Effects of phlebotomy and phenylephrine infusion on portal venous pressure and systemic hemodynamics during liver transplantation.

BACKGROUND

A regimen of fluid restriction, phlebotomy, vasopressors, and strict, protocol-guided product replacement has been associated with low blood product use during orthotopic liver transplantation. However, the physiologic basis of this strategy remains unclear. We hypothesized that a reduction of intravascular volume by phlebotomy would cause a decrease in portal venous pressure (PVP), which would be sustained during subsequent phenylephrine infusion, possibly explaining reduced bleeding. Because phenylephrine may increase central venous pressure (CVP), we questioned the validity of CVP as a correlate of cardiac filling in this context and compared it with other pulmonary artery catheter and transesophageal echocardiography-derived parameters. In particular, because optimal views for echocardiographic estimation of preload and stroke volume are not always applicable during liver transplantation, we evaluated the use of transmitral flow (TMF) early peak (E) velocity as a surrogate.

METHODS

In study 1, the changes in directly measured PVP and CVP were recorded before and after phlebotomy and phenylephrine infusion in 10 patients near the end of the dissection phase of liver transplantation. In study 2, transesophageal echocardiography-derived TMF velocity in early diastole was measured in 20 patients, and the changes were compared with changes in CVP, pulmonary artery pressure (PAP), pulmonary capillary wedge pressure (PCWP), cardiac output (CO), and calculated systemic vascular resistance (SVR) at the following times: postinduction, postphlebotomy, preclamping of the inferior vena cava, during clamping, and postunclamping.

RESULTS

Phlebotomy decreased PVP along with CO, PAP, PCWP, CVP, and TMF E velocity. Phenylephrine given after phlebotomy increased CVP, SVR, and arterial blood pressure but had no significant effect on CO, PAP, PCWP, or PVP. The change in TMF E velocity correlated well with the change in CO (Pearson correlation coefficient 95% confidence interval 0.738-0.917, P< or =0.015) but less well with the change in PAP (0.554-0.762, P< or =0.012) and PCWP (0.576-0.692, P< or =0.008). TMF E velocity did not correlate significantly with CVP or calculated SVR.

CONCLUSION

Phlebotomy during the dissection phase of liver transplantation decreased PVP, which was unaffected when phenylephrine infusion was used to restore systemic arterial pressure. This may contribute to a decrease in operative blood loss. CVP often increased in response to phenylephrine infusion and did not seem to reflect cardiac filling. The changes in TMF E velocity correlated well with the changes in CO, PAP, and PCWP during liver transplantation but not with the changes in CVP.