Heat Emergencies and
Heat Injury Prevention
Introduction
Heat emergencies are classified into three distinct categories, heat cramps, heat
exhaustion, and heat stroke. Each develops from the inability to respond adequately to
environmental conditions, inadequate correction of fluid and electrolyte deficiencies, and
a malfunction of the system through exogenous and endogenous causes. Risk factors include
infectious diseases, anticholingeric drugs, neuroleptics, diuretics, anesthetic agents,
and cerebral vascular accidents. Individuals exercising or working in a hot, humid
environment are at risk. This is especially true if they have not taken adequate
fluids/electrolyte solutions, or have consumed moderate to large amounts of alcohol the
night before.
Heat Injuries
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Many of the environments our sailors and Marines work in on a daily or
routine basis are areas of high heat or humidity. From engine rooms to flight decks to
desert sands to topical jungles, heat injuries are potential mission stoppers and are
almost completely preventable with a few basic precautions.
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Heat stroke causes 1200 deaths/year in the U.S.; is the second leading
cause of death in high school athletes, and accounts for 5 percent of hospitalized disease
in enlisted personnel.
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When individuals are going to be exposed to high heat or humidity it
takes approximately 2 weeks to acclimate to such conditions. A schedule of increasing
physical exertion and heat exposure is included in reference (a).
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Individuals with heat exposure can require from 5-13 quarts of water per
day depending upon the type of work they do. A simple rule of thumb is 1 quart or 1
canteen/person/hour and water should be kept cool to encourage consumption. Drinking
enough water to maintain hydration is one of the most important measures necessary to
prevent heat injury. Since thirst is not a good indicator of hydration status (when you
become thirsty you are already too dehydrated), enforced drinking schedules may be
necessary. Remember that prevention of heat injuries is a command responsibility.
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Salt consumption should be slightly increased to compensate for loses due
to sweating. This can be easily accomplished by over salting the food or eating all of the
meals ready to eat (MRE) rations. Since appetite is decreased with the heat, individuals
will need to be encouraged to eat the caloric requirements, which have not changed, and
cold foods are better tolerated in hot climates. Salt tablets are very rarely indicated
and never prescribed on a routine basis. If found in workspaces, confiscate them.
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Heat exposure conditions may require adjustment of work and training
schedules. The Wet Bulb Globe Thermometer (WBGT) determines the environmental heat
conditions. When the WBGT index (from the thermometer) is plotted on the physiological
heat exposure limits (PHEL) curves, the appropriate work/rest times can be determined for
particular types of work.
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All heat injuries require a report to the Navy Environmental Health
Center on NEHC- 5100/3.
Heat Cramps
Heat cramps are characterized by painful spasm of skeletal muscles including the
muscles of the extremities and abdomen, related to sodium and potassium depletion.
Clinically, body temperature is normal and there is rarely evidence of dehydration. This
condition is benign and is easily treated with rest and oral/IV sodium replacement. If the
condition does not resolve in a timely manner with the above treatment, the provider
should consider checking a creatine phosphokinase
(CPK) to rule out exertional
rhabdomyolysis.
Heat Exhaustion
Heat exhaustion is characterized by volume depletion. Fluid and electrolyte losses due
to sweating coupled with inadequate replacement result in hypovolemia and tissue
hypoperfusion. Symptoms include fatigue, vertigo, headache, nausea, vomiting, and finally
impaired judgement, hyperventilation, tachycardia, and hypotension. A headache, weakness,
or transient confusion may be present but there should be no signs of significant global
mental status changes. Core temperature is only moderately elevated (less than 40°C or
104°F). If left untreated, heat exhaustion may lead to heat stroke.
Treatment includes rest in a cool environment with volume and electrolyte
replacement. Rapid administration of moderate amounts of normal saline (1 to 2 L) may be
necessary if significanttissue hypoperfusion is evident. Elderly patients and patients
with moderate to severe symptoms should receive a workup (see heat stroke) and should be
considered for hospital admission.
