Living in Houston, I am used to heat and humidity. This past weekend the Southwest region of the United States suffered a major heat wave that left 4 hikers dead in Arizona. Now that it’s officially summer, let’s talk about the spectrum of heat illnesses.
Rewind to high school physics. There are only three ways to get rid of excess heat: radiation, convection, evaporation. When ambient temperature is hotter than body temp, radiation and convection are useless. And when humidity is >75%, sweating loses effectiveness as evaporative cooling. Welcome to Houston.
There are various easy methods to prevent heat illness.
- Wear lightweight, light colored, loose clothing.
- Use sunscreen. Sunburnt skin can’t cool as effectively as intact skin
- Drink plenty of water. A quick and dirty way to monitor is to check how much urine you’re making
- Be alert for early symptoms in yourself or fellow adventurers: nausea, headache, dizziness, cramps
Heat Exhaustion: milder than heat stroke. Body temperatures do not rise above 104 F (40 C). Individuals may experience weakness, dizziness, or syncope.
Heat Stroke: severe heat illness with body temps >104F (40 C) with central nervous system abnormalities (altered mental status [AMS], seizure, coma). Heat stroke can be passive (think old grandma in her apartment that doesn’t have AC) or exertional (marathon runner by mile 20).
With heat stroke, patients can have a variety of central nervous system findings such as confusion, hallucinations, or eye findings (nystagmus, any variation of pupillary response). The vitals will display hyperthermia >104 F although there have been cases with heat stroke at lower temperatures. Essentially, any AMS with exertion or heat exposure should be considered heat stroke until proven otherwise. Pulse and respirations can be normal or accelerated. Blood pressure can be normal or hypotensive. The patient’s skin can be cool and moist or dry and hot. Dry, hot skin is more serious as it indicates thermoregulation is so deranged or so dehydrated that the body is no longer producing sweat.
Evacuate to a hospital as end-organ damage is very possible with heat stroke.
- As always, ABCs: Airway, Breathing, Circulation.
- In this case, E (exposure) is especially important. Remove the patient from the hot environment ASAP!
- Fastest way to cool: ice baths. Unless your First Aid kit came with an immersion tub and ice this is impractical in the field.
- In the field: remove tight clothing, apply cool towels to the neck, axillae and groin, fan the patient
- New methods: glabrous cooling – ice packs to cheeks, palms, and soles show more rapid cooling rates
- Immerse/cool patient until temp is <102
- If patient begins to shiver, stop cooling efforts as it is counterproductive and attempt to stop shivering (muscle relaxants, anticonvulsants, sedatives)
- Do NOT cover the patient with a wet blanket as it would impede evaporation, Tylenol/Aspirin have no role in reducing temperatures since this is not a fever
- Less of a concern in the immediate management on the field, but administer cold IV fluids with caution. Pulmonary edema is a complication and endurance athletes could by hyponatremic as well.
- Heat stroke can happen at any temperature!
- Recognize the signs: nausea, dizziness, confusion in context of exertion or heat exposure
- get out of the hot environment ASAP, place cold towels/ice packs on axilla, groin, neck or on glabrous surfaces
- Prevent with the loose light clothing, sunscreen, and hydration
Sarah Henkel, LP, NREMT-P, MS, and Rich Henkel, “Heatstroke: A serious summer risk in Texas”, Texas EMS Magazine. July 2011
Lipman, Grant S. et al. Wilderness Medical Society practice guidelines for the prevention and treatment of heat-related illness. Wilderness Environ Med. 2013 Dec ;24(4):351-61. doi: 10.1016/j.wem.2013.07.004. Epub 2013 Oct 17