Objective: To determine whether asymptomatic exercise-associated hyponatremia (EAH) in ultramarathon runners can be corrected with either oral or intravenous (IV) 3% hypertonic saline (HTS).
Design: Prospective with randomization into 1 of 2 intervention arms.
Setting: Western States (161 km) Endurance Run, California.
Participants: Forty-seven finishers in the event consented to be screened to identify those with EAH, defined as plasma sodium ([Na+]p) <135 mmol/L at race end.
Interventions: Participants with EAH but without symptoms were randomized to receive a single 100 mL dose of either oral or IV 3% HTS. Blood was drawn before intervention and at 60 minutes postintervention to measure [Na+]p, and concentrations of plasma potassium, proteins, and arginine vasopressin (AVP). Body mass, percent total body water, and percent body fat were measured prerace and postrace using impedance scales.
Main Outcome Measures: Change in [Na+]p.
Results: Fourteen of 47 consenting finishers (30%) had EAH. Eight agreed to be randomized into the intervention protocol. Only in the IV group did [Na+]p change significantly (from 130.8 to 134.6 mmol/L) over the 60 minutes post-HTS administration. Elevated AVP concentrations were seen at race finish in both the groups and remained so after HTS treatment.
Conclusions: In this preliminary trial, prompt administration of a 100 mL bolus of IV 3% HTS was associated with normalization of [Na+]p in asymptomatic EAH, but a similar effect was not demonstrated for the same dose orally. Elevated AVP levels were observed and may play a part in the development of EAH but were not suppressed significantly by either intervention.