• Ian R Rogers, Ginger Hook, Kristin J Stuempfle, Martin D Hoffman, and Tamara Hew-Butler.
• Discipline of Emergency Medicine, University of Western Australia, Western Australia, Australia; Department of Medicine, Sir Charles Gairdner Hospital, Perth, Western Australia, Australia. ian.rogers@health.wa.gov.au
• Clin J Sport Med. 2011 May 1;21(3):200-3.

ObjectiveTo determine whether asymptomatic exercise-associated hyponatremia (EAH) in ultramarathon runners can be corrected with either oral or intravenous (IV) 3% hypertonic saline (HTS).DesignProspective with randomization into 1 of 2 intervention arms.SettingWestern States (161 km) Endurance Run, California.ParticipantsForty-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.InterventionsParticipants 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 MeasuresChange in [Na]p.ResultsFourteen 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.ConclusionsIn 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.2011 by Lippincott Williams & Wilkins.

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