Sodium status of collapsed marathon runners.

CONTEXT: Recommendations for prevention and treatment of medical emergencies in participants in marathon races center on maintenance of adequate hydration status and administration of fluids. Recently, new recommendations for fluid replacement for marathon runners were promulgated by medical and athletic societies. These new guidelines encourage runners to drink ad libitum between 400 and 800 mL/h as opposed to the previous "as much as possible" advice.

OBJECTIVE: To assess the sodium and hydration (plasma osmolality) status of collapsed marathon runners after the promulgation of new hydration guidelines.

DESIGN: Plasma sodium and osmolality values of runners who presented to the medical tent at the finish line of the 2003 Boston Marathon were measured.

RESULTS: Using reference ranges derived from the general population, of 140 collapsed runners, 35 (25%) were hypernatremic (sodium, >146 mEq/L) and 6 (12%) were hyperosmolar (osmolality, >296 mOsm/kg H(2)O), whereas 9 (6%) were hyponatremic (sodium, <135 mEq/L) and 8 (16%) were hypo-osmolar (osmolality, <280 mOsm/kg H(2)O). Compared with a population of marathon runners who had experienced no medical difficulties, 9% of the runners were hypernatremic, 5% were hyponatremic, 8% were hypo-osmolar, and none were hyperosmolar.

CONCLUSIONS: Our findings indicate a significant incidence of hypernatremia with hyperosmolality and hyponatremia with hypo-osmolality among collapsed runners despite the new fluid intake recommendations, suggesting that either further educational measures are required or that the new guidelines are not entirely adequate to prevent abnormalities in fluid balance. Furthermore, the immediate medical management of hypernatremia and hyponatremia is different. Administration of fluids to severely hyponatremic patients may result in fatal cerebral edema. Our findings caution against institution of treatment until laboratory tests determine the patient's sodium status.