Central Venous Pressure Monitoring During Bypass

Abstract

Maintenance of adequate cerebral perfusion pressure (CPP) is of paramount importance in all patients, but especially in cardiac patients undergoing surgery under conditions of cardiopulmonary bypass (CPB). CPB is associated with a significant incidence of neurologic complications, some of which, unfortunately, are irreversible and even fatal. The cause of this neurologic damage is multifactorial and still not completely understood (1). CPB diverts blood flow to an extracorporeal circuit and requires a means to deliver the blood from and then back to the body. Systemic venous return to the CPB circuit is accomplished with specially designed cannulas and occurs by gravity/siphon. Any condition that impairs the passive drainage of blood will cause a decrease in venous return to the pump. If superior vena cava (SVC) drainage is inhibited, the associated venous hypertension increases intracranial pressure and decreases CPP (2). Plochl et al. (3) nicely describe this condition in an animal model, and they conclude that the “observation of internal jugular pressure may be advantageous during initiation of CPB.” Their conclusion, although intuitive to many (as it should be), draws attention to the important question of how to monitor this pressure. We routinely pay close attention to jugular venous pressure, but do so not only throughout the surgical procedure; vigilance is especially important during procedures in which separate venous cannulas have to be used. We continue to often use the pulmonary artery catheter (PAC) during cardiac surgery, and we have observed a high incidence of spurious readings of central venous pressure (CVP) caused by either collapse of intracardiac structures onto the monitoring lumen orifice of the catheter or from the CVP monitoring orifice located in the right atrium when it has been opened to the atmosphere. If a PAC is being used, you can be assured that the CVP lumen is proximal to the SVC cannula if it registers a pressure change when running IV fluids through the sideport of the introducer. If this is not the case, we transduce the CVP during CPB from the sideport of the PAC introducer. Another technique, used in children and adults with central venous catheters in place, is to ballot the neck on the side opposite of where the central venous catheter is located. If a transient change in the CVP tracing occurs, it is likely that the reading reflects a true SVC CVP; if no change is noted, the pressure may be from a catheter port located below the SVC cannula. Another aspect of monitoring CVP and CPP during CPB in our institution is that we set the alarms on our CVP monitors to signal increases in CVP, which may occur with manipulations of the heart and/or SVC cannulas. We have been impressed by how frequently we are able to identify altered SVC and cerebral venous drainage with these alarms when it is not evident from the surgical field. In summary, we recommend these two simple maneuvers to avoid potential neurologic disasters, and we thank Plochl et al. (3) for the interesting study they reported. Felipe Urdaneta MD Nikolaus Gravenstein MD