Cardiac Output Measured by a New Arterial Pressure Waveform Analysis Method Without Calibration Compared With Thermodilution After Cardiac Surgery

Objectives: To investigate whether measuring cardiac output and its course after cardiac surgery by a new analysis technique of radial artery pressure waves, without need for calibration (FloTrac/Vigileo [FV]; Edwards Lifesciences, Irvine, CA), conforms to the standard bolus thermodilution method via a pulmonary artery catheter (PAC).

Design: Prospective study.

Setting: Intensive care unit of university hospital.

Participants: Twenty patients for up to 24 hours after cardiac surgery.

Interventions: Simultaneous and triplicate PAC thermodilution and FV cardiac output measurements at 1 and 3 hours after surgery and the following morning.

Measurements and Main Results: Fifty-six simultaneous measurement sets were obtained. Mean cardiac output (PAC) ranged between 2.8 and 10.3 L/min and for the FV method between 3.3 and 8.8 L/min. The coefficient of variation for pooled measurements was 7.3% for the PAC and 3.0% for the FV method. For pooled data, the r² was 0.55 (p < 0.001), with a bias of −0.14, precision of 1.00 L/min, and 95% limits of agreement between −2.14 and 1.87 L/min in a Bland-Altman plot. Also, the FV method tended to overestimate cardiac output when <7 L/min and increased with time, whereas mean arterial pressure increased and PAC cardiac output did not change. Changes in cardiac output correlated (r² = 0.52, p < 0.001).

Conclusions: The FV arterial pressure waveform analysis method is a clinically applicable method for cardiac output assessment without calibration, after cardiac surgery. It performs well at low cardiac outputs but remains sensitive to changes in vascular tone.

Key Words: cardiopulmonary bypass, cardiac surgery, pulse contour, pulmonary artery catheter, cardiac output, thermodilution