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Diagnosis and prevention of hyponatremia at an ultradistance triathlon
D B Speedy1, I R Rogers, T D Noakes
1Department of General Practice and Primary Care, University of Auckland, New Zealand.
Objective:
To evaluate a method of medical care at an ultradistance triathlon, 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 availability of fluid. A body weight measurement before the race was introduced as a compulsory requirement, so that weight change during the race could be 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 incidence 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 athletes receiving medical care for hyponatremia, from 25 of the 114 athletes who received care in 1997 (3.8% of race starters) to 4 of the 117 athletes who received care in 1998 (0.6% of race starters). Mean weight change among athletes 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 hyponatremia.