Three cases of severe hyponatremia during a river run in Grand Canyon National Park

We present 3 cases of severe hyponatremia occurring on a commercially guided river rafting trip on the Colorado River in Grand Canyon National Park. All 3 women appeared to have been overhydrating because of concern about dehydration and required evacuation within 24 hours of each other after the staggered onset of symptoms, which included fatigue and emesis progressing to disorientation or seizure. Each was initially transferred to the nearest hospital and ultimately required intensive care. Imaging and laboratory data indicated all 3 patients had hypervolemic hyponatremia. Unlike the well-documented exercise-associated hyponatremia cases commonly occurring in prolonged endurance athletic events, these 3 unique cases of acute hyponatremia were not associated with significant exercise. The cases illustrate the diagnostic and treatment challenges related to acute hyponatremia in an austere setting, and underscore the importance of preventive measures focused on avoidance of overhydration out of concern for dehydration.