Trawling through the medical journals, as I do!
I found an interesting article and consensus on the pathophysiology and treatment of hyponatraemia. Exercise-Associated Hyponatremia: Overzealous Fluid Consumption, Wilderness and Environmental Medicine: Vol. 20, No. 2, pp. 139–143.
The medical profession is certainly engaging with this increasingly prevalent condition. This particular article approaches the condition from a wilderness perspective and hence is more appropriate for expedition medical professionals. In essence Exercise-associated hyponatremia is hyponatremia occurring during or up to 24 hours after prolonged exertion. In its more severe form, it manifests as cerebral and pulmonary edema. There have now been multiple reports of its occurring in a wilderness setting.
It can now be considered the most important medical problem of endurance exercise. The Second International Exercise-Associated Hyponatremia Consensus Conference gives an up-to-date account of the nature and management of this disease. This article reviews key information from this conference and its statement. There is clear evidence that the primary cause of exercise-associated hyponatremia is fluid consumption in excess of that required to replace insensible losses.
This is usually further complicated by the presence of inappropriate arginine vasopressin secretion, which decreases the ability to renally excrete the excess fluid consumed. Women, those of low body weight, and those taking nonsteroidal anti-inflammatory drugs are particularly at risk. When able to be biochemically diagnosed, severe exercise-associated hyponatremia is treated with hypertonic saline.
In a wilderness setting, the key preventative intervention is moderate fluid consumption based on perceived need (“ad libitum”) and not on a rigid rule.