Hypothermia »


Cold!  The thought raises markedly different images in different athlete's minds.  For some it prompts an avoidance reaction that has them gravitating towards the fireplace or migrating south towards sunnier climes.  For others, it represents a challenge that is an integral part of their chosen sport.  Winter weather and cold temperatures do pose one very real danger for everyone involved in activities outdoors:  Hypothermia!

Hypothermia, however, is not restricted to one season to the exclusion of all others.  Sub-zero temperatures are not the only contributing factor for the onset of the condition.  Any situation that results in the body expending more heat than it creates for a prolonged period of time increases the risk of hypothermia.  For athletes who are naturally low in body fat and are involved in outdoor sports with high energy and fluid expenditures, the risk factors are even greater.


The normal body temperature is around 37o C.  Hypothermia occurs when body temperature falls below 35o C and the body's heat loss exceeds its heat production.  At this temperature the body no longer generates enough heat to maintain body functions.  The heat loss can happen in four different ways: by radiation, evaporation, conduction, and/or convection.  Of these, radiation is the main source (60%) of heat loss from the body.  Basically, if the environmental temperature is cooler than that of the body, heat travels outward.

Basic Physiology

An area in the brain called the hypothalamus acts as the body's thermostat.  It is the central controller of heat balance in the body and triggers an increase in the rate of heat production when the body temperature falls.  It is the hypothalamus that makes us shiver when we are cold.  Shivering, an involuntary muscle contraction, is the main mechanism for producing heat by increasing our metabolic rate.  This can increase the body's heat production by up to five times.  The hypothalamus is also responsible for decreasing the blood supply to peripheral areas of the body to maintain core temperature and increasing hormone production to 'up' the metabolic rate.  It is when these survival mechanisms fail, and the body is unable to maintain its core temperature, that hypothermia develops.  The signs and symptoms are progressive according to the amount of heat loss from the body.  An individual's condition deteriorates as the body temperature drops.  (See Stages of Hypothermia Table)

A Danger for All Seasons

Although hypothermia is usually associated with harsh winter conditions, it would be wrong to assume that this is the only time of year that someone involved in outdoor activities is at risk.  Walkers and hikers who are ill-prepared for the vagaries of weather that can occur in the mountains are particularly susceptible.  Wet clothing and the chilling effect of strong winds promote increased body heat loss.  Swimmers, divers, triathletes or anyone taking part in aquatic sports have to be aware that water has a much higher thermal conductivity than air and, accordingly, heat is lost from the body more rapidly during cold water immersion than during exposure to air of the same temperature.  In winter, cross country skiers are more at risk than their downhill counterparts.  This is because exhaustion and dehydration are both strong influencing components for the onset of the early stages of hypothermia.  It should also be noted that the whole process from mild exposure to severe hypothermia may take only a few hours or less.

Risk Factors

A variety of other conditions can also do their part in contributing to the increased chance of succumbing to hypothermia.  Drug or alcohol use, hunger, anemia, impaired circulation are all flags for danger when allied to some of the other factors already outlined.  Certain medical conditions such as diabetes mellitus and thyroid disorders which adversely affect the body's ability to regulate its own temperature should also be taken into consideration.  Moreover, children and the elderly are more at risk as they are less able to retain body heat in cold conditions.

Treating Hypothermia

The longer the body core loses heat, the more difficult it is to re-warm.  It is therefore imperative to treat hypothermia at the earliest possible stage.  The first step of a “cure” is to get the victim out of the cold, wind and rain (or water) and into shelter.  If the person is at the shivering stage but not exhibiting other more serious symptoms, get him or her into dry clothing and give them a hot, non-alcoholic drink with some high energy food.  It is important to remember that body cooling may increase when the hypothermia victim stops exercising because the extra heat generated by activity then ceases.  Someone who was only shivering mildly may begin to show more serious signs once they get into a warm environment.

