Part 1 of a 2 part series. (Part two is here.)
We all understand that hypothermia occurs when the patients core temperature drops secondary to exposure to cold. But, clinically, what is hypothermia really? What happens to the body as it cools down and struggles to maintain its core temperature? Can we predict a patient’s relative core temperature based on our physical findings? Is treatment really as simple as bringing them in and warming them up?
Let’s review the basics of the hypothermia progression and explore how to treat these sometimes challenging patient presentations. Put your mittens on, this is a chilly ride.
When we consider the typical hypothermia victim we often envision the lost hiker stumbling through the snowy woods looking for home. Perhaps our victim stumbles through a freezing stream, the sun begins to set and hypothermia sets in.
No doubt, our lost hiker is at risk for hypothermia, but we should consider that anything that decreases the body’s ability to produce heat or increases the body’s propensity to loose heat, can lead to eventual hypothermia. The prepared hiker may be less at risk for hypothermia than an urban soccer player who gets caught in an unexpected rain storm or an elderly nursing home patient left too long on an outdoor patio in the wind or an intoxicated transient patient who didn’t bundle up well enough before nightfall.
Hypothermia occurs more often in urban settings that rural settings and you’re just as likely to encounter it in Detroit, Michigan as you are in Missoula, Montana.
Recall that there are five ways for the body to lose heat:
Conduction: Touching cooler objects transfers body heat.
Convection: Air blowing across a warm body carries heat away.
Radiation: Heat radiates off the body into the air.
Evaporation: Sweat and moisture drying on te skin carries heat away from the body.
Respiration: Air gathers warmth in the respiratory tract and we exhale it.
Other factors both external and internal can speed the body’s willingness to sacrifice heat. Water conducts heat away from the body 25 times faster than air. Underlying medical conditions can also affect the body’s compensatory function. Any medical condition that hinders heart function, metabolic function, vasoconstriction or shivering will affect the patients ability to maintain core warmth.
Being elderly, young, sick, drunk, male or high all make you more likely to succumb to hypothermia.
So now that we know how the body looses heat and what things might accelerate it, lets take a walk through a typical plummeting core temperature. The following numbers represent degrees Fahrenheit.
103.0-96.4 The normal core temperature range. Remember that body heat fluctuates quite a bit during a typical day. Exercise might raise core temperature from a standard 98.6 to temperatures as high as 103.0. Body temperature may also fall as low as 96.4 at rest. Temperatures in our limbs tend to stay 1-2 degrees lower than our core.
95.0 Mild hypothermia. Shivering begins.
93.2 Amnesia and minor errors in judgment begin. An individual may become overly emotional or easily irritated.
91.4 Major motor coordination begins to fade.
90.0 Moderate hypothermia. More significant changes in mentation including confusion and stupor.
87.8 Shivering stops. One this vital heat generation mechanism disappears core temperature will drop more rapidly.
86.0 Irregular heart rhythms emerge. Atrial fibrillation is the most common hypothermia arrhythmia.
85.2 Loss of consciousness more likely. Pupils Dilate.
82.4 Spontaneous ventricular fibrillation possible.
80. 6 Severe Hypothermia. Inability to move voluntarily.
78.8 Unresponsiveness to pain.
75.2 Significant hypotension sets in. Pulses become difficult to discern.
71.6 Ventricular fibrillation likely.
56.7 Coldest successful adult resuscitation.
57.6 Coldest pediatric resuscitation.
A good rule-of-thumb assessment for the hypothermia patient is to lay your hand on the patients abdomen. If he abdomen feels cool to the touch, generalized hypothermia is likely.
With your basic assessment and a rough idea of how the body devolves as hypothermia progresses, you can take a fairly accurate guess at the patients core temperature before you even hit the power button on the thermometer.
Looking at the progression of symptoms above, one of the real challenges of treating severe hypothermia becomes apparent. As the body metabolically shuts down in an effort to save itself, many of the symptoms of moderate and sever hypothermia mimic death and our aggressive interventions can easily do more harm that good.
We’ll talk moe about that next time.
Now it’s your turn: Have you treated hypothermia in the field? What were the symptoms like? What challenges did you encounter?
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