CHAPTER 39 • ENVIRONMENTAL INJURIES 235HEAT ILLNESS
DEFINITIONS
- Heat illness is best thought of as a continuum of dis-
ease that progresses along a spectrum from the mild
(heat cramps), through the moderate (heat exhaus-
tion), to the life-threatening (heatstroke). Heat cramps
are involuntary, painful contractions of skeletal
muscle typically occurring during or after prolonged
exercise. Heat exhaustion is a sign of systemic vascu-
lar strain in the body’s attempt to maintain normoth-
ermia—untreated it will progress to heatstroke.
Heatstroke occurs when heat generation exceeds heat
loss leading to a rise in core temperature and ther-
moregulatory failure. Classical heatstroke is confined
to individuals without access to cool environments or
debilitated by medical illness. Exertional heatstroke is
the form most common in athletes.
EPIDEMIOLOGY
- Frequency correlates with the wet bulb globe temper-
ature(WBGT). WBGT =(wet bulb temp ×0.7) +(dry
bulb ×0.1) +(black globe ×0.2) where the wet bulb
represents the humidity, the dry bulb the air tempera-
ture, and the black globe the radiant heat. - Risk factors for exertional heatstroke include obesity,
dehydration, fatigue, recent episode of heat illness,
concomitant febrile illness, wear of impermeable gar-
ments, lack of acclimatization, sustained exercise,
use of medicines, or supplements that decrease
sweating and increase thermogenesis (antihistamines,
ephedra, caffeine, diuretics) (Haller and Benowitz,
2000).
PATHOPHYSIOLOGY- The cause of heat cramps is unclear. Heat illness
occurs when heat storage outpaces heat loss that
leads to deleterious changes at the cellular level. Core
temperature > 41 °C leads to a release of many inflam-
matory mediators to include interleuken 1 (IL-1),
interleuken 6 (IL-6), and tumor necrosis factor
(TNF). These cytokines amplify cellular and
endothelial damage that triggers systemic vascular
collapse and multiorgan failure (Khosla and Guntupalli,
1999).
CLINICAL FEATURES- Symptoms of heat exhaustion and heatstroke overlap.
The diagnosis of heatstroke rests not on absolute tem-
perature criteria—rather it is due to the presence of an
altered mental status and the progression of disease
despite first line treatments. Initial symptoms include
headache, dizziness, fatigue, irritability, anxiety,
chills, nausea, vomiting, and heat cramps. Seizures
and disordered thoughts are evidence of heatstroke. - Signs include a core temperature greater than 39.4°C,
tachycardia, hyperventilation, hypotension, and syn-
cope. Temperature elevations greater than 41°C
(106°F), a lack of spontaneous cooling with cessation
of exertion, and profuse sweating that ceasesdespite
an elevated core temperature are all ominous signs
that point toward heatstroke.
DIAGNOSIS- The diagnosis hinges on an elevated core temperature
combinedwith the presence of the symptoms and
signs noted above. Ideally this temperature should be
rectal. Any collapse during exertion should include
heat illness in the differential and early core tempera-
ture measurement is crucial. Of note, healthy athletes
can raise their core temperature to 39°C simply from
exertion alone and be asymptomatic. - Laboratory tests are normal until heatstroke is present.
Lab alterations such as increased liver function tests,
disordered coagulation profile, leukocytosis, elec-
trolyte disturbances, and evidence of acute renal fail-
ure are nonspecific and similar to other shock states.
TREATMENT- The key is to not delay treatment while trying to
determine where on the continuum of heat illness a
TABLE 39-3 Stepwise Treatment of Frostbite
Treat hypothermia and any concomitant injuries.
Rapidly rewarm the affected parts in water at 40–42°C (104–108°F)
until thawing is complete and the skin is pliable in texture.
(Typically 15–30 min of rewarming).
Debride blisters filled with clear or milky fluid. Apply Aloe Vera
(at least 70%; Dermaide Aloe). Cover with a bulky dressing.
Leave hemorrhagic blisters intact.
Splint and elevate the extremity.
Administer ibuprofen orally at standard doses. (Avoid aspirin or
steroids, but consider use of pentoxyfylline 400 mg po tid).
Give tetanus toxoid and tetanus immune globulin if >10 years since
last booster.
Administer IV penicillin 500,000 units q. 6 hours for 72 hours.
(Clindamycin is the recommended alternative for penicillin
allergic patients)
Treat pain with parenteral narcotics as needed.
Begin daily hydrotherapy with hexachlorophene at 40°C for
30–60 min daily.
No smoking.