The haemodynamic effects of phenylephrine after cardiac surgery

Background: Phenylephrine increases systemic- and pulmonary resistances and therefore may increase blood pressures at the expense of blood flow. Cardio-pulmonary bypass alters vasoreactivity and many patients exhibit chronotropic insufficiency after cardiac surgery. We aimed to describe the haemodynamic effects of phenylephrine infusion after cardiac surgery.

Methods: Patients in steady state after low-risk cardiac surgery received incremental infusion rates of phenylephrine up to 1.0 μg/kg/min with the aim of increasing systemic mean arterial blood pressure 20 mmHg. Invasive haemodynamic parameters, including pulmonary wedge pressures, were captured along with echocardiographic measures of biventricular function before, during phenylephrine infusion at target systemic blood pressure, and 20 min after phenylephrine discontinuation.

Results: Thirty patients were included. Phenylephrine increased mean arterial pressure increased from 78 (±9) mmHg to 98 (±10) mmHg with phenylephrine infusion. Also, pulmonary blood pressure as well as systemic- and pulmonary resistances increased. The ratio between systemic- and pulmonary artery resistances did not change statistically significantly (p = .59). Median cardiac output was 4.35 (interquartile range [IQR] 3.6-5.4) L/min at baseline and increased significantly with phenylephrine infusion (median Δcardiac output was 0.25 [IQR 0.1-0.6] L/min) (p = .012). Pulmonary artery wedge pressure increased from 10.2 (±3.0) mmHg to 11.9 (±3.4) mmHg (p < .001). This was accompanied by significant increases in central venous pressure. Phenylephrine infusion increased left ventricular end-diastolic volume from 105 (±46) mL to 119 (±44) mL (p < .001). All results of phenylephrine infusion were reversed with discontinuation.

Conclusion: In haemodynamically stable patients after cardiac surgery, phenylephrine increased PVR and SVR, but did not change the PVR/SVR ratio. Phenylephrine increased biventricular filling pressures and left ventricular end-diastolic area. Consequently, CO increased as ejection fraction was maintained. These findings do not discourage the use of phenylephrine after low-risk cardiac surgery.

Registration: clinicaltrial.gov (identifier NCT04419662).