These are painful, involuntary, spasmodic contractions of skeletal muscles, usually those of the calves, although they may involve the thighs and shoulders. Heat cramps usually occur in individuals who are sweating liberally and replace fluid loss with water or other hypotonic solutions. Cramps may occur during exercise or after a latent period of several hours. Unconditioned or nonacclimatized individuals who are just starting manual labor in a hot environment are at high risk for developing heat cramps. Although heat cramps usually do not cause significant morbidity and are considered to be self-limiting, the pain associated with them can readily result in an emergency department visit. In fact, the pain is commonly recalcitrant to the effects of narcotics alone.
The exact pathogenesis of heat cramps is not known but is generally accepted to be a relative deficiency of sodium, potassium, and fluid at the cellular level. The production of large amounts of sweat, which has a high sodium content, coupled with inadequate sodium replacement results in hyponatremia. This in turn produces muscle cramps by interfering with calcium-dependent muscle relaxation. Hypokalemia from hyperventilation and dehydration may also play a contributing role.
Treatment consists of rest in a cool environment and fluid and salt replacement, either orally or intravenously. For mild cases, or if an overwhelming number of patients require treatment, a 0.1% to 0.2% saline solution can be given orally. Many electrolyte drinks are commercially available. More severe cases of heat cramps will respond to intravenous rehydration with normal saline. Rarely, rhabdomyolysis occurs secondary to protracted and diffuse muscle spasm.
Heat cramps can be prevented by maintaining adequate dietary salt intake or by drinking commercial electrolyte beverages. Salt tablets by themselves should not be used because (1) the tablets are a gastric irritant and often result in nausea and vomiting and (2) they do not replace volume.
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