Intraoperative determination of cardiac output by transesophageal continuous wave Doppler

A new prototype transesophageal transducer with continuous-wave Doppler and pulsed Doppler capabilities was evaluated to calculate intraoperative cardiac output from the main pulmonary artery. Fifteen consecutive patients undergoing elective coronary artery bypass surgery were studied. The main pulmonary artery diameter above the pulmonic valve was measured with the single horizontal plane transesophageal transducer. The pulmonary artery cross-sectional area was calculated from its diameter using the formula: Area = 1 4π(diameter)². Continuous-wave Doppler and pulsed Doppler spectra were recorded from the main pulmonary artery and their flow velocity integrals were then multiplled by pulmonary artery area and heart rate to yield cardiac output. The main pulmonary artery diameter could not be confidently measured in 2 of 15 patients (13%). In the remaining 13 patients, Doppler cardiac output measurements were correlated with simultaneous thermodilution measurements. The closest correlation with thermodilution cardiac output was with the continuous-wave Doppler cardiac output method: R = 0.91, SEE = 0.2 L/min, and y = 1.1x - 0.2 (p < 0.001). The correlation of thermodilution with pulsed Doppler cardiac output was R = 0.83, SEE = 0.5 L/min, and y = 0.86x + 1.0 (p < 0.001). Transesophageal continuous-wave Doppler is a new technique that may be used in selected patients for accurate determination of intraoperative cardiac output.