The 2017 Marine Corps Marathon was one 2nd warmest on record and the second busiest in the medical tents. Temperatures started at 53.2 degrees F and reached a max of 77.3 degrees F. WBGT readings done every hour at three locations on the course. With a low of 53.2 at 0800 and a high of 73.9 at 1400 on the course. Of our 42 transports 22 were heat related and one runner; a 61 yo female runner presented confused, with several bouts of nausea and vomiting and a serum sodium of 131 mmol/L.

Various references define hyponatremia as a serum sodium <135 mmol/L and critical hypernatremia as <120 mmol/L. Other risk factors include fluid intake, gender, exercise duration > 4 hours, pre-exercise over hydration, easy access to fluids on the course and temperature. Symptoms range from confusion, nausea, vomiting, confusion, seizures and unresponsiveness. Some runners have low serum sodium levels and no visible symptoms.

The discussion point I bring up is testing and treatment. Should all runners presenting with symptoms of hyponatremia have sodium levels tested prior to the introduction of an IV? In cases where athletes are picked up on the racecourse and transported immediately by EMS service, should an IV be withheld until testing is complete? There are events that have few if any aid stations and protocols that do not cover all these possibilities. Would you start an IV on a runner in your aid station without a serum sodium level?