Severe hyponatremia develops in a runner following a half-marathon

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Abstract

It's essential to know how to distinguish dehydration from fluid overload in endurance athletes, because the treatment for one can greatly worsen the other.

CASE

A 34-year old woman sought nutritional guidance at our clinic after what she described as a recent episode of dehydration. Medical records were obtained, and the following clinical picture emerged. A month earlier, the patient had participated in a half-marathon running event (21 km, 13.1 miles) conducted in extreme heat (33°C, 100°F). Her training had been limited to exercising on a treadmill 1 to 2 days per week, not exceeding 15 km (9.3 miles) weekly, in air conditioning. Beginning 3 days before the race, she experienced symptoms of viral illness, including nausea and diarrhea, but ran the race regardless.

CASE

She remembered drinking copious amounts of water before the race and approximately another 4 liters of water during the race. Upon returning home, she felt nauseous and confused and, assuming her symptoms were due to the heat, continued drinking. A neighbor brought her to the emergency department (ED) after finding her disoriented.

CASE

Initial ED notes, made approximately 2 hours after the race, note wrist swelling, foggy mentation, BP of 123/80 mm Hg, temperature of 36°C (96.8°F), and normal skin turgor and color. The patient complained of nausea and chest pressure. Initial laboratory test results are shown in Table 1 (page 28) and were remarkable for the serum sodium level of 119 mEq/L, as well as for the below-normal values for hemoglobin, the hematocrit, albumin, and calcium. The diagnosis was dehydration/hyponatremia, and treatment consisted of 800 mL normal (0.9%) saline and observation. Within 5 hours, the patient suffered a grand mal seizure and then displayed combative behavior; she was infused with approximately 2 more liters of normal saline. During her 8 hours in the ED, the patient produced only 200 mL of highly concentrated urine. She was transferred to the ICU, and hypertonic (3%) saline was started at 25 mL/hour. In the ICU she suffered a second grand mal seizure, which was managed without intubation (see Figure 1, page 29).

CASE

The day after being admitted to the ICU, the patient complained of generalized body aches; 2.8 liters of normal saline was infused, and 5.4 liters of urine were diuresed. Creatine phosphokinase (CPK) and potassium were elevated, and a diagnosis of rhabdomyolysis was made. She was treated with half-normal (0.45%) saline at 200 mL/h. On day 4, the CPK peaked at 22,830 U/L and then declined to normal limits (less than 225 U/L) by day 7. The patient was discharged on day 8 with instructions to seek nutritional counseling before returning to running.

CASE

The client sought nutritional advice in our sports medicine institute a month after being discharged. She was urged to limit fluid intake to no more than 1% of her body weight per hour during exercise, unless thirsty, and to ingest sodium-containing beverages and foods before and during prolonged exercise. Also, the importance of heat acclimatization and adequate training were stressed.

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