Reliability of non-invasive cardiac output monitoring based on pulse wave transit time in off-pump coronary artery bypass grafting

Aim: The study was designed to evaluate the accuracy of cardiac output (CO) measurements based on pulse wave transit time (PWTT) as compared to transpulmonary thermodilution (TPTD) in perioperative off-pump coronary artery bypass grafting (OPCABG). Methods: 20 patients scheduled for elective OPCABG were enrolled for a prospective study. Parallel measurements of CO by using PWTT (COPWTT) and TPTD (COTPTD) were carried out at five stages intraoperatively and at three stages postoperatively. Also analyzed was the agreement between CO absolute values and its ability to monitor cardiac output dynamics. Results: All in all, 153 pairs of CO data were obtained. According to Bland–Altman analysis, the mean intraoperative difference between the methods was 1.2 L/min, with boundaries of agreement reaching ± 2.9 L/min and a percentage error amounting to 64%. The intraoperative analysis of a polar plot revealed an increased angular difference of 6.9º and radial boundaries of agreement of ± 70.4º, and a decreased polar concordance rate (55%). The postoperative analysis of the data showed better agreement between the methods: mean difference was 0.4 L/min with boundaries of agreement of ± 2.3 L/min and percentage error of 41%. The postoperative trending ability was also more accurate (angular difference of 3.2º, angular boundaries of agreement ± 39º, polar concordance rate 81%). Conclusion: Poor accuracy and reproducibility of non-invasive COPWTT and its insufficient trending ability to monitor cardiac output during off-pump coronary artery bypass grafting makes it impossible to recommend this technology to be used intraoperatively as an alternative to transpulmonary thermodilution technique. The calibration and trending ability of COPWTT improved after OPCAB.