Moderate Exercise-Induced Hyponatremia

Abstract

H yponatremia in exercise is a potentially dangerous clinical scenario previously thought to be limited to exercise bouts of long duration and associated with excessive water intake. We report the case of a healthy young athlete with hyponatremia after moderate-duration exercise and only moderate water intake. CASE REPORTA 19-year-old female novice triathlete presented with abrupt onset of dull, bioccipital headache associated with mild photophobia; nausea with clear, watery emesis; and generalized malaise 90 minutes after completing a sprint distance event (0.4-km swim, 17-km bike, and 5-km run) in 1 hour 33 minutes. The outdoor ambient temperature at the race's completion at approximately 9 AM was 32°C. She reported hydration with 3 L of water the evening before the race, approximately 500 mL during the race, and 700 mL after the race. Her food intake was minimal on the morning of the race.Although she was an inexperienced triathlete, she was physically fit (weight, 57 kg; height, 160 cm; body mass index, 22 kg/m 2 ) and finished the race first among female novices. The patient's medical history included exercise-induced bronchospasm and a seizure disorder that had been asymptomatic for years. For seizure prophylaxis, she was taking carbamazepine and lamotrigine, tapering down her carbamazepine while increasing her lamotrigine. Serum levels of carbamazepine and sodium drawn 3 days before the race were 5.7 mg/mL (therapeutic range, 4-10 mg/mL) and 142 mmol/L, respectively.Physical examination revealed an oral temperature 36.1°C, heart rate of 70 beats/min, blood pressure of 128/82 mm Hg without orthostatic change, and respiratory rate of 12 breaths/min. She was alert and oriented, with equal and reactive pupils, intact extraocular motion, and a noticeable tearing mechanism. Her oral mucus membranes were moist, her skin was cool and moist, and she had no detectable edema. Findings on cardiac, pulmonary, abdominal, and neurologic examinations were all normal, as was her mental status. Possible hyponatremia was diagnosed, and she was transported to a local emergency department for further evaluation and management.Laboratory studies in the emergency department confirmed the diagnosis: sodium, 127 mmol/L; potassium, 3.5 mmol/L; chloride, 97 mmol/L; bicarbonate, 21 mmol/L; glucose, 4.8 mmol/L; creatinine, 88.4 mmol/L; urea nitrogen, 3.6 mmol/L; and serum osmolality, 254 mOsm/kg.

Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015

“…For instance, symptomatic EAH has been reported in shorter distance endurance competitions, such as a half marathon79 with slower finishers completing the distance in 2–3 h and a sprint triathlon with slower finishers taking approximately 2 h to complete 80. In addition, EAH has been reported in US professional and college American rules football players,40 41 and has led to the deaths of three US high school football players between 2008 and 2014 63 64 69.…”

“…On departure from the event site, athletes with asymptomatic EAH should be advised to seek urgent medical attention if any neurological signs or symptoms of EAH develop within 24 h after event completion, since delayed-onset symptomatic EAH may frequently occur 40 42 46 52 72 80 82 91 100 122 156. Ideally, an athlete with asymptomatic EAH should have a companion on discharge from the medical area to observe the affected athlete for signs and symptoms of evolving EAH, since the neurological impairments associated with EAH may limit the athlete's ability to accurately self-assess his or her own status.…”

Prevalence of Hyponatremia, Renal Dysfunction, and Other Electrolyte Abnormalities Among Runners Before and After Completing a Marathon or Half Marathon

“…Recognized risk factors for exercise-associated hyponatremia (but not necessarily renal dysfunction or hemoconcentration) include female sex 2,4,14,22,41 and event inexperience. 22,39,53 …”

Exercise-Associated Hyponatremia

“…This was the case for one female runner who drank 10 L of fluid on the evening before a marathon and then experienced postrace hyponatremia (57).…”