Background: The ccNexfin System uses the CO-trek algorithm to analyze a non-invasively obtained arterial pressure waveform and calculate cardiac output (NEXCO). It remains matter of debate whether NEXCO can replace invasive, pulmonary artery catheter-derived, cold-bolus pulmonary thermodilution cardiac output measurement (PACCO). This study aimed at testing NEXCO-PACCO agreement in a large sample size, multicenter study. We hypothesized that agreement between NEXCO and PACCO would be demonstrated by a mean accuracy (bias) <0.6 L/min with a percentage error <30%.
Methods: Patients undergoing cardiac surgery in three academic hospitals clinically requiring pulmonary artery catheterization were included. Exclusion criteria were aortic, pulmonary and tricuspid (valve) abnormalities, non-sinus rhythm and insufficient perfusion of the digits such as in Raynaud's disease. After induction of anesthesia, cardiac output was measured with four cold bolus thermodilution measurements and four averaged 30-second ccNexfin measurements randomized through the respiratory cycle to obtain one measurement pair. Mean accuracy and precision of ccNexfin were expressed as bias (mean of all NEXCO-PACCO differences) and limits of agreement (LOA) (1.96·SD of bias). Percentage error was calculated as [LOA / (NEXCO-PACCO average)].
Results: Fifty-five patients were enrolled in the study, 51 completed the protocol. Median PACCO was 3.7 (IQR: 3.2 to 4.6) L/min and median NEXCO was 3.8 (IQR: 3.1 to 4.7) L/min. NEXCO-PACCO bias was 0.1 (LOA: -1.4 to +1.6) L/min with a 37% percentage error.
Conclusions: In this study, cardiac output measurement with ccNexfin failed to meet the predefined criteria for agreement with cold-bolus pulmonary artery thermodilution.