Background and Goal of Study: Several studies have shown that goal-directed perioperative optimization of cardiac index (CI) reduce morbidity after major surgery and the length of stay on the intensive care unit . Therefore, non - or less-invasive, simple to interpret and quickly available continuous monitoring of CI has gained increasing interest. One of these non-invasive monitoring systems is the Nexfin-Monitor (bmeye, Amsterdam, NL) based on the calculation of CI by arterial waveform analysis without the need for calibration. The aim of our study was to investigate the accuracy of uncalibrated CI generated by arterial waveform analysis in patients undergoing coronary artery bypass grafting.
Materials and Methods: After ethics committee approval and written informed consent, 20 patients scheduled for elective CABG operation were studied before and after cardiopulmonary bypass (CPB). Each patient was monitored with the PiCCO system (Pulsion Medical System, Munich, Germany), a central venous line and the recently introduced Nexfin monitoring system. Haemodynamic variables included measurement of CI derived by TPTD (CITPTD) and CI derived by Nexfin (CINexfin). To describe the agreement between CITPTD, CINexfin and haemodynamic trends (ΔCITPTD, ΔCINexfin) Bland-Altman plots were performed before and after CPB. Before CPB and within the first 40 minutes after CPB CI derived by Nexfin was performed without additional calibration.
Results and Discussion: There was a significant correlation between CINexfin uncal and CITPTD(r=0.77, p< 0.0001) before CPB. Bland-Altman analysis showed a mean bias of 0.35 L/min (95% limits of agreement: -0.81 L/min to +0.57 L/min) with a percentage error (PE) of 25% [Figure 1]. After CPB CINexfin uncal showed a mean bias of 0.32 L/min (95% limits of agreement: -0.77 L/min to +0.49 L/min) with a percentage error (PE) of 22%. Trends of percentage changes in CI measured by uncalibrated Nexfin (ΔCINexfin uncal) and transpulmonary thermodilution (ΔCITPTD) revealed a significant correlation before (r=0.54, p< 0.0001) and after (r=0.67, p< 0.0001) CPB [Figure 2].
Conclusion(s): CI measurement by uncalibrated Nexfin monitoring system was able to reliably measure CI and track haemodynamic changes and trends compared with TPTD.
1. Pearse R. Crit Care, 2005. 9(6): p. 687-93.
Acknowledgements: The authors are indebted to Volkmar Hensel-Bringmann, for excellent technical assistance and logistic support.