Diagnosis and prevention of hyponatremia at an ultradistance triathlon

Objective: To evaluate a method of medical care at an ultradistance triathl on, with the aim of reducing the incidence of hyponatremia. Design: Descriptive research. Setting: New Zealand Ironman triathlon (3.8 km swim, 180 km cycle, 42.2 km run). Participants: 117 of 134 athletes seeking medical care after the triathlon (involving 650 race starters). Interventions: A prerace education program on appropriate fluid intake was undertaken. The number of support stations was decreased to reduce the avai lability of fluid. A body weight measurement before the race was introduced as a compulsory requirement, so that weight change during the race could b e included in the triage assessment. An on-site laboratory was established within the race medical tent. Main Outcome Measures: Numbers of athletes and diagnoses, including the inc idence of symptomatic hyponatremia (defined as symptoms of hyponatremia in association with a pretreatment plasma sodium concentration [Na] < 135 mmol /L); weight changes; and changes in [Na]. Results: The common, diagnoses in the 117 athletes receiving attention were exercise-associated collapse (27%), musculoskeletal complaints (26%), and dehydration (12%). There was a significant reduction in the number of athle tes receiving medical care for hyponatremia, from 25 of the 114 athletes wh o received care in 1997 (3.8% of race starters) to 4 of the 117 athletes wh o received care in 1998 (0.6% of race starters). Mean weight change among a thletes in the 1998 race was -3.1 kg, compared with -2.6 kg in 1997. Conclusion: A preventive strategy to decrease the incidence of hyponatremia , including education on fluid intake, and appropriate placement of support stations, was associated with a decrease in the incidence of symptomatic h yponatremia.