BACKGROUND: The ccNexfin system uses the CO-trek algorithm to analyse 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, multi-centre study. We hypothesized that agreement between NEXCO and PACCO would be demonstrated by a mean accuracy (bias) < 0.6 l·min-1 with a percentage error < 30%.
METHODS: Patients undergoing cardiac surgery in three academic hospitals clinically requiring pulmonary artery catheterisation 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 anaesthesia, cardiac output was measured with four cold bolus thermodilution measurements and four averaged thirty second ccNexfin measurements randomised 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-1 and median NEXCO was 3.8 (IQR: 3.1 to 4.7) l·min-1. NEXCO-PACCO bias was 0.1 (LOA: -1.4 to +1.6) l·min-1 with a 37% percentage error.
CONCLUSION: In this study, cardiac output measurement with ccNexfin failed to meet the predefined criteria for agreement with cold-bolus pulmonary artery thermodilution.