Cardiac output--pulse contour analysis vs. pulmonary artery thermodilution

The aims of this study were to determine the agreement between pulmonary artery thermodilution (PA-TD), transpulmonary thermodilution (TP-TD) and the pulse contour method, and to test the ability of the pulse contour method to track changes in cardiac output.

Cardiac output was determined twice before cardiac surgery with both PA-TD and TP-TD. The precision (two standard deviations of the difference between repeated measurements) and agreement of the two methods were calculated. Post-operatively, cardiac output was determined with the PA-TD and pulse contour methods, and the bias and limits of agreement were again calculated. Finally, in patients with heart rates below 60 beats/min or a cardiac index of less than 2.5 l/min/m2, atrial pacing was started and the haemodynamic consequences were monitored with the PA-TD and pulse contour methods.

Twenty-five patients were included. The precisions of PA-TD and TP-TD were 0.41 l/min [95% confidence interval (CI), +/- 0.07] and 0.48 l/min (95% CI, +/- 0.08), respectively. The bias and limits of agreement between PA-TD and TP-TD were - 0.46 l/min (95% CI, +/- 0.11) and +/- 1.10 l/min (95% CI, +/- 0.19), respectively. Post-operatively, the bias and limits of agreement between the PA-TD and pulse contour methods were 0.07 l/min and +/- 2.20 l/min, respectively. The changes in cardiac output with atrial pacing were in the same direction and of the same magnitude in 15 of the 16 patients.

The precision of cardiac output measurements with PA-TD and TP-TD was very similar. The transpulmonary method, however, overestimated the cardiac output by 0.46 l/min. Post-operatively, cardiac output measurements with the PA-TD and pulse contour methods did not agree, but the pulse contour method reliably tracked pacing-induced changes in cardiac output.