Pulmonary artery catheter: Rest in peace? Not just quite yet…

Abstract

Patients with severe liver disease have a hyperdynamic circulation with an elevated cardiac output (CO), low systemic vascular resistance, and increased heart rate. During liver transplantation (LTx), most clinicians prefer to keep CO elevated in order to maintain tissue perfusion; this practice is based on common sense and supported indirectly by a clinical study by Parker et al. CO is one of the most important parameters that the anesthesiologist follows because it is a major factor in oxygen transport. Intraoperative hemodynamic management during LTx is based on the interpretation of the CO, heart rate, pulmonary artery (PA) pressures, filling pressures, and mixed-venous oxygen saturation (SvO2) and is influenced by the stage of the procedure and other factors (for example, the use of venovenous bypass). The pulmonary artery catheter (PAC) readily provides all this hemodynamic information, and every LTx anesthesiologist is very familiar with the PAC. Modified PACs give us continuous CO or additional information about the right ventricle (ejection fraction and end-diastolic and end-systolic volumes). The right ventricular ejection fraction catheter is used infrequently despite the better preload information it provides: filling pressures do not reflect preload very well because of compliance issues. Transesophageal echocardiography (TEE) gives other important hemodynamic information that is unavailable from the PAC: TEE allows the direct visualization of the volume status, overall contractility, regional wall motion, embolization, and large vessels. However, it does not provide the kind of hemodynamic information that is available from the PAC and is not as good at trending information (especially preload). Few LTx anesthesiologists are familiar with it, and the interpretation is highly user-dependent. Finally, TEE monitoring cannot be continued easily postoperatively. For these reasons, TEE is used fairly infrequently during LTx. The few anesthesiologists who do use TEE consider the information that it provides to be complementary to that provided by the PAC; in other words, TEE does not replace the PAC at this moment and is indicated only when there is a specific condition (for example, cardiac disease and pulmonary hypertension). In this issue of Liver Transplantation, 2 teams report that CO determined by ultrasound cardiac output monitoring (USCOM) correlates very well with thermodilution CO, the gold standard. These reports on USCOM are important because they are the first to document that in these hyperdynamic patients there is also a good correlation. USCOM is a noninvasive technique (the probe is placed at the suprasternal notch) and therefore is expected to have a very low complication rate. Whether USCOM-derived information such as the corrected flow time and stroke volume variation will provide clinically valuable information regarding preload, as promised by some, remains to be seen. Also, USCOM estimations of PA pressures based on Doppler interrogation of the PA remain unvalidated (especially in those with pulmonary hypertension), and the ability to estimate left ventricular contractility is currently just a promise. Particularly worrisome is that 3 of 13 patients in one of these studies were excluded: in 2 patients, diagnostic-quality images could not be obtained, and this occurred after the patients were screened preoperatively to see whether the suprasternal insonation window was appropriate.