[Hyponatraenmia during a long-distance run: due to excessive fluid intake]

Hyponatraemia during a long-distance run, such as a marathon, is usually mild and asymptomatic. However, in runners who present with symptoms at a healthcare station, the diagnosis of hyponatraemia can have significant consequences. The complaints are usually aspecific, but in more severe hyponatraemia, signs of cerebral dysfunction due to incipient to severe cerebral oedema predominate. The most important aetiological factor is an excessive electrolyte-free fluid intake. The most important risk factors for the development of hyponatraemia are: a long duration of the run, female gender, recent use of NSAIDs, lower body weight and environmental factors like high temperature and high humidity. In the presence of symptoms, rapid correction must be started by administration ofhypertonic saline, sometimes in combination with a loop diuretic in cases of eu- and hypervolaemia. Isotonic saline must be added in case of dehydration. Prevention consists primarily of advice to moderate the fluid intake.