What is the differential diagnosis and management of postoperative polyuria?
The differential diagnosis for postoperative polyuria includes (1) fluid mobilization from perioperative fluid administration; (2) central DI; (3) osmotic diuresis (i.e., glycosuria); or (4) GH salt and water mobilization after resection of a GH-secreting tumor. The hallmark of central DI is high-volume output (> 250 cc/hr for > 2 to 3 consecutive hours, or > 3 L/day in adults) of dilute urine (< 300 mOsm/kg of water, urine specific gravity < 1.005). Mild postoperative DI can be managed with free water replacement or hypotonic fluids. More severe or persistent DI cases, particularly if associated with hypernatremia, can be treated with desmopressin (trade name DDAVP). Desmopressin, a synthetic analogue of ADH, has advantages over ADH of a longer half-life and an absence of vasopressor effects. In the post-operative setting, low-dose DDAVP can be administered as a single 0.5-1.0 mcg dose, intravenously or subcutaneously, as needed to normalize polyuria and possible hypernatremia. Patients with persistent DI symptoms at the time of hospital discharge can be treated judiciously with PRN (as needed) night-time DDAVP (starting with either a 10-mcg intranasal spray or 0.1-mg oral tablets). In anticipation of spontaneous recovery, patients should be counseled to hold the nighttime DDAVP dose periodically to assess for continued need.