Exercise-associated Hyponatremia Research Articles

Exertional heat illness and hyponatremia in hikers

We compared clinical presentation and course of exercise-associated hyponatremia with heat exhaustion among summertime hikers in Grand Canyon National Park. Cases were selected from among hikers who requested medical help from the National Park Service Emergency Medical Service (EMS) or who presented to the medical clinic on the rim of the canyon with complaints related to exercise in the heat. Of 44 patients who had serum samples analyzed, 7 had hyponatremia with clinically significant symptoms and serum sodium levels <130 mmol/L: 3 had grand mal seizures, 2 had other major central nervous system disorders, and 2 had minor neurological symptoms. Seizures and change of mental status distinguished hyponatremia, ( P = 0.0002). Indirect evidence suggests that hyponatremic patients were hyperhydrated. Other common symptoms included nausea, vomiting, headache, and dizziness, but these symptoms did not predict the level of serum sodium. When exercise in the heat is prolonged, hyponatremia is suggested either by altered mental status or by seizures without hyperpyrexia or hypoglycemia. No mortality or long-term morbidity occurred in any of these cases of hyponatremia.

Use of a Handheld, Battery-operated Chemistry Analyzer for Evaluation of Heat-related Symptoms in the Backcountry of Grand Canyon National Park: A Brief Report

Study objectives: To test the feasibility of using handheld, battery-operated chemical analyzers by EMS personnel in a wilderness environment to aid in the diagnosis and management of heat illness. Methods: During the summer of 1996, 3 portable clinical analyzers (i-STAT Corp, Princeton, NJ) were kept at different locations along the main hiking trail into the Grand Canyon. An operational protocol was designed for field use, and Park Service EMS personnel used the instruments at their discretion, primarily to determine serum sodium concentration and identify cases of hyponatremia. Data were collected on all EMS encounters. This study reviews our experience with the instruments. Results: The i-STAT analyzer was used for 64 patients in the backcountry; of these uses, at least 22 were in the field and the remainder in backcountry ranger stations. Eight error messages were recorded in 6 patients. Subsequently, all but 1 had a successful determination. Among patients evacuated for further evaluation and care, serum sodium values were highly consistent with later analysis using standard laboratory equipment. The instrument was used in 31 (48%) of 64 of patients evaluated and released for self-treatment and self-evacuation, and 31 (36%) of 87 of patients evacuated by EMS personnel from the canyon. Nine cases of hyponatremia were confirmed in the field, allowing appropriate intervention. Conclusion: Portable clinical analyzers can reliably be used in a hot wilderness environment. In our application, it allowed identification of exercise-associated hyponatremia, an important cause of serious heat illness during endurance exercise in a hot environment. The results helped make treatment and disposition decisions.[Backer HD, Collins S: Use of a handheld, battery-operated chemistry analyzer for evaluation of heat-related symptoms in the backcountry of Grand Canyon National Park: A brief report. Ann Emerg Med April 1999;33:418-422.]

Exercise-associated hyponatremia in Alaskan sled dogs: urinary and hormonal responses.

Exercise-associated hyponatremia occurs in horses and humans, both species that sweat, and in sled dogs, which do not sweat. To investigate the mechanism of exercise-associated hyponatremia in sled dogs, we measured water turnover, serum electrolyte concentrations and osmolality, plasma renal hormone concentrations, and urine composition of 12 fit Alaskan sled dogs before, during, and after a 490-km sled dog race (Ex group). Water turnover and serum electrolyte concentrations were measured in six similarly fit dogs that did not run (Sed group). Water turnover was significantly larger (P < 0.001) in Ex [190 +/- 19 (SD) ml . kg-1 . day-1] than in Sed dogs (51 +/- 13 ml . kg-1 . day-1). There were significant (P < 0.001) decreases in serum sodium concentration (from 148.6 +/- 2.8 to 139.7 +/- 1.9 mmol/l) and osmolality (from 306 +/- 9 to 296 +/- 5 mosmol/kgH2O) of Ex, but not Sed, dogs during the race. Plasma concentrations of arginine vasopressin decreased, whereas aldosterone and plasma renin activity increased significantly (P < 0. 01) during the race. Urine osmolality was unchanged, whereas urine sodium, potassium, and chloride concentrations decreased significantly (P < 0.05) and urine urea concentration increased (P = 0.06). These results demonstrate increased water turnover associated with hyponatremia and renal sodium conservation with maintained high urine osmolality in exercising Alaskan sled dogs.

This Month in the Journal

This Month in the Journal

Enzyme blood levels and water balance during a marathon race.

Enzyme blood levels and water balance during a marathon race.

Serum electrolyte changes after marathon running.

Serum electrolyte changes after marathon running.