Phenylephrine to increase blood flow in the radial artery used as a coronary bypass conduit

Objective: The radial artery has more smooth muscle in its wall than the other arterial conduits and is known to be vasospastic. Because it is frequently necessary to use vasoconstrictors early after coronary bypass surgery we investigated the effects of phenylephrine on conduit flow in this setting. Methods: Thirty patients undergoing coronary artery bypass with all arterial conduits in which the radial artery was used as a T-graft were randomly assigned to receive intravenous infusions of normal saline (n = 10); nitroglycerin, 0.5 μg·kg·min (n = 11); or nicardipine, 0.5 μg·kg· min (n = 9), beginning early in the operation. After discontinuation of cardiopulmonary bypass and achievement of stable hemodynamics, control measurements were obtained, and this was followed by phenylephrine infusion to achieve a 20% increase in mean arterial pressure, after which the measurements were repeated. Results: Mean radial artery flow increased similarly in all groups: normal saline, 40% ± 25%; nicardipine, 37% ± 27%; nitroglycerin, 48% ± 36% (P = .533). Comparable changes occurred in arterial pressure and systemic vascular resistance, whereas the cardiac index remained unchanged. Conclusion: Radial artery blood flow increases when the mean arterial pressure is increased with phenylephrine. There was no evidence of a conduit vasoconstrictive effect, which could limit or reduce conduit flow. Vasocontriction with phenylephrine is appropriate to provide adequate perfusion pressure for radial artery grafts.