Measurement of pulmonary blood flow with transesophageal two-dimensional and Doppler echocardiography

Abstract

Transesophageal echocardiography permits measurement of the pulmonary artery diameter (two-dimensional echocardiography) and pulmonary artery blood flow velocity (pulsed-wave Doppler). These measurements considered with the heart rate allow for the determination of pulmonary artery blood flow, which is equivalent to cardiac output. This study compared the precision of transesophageal Doppler-derived cardiac output (DdCO) with the precision of thermodilution cardiac output (TdCO) and examined the agreement between DdCO and TdCO in 33 cardiac surgical patients. The proximal pulmonary artery diameter was measured in triplicate during systole and end expiration, and the local blood flow velocity was recorded on video tape. The instantaneous pulmonary artery blood flow velocity (centimeters per second) for three random cardiac beats was integrated with respect to time. DdCO was calculated as the product of the flow velocity integral (centimeters per beat), heart rate (beats per min), and the mean cross-sectional area (centimeters squared) of the main pulmonary artery. At the same time that the velocity recordings were made, three serial determinations of TdCO were made by an independent observer. Pulmonary blood flow could be measured in 25 of the 33 patients. The anatomical relationship among the esophagus, the left main stem bronchus, and the pulmonary artery did not allow adequate imaging of the pulmonary artery in 8 (24%) of the patients. A total of 45 sets of triplicate measurements were made. The range of cardiac outputs encountered was 1.7-6.6 1·min-1 by TdCO and 1.5-6.9 1·min-1 by DdCO. The 95% confidence limits for the difference between the two methods (agreement) was 0.030 ± 0.987 1·min-1. The repeatability coefficient for DdCO, using a single mean value for pulmonary artery diameter, was ± 0.588 1·min-1 and for thermodilution was ±0.947 1·min-1. Transesophageal echocardiographic analysis of axial flow velocity and flow volume in the pulmonary artery is an alternate method of measuring cardiac output that compares favorably with the thermodilution technique.