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How to estimate the increase in plasma sodium with oral urea? #ureaforhyponatremia
A 50 y/o woman with SIADH has a weight=70kg, UOP=1L/day, plasma sodium (PNa)=125 mEq/L, and UOsm=500 mOsm/kg. Which of the following is the expected PNa one day after fluid restriction 1 L/day and urea 15 g BID? (assume baseline solute balance and insensible losses of 0.8 L/day)
Step 1: Calculate baseline solute intake
Under solute balance conditions, solute intake = urine solute excretion (USE). We know UOsm=USE/V...(1), where V=24h urine volume. Reordering the terms of (1): USE= UOsm x V. USE = 500 mOsm/L x 1 L/day = 500 mOsm/day.
Under solute balance conditions, solute intake = urine solute excretion (USE). We know UOsm=USE/V...(1), where V=24h urine volume. Reordering the terms of (1): USE= UOsm x V. USE = 500 mOsm/L x 1 L/day = 500 mOsm/day.
