Electrolyte Disorders USMLE Step 1 Practice Question
A 19-year-old female cross-country athlete collapses after running a 10 km race in 95°F weather. On scene, she is confused and complains of nausea. Her teammates report she drank approximately 3-4 liters of water during and immediately after the race. Vital signs: BP 98/62 mmHg, HR 112/min, RR 22/min, core temperature 37.8°C, SpO2 98% on room air. Physical examination reveals no focal neurologic deficits and normal skin turgor. Laboratory results: serum sodium 122 mEq/L (normal 135-145), serum osmolality 252 mOsm/kg, BUN 12 mg/dL, creatinine 0.9 mg/dL, urine osmolality 580 mOsm/kg, urine sodium 32 mEq/L. She denies use of diuretics, NSAIDs, or recent illness. Which of the following is the most appropriate initial management?
Answer choices
- AAdminister desmopressin 4 mcg IV to suppress water reabsorption
- BInitiate hypotonic saline (0.45%) infusion at 100 mL/hr with sodium correction target of 8-10 mEq/L per 24 hours
- CAdminister 3% hypertonic saline with loop diuretic to rapidly normalize serum sodium
- DEstablish large-bore IV access and rapidly infuse normal saline (0.9%) boluses
- ERestrict fluid intake to 500-800 mL per day and monitor serum sodium every 2-4 hoursCorrect answer
- FAdminister furosemide with normal saline replacement to induce osmotic diuresis
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