Hypothermia occurs in extreme cold, and is defined as a drop in core body temperature to less than 35°C. If you believe you could become at risk of hypothermia it is important to know that at least half of heat loss recorded temperatures due to radiation by the skin. The head itself is a significant source of this skin heat loss.
For those out in the wild, becoming dehydrated or hungry will put you at higher risk of hypothermia. If you want to be prepared, you will need to have an oral electronic thermometer to hand, as this is as close as possible to core temperature measurements.
To be prepared in all situations, you will also want to carry a mercury or liquid thermometer as a backup. Bear in mind if you are taking rectal temperatures that this may read slightly higher and therefore you will need to adjust the reading slightly for any temperature reading.
Table of Contents
The Clinical Definition of Hypothermia
The Swiss Mountain medicine field guide is likely the best review of hypothermia available. They define hypothermia into four categories.
Mild hypothermia is defined as a temperature drop from the usual 37°C to 35-32°C (95 to 90°F). People in this temperature range often find themselves shivering, which is the best way to increase body temperature.
If they are showing signs of hunger or dehydration then eating and drinking, along with limited exercise may be of benefit.
Moderate hypothermia at temperatures between 32 to 20°C (or 90 to 82°F) people may find that their shivering stops and there is some altered cognitive ability.
Because active shivering has stopped people suffering from moderate hypothermia must be actively warmed as they are unable to warm themselves.
Severe hypothermia between 28 to 24°C (82 – 75°F) means decreased cognitive function and increased danger to the heart.
Stage IV hypothermia below 24°C or 75°F – people usually stop breathing and their body enters a state of stasis if they do not die.
The Development of Hypothermia
While there may be many stages of hypothermia, the main intervention required is, of course, heating up the affected person. If you find someone shivering, this is a good sign, as it implies that they are still in the initial stages of hypothermia.
Shivering is a mechanism used by the body to raise the peripheral or external temperature of the skin. As the skin cools the body redirects central blood flow to the surface.
Stage II hypothermia and onwards is caused by the continuous return of this cold blood from the skin, which in turn drops the core body temperature.
Resuscitating victims of hypothermia
Due to the metabolic changes hypothermia induces at the cell level, CPR is actually not recommended for moderate stages of hypothermia and above.
This is due to the irritability of the heart, and unless professional care is more than three hours away nothing more than respiratory support and evacuation should be provided.
Keep in mind that evacuation is recommended for all people who are suffering from moderate hypothermia and worse.
The main goal of hypothermia treatment in the wild, that is hypothermia first aid, is to prevent further heat loss of the victim whilst rewarming them as much as possible.
If the victim has fallen into a body of water, the obvious first step is to remove him or her from it. It is important to be gentle with hypothermia victims, and to limit moving them only as necessary. Do not try to massage or rub heat back into them. Sudden, jarring movements may in fact trigger a heart attack.
Once they’re out of the water move them to as dry and warm a location as possible. If you are not able to do this, then block them from the cold and wind as much as able.
Regardless of how cold it is you must then remove any wet clothing which the person is wearing. If you have any sharp implements to hand, use them to cut away clothing to avoid unnecessary movement.
The person then must be insulated from both the ground and air using as many blankets or pieces of clothing available to hand. Do not forget to cover the head completely, except for the face, leaving space for the victim to breathe freely.
If the person is alert try warming them up with warm drinks. If you are afraid that they may choke or breathing any fluids do not attempt this step.
While adding sugar to any drinks will help, make sure that you do not give any alcohol or caffeine as these were either drop the body temperature or increase the heart rate respectively.
If you have anything warm to hand, such as a hot water bottle or other warm item, make sure to apply it to the torso and neck only.
Applying heat directly to the limbs will, in fact, force the problem back towards the heart lungs and brain. Counterintuitively, this may in fact drop the core body temperature and the lethal to the victim.
If you are able to heat the patient safely, make sure that there is no direct contact to the skin. The temperature difference can damage the skin, leading to further complications at a later date or it can induce an irregular heartbeat, at worst causing a cardiac arrest.
The Body to Body Rewarming Myth
Popularization of emergency situations has led to some well-meaning myths propagating through the survival community.
Body to body contact for rewarming hypothermia victims does seem like a sensible decision on the surface. This is because humans all exist at the same body temperature and it was assumed that skin to skin contact was a safe way of rewarming a victim without inducing any heat-related injury.
However recent research has suggested that this technique may not be beneficial at all, and may actually be harmful to both the rescuer and the victim. Studies seem to indicate that while heat is transferred from a rescuer to the victim, the act of holding the victim restricts their ability to shiver.
A study which looked at whether body to body warming would enhance recovery of a victim experiencing mild hypothermia found that sharing body heat was only as effective as letting the person rewarm by shivering alone.
When this study was repeated in those victims with simulated severe hypothermia, then it was found in these cases that body to body rewarming yielded a faster recovery than letting the victim passively rewarm by themselves.
That being said, the research team found it was still significantly less effective than applying a heat source and a rigid cover to the victim’s chest.
The Alcohol Myth
For centuries specific spirits have been used around the world to warm victims of hypothermia. This has developed due to the vasodilatory properties of alcohol. This means that consumption of alcohol makes your blood vessels in your skin dilate.
