Recalibration of pulse contour cardiac output using the PiCCO-2 device: when to perform the next thermodilution?

Introduction

Haemodynamic monitoring is a cornerstone of intensive care. In addition to parameters of preload and afterload, the assessment of cardiac output (CO) is of paramount importance. Thermodilution (TD) using the pulmonary artery catheter and transpulmonary TD using the PiCCO device are the gold standards for CO determination. After calibration by TD, the PiCCO device is able to assess CO using pulse contour (PC) analysis. Despite an overall good correlation of PC-CO and TD-CO in several studies, the manufacturer suggests recalibration by TD after 8 hours. Little is known about the long-term accuracy of PC-CO. Therefore it was the aim of our prospective study to investigate the long-term accuracy of PiCCO-2-derived PC-CO in the daily ICU routine.

Methods

In 10 consecutive patients (five male, five female, age 65 ± 15 years) the PC-CO was recorded immediately before recalibration by TD-CO. One hundred and ninety-four measurements with a mean time-lag between two measurements of TD-CO of 663.5 ± 371 min (100 to 2,700) were recorded. Mechanical ventilation, catecholamine and arrhythmia occurred in 60 (31%), 132 (68%) and 154 (79%) of the measurements.

Results

The 194 pairs of PC-CO and TD-CO showed a highly significant correlation (P < 0.001; r = 0.875). There was no significant difference between PC-CO versus TD-CO (4.1 ± 1.6 vs. 4.07 ± 1.4 l/min m²). Analysis according to Bland–Altman demonstrated a mean bias of -0.036 ± 0.778 l/min m² (lower and upper limits of agreement -1.56 and 1.49 l/min m²; percentage error of 38%). The difference of PC-CO and TD-CO was not correlated to the time-lag to the last calibration (P = 0.257; r = -0.083 for uncorrected difference; P = 0.067; r = 0.134 for absolute values of the difference). Further analysis demonstrated that the absolute value of the differences correlated to TD-CO (P = 0.02, r = 0.226). Subgroup analysis of 160 measurements with CO-TD <5.5 l/min m² demonstrated an improved bias of 0.085 ± 0.53 l/min m² (lower/upper limits of agreement: -0.98 and 1.12 l/min m²) and a percentage error of 28%.

Conclusion

PiCCO-2-derived PC-CO and TD-CO are highly significantly correlated. Accuracy is not influenced by the time-lag to the last calibration. Similar to previous data, PC-CO might overestimate very high CO, which usually does not influence clinical practice. Recalibration should be considered in patients with markedly increased PC-CO.