May 5, 2000 -- Seven marathoners were admitted recently to an ER with nausea, vomiting, mental confusion and pink, frothy fluid in their lungs. All of them had the potentially fatal condition pulmonary edema, in which fluid accumulates in the lungs. All but one of the patients were tested and treated for excess fluid in the brain. The seventh patient was not tested for edema and died from the fluid in the lungs and brain.
Doctors who studied these cases found that the main culprit was sodium loss during intense exercise, causing the excess fluid to build up in the brain and lungs.
"Heat stroke isn't the only reason that runners collapse after marathons," study author J. Carlos Ayus, MD, tells WebMD. "And if left untreated, sodium loss can be fatal."
Ayus, a kidney specialist and professor at Baylor College of Medicine in Houston, and his colleagues published their findings in the May issue of Annals of Internal Medicine. They report that diagnostic tests showed sodium losses of up to 13%. The patients were placed on ventilators and treated with intravenous salt solution. Over 12 hours, lung fluid and brain swelling decreased as sodium levels increased.
The authors believe low sodium first causes brain swelling, which then causes a build up of fluid
in the lungs. "Doctors need to be aware of the association between these two conditions," says Ayus, "because successful therapy depends on it."
During exercise, blood is directed from the stomach to the muscles, causing ingested fluid to remain in the gut. After exercise, blood returns to the stomach, allowing ingested fluid to be quickly absorbed by the bloodstream. But because marathoners have sweated for hours, this high volume of fluid is often low in sodium.
To prevent sodium loss, sports medicine experts advise sodium loading. "Marathoners should use table salt before races, drink sports beverages during races, and eat salted pretzels in the last half," says Lewis Maharam, MD. Maharam, the medical director of two marathons and a board member of the International Medical Marathon Directors Association, commented on the study for WebMD.