Heat Stroke
Heat stroke is defined as hyperpyrexia (greater than 40.5°C or 105°F) and
neurological impairment, usually severe CNS dysfunction. While in younger individuals the
onset of heat stroke is most commonly associated with exertional activity; classic heat
stroke is described as non-exertional onset in the elderly. It represents a failure of the
body's thermoregulatory mechanisms. As temperatures climb above 105°F, the normal
cellular systems for tasks such as aerobic metabolism fail. Lack of sweating is often
present; however, patients with early heat stroke will typically demonstrate marked
sweating. In contradistinction to heat cramps and heat exhaustion, heat stroke is a
medical emergency which may result in multisystem tissue damage and organ dysfunction with
a potentially high mortality rate.
The clinical onset of heat stroke begins with alteration of neurological function,
often a sudden loss of consciousness with little or no prodrome. Irritability, bizarre
behavior, combativeness, hallucinations, or coma may occur. Virtually any neurological
abnormality may be present, and signs of trauma should be assessed.
On presentation, the provider should immediately measure core temperature. A
conservative approach should be taken as the patient may present with a lower than peak
core temperature if cooling measures have already been initiated. The primary goal in
treatment is rapid reduction of body temperature. This can be achieved initially by
removing the patient from external sources of heat, removing clothing, and applying cool
or ice water to the entire skin surface, and fanning with humidified air/mist.
Additional immediate supporting measures should include oxygen therapy or endotracheal
intubation, and IV fluid administration. It is important to note that dehydration and
volume depletion may be limited in heat stroke (the majority of previously healthy
individuals have lost approximately 2 liters), as opposed to heat exhaustion, and
overzealous fluid administration may produce pulmonary edema (especially in the elderly).
This is compounded by the predisposition of heat stroke patients to circulatory failure. A
nasogastric (NG) tube and Foley catheter should be placed and urine output monitored. If
there is inadequate urine output after continued IV fluid resuscitation, osmotic diuretics
may be considered. Small doses of benzodiazepines may assist in controlling shivering and
agitation. Antipyretic agents are not indicated.
Labs should be drawn for CBC, platelets, PT/PTT, electrolytes (including calcium, magnesium, and phosphate), glucose, BUN, creatinine, CPK, liver function tests, urinalysis, and urine for
myoglobin. An ECG and chest x-ray should be performed. If an
arterial blood gas (ABG) is deemed necessary, the lab should be informed of the patient's
body temperature in order to make corrections in determining the results. As in any
patient with altered mental status and fever, a toxicologic screen and lumbar puncture may
be indicated if the etiology is unclear.
Additional methods of reducing the patient's body temperature include hypothermia
blankets, iced water gastric lavage, enemas, bladder irrigation, and peritoneal lavage.
These aggressive measures should be ceased when shivering begins or the temperature is
less than 102° F. Submersing a patient in an iced bath may produce intense
vasoconstriction and decrease heat transfer from the skin. All patients suffering from
heat stroke should be hospitalized for potential complications, which can include the
following: heart failure, cardiovascular collapse, hepatic failure, disseminated
intravascular coagulation (DIC), rhabdomyolysis, cerebral edema, pulmonary edema, and
myoglobinemia with renal failure.
Prevention of heat stroke should follow these basic tenets:
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Conditioning and acclimation to environmental heat.
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Adequate fluid intake (600-1200 cc/hr) with strenuous activity.
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Avoidance of strenuous activity during peak hours of hot, humid weather.
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Avoidance of strenuous activity with certain medications (thyroid drugs, sympathomimetics, antihistamines, sedatives, and phenothiazines).
References
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Emergency Medicine: A Comprehensive Study Guide, 3rd Ed. Tintinalli et al. McGraw-Hill,
1996.
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Emergency Medicine: Concepts and Clinical Practice, 3rd Ed. Rosen et al. Mosby, 1992.
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NAVMED P-5052-5, Technical Information Manual for Medical Corps Officers, chapter 5,
(1980) Prevention and Control of Heat Injuries. S/N 0510-LP-060-005.
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NEHC-TM92-6, June 1992, Prevention and Treatment of Heat and Cold Injuries.
Revised by LCDR A. Johnson, MC, USN and LCDR L. Schenden, MC, USNR, Department of
Emergency Medicine, Naval Medical Center San Diego, San Diego, CA (1999).
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Preface
· Administrative Section
· Clinical Section
The
General Medical Officer Manual , NAVMEDPUB 5134, January 1, 2000
Bureau
of Medicine and Surgery, Department of the Navy, 2300 E Street NW, Washington, D.C.,
20372-5300
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