Polyuria after cessation of vasopressin in a child after cardiac surgery.

A 3-year-old, 12.5-kg girl, who had a late diagnosis of transposition of the great vessels with atrial and ventricular septal defects, underwent pulmonary artery banding along with a Blalock-Taussig shunt for left ventricular retraining in case of a possible arterial switch operation. She had an unstable course in the initial days in the intensive care unit, requiring inotropic and ventilator support. She was started on a vasopressin infusion at 0.0003 units/kg/min intravenously to maintain blood pressure, along with epinephrine at 0.1 μg/kg/min and milrinone at 0.75 μg/kg/min. As her clinical condition stabilized it was decided to taper off vasopressin on day 4 over 6 to 8 hours. She was maintaining adequate urine output of 1 to 2 mL/kg/hour with intravenous furosemide administered at 0.05 to 0.1 mg/kg/hour. The patient’s serum sodium had fallen from 142 mEq/L to a low of 120 mEq/L when started on vasopressin infusion for which slow correction was done with 3% hypertonic saline. She had a sodium level of 130 mEq/L when weaning of vasopressin was started. After discontinuation of vasopressin the child became polyuric with urine output