Peak Lag Between Plasma Vasopressin and Urine Aquaporin-2 Following Cardiac Surgery.

Tolvaptan, a vasopressin type-2 receptor antagonist, is utilized to ameliorate fluid retention following cardiac surgery. However, the optimal timing of tolvaptan administration considering novel biomarkers remains unknown. We prospectively included patients who underwent cardiac surgery between 2016 and 2020. We measured perioperative trends of free water reabsorption mediators including plasma arginine vasopressin and urine aquaporin-2. A total of 20 patients (68 [60, 75] years old, 18 men) were included. Urine volume decreased gradually after the initial 3 hours following cardiac surgery. The plasma arginine vasopressin level increased significantly with a peak at postoperative 6 hours, whereas the urine aquaporin-2 level increased later with a delayed peak at postoperative 12 hours. As a result, urine aquaporin-2 relative to the plasma arginine vasopressin level, which represents the activity of the collecting ducts and indicates predicted responses to tolvaptan, was a minimum at postoperative 6 hours. Tolvaptan administration immediately after cardiac surgery might not be recommended given the transient refractoriness to tolvaptan probably due to the stunning of kidney collecting ducts.