Heat Stroke

Etiology

A) Increased heat production:
1) Cocaine (idiosyncratic reaction: dose and route-independent): due to central neurotransmitter alterations/ increased peripheral muscle tone and contraction/ vasoconstriction (with decreased peripheral heat loss)
2) Other sympathomimetics: amphetamines
3) Exercise:
4) Fever:
5) Thyrotoxicosis:
6) Hypothalamic dysfunction:
7) Environmental heat stress:
B) Decreased heat loss:
1) Environmental heat stress:
2) Heart disease:
3) PVD:
4) Dehydration:
5) Obesity:
6) Skin disease:
7) Anticholinergics: impaired sweating and altered hypothalamic function
8) ETOH: due to diuresis/ vasodilation with heat gain/ impaired perception of environement
9) ß-blockers: due to decreased cutaneous blood flow/ impaired cardiac compensation


Pathogenesis

  • Inability of body to dissipate adequate amonuts of heat -> rise in body temperature

Diagnosis

CBC:
-Hemoconcentration
-Thrombocytopenia (due to thermal platelet destruction and aggregation and also DIC)
-Hemolysis (occurs late)
-DIC (due to thermal endothelial degradation and activation of clotting factors)

CHEM:
-Hypernatremia
-Elevated LFT’s
-Elevated muscle enzymes
-Hypokalemia (may be elevated if rhabdo is severe)
-Hypophosphatemia (may be elevated if rhabdo is severe)
-Hypocalcemia
-Hypoglycemia (some cases)
-Myoglobinuria

ABG: lactic acidosis

EKG: tachyarrhythmias


Clinical

Clinical types (usually sudden onset of symptoms):
1) Exertional Heat Stroke: usually occurs in healthy, young patients (sporadic)
-Neuro (usually non-focal neuro exam): headache/ hyperventilation/ dysarthria/ ataxia/ vertigo/ faintness/ hallucinations/ seizures/ altered MS/ coma/ cerebral edema
-Cardiovascular: tachycardia/ hypotension (with low SVR state/ due to high output heart failure or thermal myocardial damage)
-GI: N/V
-Renal: ARF (due to ATN)
-Other: normal sweating/ hyperthermia (often to >41°C=106°F)/ muscle cramps/ piloerection/ chills/ rhabdomyolysis/ multi-organ failure

2) Classic Heat Stroke: usually occurs in elderly patients during heat waves (epidemic)/ patients usually have chronic disease (like atherosclerosis/ CHF/ DM/ ETOH abuse) or are on a drug that impaires heat loss/ may occur with few warning signs
-Neuro: coma (may occur early)/ headache/ hyperventilation/ vertigo/ faintness/ altered MS/ flaccid muscles with hyporeflexia
-Cardiovascular: tachycardia/ hypotension/ right-sided CHF
-GI: abdominal pain/ hepatic damage (common)
-Renal: ARF (due to ATN)
-Other: abnormal sweating (hot, dry skin)/ hyperthermia (often to rectal temp >41°C=106°F/ internal temperatures have been recorded as high as 113°F)/ weak respirations/ rhabdomyolysis/ multi-organ failure


Treatment

Prevention of exertional heat stroke:
-Run races early in the day
-Water ingestion (avoid salt and glucose solutions)
-Avoid ETOH before race

Heat dissipation: -Remove clothing:
-Ice packs:
-Shower:
-Fan:
-Chilled IV fluids
-Immersion in ice-water bath: used in past, but poses difficulty with resuscitation
-Cooling blankets:
-Gastric and rectal lavage:

Hydration: carefully (since fluid requirement over the first 12 hrs is usually only 1000-1200 mL)
Dantrolene: may be useful


References

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