Techniques for Determining Cardiac Output in the Intensive Care Unit

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362 Mohammed & Phillips postoperative cardiac surgery patients compared bioreactance and pulse contour analysis (Flo-Trac Vigileo) with PAC TD and showed similar correlations of the two techniques to TD (0.77 and 0.69, respectively). Sensitivity and specificity for predicting trends in changes in cardiac output changes were 0.91 and 0.95, respectively, for the bioreactance and 0.86 and 0.92, respectively, for the FloTrac-Vigileo. 28 Esophageal Doppler Technique The esophageal Doppler technique measures blood flow velocity in descending aorta by a Doppler transducer (4 MHz continuous or 5 MHz pulsed wave) placed on the tip of an esophageal probe. The probe is introduced in the esophagus and rotated toward the descending aorta. The depth, rotation of the probe, and gain are adjusted to obtain an optimal aortic velocity signal. The positioning of probe is critical in estimating CO, as poor positioning can lead to underestimation of CO. It is operator-dependent and requires specialized training to use effectively. Studies have shown good correlation to TD (r 5 .95). 29 Advantages to its use are that it is relatively less invasive than a PAC, and it provides continuous flow information. Disadvantages are its initial cost, the need for sedation, and the need for a specialist trained in its use. Transgastric Doppler Technique Transgastric Doppler is a similar technique to esophageal Doppler with the probe positioned in the stomach instead of esophagus. In this technique, a thinner silicone probe (6 mm) is used, and its placement usually does not require sedation. The thinner probe can be more difficult to position, and it requires frequent repositioning. It has been shown to have acceptable correlation to TD in a study of 31 patients with 57 simultaneous TD and Doppler readings, which revealed a close correlation with r 5 .91, and P
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