Hypothermia

Hypothermia is one of the biggest risks to your life at high altitude.

Hypothermia is defined as a core temperature below 35 degrees. It is broadly categorised into:

  • Mild hypothermia (32-35 degrees C)
  • Moderate hypothermia (30-32 degrees C)
  • Severe hypothermia (<30 degrees C)
  • It is estimated that up to 25% of people brought off the hill by Mountain Rescue in the UK may have some form of hypothermia. Onset of hypothermia in an individual depends on multiple factors both individual and environmental. Individual factors include fitness, food intake, clothing, injury and illness. It is important to remember it can occur at modest temperatures when there is prolonged exposure to water, driving rain or wind chill. (1)The two most common causes of hypothermia on the hill are exhaustion and injury (2).

    Hypothermia, dehydration, low blood sugar and altitude sickness share common symptoms and signs. If an individual develops one condition the others should be sought and if one member of a group develops hypothermia the whole group should be checked.

    Thermoregulation

    Normally thermoregulation within the body balances heat loss into the environment with heat production by the body organs and muscles. This is important as the body's enzyme systems only function within a narrow range of temperature around 37degrees C. In mild hypothermia this process is still active producing voluntary and involuntary responses. Involuntary responses include skin vasoconstriction and shivering. Unfortunately shivering is an extremely inefficient way of producing heat, significantly increasing utilisation of energy stores. Voluntary responses include seeking shelter, putting on clothes, exercise and eating. These are much more effective, especially eating and exercise, which increases heat production by a factor of 10-15 and eating.

    Once the core temperature goes below 32, shivering stops as thermoregulation fails. The body then gets stuck in a vicious cycle as dropping core temperature itself reduces body metabolism which in turn reduces the body temperature more. The victim's body systems, particularly the heart and brain function, gradually slow down.

    Classification

    The temperature at which any individual displays the various signs and symptoms of hypothermia varies as it depends on the factors mentioned above. It is also unusual to be able to accurately measure core body temperature in the pre-hospital environment. Oral, rectal or tympanic/inner ear temperatures are all inaccurate. Therefore diagnosis must be made on clinical signs and symptoms alone.

    There are a number of different classifications of hypothermia. These have been developed in seperate areas of the world in response to their differing geography, rescue services and medical back-up. The Swiss Society of Mountain Medicine grade hypothermia from one to five whereas the UK Lake District Search and Mountain Rescue Association simply classify hypothermia as mild (alert and shivering) or severe (no longer shivering and/or reduced level of consciousness) which is safe and adequate for rescuers without additional equipment. For the purposes of this article severe hypothermia is subdivided into moderate hypothermia, where the victim has stopped shivering but is not completely unconscious and severe hypothermia, where the victim is unconscious and signs of life are difficult to detect.

    Ability to estimate which stage of hypothermia the victim has reached is important as this then allows treatment and possible evacuation to be planned.

    Symptoms

    Mild.

    As described above, in mild hypothermia the victim will be shivering with cold white peripheries. There is loss of manual dexterity. They may become quiet and feel cold to touch, be mildly confused or be disorientated and irritable. They may also lose insight - denying having any problem - and reject help, which can make it quite difficult to treat them.

    Moderate.

    The moderately hypothermic victim has slurred speech, is apathetic, confused, irrational, and clumsy. Lips may turn blue and consciousness may be reduced. The pulse first slows down and then the heart becomes more irritable as temperature reduces further, often leading to an irregular pulse (atrial fibrillation) at core temperatures below 32 degrees C.

    Severe.

    As temperature drops below 30degrees C the victim will become unresponsive. The breathing and pulse will be faint or even undetectable and they may look dead. Below 30 there is a high risk of the heart going into Ventricular Fibrillation (VF - a form of cardiac arrest) with any kind of rough handling. This includes large limb movements or rapid changes in body position i.e. sitting them up from horizontal position.

    Death from hypothermia.

    This is a very difficult situation in the wilderness. Technically only trained health care staff can actually pronounce death however in some circumstances it is recognised that attempts at resuscitation are futile. According to the Alaskan Guidelines these include obvious fatal injury, a core temperature of less than 10degrees C, an airway blocked by snow or ice, incompressible chest or eyeballs (on gentle pressure - compare with live persons eyeball) or finally not coming back to life once re-warmed.

    Treatment

    Below simple and effective treatments that can be given by non healthcare personnel in a wilderness environment are described.

    Mild hypothermia can be reversed relatively easily. The key is to recognise it early and act swiftly. Shelter, warm clothes and warm food and drink will raise core temperature. Remember to insulate them from the ground. A thick plastic survival bag helps them retain any heat they are producing (these have been shown to be more efficient than 'space blankets'). To add heat, body warmth can be used, for example putting the victim in a sleeping bag with someone else or using manoeuvres like a penguin huddle. Once re-warmed victims can generally then get themselves to a place of safety but should be watched carefully.

    Moderate hypothermia: The patient will no longer be shivering and may have reduced level of consciousness. This is a life-threatening situation. Their heart will already be at risk of arrhythmias. Good shelter needs to be found rapidly and the group should be prepared for a prolonged stop.

