Hypothermia occurs when the core temperature of the body falls below 35°C.
Exposure Hypothermia occurs over several hours following exposure to moderate cold. The casualty becomes exhausted and then cools rapidly as their energy reserves are depleted and they are no longer able to shiver to re-warm themselves.
Immersion Hypothermia occurs where the casualty has had a sudden immersion in cold water or snow, the cold rapidly overwhelms heat production. Although rarer in the mountains, it can happen if someone falls in an icy stream.
Main Causes and factors
Hypothermia occurs when a body loses heat to the environment faster than its ability to generate heat.
Weather – wind and rain in combination will decrease the body’s temperature rapidly due to the effect of wind-chill. This means that even on a relatively mild day, it is possible to succumb to hypothermia if it is windy and raining. The colder the air temperature, the higher is the risk.
Clothing/equipment – A lack of suitable waterproof clothing will lead to clothing layers getting wet, which will increase heat loss considerably. A wet body losses heat 20 times faster than a dry one. Waterproof jacket and trousers as well as at least two decent insulating layers such as a fleece or synthetic belay type jacket are important in trapping heat and cutting out wind-chill. The body can also lose substancial amounts of heat through the head, so a hat is a must.
Dehydration and lack of food – The body needs food and drink in order to metabolise effectively and efficiently. The energy released by our metabolism heats our body, if our fuel reserves are depleted then we cannot produce the heat we need to stay warm.
Ill health – People who are ill may be less able to metabolise and generate heat, and so are more likely to chill quickly.
There are several ways of classifying hypothermia. Perhaps the easiest is to think of hypothermia in terms of mild, moderate and severe. However, it must be noted that different people exhibit different signs before others, and not all the signs and symptoms may be present in everyone.
At this stage the body still has resources of its own to try to fight the effects of the cold, shivering will occur which is a voluntary response of the body to re-warm itself. Asking the casualty to stop shivering is a good test, if they can then the hypothermia is mild.
Mild hypothermia can be treated quite easily. Stop, find shelter, put more layers on and get high energy foods and warm drinks into the casualty. The food needs to be high energy e.g. a Mars Bar or glucose gels to help fuel the body’s production of heat. The casualty should then be able to walk off the mountain without any extra help from the emergency services.
If, on asking, the casualty cannot stop shivering, they are in the realms of moderate hypothermia. By now the body’s energy resources are depleted and it has no way of reheating. The brain itself is affected and people act out of character with the ‘Umbles’. Speech may become Mumbles, they Stumble as they lose co-ordination, they may become irritable and Grumble, their ability to do small tasks such as do up their rucksack or close zips on their clothing will reduce to Fumbles.
Confusion occurs and sometimes a casualty maybe under the illusion that they are warm and start to strip clothes off. While the casualty is still conscious it may be possible to re-warm by extra layers and warm clothing. However around these temperatures, the heart is in danger of fibrillation and the casualty may collapse and become unresponsive.
32°C and below, the casualty is in a serious way. Their heart is now in serious danger of ventricular fibrillation, this is an abnormal heart rhythm where the heart muscles contract in an uncoordinated manner out of rhythm with each other. This is life threatening and can be caused by the shock of cold blood rushing into the heart if the casualty is moved roughly.
The severely hypothermic casualty now has a cooled brain and so their usual functions will disappear. It may be difficult to detect signs of life as the muscles become more rigid and so pulses may not be found. The body falls into a dormant like state and breathing may be so shallow and slow that this too may be undetectable, the casualty’s eyes may not react to light and may be dilated.
Prevention of hypothermia
- Check the weather forecast and make sure that you are adequately equipped for the conditions. Even if the forecast is good, conditions can change rapidly in the mountains, particularly as you gain height. When it’s chilly in the car park, it will surely be considerably colder at 900 metres.
- Make sure you have adequate clothing, waterproof trousers and jacket and spare warm layers. Folks generally overestimate the effectiveness of their gloves. Ensure you have insulated winter gloves and a warm beanie hat to wear. Take spare gloves in case they get wet or lost.
- Carry a survival bag, or even better a blizzard bag to wrap yourself or the casualty in an enforced stop or emergency. This will help to retain body heat.
- A mountain shelter is a great addition to your winter kit, it will provide protection form wind and rain and can become quite warm and cozy if you have several occupants.
- Take plenty of high energy food and preferably a hot drink.
- Plan an appropriate route for the conditions and make sure that you can navigate using a map and compass so that you do not become disorientated in poor weather conditions.
A summary of symptoms, signs and treatment of hypothermia:
- Shivering, cold, pale skin
- Paleness/blueness of lips and extremities
- Fast breathing
- STOP! Seek shelter
- Extra layers
- Food & hot drinks (although often it is said that caffeine should be avoided because it is a diuretic, if it is the only hot drink available then it will still help the casualty)
- Uncontrollable and violent shivering
- Pale, cold skin
- Blue lips
- Slurred speech
- Lack of co-ordination
- Loss of motor skills
- Fumbling of easy tasks
- Irrational behaviour (e.g. stripping off clothes)
- As for mild hypothermia
- Monitor carefully
- If the casualty stops shivering, check that they really have warmed up before deciding to walk off, i.e. are they looking warmer, do they feel warmer to touch? Is their skin pinker? Are they back to their usual character? (Because casualties also stop shivering in severe hypothermia).
- Shivering ceases
- Cold, pale skin
- Blue lips
- Dilated pupils and not reacting to light
- Unconscious and unresponsive
- Muscle rigidity
- Breathing and pulse may be undetectable
- Move as little and gently as possible
- Insulate from ground and air with as many layers as possible (but do not make big movements of the casualty)
- Glucose gels smeared on the gums might possibly help, however, do not try to force feed an unresponsive casualty!
- Do not do CPR (you may not be able to detect the pulse and breathing although it may be present) N.B. a casualty is never cold and dead, only warm and dead
- Protect the airway; Safe Airway Position
Russ Mills runs Mountaintrails, a guiding hiking and skills training business based in Dublin.