Hypothermia: What is is; and isn’t:
With winter comes the possibility of hypothermia. And with long immersion in water, even not-that-cool-water, comes the possibility of hypothermia (water conducts your heat away 25x faster than does dry air). And being damp in a sharp wind comes with the possibility of hypothermia. In fact, any time your core temperature drops by much, you’re hypothermic. Normal body temperature is 37 C (98.6 F); 35 C (95 F) and below is hypothermia.
Hypothermia is very different than frostbite. In hypothermia, core body temperature is low. Your life processes slow to an amazing degree. If you rewarm the person before the processes actually stop, the biggest risk is the heart failing from messed up electrical conduction. Frostbite is when parts of you, usually the most distant from the core and exposed parts, literally freeze solid. There’s another post here (clicky) that talks about frostbite. A person could have both frostbite and hypothermia at once of course. If so, treat the hypothermia first and worry about the frostbite afterward.
Since hypothermia is a risk common to a lot of outdoor or out-of-power situations, dealing with it is a valuable thing for preppers to know. In this article and on this podcast (CLICKY) we summarize the recommendations of the Wilderness Medical Society (1). This society has a group of physicians that does a Lovely job of combing through the medical literature, coming to a consensus on practical, clear recommendations, and telling you how reliable they consider each recommendation based on the research behind it. I myself am not a physician and make no recommendations; I’m just transmitting the most prepper-relevant parts of what these experts have published.
Hypothermia is weird. It can incapacitate a person very quickly; within minutes after immersion in icy water. However, as one EMT explained it to me, “They’re not dead until they are warm and dead.” People have been revived, without brain damage no less, after more than nine hours of immersion in cold water. The cold slows the metabolism, and with the very slow metabolism the cells can live a very long time with no oxygen. The key is obviously to get the person warmed up; but there are some tricks to doing this with the least chance of having the heart misbehave with tragic consequences.
How hypothermic are they?
First, don’t trust normal body temperature thermometers. They’re not designed to deal with a person in this state and aren’t reliable.
Shivering starts when the skin is cooled, even when core temperature is fine; so shivering doesn’t mean the person is hypothermic. However, people do start shivering as core temperature drops. Shivering is controlled muscle action meant to produce heat, and it does a good job. It gets more violent until the person gets down to about 32 C (90 F), then fades away and is done by a body temp of about 30 C (86 C). That’s a bad thing; once the shivering stops the person is incapable of rewarming himself.
By 34 C (93 F), the brain starts slowing down. The person gets irritable, confused, lethargic, sleepy. Decision making gets very poor.
The heart starts slowing down at about 30 C (86 F). It may stop around 28 C (82 F); but that doesn’t mean it won’t restart if the rewarming is done well (and you get lucky).
By 24 C (75 F) the person seems dead; no detectable pulse or respiration. But are they? People have been revived, brains intact, from as low as 9 C (48 F) … hence the “they aren’t dead until they’re warm and dead” approach. In the absence of professional medical care, how do you know when to stop treating? When the chest is too stiff for CPR, or the person has been buried for more than 35 min and the airway (mouth an nose) is full of snow, or they’ve been warmed and still seem dead.
Afterdrop, the bane of inexpert attempts to re-warm:
Afterdrop happens when core temperature drops further after rescue efforts have begun. The most usual reason is that the rescue attempts improved blood flow to from core to limbs before the limbs were successfully warmed. The result is bringing colder blood from the limbs back to the core and further chilling the core. This can be fatal. Many of the recommendations below are designed to re-warm without causing afterdrop.
Activity is good only if the person is only mildly hypothermic
How can you tell? If the person is completely alert and mentally competent and not exhausted but still shivering, then and only then is it good to have them warm by moving. Afterdrop isn’t a real risk yet. The main help you can give beyond the obvious of getting them as dry and well insulated as possible is to keep them well fed. Drinks and food with sugar to provide plenty of energy will support their ability to shiver and move, and those are their best defenses. Hot food and drink is most welcome of course, but the energy difference between hot and cold is minimal, so use whatever you’ve got.
When hypothermia is more than mild, let the rescuers do all the work
It’s best for a more hypothermic person to lie prone and still, even if they’re capable of moving. Moving encourages blood flow to and from the limbs, and that’s not wanted. Having the head above the heart makes it harder to get enough blood to it, and having legs or arms above the heart brings cold limb blood back to the core, so that’s no good either. Have them lie warm and still. Don’t move the person’s limbs passively any more than necessary for the same reason.
While they’re there, make sure they have a moisture barrier as well as insulation. Evaporative cooling (wind chill) is the enemy here. The moisture barrier should go over any wet clothes but under some of the insulation. Those emergency blankets made of mylar that many of us have in our bug-out bags would be great. Even plastic bags or bubble wrap work well. Don’t forget to have insulation underneath them as well as on top; even more underneath if my camping experiences are any indicator. Minimize exposure of the head and heat loss around the neck.
Rewarming: What works well and not as well
Warming the core first is best: chest, back, and armpits are the best targets. Large heating pads, large water bottles, and mild chemical heaters designed for the task work well, but put a cloth barrier between heater and skin. The skin of a hypothermic person is exquisitely sensitive to heat or pressure injury. Hand and foot warmer chemical packs are too hot (unless perhaps if well separated from direct contact with skin). The military made Hypothermia Prevention Kits (HPMK) that are a combo of vapor barrier/heat shell and appropriate chemical heater pad. This kind of thing is commercially available.
To prevent afterdrop, don’t do things that warm the limbs first. Warm baths or showers aren’t recommended for this reason. Neither is massage.
What about rewarming with someone else’s body heat? If the person is shivering and the potential body warmer would have to interrupt other rescue actions, it’s not worth it; the body rewarming works about as well as the shivering. If the warm volunteer couldn’t be doing anything else productive anyway, it’s worth doing.
Serious hypothermia and the heart
Should you give CPR? If there’s any pulse, no. The pulse may be very slow and weak, so check it for a minute at a time at the neck (carotid artery). If there’s no detectable heart beat, yes, CPR during rewarming is recommended. Unlike with a warm victim, CPR can be intermittent if necessary to allow other rescue actions (or even rest; CPR is hard work). Also unlike with a warm victim, CPR can still have good results after it’s been needed for a very long time; hours even.
If there is an AED to use and it wants to give a shock, let it give one at max power. Don’t let it try again until the person has been warmed somewhat.
Hypothermia with Friends (other problems)
Leave frostbite until hypothermia has been resolved. Treat other traumas as you normally would. If you have to transport someone to shelter, reduce any fractures or dislocations and immobilize before moving them, and cover any open wounds.
Be careful with drugs. They won’t have much effect on the hypothermic person because the metabolism is so slow; but the drugs administered then will take effect as the person warms. If you got impatient and gave more to get an effect, it could turn into an overdose on warming.
I was amazed by the depths of cold and lengths of time, even immersed in water, that hypothermia victims had survived. It’s dicey, as the heart can be so unpredictable, but good outcomes are possible. Hang in there, and … be warm.
1) Ken Zafren et al. 2014. Wilderness Medical Society Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia. Volume 25, Issue 4, Pages 425–445, DOI: http://dx.doi.org/10.1016/j.wem.2014.09.002