A person who has slipped further into hypothermia syndrome than the stage of moderate shivering needs more help.  Putting the victim into a sleeping bag with another person is a very effective method of re-warming.  Skin to skin contact especially in the neck and chest is most beneficial.  If available, warm baths are also an effective way to re-warm the moderately hypothermic person.  However, the water should be between 30-35o C and the arms and legs should be kept out of the water (it is the core temperature that needs to be raised, not the extremities).  Gradually raise the water temperature to 42-44o C over a period of five to ten minutes. For severe victims, one whose temperature has dropped below 30o C, hot bath re-warming should not be undertaken without medical supervision.

Severe Cases

Make no mistake, hypothermia can be fatal.  The adage of mountain rescue teams when dealing with hypothermia cases is that "you are not dead till you are warm and dead".  This is because severe hypothermia can mimic death and before presuming someone is deceased, re-warming must be carried out until the core temperature reaches at least 35o C.  In addition to this, extremely careful handling of the victim is essential to avoid causing erratic heart beats which could lead to a heart attack.

Resuscitation on-site would include the ABCs (airway, breathing and circulation) but no cardiac compression should be applied until a diagnosis of cardiac arrest is certain.  As quickly as possible, the victim should be taken to a warm environment and any wet clothing removed.  Warm, dry clothes should then put on.  The next step would then be to transport the victim to a hospital for comprehensive assessment and treatment.  Expert medical supervision is needed for severe cases of hypothermia as the victims usually require both internal and external re-warming.  In many instances, this involves putting the person in a bath where the temperature is 40o C.  Core temperature can also be increased with the inhalation of heated, humidified oxygen and the administering of warm IV fluids.  At this time, the administration of drugs is usually avoided, and due to slowed gastric emptying and absorption in the stomach, no medication is given by mouth.  Exercise is not used as a method of re-warming due to the increased risk of heart failure related to the release of chemicals from blood retained in the extremities of the body.


The best defense against hypothermia is common sense. All outdoor activities should be planned with safety and hypothermia in mind.  Key points to bear in mind are:

  • Taking proper clothing for the worst conditions you might encounter is one of the best precautions.

  • Wool is one of the best materials for all weather warmth.

  • Include a hat in your back-pack.Over 50% of a person’s heat loss comes from the head and neck area.

  • Staying dry and avoiding any type of exposure are the key elements in staying warm.Wet clothes lose most of their insulating value.

  • Pack high carbohydrate snacks to keep energy levels up if you are forced to take shelter in poor weather conditions.

  • There is safety in numbers.Don't venture out on the trails or the mountain alone.

    What Not To Do

    Do not massage the limbs of a hypothermic person.  This will only draw heat/blood flow away from the core where it is needed.

  • Never give an alcoholic drink.This will actually inhibit re-warming.

  • Never give a semi-conscious or unconscious person anything to eat or drink due to the possibility of choking.

  • Don't treat any hypothermia case lightly.


    Familiarity with the signs of hypothermia will enable anyone involved in outdoor sports or recreation to use their own good judgment in situations where hypothermia is a danger.  It is important to remember that while some people have miraculously survived under extremely hostile conditions, others have died from “exposure” under mild ones.



  • Stage                          Core Temp. (o C)      Characteristics                                                                                                                         

    NORMAL:                     37.5                             

    MILD:                            38                             Increased metabolic rate
                                          36                            Temperature at which hypothermia begins by definition. Shiver to create heat
                                          34                             Violent shiver, mental changes, amnesia, poor judgement, ataxia, apathy
    MODERATE:                 32                            Stupor, decreased gut mobility
                                          31                             Shivering stops
                                          30                             Rigors, decreased deep tendon relaxes, dilated pupils, weak pulse, low cardiac output, increased risk of dysrhythmias
                                          28                             Decreased coordination with muscle control, staggered gait, increased risk of ventricular fibrillation , increased blood viscosity, decreased inter vascular volume
                                          27                             Loss of deep tendon reflexes and voluntary motion
    SEVERE:                      26                             Acid base change, no pain response, decreased cerebral flow, decreased cardiac output
                                          25                             Increased risk of pulmonary edema. Increased blood pressure
                                          22                             Maximum risk of ventricular fibrillation
                                          19                             Flat ECG
                                          18                             Asystole


    Hypothermia:  Sports Medicine Council of BC