Comparison of thermodilution bolus cardiac output and Doppler cardiac output in the early post-cardiopulmonary bypass period.

Objective: To evaluate the accuracy of measuring cardiac output (CO) in the early post-cardiopulmonary bypass (CPB) period by comparing thermodilution with Doppler methods.

Design: Prospective and blinded human trial.

Setting: Academic medical center.

Participants: Thirty adult patients undergoing elective coronary artery bypass graft surgery.

Measurements And Main Results: Thermodilution CO (TCO) was obtained in triplicate. Doppler CO (DCO) in triplicate was obtained at the left ventricular outflow tract (LVOT), aortic valve (AV), and right ventricular outflow tract (RVOT). CO measurements were made (1). before CPB (baseline), (2). immediately after CPB, (3).15 minutes after CPB, and (4). 30 minutes after CPB. Before CPB, the DCO at LVOT, RVOT, and AV showed good correlations (r = 0.87, r = 0.88, and r = 0.84, respectively) with TCO. Bias analysis showed no significant difference among TCO and 3 DCOs (p > 0.05 each). Correlation between DCO and TCO decreased but remained significant after CPB (r between 0.57 and 0.85, p < 0.001). The bias among TCO and each of the DCOs at the LVOT, RVOT, and AV increased immediately after CPB (p < 0.01, p < 0.01, and p < 0.05, respectively) and remained significant at 15 minutes and 30 minutes post-CPB except for DCO at the AV. TCO exceeded DCO by 0.44 to 0.72 L/min immediately after CPB. The CO measured by both thermodilution and Doppler methods gradually decreased over time post-CPB. The decrease in CO was significant at 30 minutes post-CPB (p < 0.01).

Conclusion: This study adds further support that DCO is a clinically acceptable method to accurately assess the CO in patients even during periods of uneven regional body temperatures as may occur in the early post-CPB period.