Arterial pressure waveform analysis enables continuous, minimally invasive measurement of cardiac output. Haemodynamic instability compromises the reliability of the technique and a means of maintaining accurate measurement in this circumstance would be useful.OBJECTIVES
To investigate the accuracy, precision and trending ability of arterial pressure waveform cardiac output obtained with FloTrac/Vigileo, versus pulmonary artery thermodilution in patients undergoing elective open abdominal aortic aneurysm repair.DESIGN
A prospective observational study.SETTING
Operating room in a university hospital.PATIENTS
Twenty-two patients scheduled for elective, open abdominal aortic aneurysm repair.MAIN OUTCOME MEASURES
Bias, limits of agreement and mean error as determined with Bland–Altman analysis between arterial waveform and thermodilution cardiac output assessment at four time points: after induction of anaesthesia (t1); after aortic cross-clamping (t2); after clamp release (t3); and after skin closure (t4). Trending ability from t1 to t2, t2 to t3 and t3 to t4, determined with four-quadrant and polar plot methodology. Clinically acceptable boundaries were defined in advance.RESULTS
Bland–Altman analysis revealed a bias of 0.54 l min−1 (thermodilution minus arterial waveform cardiac output) for pooled data, and 0.51 (t1), −0.42 (t2), 0.98 (t3) and 0.98 (t4) l min−1 at the different time points. Limits of agreement (LOA) were [–3.0 to 4.0] (pooled), [−2.0 to 3.0] (t1), [−3.1 to 2.3] (t2), [−2.5 to 4.4] (t3) and [−1.7 to 3.7] (t4) l min−1, resulting in mean errors of 58% (pooled), 45% (t1), 53% (t2), 52% (t3) and 41% (t4). Four-quadrant concordance was 65%. Polar plot analysis resulted in an angular bias of −12°, with radial LOA of −60° to 36°.CONCLUSION
Bias between arterial waveform and thermodilution cardiac output was within a predefined acceptable range, but the mean error was above the accepted range of 30%. Trending ability was poor. Arterial waveform and thermodilution cardiac outputs are, therefore, not interchangeable in patients undergoing open abdominal aortic aneurysm repair.