Exertional Heat Illness and Hyponatremia: An Epidemiological Prospective

by R. Carter
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA489367&Location=U2&doc=GetTRDoc.pdf

While performing demanding physical activity for long durations, fluid and electrolyte imbalance is common in athletes, military personnel, and recreational hikers. The military and civilian communities have introduced extensive heat mitigation measures to manage heat strain and reduce the risk of serious exertional heat illnesses (EHI). These heat mitigation measures include fluid and electrolyte replacement guidelines, vigilance, and identifying high-risk individuals. Despite these measures, exercise in hot weather continues to result in preventable injuries and deaths in young, healthy individuals. With existing emphasis on appropriate fluid intake during exercise for the avoidance of dehydration, heat illness, and associated performance decrements, there has been a subsequent increase in reported exertional hyponatremia (HYPO) cases related to excessive water intake, elevated sweating rates, excessive sodium losses in sweat, and inadequate sod ium intake in soldiers (1), athletes (2,3,4), and recreational hikers (5,6). The primary purpose of this article is to systemically examine the epidemiological literature of fluid and electrolyte imbalances that occur during physical activity. The secondary purpose of this article is to examine signs and symptoms of HYPO and EHI cases from the literature (1,2,5,7Y26) and the U.S. Army Research Institute of Environmental Medicine (USARIEM) Total Army Injury and Health Outcomes Database (TAIHOD). While it is acknowledged that the populations at risk for HYPO and EHI may differ, reasonable comparisons are made by examining incidence rates to better understand relative magnitude of each condition. It has been reported that these two conditions have several overlapping clinical features, which has led to misdiagnosis in some rare cases. This article is not intended to persuade the reader of the relative importance of either condition.