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CARDIOVASCULAR ANESTHESIA

Cardiac Output Measurement Using the Transesophageal Doppler Method Is Less Accurate Than the Thermodilution Method When Changing Paco₂

Department of Anesthesiology, Osaka Medical College, Takatsuki, Japan; Department of Anesthesia, National Cardiovascular Center, Suita, Japan

Address correspondence and reprint requests to Toshiyuki Sawai, MD, Department of Anesthesiology, Osaka Medical College, 2–7 Daigaku-machi, Takatsuki 569–8686, Japan. Address e-mail to ane026{at}poh.osaka-med.ac.jp.

Cardiac output (CO) determination using transesophageal Doppler is based on the measurement of descending aortic blood flow. Because cerebral blood flow is dependent on Paco₂, an increase in Paco₂ would result in an increase of CO because of the increase in cerebral blood flow and vice versa. We enrolled 30 patients undergoing off-pump coronary artery graft surgery in the study. The CO was determined by both transesophageal Doppler and thermodilution while Paco₂ was maintained at either 30 mm Hg or 40 mm Hg in random order. The CO by thermodilution was significantly higher at Paco₂ of 40 mm Hg (4.17 ± 0.94 L/min) than at 30 mm Hg (3.78 ± 0.85 L/min). On the other hand, there were no significant differences in CO by transesophageal Doppler: 3.85 ± 0.76 L/min at Paco₂ of 40 mm Hg and 3.77 ± 0.74 at 30 mm Hg. Bland-Altman analysis yielded bias and precision of –0.32 and 0.49 L/min at Paco₂ of 40 mm Hg, and –0.01 and 0.34 L/min at 30 mm Hg. These results indicate that both methods of CO measurement are in agreement at 30 mm Hg of Paco₂, but the thermodilution method provides higher values at 40 mm Hg of Paco₂.