Page 110 - JSOM Summer 2019

An Ongoing Series

Exertional Heat Stroke

Pathophysiology, Epidemiology, Diagnosis, Treatment, and Prevention

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Joseph J. Knapik, ScD *; Yoram Epstein, PhD 2

ABSTRACT
Temperature increases due to climate changes and operations Commanders and trainers should be alert to any change in the
expected to be conducted in hot environments make heat- Soldier’s behavior. Proper attention to these factors should con-
related injuries a major medical concern for the military. The siderably reduce the incidence of EHS.
most serious of heat-related injuries is exertional heat stroke
(EHS). EHS generally occurs when health individual perform Keywords: temperature; hot environments; heat-related in-
physical activity in hot environments and the balance between juries; exertional heat stroke
body heat production and heat dissipation is upset resulting in
excessive body heat storage. Blood flow to the skin is increased
to assist in dissipating heat while gut blood flow is considerably Introduction
reduced, and this increases the permeability of the gastrointes-
tinal mucosa. Toxic materials from gut bacteria leak through Heat-related injuries are of growing concern in the military
the gastrointestinal mucosa into the central circulation trig- because of expected temperature increases due to climate
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gering an inflammatory response, disseminated intravascular changes and military operations that might be expected to
coagulation (DIC), multiorgan failure, and vascular collapse. be conducted in hot environments. Numerous cases of heat-
In addition, high heat directly damages cellular proteins result- related problems among military forces throughout history
ing in cellular death. In the United States military, the over- have been document going back to the earliest of recorded
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all incidence of clinically diagnosed heat stroke from 1998 to history. For example, in about 400 BCE the Greek historian
2017 was (mean ± standard deviation) 2.7 ± 0.5 cases/10,000 Herodotus described the effects of heat on Greek (Ionian) war-
Soldier-years and outpatient rates rose over this period. The riors conducting rigorous training for battle. They were “. . .
cornerstone of EHS diagnosis is recognition of central nervous worn out by the harness of the work and the heat of the sun . . .
dysfunction (ataxia, loss of balance, convulsions, irrational be- many have fallen sick already-many more expected to fol-
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havior, unusual behavior, inappropriate comments, collapse, low.” In 24 BCE heat stroke and other heat-related problems
and loss of consciousness) and a body core temperature (ob- resulted in the loss of a large part of the Roman Army and
tained with a rectal thermometer) usually >40.5°C (105°F). The defeats in combat operations conducted in Arabia. 4
gold standard treatment is whole body cold water immersion.
In the field where water immersion is not available it may be The most serious of heat-related problems is heat stroke.
necessary to use ice packs or very cold, wet towels placed over This has typically been separated into two types based on the
as much of the body as possible before transportation of the presence or absence of exertion. Classic (nonexertional) heat
victim to higher levels of medical care. The key to prevention stroke develops in the elderly or in individuals with other co-
of EHS and other heat-related injuries is proper heat acclima- morbidities (e.g., obesity, diabetes, hypertension, heart disease,
tion, understanding work/rest cycles, proper hydration during renal disease, dementia and alcoholism) when exposed to high
activity, and assuring that physical activity is matched to the environmental temperatures. Exertional heat stroke (EHS) de-
Soldiers’ fitness levels. Also, certain dietary supplements (DSs) velops in health individuals (e.g., Soldiers and athletes) who
may have effects on energy expenditure, gastrointestinal func- are typically performing high-intensity physical activity in the
tion, and thermoregulation that should be considered and un- heat. In 1859 the physician James Levick remarked in rela-
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derstood. In many cases over-motivation is a major risk factor. tion to EHS:
*Correspondence to joseph.knapik@JSOMonline.org
1 MAJ (Ret) Knapik served in the US military as a wheel vehicle mechanic, medic, Medical Service Corps officer, and Department of Defense civil-
ian. He is currently a senior epidemiologist/research physiologist with the Henry M. Jackson Foundation and an adjunct professor at Uniformed
Services University (Bethesda, MD) and Bond University (Robina, Australia). LTC (Res) Epstein served in the Israel Defense Force as head of the
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Institute of Military Physiology. He is currently a full professor in the Sackler Faculty of Medicine at Tel Aviv University, head of Environmental
Physiology in the Sylvan Adams Sport Institute at Tel Aviv University, and a senior researcher in the Heller Institute of Medical Research, at the
Sheba Medical Center, Tel Hashomer, Israel.
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