Reliability of the continuous cardiac index measurement using the pulse contour analysis of the PiCCO system

Introduction

Reliable continuous hemodynamic monitoring of critically ill patients is essential for effective volume management and adequate administration of vasoactive drugs. The PiCCO system allows continuous measurement of the cardiac index using arterial pulse contour analysis. Calibration of this system by transpulmonary thermodilution is recommended every 8 hours. In this study we compared the difference of the continuous measurement of the cardiac index using the arterial pulse contour analysis (CIpc) with the cardiac index acquired by the transpulmonary thermodilution (CItd) when calibrating the system.

Methods

Our study includes 140 measurements in 10 critically ill patients (eight males, two females, age 37–84 years, mean 64.1 ± 13.0 years) requiring hemodynamic monitoring with the PiCCO system. Five patients had septic shock, three hepatorenal syndrome and two acute heart failure. First the CIpc was recorded immediately before the next calibration and afterwards the CItd was measured three times, which resulted in a simultaneous calibration of the pulse contour algorithm of the PiCCO system. We performed a mean of 14 ± 9.4 measurements per patient. The time-lag between the measurements was 12 hours 54 minutes ± 7 hours 47 minutes.

Results

The comparison of the CIpc immediately before calibration and the calibration-derived CItd resulted in a correlation coefficient of 0.84 with a P value of 0.02. In the Bland–Altman analysis the CIpc was a mean 0.14 l/min/m² lower than the CItd. The standard deviation was 0.72 l/min/m². There was no correlation of the time-lag between the calibrations and the difference of CIpc and CItd (r = -0.03; P = 0.13).

Conclusion

The PiCCO system allows a reliable continuous measurement of the cardiac index using the pulse contour analysis. In our study we could not find an increased difference of CIpc and CItd even with longer time periods between the calibrations using transpulmonary thermodilution. Because calibration is easy to achieve and additional data for the intrathoracic blood volume and the extravascular lung water are obtained, a 12-hour period between the calibrations is reasonable.