![]() ![]() Mild symptoms include lightheadedness, malaise, fatigue, irritability, generalized weakness, headache, nausea, and sluggish urine output. Presenting symptoms range from asymptomatic, to mild, to severe. The likelihood of EAH is increased if the exertional event occurred over a period greater than 2 hours or in hot weather. Healthcare providers should suspect EAH when athletes present during or within 24 hours following intense physical exertion, such as marathon running, cycling, triathlon, hiking, backpacking, or prolonged military field training or combat operations. Prompt identification and differentiation from other common exertional injuries are essential to caring for an athlete with EAH. Subsequent hyponatremia results in an osmotic gradient that favors free water movement from the vascular space to the extravascular and intracellular spaces, leading to tissue edema (particularly brain and lung), which drives the most severe symptoms of EAH. The retained free water is returned to the extracellular fluid resulting in a net lowering of serum sodium concentration. Elevated ADH leads to stimulation of renal V2 receptors, causing water reabsorption rather than excretion. These stimuli include pain, emotional stress, nausea, emesis, hypoglycemia, heat exposure, and medication use (particularly NSAIDs). It is postulated that stimuli related to physical exertion may result in sympathetic activation of the hypothalamus, which stimulates ADH secretion from the posterior pituitary inappropriately during low osmolar states. The contribution of sodium loss from excessive sweat is controversial and not well characterized, as sweat loss varies greatly between individual athletes. When intake exceeds that of water lost via urine, sweat, and insensible respiratory and gastrointestinal losses (often greater than 1.5 liters), athletes may retain free water, resulting in dilutional hyponatremia. Before and throughout strenuous physical activity, athletes often over hydrate with hypotonic fluids (water, sports drinks). ĮAH stems from both increased consumption of hypotonic fluids and inappropriate water retention. ![]() The incidence in military service members is 6.9 cases per 100,000 person-years. It is estimated that 0.1% to 1.0% of endurance athletes experience symptomatic EAH, with marathon runners, ultramarathon runners, Ironman athletes, long-distance backpackers, and military service members most commonly affected. Incidences of 5-51% are reported following endurance events where athletes are screened, or their serum is analyzed for another reason. ĮAH is commonly an incidental finding in asymptomatic athletes. Non-steroid anti-inflammatory drug use may exacerbate or propagate EAH by potentiating the water retention effects of ADH by the kidney. Low oral intake, specifically of high sodium foods, may also contribute. Men and women are at equal risk for EAH when adjusted for body mass index and exercise duration. The greatest risk factors for EAH are excessive hypotonic fluid consumption beyond the capacity for normal renal free water excretion, high ambient temperature, and longer exercise time, usually exceeding 2 hours. Several studies demonstrate a linear relationship between temperature and incidence of EAH. EAH occurs in a wide variety of athletes in activities of various intensities, including ultramarathon and marathon running, triathlon, shorter distance running, military training operations, team ball sports, recreational hiking, and yoga. ![]()
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