Hypernatremia and intravenous fluid resuscitation in collapsed ultramarathon runners

Objective: To determine if a return to normonatremia is required for symptomatology to resolve in collapsed hypernatremic runners and if intravenous (IV) administration of an isotonic solution would adversely affect serum sodium concentration ([Na+]) in collapsed normonatremic runners. Design: Observational study. Setting: 2006 Comrades Marathon. Participants: 103 collapsed runners. Main Outcome Measure: Final serum [Na+] upon discharge. Results: 58% of all collapsed runners were hypernatremic. Hypernatremic runners reported significantly more vomiting than normonatremic runners (79 versus 34%; P < 0.001). A significant decrease in serum [Na+] in hypernatremic collapsed runners occurred after the IV administration of either 1L of 0.45% normal saline (150.5 +/- 3.5 versus 148.0 +/- 4.6; P < 0.05) or Ringers lactate solution (147.7 +/- 2.2 versus 146.2 +/- 2.1; P < 0.05). One liter of IV fluid administration caused an increase in plasma volume that was not significantly different between (1) hypernatremic runners receiving a hypotonic solution (13.5 +/- 12.7%) and (2) normonatremic runners receiving an isotonic solution (15.6 +/- 11.3%). The final serum [Na+] of hypernatremic runners was above the range for normonatremia upon discharge (> 145 mmol/L). Conclusions: A return to normonatremia was not required for hypernatremic runners to recover and be discharged from the medical tent. Vomiting either aggravated and/or facilitated the development of hypernatremia. IV administration of I L of either (1) a hypotonic solution to hypernatremic runners or (2) an isotonic solution to both normonatremic and hypernatremic runners did not produce any adverse biochemical or cardiovascular changes and can therefore be considered a safe and effective treatment for collapsed runners if used in this context.