Continuous cardiac output measurement: effect of time

Introduction

Calibration turns pulse contour methods of cardiac output measurement from continuous to intermittent. We evaluated the necessity to recalibrate pulse contour cardiac output methods; LiDCO™plus (LCO), FloTrac/Vigileo (FCO), PiCCO (PCO) and continuous CO measurement with pulmonary artery catheter (Vigilance) (CCO).

Methods

In 28 cardiac surgery patients, data were collected at 1 hour (T1), 2 hours (T2), 4 hours (T3), 8 hours (T4), 12 hours (T5), 24 hours (T6), 36 hours (T7), and 48 hours (T8) after ICU admission. Devices were only calibrated at start of the investigation period. To compute effect against time, at each time point, the CO values from LCO, FCO, PCO and CCO were subtracted, and compared with COtd (ICO). Effect of time was quantified by calculating the slope values using linear regression. Slope values of the regression line were tested against a horizontal line (no effect).

Results

No change with time was found for CCO (slope = 0.02 l/minute/hour, 95% CI -0.12 to 0.17, P = 0.763) nor for LCO (slope = 0.011 l/minute/hour, 95% CI -0.11 to 0.03, P = 0.322). Time effect for PCO was (slope = -0.017 l/minute/hour, 95% CI -0.032 to -0.001, P = 0.036) and for FCO (slope = 0.029 l/minute/hour, 95% CI 0.003 to 0.055, P = 0.027). For the LCO system, the data range indicated by the 95% CI crosses the threshold value of 10% at 2, 12 and 24 hours, implying more than 2.5% of the data points are outside the chosen 10% limits at these time points (Figure 1). This occurs with PCO from 1 hour to 24 hours, with FCO at 4, 8, 12 and 24 hours, and with CCO at 4, 12 and 24 hours.

Figure 1

Stability range of ±10% indicated by dashed lines.

Conclusions

PiCCO and FloTrac/Vigileo showed an effect with time. For PiCCO, our findings are in accordance with the publications of Boyle and Hanzaoui.