As these blood vessels dilate, this draws heat from the core of your body to the surface of your skin. This leaves those who drink alcohol feeling flushed, and the hot sensation is increased with increased alcohol consumption.
What this actually means is that alcohol can serve as something that may make you feel warmer, but in fact drops your core body temperature. To make matters worse, alcohol damages thermoregulation, which lowers the body’s resistance to external cold temperatures.
As with any serious situation in the world, it is always a poor idea to consume alcohol. Not only does it impair motor skills and coordination ability, your ability to think clearly and safely is greatly reduced. Alcohol is always a poor idea in a survival situation.
Staying Alive Underwater
There have been stories in the news that may appear as hearsay, but are in fact medical truth. All mammals, including humans, have an inbuilt response to cold water which is triggered when contact is made with their face.
This protective mechanism shunts warm blood and oxygen away from the extremities of the body towards the heart and brain. The heart then slows, which limits blood flow around the extremities of the body maintaining flow around the core. Any water below 70°F touching the face will cause this reflex. Luckily in children under three the reflex is even stronger.
The result of this reflex is that victims of both hypothermia and drowning have been revived from underwater despite being submerged for over 60 minutes. Chances of survival in these conditions increases with colder temperature, younger age and decreased time underwater.
Instant Hypothermia Death
In a minority of cases, hypothermia can be such a shock that it causes almost immediate death. There are two mechanisms for this the most common being the torso reflex. This is called a reflex as it cannot be fought against, and is a natural reaction of the body.
When a mammal suddenly enters cold water, the body tries to quickly draw in a last gasp of air in order to increase the chances of survival. Of course if you are already underwater when this reflex kicks in you will then breathing in a lung full of water.
In some cases, while victims may not breath in water, the shock to the heart of the sudden temperature drop can be too much and induce cardiac arrest.
Applying hot water bottles or hot damp cloth to the victim’s head, neck, trunk and groin are recommended. At a minimum the heat source must be rotated to reduce the chance of any damage to the victim.
Current guidelines state that a maximum temperature of 115°F or 46° should be used when heating the body. If using a bath of warm liquid, the same rules apply with regard to avoiding heat application to the arms and legs. When lowering the victim into the bath, ensure that the arms and legs are kept out while the trunk is submerged.
Slow rewarming is key due to a danger called ‘after drop’. After drop is caused when a hypothermic victim is rewarmed very quickly externally, causing cold blood in the extremities to return to the core, potentially causing death.
Care must be made moving the patient either when undressing, warming, or simply transferring to a medical facility. Due to the low temperature of their organs, they are particularly susceptible to any physical movement or shock.
When exploring the wild, or simply surviving in it, it is always ideal to have a friend or partner with you. Not only is as vital for any help that is required if there is an incident, a second pair of eyes will also give you an important third party perspective. While hypothermia may cause a number of physical symptoms, the most serious of those of mental derangement.
A hypothermic person will become confused, mentally sluggish and unable to make clear and sensible decisions. As the symptoms come on gradually, you may be unable by yourself to discern whether you are not you are becoming hypothermic.
Another concern of note is that of malcoordination, or an inability to perform physical tasks. This will greatly impair your ability to seek help, and therefore travelling through the wilderness is recommended with a friend by your side.
Prepping for Hypothermia
Any expedition into the outdoors obligates warm clothing, food, water and some form of shelter if you are planning a longer trip. But are warm clothes enough if you or someone else has already developed hypothermia?
If your body temperature has dropped so far you are experiencing symptoms then either your clothing was inadequate or something external has caused it to fail.
Falling in water through ice is a classic example. If there is one rescuer only, they have to strip the victim of their wet clothes, somehow dry them and then share the remaining dry clothing material between two people.
When put in this light you can see how warm clothing isn’t enough. The following list will give you an idea of the extras needed but will depend on how big your party is and if you are travelling by foot or by vehicle.
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- Two large waterproof bags All of the items on this list should go inside the first waterproof bag. This makes sure they are useable in an emergency even if the bag is submerged in water. The second bag is for carrying any wet or damp items removed from the person being treated.
- Foil Blankets these are lightweight and small which make them great for travelling
- Emergency Mylar (Space) blankets a bit more expensive, these are made from laminated polyethylene, which reflects up to 90% of a body’s heat back to it.
- Heat packs these are single use or can be frozen and reused. They store heat which is released in a chemical reaction when they are activated. Apply to the torso and not the limbs.
- Bivvy / Sleeping Bag these all importantly will cover the head and help reduce the impact of wind on the above blankets and heat packs
- Spare thermal clothing if you have the space take complete sets of spare clothing inside a waterproof bag for each traveller
Have you ever experienced hypothermia? What happened? Write a quick comment below and share your experience, so we all know better next time.
Shane is a medical doctor with over 8 years experience in both hospital medicine and surgery. He’s completed over 2 years of surgical work focusing on trauma & orthopaedics alongside maxillofacial surgery. He has been involved in education since medical school and have written courses and taught classes.
Having trained in Advanced Trauma and Life Support he is at the forefront of practical, out-of-hospital medicine which can be applied by the public to save lives.