Comparative hemodynamic effects of vasopressin and norepinephrine after milrinone-induced hypotension in off-pump coronary artery bypass surgical patients

Objective: Phosphodiesterase inhibitor is essential to the pharmacologic management of decompensated heart failure because it increases contractility and decreases afterload of right ventricle. It also improves hemodynamics and increases blood flow of the grafted internal mammary arteries and middle cerebral arteries during coronary artery bypass surgery. However, it induces vasodilation and necessitates the use of vasoconstrictors, such as norepinephrine. We hypothesized that vasopressin could recover hypotension induced by milrinone with less effect on pulmonary vascular resistance (PVR) compared to norepinephrine. Methods: Fifty patients, undergoing coronary artery bypass graft (CABG) surgery, were assigned randomly in a double-blind manner to receive either vasopressin or norepinephrine. After baseline hemodynamic measurements, a loading dose of milrinone 50 μg/kg was infused slowly for 20 min followed by continuous infusion of 0.5 μg/(kg min). Immediately after the loading dose of milrinone, hemodynamic variables were measured, and vasopressin (VP group) or norepinephrine (NE groups) was infused. After being titrated until the mean arterial pressure was increased by 20%, hemodynamic variables were measured again. Results: Milrinone infusion reduced both systemic vascular resistance (SVR, 1218 ± 299 dyne s/cm⁵ vs 838 ± 209 dyne s/cm⁵, 1345 ± 299 dyne s/cm⁵ vs 1011 ± 195 dyne s/cm⁵) and PVR (95 ± 34 dyne s/cm⁵ vs 72 ± 30 dyne s/cm⁵, 119 ± 85 dyne s/cm⁵ vs 87 ± 33 dyne s/cm⁵) in the VP and NE groups, respectively. Vasopressin and norepinephrine infusion increased both SVR (838 ± 209 dyne s/cm⁵ vs 1100 ± 244 dyne s/cm⁵, 1011 ± 195 dyne s/cm⁵ vs 1446 ± 681 dyne s/cm⁵, respectively) and PVR (72 ± 30 dyne s/cm⁵ vs 84 ± 18 dyne s/cm⁵, 87 ± 33 dyne s/cm⁵ vs 139 ± 97 dyne s/cm⁵, respectively). The PRV/SVR ratio was decreased after vasopressin infusion (0.10 ± 0.03 vs 0.08 ± 0.03), while no changes were found after norepinephrine infusion (0.09 ± 0.02 vs 0.09 ± 0.02). Conclusions: In the patients undergoing CABG surgery, both norepinephrine and low dose vasopressin were effective in restoring milrinone-induced decrease of SVR. However, only low-dose vasopressin decreased the PVR/SVR ratio that was increased by milrinone. Considering the importance of maintaining systemic perfusion pressure as well as reducing right heart afterload, milrinone-vasopressin may provide better hemodynamics than milrinone-norephinephrine during the management of right heart failure.