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Exercise-associated hyponatraemia — MRCP Part 1 MCQ

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HardExercise PhysiologyExercise-associated hyponatraemiaMRCP Part 1

Near the finish of an ultramarathon, a runner becomes confused and vomits. He has gained 2.2 kg during the race, serum sodium is 121 mmol/L and glucose is normal. There are basal crackles but blood pressure is maintained. What is the immediate fluid treatment?

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Correct answer: D — Give 100 mL of intravenous 3% sodium chloride

The best answer is “Give 100 mL of intravenous 3% sodium chloride”. Weight gain, encephalopathy and hyponatraemia indicate water-overloaded exercise-associated hyponatraemia with cerebral symptoms. A rapid small bolus of 3% saline is the indicated treatment and can be repeated at short intervals according to neurological response. Isotonic saline may worsen dilution when non-osmotic vasopressin remains active; free water and glucose worsen hypotonicity. Diuresis before urgent hypertonic therapy delays reversal of cerebral oedema and is not the first fluid intervention.

Reference: Exercise-associated hyponatraemia clinical review: https://pmc.ncbi.nlm.nih.gov/articles/PMC6735969/