normal lifetime of snowboarding or skiing unless you start to complete some off piste certifications, yet some of it could come in useful. For example, if you’re a fast rider on a cold day you might have to be aware of frostnip on your face. It’s the first stage of frostbite and more common than you might think.
Here is a summary of the key facts after reading Hypothermia Frostbite and other Cold Injuries by James A Wilkerson with some extra infographics.
Is localised cold injury characterised by freezing with ice crystals forming. There are two main mechanisms of tissue injury. One is actual freezing of tissues, the other is obstruction of blood supply to tissues. Earliest symptoms of frostbite is pain. However, as tissue freezes pain disappears. frostbite tissues are usually quite pale because the blood vessels are constricted. They are also hard or firm. If it is a large area it may appear purple with the blood sludging.
Treatment consists of rewarming the frozen tissues and minimising the circulatory impairment that follows thawing. Slow warming can result in more tissue damage.
Treatment consists of rewarming the frozen tissues and minimising the circulatory impairment that follows thawing. Slow warming can result in more tissue damage. No rewarming should be attempted until the victim has been evacuated where no significant additional freezing can occur. A water bath can assist in the rapid warming process. The temperature should be maintained between 100 F and 108 F (38–42c). Hotter water will further damage the tissues. The temp should also be maintained. The injured part should be moved out of water when adding more hot in. The injured part should be suspended in the centre of the bath and not be permitted to rest against the sides of bottom. Warming usually requires 20–40 mins. Promoting blood supply is key. Aspirin taken whilst the item is frozen and then every 6 hours afterwards will help.
After warming the patient must be kept warm and the injured tissues elevated and protected. The area should be disinfected every day. Recovery can take many months. Keeping blisters intact will reduce the chance of infection.
Man is a warm blooded mammal so most of the heat in maintained by metabolism. Normal body temp is around 98.6F or 37c. Normal body temp can vary between 1.25c and 3.75c over a 24 hour period. Lowest temp during sleeping is around 3–5am.
Hypothermic people stop shivering around below 30–31c. Shivering is around 5x greater than heat production at rest, but it depletes the muscles of nutrients.
Methods of Heat Loss
Convection — Heat loss occurs when air or water has a temperature below that of the body it comes into contact with. The amount of heat loss depends on the temperature difference between each surface in contact or the speed of air moving over it. Think of it as the way soup is cooled by blowing on it. Wind chill is the resulting change due to convection.
Conduction — Transfer of heat energy away by substances in direct contact. Stones and ice are very good conductors. Just standing on ice or snow will drain heat from your feet. Having an insulating layer between your feet and the snow will reduce that heat loss significantly.
Evaporation — Responsible for 20–30% of heat loss in temperate climates.
Radiation — Usually by far the largest source of heat loss. Consists of direct emission or absorption of heat energy. The human body continually radiates heat to nearby solid objects that have a cooler temperature. It is the heat picked up by infrared cameras.
Oxygen consumption increases when the body core temperature has fallen below normal. Since oxygen is used to metabolise food, heat production can be measured conveniently in terms of oxygen consumed in the process.
Changes due to Cooling
Muscles — Mild cooling causes muscle stiffness and incoordination by directly affecting the muscle tissue. The amount of oxygen consumed in performance of simple tasks increases. Profound cooling causes decrease in nerve impulses and muscle response. As a result the muscles to not contract effectively. Contracted muscles may be unable to relax.
Brain — Mild cooling decision making becomes slower. Profound hypothermia leads to confusion, disorientation and erroneous decision making. Slurred speech and loss of vision is reported just prior to coma.
Circulatory System — Profound hypothermia results in a reduction in the volume of circulating blood. It also increases fluid loss by producing ‘cold diuresis’, increased excretion by kidneys. Water is also moved from blood to tissues. Cold also induces contraction of the spleen, which increases the number of circulating red blood cells thereby increasing the blood viscosity.
Oxygen is decreased due to constriction of blood vessels. Plus cold Hemoglobin releases oxygen a lot more slowly to tissues.
Heart — Under hypothermia the heart pumps weakly and slowly. It becomes stiff and weak and the volume of blood pumped with each beat (The stroke volume) is markedly decreased. The number of beats per minute falls.
Lungs — Carbon dioxide accumulation occurs and increased mucus secretion lining the trachea and bronchi. The cough reflex may be decreased allowing excessive collection of mucus.
Complications of Profound Hypothermia — Top 5
Intravascular clots causing myocardial infarcts and strokes
Acute renal failure due to tubular necrosis
Increased renal potassium excretion leading to alkalosis
The only definitive way of documenting hypothermia is measuring temperature.
Mild Hypothermia — Complains of feeling cold. Person is often wet and usually shivering to some extent. Loses interest, negative attitude. First sign is inability to keep up with the rest of the group and difficulty in walking over rough terrain.
Profound Hypothermia — Core temperature drops below 90F (32c). People will have have a carelessness about protecting against the cold. They will have cold skin, fruity acetone breath and urine soaked clothing.
No one should be considered cold and dead until they are warm and dead.
Mild hypothermia victims only need to be protected from further cooling and may be rewarmed by any convenient means. Warm liquids may be given by mouth, even though they have virtually no warming effect on core temperature. The benefits of having the individual feel better is significant. A safe guideline is that mildly hypothermic people who can easily drink warm liquids can benefit. Alcohol produces a similar warming sensation, but its other effects are negative that it should not be given.
Profound hypothermia (core temp below 90 F or 32 c) care consists of avoiding ventricular fibrillation while the victim is slowly warmed. Events known to trigger ventricular fibrillation are:
- Endotractheal intubation
- Mouth to mouth resuscitation
- Alkalosis caused by excessive intravenouse sodium bicarbonate
- Precordial thump
- Inserting a large bore needle in central veins
- Physical exertion
- Rough handling while lifting or transporting
- Inserting endocardial catheters or pacing wires
- Rapid external re-warming
- Cardiac stimulation medications
Sudden death has been observed when victims suddenly exert themselves after some time of lying still. The victim must not walk, climb, swim, or even move when lifted. Any rescue must be carried out gently. Rapid re-warming can lead to shock.