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Cardiac index derived from arterial pressure waveform: uncalibrated analysis vs once-only calibrated analysis


As the need for recalibration and the best time point to recalibrate has been a matter of debate since the introduction of the PiCCO monitor (Pulsion, Germany), we set out to analyze the performance of its pulse contour (PC) analysis without recalibration over a 24-hour period.


We studied the cardiac index (CI) over a 24-hour period in eight nonoperative patients admitted to our ICU. Seven CI measurements (median number; every 4 hours) by thermodilution (TD) were performed in each patient (in triplicate), PC-derived data were recorded continuously. We used a special PiCCOplus monitor with a disabled auto-recalibrate feature; that is, TD did not lead to an automatic calibration of the PC analysis. Calibration was only performed manually once at the start of the analysis for each patient. Later TD measurements were recorded but had no effect on the CIPC. An additional comparison was performed using the FloTrac/Vigileo System (Edwards, USA), which does not need manual recalibration and instead recalibrates itself every 60 seconds based on the arterial waveform. The FloTrac/Vigileo monitor used was a second-generation device (software version 1.14). Both the pressure transducers of the PiCCO and the FloTrac were connected in series to the same femoral artery catheter.


A total of 59 TD measurements of CI (CITD) were compared with FloTrac CI measurements (CIFloTrac) and PC-derived CI measurements (CIPC) from the PiCCO device. CITD ranged from 2.1 to 7.6 l/minute/m2 (mean 4.3 ± 1.39 l/minute/m2). PC (PiCCO) compared with TD: bias and precision (1.96SD of the bias) were 0.18 l/minute/m2 and ±1.35 l/minute/m2, the percentage error was 30.9%. FloTrac compared with TD: bias and precision were -0.75 l/minute/m2 and ±1.79 l/minute/m2, the percentage error was 46.2%. The mean absolute value of the difference |CITD - CIPC| and |CITD - CIFloTrac| was 0.48 ± 0.49 l/minute/m2 for PiCCO pulse contour values and 0.97 ± 0.76 l/minute/m2 for FloTrac/Vigileo values, respectively. This higher difference of CIFloTrac from CITD was significant (P = 0.0002) and remained significant even when only data from the last time point (24 hours) was analyzed (P = 0.03).


PC-derived CI values obtained over a 24-hour period from the PiCCO device after only one manual calibration provide significantly better estimates of CI than measurements by the FloTrac/Vigileo device, even after a calibration-free interval of 24 hours.

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Correspondence to H Einwaechter.

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Einwaechter, H., Hiemer, S., Treiber, M. et al. Cardiac index derived from arterial pressure waveform: uncalibrated analysis vs once-only calibrated analysis. Crit Care 14, P109 (2010).

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  • Cardiac Index
  • Percentage Error
  • Pressure Waveform
  • Pulse Contour
  • Additional Comparison