Effect of norepinephrine dosage and calibration frequency on accuracy of pulse contour-derived cardiac output

INTRODUCTION: Continuous cardiac output monitoring is used for early detection of hemodynamic instability and guidance of therapy in critically ill patients. Recently, the accuracy of pulse contour-derived cardiac output (PCCO) has been questioned in different clinical situations. In this study, we examined agreement between PCCO and transcardiopulmonary thermodilution cardiac output (CO(TCP)) in critically ill patients, with special emphasis on norepinephrine (NE) administration and the time interval between calibrations. METHODS: This prospective, observational study was performed with a sample of 73 patients (mean age, 63 ± 13 years) requiring invasive hemodynamic monitoring on a non-cardiac surgery intensive care unit. PCCO was recorded immediately before calibration by CO(TCP). Bland-Altman analysis was performed on data subsets comparing agreement between PCCO and CO(TCP )according to NE dosage and the time interval between calibrations up to 24 hours. Further, central artery stiffness was calculated on the basis of the pulse pressure to stroke volume relationship. RESULTS: A total of 330 data pairs were analyzed. For all data pairs, the mean CO(TCP )(±SD) was 8.2 ± 2.0 L/min. PCCO had a mean bias of 0.16 L/min with limits of agreement of -2.81 to 3.15 L/min (percentage error, 38%) when compared to CO(TCP). Whereas the bias between PCCO and CO(TCP )was not significantly different between NE dosage categories or categories of time elapsed between calibrations, interchangeability (percentage error <30%) between methods was present only in the high NE dosage subgroup (≥0.1 μg/kg/min), as the percentage errors were 40%, 47% and 28% in the no NE, NE < 0.1 and NE ≥ 0.1 μg/kg/min subgroups, respectively. PCCO was not interchangeable with CO(TCP )in subgroups of different calibration intervals. The high NE dosage group showed significantly increased central artery stiffness. CONCLUSIONS: This study shows that NE dosage, but not the time interval between calibrations, has an impact on the agreement between PCCO and CO(TCP). Only in the measurements with high NE dosage (representing the minority of measurements) was PCCO interchangeable with CO(TCP).