Hyponatremia is when the serum sodium is below 136 mmol/L. An athlete tends to develop symptoms when the serum sodium is below 125 mmol/L.
Factors contributing to its development:
(1) salt loss through sweating
(2) replacement with water or hypotonic fluids
(3) release of interleukin-6 from muscle
(4) secretion of antidiuretic hormone (ADH, arginine vasopressin)
Athletes at risk:
(1) female gender
(2) prolonged periods of exercise (marathon, ultramarathon, triathlon)
Clinical findings:
(1) nausea and vomiting
(2) obtundation (associated with cerebral edema)
(3) noncardiac pulmonary edema
(4) often oliguria
(5) The patient may be hypovolemic, euvolemic or hypervolemic.
The diagnosis may be difficult if the serum sodium is not measured.
Complications if aggressively treated (damned if you):
(1) central pontine myelinolysis
Complications if not treated (damned if you don't):
(1) hyponatremic encephalopathy
Differential diagnosis:
(1) hypernatremic encephalopathy
