Hypothermia

An overview on Hypothermia for Boaters by Chris Joosse

Resources:

Hypothermia: Basic Essentials by William W. Forgey, MD

Protocols:

Hypothermia is a serious disease that seems to be misunderstood- for all that it's fairly common, it should not be equated with merely 'being cold'- it's a serious condition that warrants medical attention. This overview is not intended to be a comprehensive or authoritative reference- it's a place to begin- note in the left-hand panel there are links to other resources.

First of all, hypothermia comes in several varieties, which demand very different treatments:

Chronic: the term 'chronic' is used to refer to hypothermia that sets on over a long period of time, generally 6 or more hours. Heat loss has occurred slowly, and initially is blunted by the patient's withdrawal of blood from peripheral tissues.

Acute: the term 'acute' is used to refer to rapid-onset hypothermia that sets in rapidly, generally in under two hours. Heat loss has occurred rapidly, and in a linear fashion- the patient has not had the chance to make any metabolic changes to his/her system. Victims immersed in water without protective clothing can be described as 'acute'.

Sub-Acute: A victim immersed in water with protective clothing on may lose heat slowly enough to become a genuine chronic hypothermic if rescued as much as 6 hours into their ordeal. Sub-acute refers to persons 2-6 hours into hypothermia.

Profound: the term 'profound' describes the degree of cold- a patient whose core temperature has dropped to 90F is said to be a 'profound' case.

If your patient's temp has gone below 95F, recommend that they see a doctor once they're warmed up. If you measure a core temp at or below 90F, don't give them the option because when they're in that condition they're unfit to make that decision- your first step, beyond making sure your patient is warm and stable, should be to arrange a way for them to get to an emergency room and see to it that they get there.

When you experience a thermal deficit over a long period of time, like, say, over the course of 6 or more hours, your body engages it's 'withdrawal' defense- a decrease in peripheral circulation in order to protect the body's core temperature-, and in doing so it makes some serious changes to your blood chemistry and metabolic condition.
'Withdrawal' is generally a peripheral vasoconstriction, focusing the majority of your blood and fluids in your core, which usually results in profound dehydration, even with adequate fluid uptake. This strategy will protect the body's core temperature by delaying heat loss, but a patient in this condition should be considered unstable. If their systemic sugar/carbohydrate levels become exhausted, they will be reduced to burning fat for metabolic fuel- and in a dehydrated and exhausted state, burning fat (especially peripheral fat that is in parts of the body that are 'shut down') may not be sufficient. If you've ever 'bonked' while exercising (that feeling that occurs when you run your system out of carbohydrates) you can appreciate that if your patient bonks in their hypothermic state, the result could be very bad. Warm fluids and simple sugars are recommended for the short term.

If your patient has been cold for a long time, they need to warm up at their own rate, in order to
allow their system to undo the changes it's made in order to protect itself. If you add a lot of heat to someone who's been cold for more than a few hours or so, you risk stimulating peripheral circulation before they can handle it, and you risk killing your patient if the case is profound enough. Adding heat to otherwise cold limbs could stimulate peripheral blood flow, dumping a bolus of dehydrated and cold peripheral blood into the body core, sending the patient into chemical or thermal shock and possibly killing them.

For the chronic patient (who's had 6 or more hours of hypothermia in which to change their blood chemistry) it's best to insulate them and keep them from getting colder, and if they can safely swallow, to administer fluids to aid in rehydrating their peripheral tissues. If they haven't become 'profoundly' hypothermic, (90 degrees F is roughly the threshold for 'profound') virtually any course of treatment is fine- add heat, whatever- but keep in mind that this person is exhausted, and needs calories, hydration, shelter, and rest. If the victim is profoundly chronically hypothermic, however, (with a core temp less than 90F and has been cold for 6 or more hours) go slow and conservative with your treatment- huddling in a sleeping bag with the
victim should be the most aggressive form of heat replacement you administer.

If, however, a person has been chilled very rapidly, (say, from water immersion) their system didn't get the opportunity to undergo all of those metabolic and chemical changes involved with peripheral vasoconstriction; in this case, aggressive heat replacement is nearly ideal- immersion in a bath at 110 deg F is prescribed.

Remember, hypothermia is an exceptionally serious condition and fatality is a very real outcome. Don't be shy about getting your patient to medical attention- in fact, if your patient has experienced any serious symptoms (confusion, nausea, slurred speech, impaired motor coordination, not shivering despite being cold) get them to a doctor! Just because they're getting better does not mean that they'll continue doing so.