Efficacy of oral versus intravenous hypertonic saline in runners with hyponatremia.

Objectives: To determine more conclusively whether intravenous (IV) administration of 3% saline is more efficacious than oral administration in reversing below normal blood sodium concentrations in runners with biochemical hyponatremia.

Design: Randomized controlled trial.

Methods: 26 hyponatremic race finishers participating in the 161-km Western States Endurance Run were randomized to receive either an oral (n=11) or IV (n=15) 100mL bolus of 3% saline. Blood sodium concentration (Na(+)), plasma protein (to assess %plasma volume change), arginine vasopressin (AVP), blood urea nitrogen (BUN) and urine (Na(+)) were measured before and 60 min following the 3% saline intervention.

Results: No significant differences were noted with respect to pre- to post-intervention blood [Na(+)] change between intervention groups, although blood [Na(+)] increased over time in both intervention groups (+2 mmol/L; p<0.0001). Subjects receiving the IV bolus had a greater mean (± SD) plasma volume increase (+8.6 ± 4.5% versus 1.4% ± 5.7%; p<0.01) without significant change in [AVP] (-0.2 ± 2.6 versus 0.0 ± 0.5 pg/mL; p=0.49). 69% of subjects completing the intervention trial were able to produce urine at race finish with a mean (± SD) pre-intervention urine [Na(+)] of 15.2 ± 8.5 mmol/L (range 0-35; NS between groups). [BUN] of the entire cohort pre-intervention was 30.7 ± 10.5mg/dL (range 13-50).

Conclusions: No group difference was noted in the primary outcome measure of change in blood [Na(+)] over 60 min of observation following a 100mL bolus of either oral or IV 3% saline. Administration of an oral hypertonic saline solution can be efficacious in reversing low blood sodium levels in runners with mild EAH.