Effects of changes in vascular tone on the agreement between pulse contour and transpulmonary thermodilution cardiac output measurements within an up to 6-hour calibration-free period

Objectives: To examine whether the agreement between pulse contour and transpulmonary thermodilution cardiac index (CI) measurements is altered by changes in vascular tone within an up to 6-hr calibration-free period. Design: Observational study. Setting: Medical intensive care unit of a university hospital. Patients: Fifty-nine critically ill patients. Interventions: None. Measurements and Main Results: Data from 59 critically ill patients equipped with a PiCCO device were retrospectively analyzed. The database contained the transpulmonary thermodilution CI (CIT) value obtained at each time point the device was calibrated and the pulse contour CI (CIpc) value recorded immediately before this time point. Seven subsets of CI pairs were defined according to intervals of time elapsed from the previous calibration (within the first 30 mins, between 30 mins and 1 hr, and every hour up to 6 hrs). In the whole set of 400 CI pairs, CIpc correlated with CIT (r(2) = .68, p < .001). The bias +/- SD was 0.12 +/- 0.61 L/min/m(2), and the percentage error was 35%. Among the seven time-interval subsets, the percentage error was < 30% only in the two first ones (27% and 26%, respectively). When changes in systemic vascular resistance by > 15% occurred (129 times), CIpc correlated with CIT (r(2) = .64), the bias +/- SD was 0.12 +/- 0.62 L/min/m(2), and the percentage error was 36%. In the subset of CI pairs recorded within the 1-hr calibration-free period while vascular resistance changed by > 15% (n = 32), the bias +/- SD was 0.04 +/- 0.47 L/min/m(2) and the percentage error was 29%. Conclusions: Our study in critically ill patients suggests that the agreement between pulse contour cardiac output and transpulmonary thermodilution cardiac output was not significantly influenced by changes in vascular tone. However, after a 1-hr calibration-free period, recalibration may be encouraged. Such a procedure provides helpful information drawn from other thermodilution-derived variables.