If you've ever taken a Wilderness First Aid course you should be familiar with the Wilderness Triangle.
Hypothermia is a little more complicated, and not always completely intuitive, but for the Wilderness First Aid practitioner, this is arguably the most important element of the Wilderness Triangle (not only do cold patients consume huge amounts of glucose while shivering, but they are also highly prone to dehydration. Effective prevention and treatment of hypothermia can make the difference between a patient who improves under your care, and one who gets catastrophically worse.
This article is concerned primarily with preventing hypothermia during treatment of injured or ill patients. Assessing and treating hypothermia will be covered next week.
Methods of Heat Loss
By far the most effective treatment for hypothermia is prevention. The human body has many mechanisms – sweating and shivering, most obviously – to keep its core temperature in a 'Goldilocks Zone' of 36º C to 37º C. Unfortunately, these mechanisms become compromised in sick or injured people. As a result, temperatures and conditions that might be nearly unnoticeable to a healthy person can be dangerous to someone who is sick. As a Wilderness First Aid practitioner, one of your primary goals is to help your patient conserve body heat against all methods of heat transfer. These methods include:
- Conduction (heat transfer through direct contact, especially with water or the ground): Get patients out of wet clothes and swaddled in something dry, then make sure that they have something non-conductive to sit or lie on – foam pads, air mattresses, or thick beds of evergreen boughs are all options to prevent heat loss into the earth.
- Convection (heat transfer to moving currents of air or water): Because warmed air or water is continually being whisked away and replaced with cooler pockets, this process is more continuous than conduction. Furthermore, the faster the current, the greater the heat loss (think wind chill). Protect your patient with plenty of dry. insulating layers.
- Radiation (emission of heat from your body to cooler objects around you): When not being directly heated by the sun, we radiate heat. Radiation is generally poorly understood and easily overlooked, but it can account for more heat loss then other methods, especially in very cold environments (-29 C). It is also how alien Predators find you. Clothing does little to prevent radiative heat loss - emergency foil blankets are your primary tool.
- Evaporation (transfer of heat from your body as water evaporates from your skin): This is how sweat works. Sick people and injured people – especially if they're in shock – sweat. There isn't much you can do to prevent this (although wiping obvious sweat away before it evaporates can help).
Taking all of these methods of heat loss into account while providing treatment, supportive care, and arranging evacuation might seem daunting. Fortunately, there is an easily-constructed tool that can protect your patient from all these forms of heat loss: the Hypowrap.
Constructing a Hypowrap
The Hypowrap is a multi-layered burrito-looking thing that offers maximum protection to the hypothermic patient, and also creates a package that can be moved as a single unit, if necessary. From outside to inside, the layers include:
- Waterproof shell: a tarp, tent fly or tent that will protect insulating layers – and the patient – from rain or ground wetness.
- Sleeping pads: a few layers if possible, to lift the patient off the ground. Foam pads or air mattresses.
- Emergency blankets: two if you have them, overlapped and laid out sideways, to make sure that you have enough coverage. Foil goes on the inside, despite what TV has taught you.
- Sleeping bag: two is best, if you have them. These are insulating layers that protect against conductive heat loss. It is highly recommended that you use the patient's own sleeping bag – see the diaper, below.
- Diaper: yes, a diaper. Two layers – an absorbent inner layer, such as a sweater or blanket, and a waterproof outer layer, such as a garbage bag, duct-taped to the skin. If you are using the hypowrap to prevent someone from becoming hypothermic, the patient may be wrapped for the duration of evacuation; if you are using it to treat someone who is moderately to severely hypothermic, it might take 24 hours or more for their temperature to return to normal. During this time, the diaper protects the sleeping bag from becoming wet due to... umm... bodily functions, which would destroy its insulating properties. Some leakage is probably inevitable.
Fold the extra material up over the foot end, then bring the edges together like a burrito, folding the corners back to leave the face exposed. Duct tape the package closed, and finish it off with a warm hat and some extra insulation stuffed in around the neck. Remember that critically ill patients still have to be reassessed and monitored – if you have to open the hypowrap, plan so that heat loss is minimized.
If neither available resources nor time permits construction of a hypowrap, do the best you can with what you have available, taking all methods of heat transfer into account.
Despite your best efforts, seriously injured or ill patients might become hypothermic over time. Be sure to check in next week to learn essential Wilderness First Aid skills in assessment and treatment of the different levels of hypothermia.