Effect of Phenylephrine Versus Norepinephrine on Venous Return

Overview

Induction of general anesthesia often induces a decrease in the mean arterial blood pressure (MAP) caused by arterial and venous dilatation. Fluid administration is conventionally used to increase the patient's total blood volume, but is often associated with multiple adverse events such as postoperative edema. Arterial hypotension can also be treated by vasopressor agents such as norepinephrine and phenylephrine which mainly increase the blood pressure by arterial vasoconstriction. Compared to phenylephrine, norepinephrine has a shorter half-life (2 - 3 minutes) and improves the MAP by increase in cardiac contractility. In a recent study at our department it was demonstrated that besides arterial vasoconstriction, phenylephrine also improves venous return and cardiac output by venous vasoconstriction. The aim of this study is to compare the hemodynamic effects of both vasopressor agents in patients undergoing deep inferior epigastric perforators (DIEP) flap surgery. If significant differences between both agents are demonstrated, these findings can provide an important basis for future recommendations.

In consecutive patients scheduled for DIEP flap surgery, all hemodynamic and respiratory variables are recorded electronically for subsequent off line analysis. A systolic blood pressure of minimal 100 mmHg will be maintained during surgery by optimization of the cardiac preload and titrated norepinephrine (1.5 µg/kg/h) or phenylephrine (15 µg/kg/h) administration. Cardiac preload optimization will be based on pulse pressure variation (PPV) measurement, which is calculated by pulse contour analysis of the radial arterial pressure curve. Following the international goal-directed fluid therapy guidelines, plasmalyte will be administrated if the PPV\>11%. The tricuspid annular plane systolic excursion (TAPSE) will be measured by transthoracic echocardiography (TTE) to evaluate the inotropic effect of norepinephrine and phenylephrine. In addition, TTE will be used to measure the cardiac output to calibrate the PPV measurements.