Exercise-Associated Hyponatremia

An excellent case report, entitled "Severe Exercise-Associated Hyponatremia on the Kokoda Trail, Papua New Guinea," appears in the first issue of Volume 19 of the journal Wilderness & Environmental Medicine. Sean Rothwell and his co-authors describe the plight of a 43 year old man who collapsed and had a seizure in the afternoon of the third day of a guided trek. The amount of sodium in his blood was found to be dangerously low, and was attributed to (presumed) fluid replacement with water without sufficient electrolyte supplementation.

Exercise-associated hyponatremia (low serum [in the blood] sodium) is a common complication of "ultradistance" exercise and other situations (e.g., heavy sweating) in which there are large fluid losses without adequate sodium replacement. When someone becomes hyponatremic (e.g., suffers from low serum sodium) to the extent that symptoms appear, the following are noted: nausea, vomiting, headache, weakness, fatigue, muscle weakness, difficulty with balance and walking, confusion, fluid in the lungs (shortness of breath and coughing, sometimes productive of frothy and/or blood-tinged sputum), and seizures. The condition can be fatal. Other conditions, such as dehydration, can cause the same symptoms. If the person is known to have ingested a large amount of plain water without any electrolyte supplementation, then hyponatremia should be suspected.

According to the authors, risk factors for the development of exercise-associated hyponatremia are low body weight, female gender, greater than 4 hours of continuous exercise, slow performance pace, inexperience with the activity, excessive water drinking, kidney dysfunction, and hot environmental conditions.

If someone is felt to suffer from exercise-associated hyponatremia, he or she should be prevented from making the situation worse. In other words, any ingested fluid must be high in sodium content. If the victim is in a very bad condition, such as suffering from seizures, then it will be necessary to have a medical provider initiate an intravenous line in order to administer fluid with high sodium content. If the victim is short of breath and supplemental oxygen is available, it should be given.

The best way to prevent exercise-associated hyponatremia is to be certain that fluid replacement during times of heavy exertion and sweating takes into account fluid losses. There is no absolute prescription for success with regard to prevention. Some experts believe that in an endurance situation (e.g., adventure race), fluid replacement should be guided by thirst, while other experts believe that thirst alone underestimates fluid requirements. The ingestion of electrolyte-containing beverages (e.g., "sports drinks") has not been shown to prevent the development of exercise-associated hyponatremia in athletes who drink "to excess." The precise definition of "to excess" remains to be determined. In general, it is prudent to drink enough liquids to keep one's urine copious and light-colored, but now so much that excessive urination or bloating are the results of personal oral hydration efforts.

image of the Kokoda track (trail) courtesy of www.peregrineadventures.com

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Tags: fluid replacement, hyponatremia, wilderness medicine, outdoor medicine, healthline

Labels: dehydration, exercise, fluid replacement, hyponatremia

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