The aim of this study was to compare cardiac output measurements of the non-invasive cardiac output and the pulmonary artery catheter during repeat surgery for hip replacement.

In this prospective observational study, patients undergoing repeat hip surgery who needed a pulmonary artery catheter were included. A standard protocol was followed for induction, endotracheal intubation and maintenance of anaesthesia (sufentanil, etomidate, sevoflurane, cisatracurium). After endotracheal intubation, the non-invasive cardiac output was connected and a pulmonary artery catheter was inserted. Data were collected every 3 min until patients were extubated.

Ten patients were included and 2455 points of comparison recorded. Cardiac output from the pulmonary artery catheter varied from 1.7 to 8.9 L min−1 (mean 4.1 L min−1) and the non-invasive cardiac output (using averaging mode) from 1.7 to 8.0 L min−1 (mean 3.7 L min−1). There was a significant correlation between them (P < 0.01; bias 0.3 L min−1; limits of agreement +1.9 and –2.5 L min−1), although these differed between patients.

The perioperative bias was small and the non-invasive cardiac output slightly underestimated cardiac output intraoperatively compared to the pulmonary artery catheter. The bias was smaller when mean cardiac output was below 3 L min−1. Core temperature between 34.4°C and 37.6°C had no influence on the differences.