Plasma Vasopressin Levels and Urinary Sodium Excretion during Cardiopulmonary Bypass with and without Pulsatile Flow

The use of pulsatile perfusion during bypass should create a more physiological milieu and thus attenuate the vasopressin stress response. To determine this, 20 patients scheduled for elective coronary artery bypass operation were studied in two groups. Group 1 had standard nonpulsatile perfusion, and in Group 2 a pulsatile pump was used. Measurements were made before and after anesthesia, after surgical incision, and at 15 and 30 minutes during and after cardiopulmonary bypass.In both groups, vasopressin levels were significantly elevated after sternotomy (4.5 ± 1.5 to 37 ± 10 pg/ml in Group 1 and 3.1 ± 1.2 to 33 ± 9 pg/ml in Group 2, p < 0.05) and during bypass (198 ± 19 pg/ml in Group 1 and 113 ± 16 pg/ml in Group 2) but were higher in Group 1 (p < 0.05). With comparable perfusion pressures in both groups, Group 2 required higher flow (4.5 ± 0.2 versus 3.5 ± 0.3 L/min, p < 0.05) and had lower resistance (1,351 ± 182 versus 1,841 ± 229 dynes sec cm^-5, p < 0.05) and higher urine Na⁺ (123 ± 5 versus 101 ± 8 mEq/L, p < 0.05). These data demonstrate that pulsatile flow can significantly attenuate the vasopressin stress response to bypass. Since vasopressin, at these concentrations, is a potent vasoconstrictor and is capable of producing a Na⁺ diuresis, this may partially explain the higher flow requirements and the decrease in Na⁺ excretion.