This blog posts contains information about hypothermia. First of all, it describes what hypothermia is. As hypothermia is known to have different stages, these are explained next – including the symptoms of these stages.
The next 2 chapters are about prevention of hypothermia and treatment of hypothermia.
Bear in mind: the oppossite of hypothermia is hyperthermia. Hyperthermia is about overheated bodies, where hypothermia is concerning low body temperatures.
What is hypothermia?
Your body has a core temperature of 37 degrees, +/- 0.5 degrees Celsius. For those living in the imperial system: that’s 97.7 tot 99.5 degrees Fahrenheit. All temperatures from now are in Celsius.
The body of warm blooded animals, which includes humans, is set to retain a level of homeostasis. This homeostasis is a result of millions of years of evolution and is the temperature at which all chemical and physical responses work optimal. This is a narrow bandwidth: above the normal temperature certain enzymes don’t work anymore. Below this temperature, systems start to shut down as blood is retained in the core of your body.
When your body temperature drops below 35.0°C, you are hypothermic. Bear in mind: you probably already feel cold above 35°C. Feeling cold is the first sign that you are cooling down – staying active is a good way to overcome this. Unvoluntary shivering is the first noticable action as a result of a dropping core temperature.
Hypothermia is dangerous, especially when you are alone and at high altitude (as your blood thickness increases or altitude sickness kicks in too). Being able to recognize the symptoms and providing basic care is essential to any hiker (or other outdoor sports).
Stages of hypothermia and their symptoms
Obviously when being outdoors, or even outside a hospital, it’s very difficult to accurately determine the core body temperature. For this, the so-called “Swiss Clinical Stages of Hypothermia(1)”, or in short “Swiss model” has been introduced by Brown et al, 2012.
This model has 4 stages, called, not surprisingly “HT1, HT2, HT3 and HT4”.
HT1 is associated with a core body temperature between 32°C and 35°C . Symptoms: The victim is conscious but has started (uncontrollable) shivering.
The second stage, HT2, is worse. Be aware: shivering has stopped but consciousness is less. People may lose their orientation, talk nonsens or incomprehensible. The associated core body temperature is below 32°C but above 28°C.
HT3 is when the previous stage is not treated: loss of consciousness. There are still vital signs present: a pulse, noticeable breathing etc. The temperature is below 28°C, but above 24°C.
HT4 is easily mistaken for death. There are no vital signs: the body has shut everything down. Core body temperature is below 24°C.
There is an addition (2) to this system: the temperatures are not very precise. They usually steer on the safe side. Better be too pessimistic about one’s situation, rather than optimistic.
Treatment of hypothermia
Treatment of hypothermia before stage 3 is rather easy: get the patient in a warmer environment. When possible, release wet clothing and replace them with dry clothing. Even if the dry clothing is a thinner layer, it will provide more insulation than the previous wet clothing.
Beyond stage 1, as shivering has stopped, the body is unable to generate sufficient heat. So even the dry clothes and potential warm sleeping bags are insufficient. Extra heat needs to be generated from the outside. Share your body heat (get in the sleeping bag with the patient!), light a fire and prevent any heat loss. Do not rub the skin, as impaired blood flow might lead to tissue damage. Bear in mind that hypothermia is about the core temperature: the cold limbs are just a sign of this. You do not want the blood vessels in the skin to open up. This extracts heat from the core and decreases blood pressure.
Shivering and adding body heat (or other external practical treatment methods) are found to be the most effective re-warming methods in the field. Although still possible in stage 1 & 2, exercise is found to be less effective. This actually makes sense: the major muscle groups that are able to contribute to the heating system of your body are being shut down already. The blood flow is limited and the blood inside the muscles is colder than in the core of your body. Getting this blood flowing at a higher rate actually leads to cooling of the core body temperature, before it starts rising (3).
After stage 1, it is important to get professional help. Stage 3 and 4 are (well) beyond the limits of field-operation treatment methods and the person becomes immobile.
Do take in consideration that stage 2 is already quite dangerous, depending on your location: as body momevement is becoming less controlled, ridges, cliffs, ladders and any other technical terrain becomes a challenge.
Also check for signs of frostbite: frostbite can be serious and these conditions can go hand-in-hand.
Prevention of hypothermia
Many hikes are done in remote, mountaineous or tundra-like terrain. There is no hiding against the elements and the risk of getting wet from precipitation, streams or lakes is real.
Mountains are also famous, if not notorious, for the unpredictable weather. It may feel like 20°C at 2000 meters at one moment. It may actually be 20°C at 2000 meters at that moment – only to be caught in a thunder storm with hail or snow moments later. Your sweaty body cools down rapidly as the wind picks up and drains the heat from your skin. Exposed to the elements, you do not have time to stop: you don’t want to be stuck on this ridge during a thunder storm.
What to do? Make sure you carry dry clothes in your backpack – in a waterproof-bag of course! Anything and everything might get soaking wet, but one spare set of dry clothes and a dry sleeping bag can be literally life-saving.
Another advice: dress yourself in layers. When you get hot, you can take layers down. And when it gets chilly, you simply add layers. This helps your body regulate temperature beyond its own limits and prevents sweating. Not all sweating is preventable: you will lose some droplets and probably more than some. But being able to take layers of, avoids these layers getting soaked.
Third advice: carry a stove when in colder conditions. This helps in multiple ways. First of all: you can get some warm fluids or meal into your body. Being well-hydrated and well-nutritioned are key-elements of keeping warm and preventing hypothermia.
But it also provides heat when actually preparing the food. It might not be much – but it’s better than something.
Advice 4: don’t drink alcohol or smoke cigarettes (5). Alcohol does not make or keep your body warm (4), contrary to many believes. Similar for doing drugs…
Advice 5: sleep well (6). Sleeping is the most important cure to anything. It helps your immune system but is also key to maintaining homeostasis.
Advice 6: be well-trained and adapted to the altitude. Heart rate increases due to the exposure to heigher elevation as a first response to adapt to the limited oxygen supply. Being well-trained helps by having a larger group of muscles to pull energy from, and to have the energy reserves and muscle power to get to shelter when needed.
- Brown DJ, Brugger H, Boyd J, Paal P. Accidental hypothermia. N Engl J Med.
- Deslarzes, T., Rousson, V., Yersin, B., Durrer, B., & Pasquier, M. (2016). An evaluation of the Swiss staging model for hypothermia using case reports from the literature. Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine, 24(1), 1-7.
- Giesbrecht, G. G., Bristow, G. K., Uin, A. N. T. S., Ready, A. E., & Jones, R. A. (1987). Effectiveness of three field treatments for induced mild (33.0 degrees C) hypothermia. Journal of Applied Physiology, 63(6), 2375-2379.
- Danel, T., Libersa, C., & Touitou, Y. (2001). The effect of alcohol consumption on the circadian control of human core body temperature is time dependent. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 281(1), R52-R55.
- Gilbert, R. M., & Pope, M. A. (1982). Early effects of quitting smoking. Psychopharmacology, 78(2), 121-127.
- Young, A. J., Castellani, J. W., O’Brien, C., Shippee, R. L., Tikuisis, P., Meyer, L. G., … & Sawka, M. N. (1998). Exertional fatigue, sleep loss, and negative energy balance increase susceptibility to hypothermia. Journal of Applied Physiology, 85(4), 1210-1217.