Arterial pressure waveform analysis versus thermodilution cardiac output measurement during open abdominal aortic aneurysm repair: A prospective observational study

Abstract

BACKGROUND 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 (t<inf>1</inf>); after aortic cross-clamping (t<inf>2</inf>); after clamp release (t<inf>3</inf>); and after skin closure (t<inf>4</inf>). Trending ability from t1 to t<inf>2</inf>, t<inf>2</inf> to t<inf>3</inf> and t<inf>3</inf> to t<inf>4</inf>, 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 (t<inf>1</inf>), -0.42 (t<inf>2</inf>), 0.98 (t<inf>3</inf>) and 0.98 (t<inf>4</inf>) l min^-1 at the different time points. Limits of agreement (LOA) were [-3.0 to 4.0] (pooled), [-2.0 to 3.0] (t<inf>1</inf>), [-3.1 to 2.3] (t<inf>2</inf>), [-2.5 to 4.4] (t<inf>3</inf>) and [^-1.7 to 3.7] (t<inf>4</inf>) l min^-1, resulting in mean errors of 58% (pooled), 45% (t<inf>1</inf>), 53% (t<inf>2</inf>), 52% (t<inf>3</inf>) and 41% (t<inf>4</inf>). Four-quadrant concordance was 65%. Polar plot analysis resulted in an angular bias of ^-128, 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.