Accordingly, we found an acceptable agreement of PCCO with COTCP only in data subsets obtained with high NE dosage, although a percentage error of 28% is still reasonably high. However, the results of the present study tend to refute our first hypothesis. Increasing NE dosage does not protein inhibitors seem to be associated with decreased agreement between PCCO and COTCP, but rather with improved interchangeability. PCCO further showed a better performance in tracking changes in CO during increased NE dosage because the coefficient of correlation between ��PCCO and ��COTCP was higher. Vascular tone seems to be an important issue regarding the agreement of PCCO methods with a reference method such as transcardiopulmonary thermodilution. Rodig et al. [12] described an increased bias between PCCO and CO measured by thermodilution after administration of phenylephrine.

The observed change of SVR >60% between calibrations may explain their findings. A recent publication applying the same PCCO software used in our study concluded that agreement was not influenced by changes in SVR due to better adaptation of the newer algorithm [14]. In the present study, SVR was not different between NE subgroups. Therefore, we hypothesize that despite a comparable SVR, a differing compliance of the vascular tree between subgroups of different NE dosages may explain the different level of agreement. A higher NE dosage may result in an increased central arterial stiffness and therefore reduced arterial compliance [24], as recently reported by Wittrock et al. [16].

In agreement with these findings, high NE dosage resulted in a significantly higher PP/SV relationship as an indicator of arterial stiffness. Increasing arterial stiffness leads to a more rigid vascular system and therefore may result in better agreement between methods. It is conceivable in this context that the vasculature of patients on high NE has less oscillatory capacity, which limits changes in arterial compliance and consequently on the deviation from the compliance obtained upon calibration. In clinical practice, however, many patients may be treated with either a low dose of NE or no NE, and according to our results, PCCO is not interchangeable with COTCP in these patients.Our results do not show a time-related effect on the agreement between PCCO and COTCP, thus refuting the second hypothesis.

The percentage error was above 30% in all calibration interval subgroups. The manufacturer recommends recalibration every 8 hours. Godje et al. [9] reported an overall acceptable agreement up to 44 hours; however, they did not indicate the bias and percentage error of subsets regarding different Entinostat calibration intervals. Hamzaoui et al. [14] reported a percentage error below 30% only within the first hour after calibration of PCCO, but up to 37% within a 6-hour calibration interval.