Comparison of uncalibrated arterial waveform analysis in cardiac surgery patients with thermodilution cardiac output measurements

INTRODUCTION: Cardiac output (CO) monitoring is indicated only in selected patients. In cardiac surgical patients, perioperative haemodynamic management is often guided by CO measurement by pulmonary artery catheterisation (CO(PAC)). Alternative strategies of CO determination have become increasingly accepted in clinical practice because the benefit of guiding therapy by data derived from the PAC remains to be proven and less invasive alternatives are available. Recently, a device offering uncalibrated CO measurement by arterial waveform analysis (CO(Wave)) was introduced. As far as this approach is concerned, however, the validity of the CO measurements obtained is utterly unclear. Therefore, the aim of this study was to compare the bias and the limits of agreement (LOAs) (two standard deviations) of CO(Wave )at four specified time points prior, during, and after coronary artery bypass graft (CABG) surgery with a simultaneous measurement of the gold standard CO(PAC )and aortic transpulmonary thermodilution CO (CO(Transpulm)). METHODS: Data from 30 patients were analysed during this prospective study. CO(PAC), CO(Transpulm), and CO(Wave )were determined in all patients at four different time points prior, during, and after CABG surgery. The CO(PAC )and the CO(Transpulm )were measured by triple injection of 10 ml of iced isotone sodium chloride solution into the central venous line of the PAC. Measurements of CO(Wave )were simultaneously taken at these time points. RESULTS: The overall correlation showed a Spearman correlation coefficient between CO(PAC )and CO(Wave )of 0.53 (p < 0.01) and 0.84 (p < 0.01) for CO(PAC )and CO(Transpulm). Bland-Altman analysis showed a mean bias and LOAs of 0.6 litres per minute and -2.2 to +3.4 litres per minute for CO(PAC )versus CO(Wave )and -0.1 litres per minute and -1.8 to +1.6 litres per minute for CO(PAC )versus CO(Transpulm). CONCLUSION: Arterial waveform analysis with an uncalibrated algorithm CO(Wave )underestimated CO(PAC )to a clinically relevant extent. The wide range of LOAs requires further evaluation. Better results might be achieved with an improved new algorithm. In contrast to this, we observed a better correlation of thermodilution CO(Transpulm )and thermodilution CO(PAC )measurements prior, during, and after CABG surgery.