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 race course 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?