Cardiac output estimation with transesophageal Doppler

Background

Transesophageal Doppler monitoring provides continuous, non invasive monitoring of cardiac output by measurement of aortic flow velocities. The first transesophageal monitors developed for clinical use performed inconsistently in anesthetized patients and thus failed to gain wide clinical acceptance [1,2]. A second generation of transesophageal Doppler improved performance compared to the first generation, even if it was still unsuitable to accurately measure absolute cardiac output values [3].

Material and methods

A new developed transesophageal Doppler device for cardiac output estimation (COdopp) monitoring (ODM II, Abbott, USA), which displays aortic blood flow velocity in real time, was prospectively evaluated in 7 critically ill patients. One patient was a COPD with an acute heart failure, the second was abdominal aortic aneurysm post-operative with multiple organ failure, the third a politrauma, and the last a comatose patient affected by an intracerebral hemorrhage. The aim of the study was to assess the reliability and accuracy of this Doppler device, in comparison with the thermodilution method. A 7.5-Fr pulmonary catheter (Abbott, USA) was inserted via left succlavian vein in the 4 patients, and, after hemodynamic stabilization, a Doppler probe was positioned in esophagus, following Doppler signals of discending aorta. To estimate cardiac output, diameter of aorta was automatically calculated from a nomogram based on patient characteristic, including sex, age, height and weight. As reference standard, thermodiluition CO measurements (COtd) were obtained using iced temperature injectate and a dedicated, calibrated computer (Horizon 2000, Mennen). During a 5-min period where the mean arterial pressure variation was less than ± 5 mmHg, repeated simultaneous COtd and COdopp measurements were obtained and defined an epoch. An epoch was accepted for analysis when three CO values with less than 15% variation, largest to smallest, were obtained for each method of CO determination.

Results

51 couplets of data were obtained. Hearth rate range was 56-124. Cardiac output range measured by thermodiluition was 3.4-11.5 while CO range measured by Doppler was 3.6-11.2. Linear regression was good (COdopp = COtd × 0.9155 ± 0.7334; r = 0.9745 and P < 0.0001; r² = 0.9496). Bland and Aitman test [4] showed an acceptable difference of the two standard deviation range of 1.56 l/min (bias = 0.141176 ± 0.389449 l/min [SD]).

Conclusion

Compared with previous results these data improved the reliability of the new transesophageal Doppler to measure absolute value of cardiac output. Further studies are needed to confirm the accuracy of this new transesophageal Doppler device in hemodynamically instable patient.