Sodium Status of Collapsed Marathon Runners

Archives of Pathology & Laboratory Medicine, Feb 2005 by Kratz, Alexander, Siegel, Arthur J, Verbalis, Joseph G, Adner, Marvin M, Et al

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 H2O), whereas 9 (6%) were hyponatremic (sodium,

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.

(Arch Pathol Lab Med. 2005;129:227-230)

Many modern-day marathon races are mass events with tens of thousands of participants. Most of these contestants are not professional athletes but recreational runners who are physically challenged by a 42.2-km (26.2-mile) race. In some marathons, hundreds of these amateurs collapse and require immediate medical attention, necessitating the establishment of medical support services at these events.1 Losses of water and electrolytes have historically been assumed to be the dominant cause of collapse in marathon runners. Consequently, the administration of intravenous fluids is frequently the first line of treatment for exercise-associated collapse.1

The best strategy to prevent the development of medical emergencies in marathon runners has been the subject of a longstanding debate centered on the ideal recommendations for fluid intake. From antiquity until the late 1960s, athletes were advised not to drink during exercise.2 This recommendation changed after a series of articles published after 1969 stressed the dangers of dehydration during marathon running. By 1996, various medical and athletic societies had issued forceful guidelines promoting vigorous fluid intake, usually encouraging runners to drink "as much as possible."1,3,4 Data obtained from healthy runners who did not experience any adverse medical events suggest that by 2001 these recommendations were achieving the desired effect and that the biochemical markers of dehydration could be largely mitigated by these recommendations.5 However, although these recommendations may have reduced the prevalence of dehydration among marathon runners, overhydration with hyponatremia has become an increasingly important problem.267 At least 250 cases of cerebral edema, 7 of them fatal, have been reported in the literature.2 Between 1989 and 1999, there were 190 hospitalized cases of water intoxication in the US Army alone, leading to a revision of the fluid replacement guidelines in the military in 1999.8 To protect runners from the effects of overhydration, the International Marathon Medical Directors Association (IMMDA), representing medical experts in the field, and USA Track and Field, the national governing body for long-distance running, also issued new fluid replacement guidelines in 2003. These recommendations advise runners to drink ad libitum between 400 and 800 mL/h, as opposed to the previous "as much as possible" recommendation.1

In view of the controversies and changes surrounding recommendations for fluid replacement for marathon runners, there is a clear need for up-to-date information on the fluid status of collapsed marathon runners. This need arises from the desire to know if the latest recommendations are effective and from the need for data to provide the best diagnostic tools and treatment to collapsed runners. We therefore investigated the incidence of hyponatremia and hypernatremia in a subset of participants in the Boston Marathon of 2003, which took place after the new fluid replacement guidelines were announced.

MATERIALS AND METHODS

Specimens

The study participants included 140 runners who took part in the 107th Boston Athletic Association Marathon in 2003 and who collapsed during or immediately after the race and for whom physicians at the medical station ordered a chemical blood analysis. To participate in the Boston Marathon, runners were required to have run a qualifying time at a certified marathon within the last 18 months. Qualifying times were age and sex specific and between 3 hours 10 minutes and 5 hours 30 minutes. The protocol for this study was approved by the institutional review board of McLean Hospital (Belmont, Mass).