    The victim should be nursed lying down and insulated from the ground. If the conscious level is significantly reduced they should be placed in the recovery position to protect their airway. Any movement should be slow and gentle - a good policy is to treat them as if they have a spinal injury. Start re-warming as soon as possible:

  • Removing wet clothing and gently patting dry.
  • Place them in a pre-warmed sleeping bag (another person or hot water bottles can be used for this).
  • Add heat by using chemical heat packs or hot water bottles (wrapped in cloth to prevent burns) placed against armpits, upper abdomen, neck and groin. Heat sources should not be placed on limbs, the person should not be immersed in hot water and limbs should not be massaged as all these produce peripheral blood vessel dilatation which can cause paradoxical core cooling.
  • Warm the tent/bivvy (taking care not to cause Carbon Monoxide poisoning).
  • If/once awake enough to swallow give hot sweet drinks and energy foods.
  • Generally these patients should be evacuated as they can need ongoing medical care following an episode of hypothermia. Only evacuate by stretcher if the victim is re-warmed, stable and you are sure they won't get cold again during evacuation

    Severe hypothermia.

    The victim will be unconscious. Concerns are:
    a.Their airway is at risk of compromise.
    b.They may also be on the cusp of a fatal cardiac dsyrythmia.
    The pulse and breathing may be so slow that the rescuer has to look, listen and feel for at least a minute to detect them.

    If there are no detectable signs of life then key decisions need to be made. The following recommendations are based on the State of Alaska cold Injuries Guidelines. (3)

    1.Are they salvageable? I.e. should re-warming be attempted - this being both an energy and time consuming process in the wilderness. If the signs discussed above in the death from hypothermia section are present then the only thing to do is organise appropriate evacuation . Other factors that should be taken into account are if the rescuers are exhausted or the rescue will put more people in danger.

    2.If there are no signs of life then rescue breaths (as per basic life support) should be given for 3 minutes and then cardiac activity reassessed, as this simple manoeuvre can improve previously undetectable cardiac activity.

    3.If the victim still has no signs of life then continued treatment depends on whether it is possible to evacuate to an appropriate medical facility which has a cardiac monitor and can give definitive care, within three hours.

    If evacuation to a medical facility is possible within three hours then the victim should be protected from further cooling (by drying and insulation) whilst rescue ventilation should be continued throughout the evacuation. Chest compressions should NOT be started. The reason for this is that the patient may be in a very slow, undetectable heart rhythm which is maintaining their life and commencing chest compressions could actually tip the irritable heart into VF/cardiac arrest as discussed above. For this reason CPR is only recommended if swift evacuation to a medical facility is possible as once it is commenced it must be continued until the patient's heart can be monitored with an ECG.

    If evacuation cannot happen within three hours then rescue breaths should be continued and chest compressions should be commenced. Oxygen should be given if available. This basic life support should be continued for 60 minutes (30 minutes for medical staff using ALS protocols ) whilst all the above active warming measures are instituted. If after 60 minutes the patient has been warmed up but there is still no pulse or breathing effort to be seen then life support should be stopped and the victim evacuated as appropriate. If possible this decision should be made in conjunction with the expedition/base camp health care professional.

    Other problems

    Two physiological phenomena that are useful to know about in severe hypothermia are:

    1. Afterdrop: this is defined as a continued fall in the core temperature, after removal from the cold stress, which may even occur during rewarming. It is due to heat redistribution within the body. The importance of this is that even when re-warming has started the patient may be at risk of cardiac arrest.

    2. Circum-rescue collapse: this is when a hypothermic victim is found with stable vital signs but then collapses during or soon after rescue. It is thought to be caused by a massive drop in blood pressure or precipitation of VF (as above) on handling of the victim. This phenomenon was initially described in maritime rescue but it has also been seen with rescue of hypothermic victims in the mountain environment.

    Prevention is better than cure

    The old adage that prevention is better than cure counts for double when dealing with illness in the wilderness. Although it is important to know the steps of treatment the take home message should be that anyone in the mountains should be able to recognise the symptoms of hypothermia in themselves and those around them and act upon the diagnosis.

  • Remember high altitude makes hypothermia (and frostbite) more likely.
  • Avoid sweating and/or exchange damp clothes for dry ones.
  • Adequate food and drink gives your body fuel to sustain exercise.
  • Always be prepared to stop and shelter. Multi-person both/bivvy bags are available that are light and compact enough to be carried in a personal pack. These are very efficient at maintaining heat and allow you to gain shelter from the wind anywhere.
  • Keep an eye on other members of your party to watch for the early signs of hypothermia and be prepared to change your route, or go back, if necessary. A buddy system for this works well.
  • References

  • 1.Casualty Care in Mountain Rescue. Ellerton J. 2nd. Edition 2006.
  • 2.Mountaineering Council of Scotland Information Leaflet 'Freezing to Death'. 1997.
  • 3.State of Alaska Cold Injuries Guidelines: Alaska Multi-level 2003 (Rev. 2005) Prepared by: Department of Health and Social Services, Division of Public Health, Section of Community Health and EMS.
  • Last updated March 2010