[The effects of arterial blood halothane or enflurane concentration on the circulatory system]

The effects of halothane (H) or enflurane (E) concentration on the circulatory system were studied in dogs. Two hours of halothane or enflurane anesthesia resulted in a linear dose-dependent decrease in circulatory indices including mean arterial pressure (mAP), cardiac index (CI) and left ventricular peak dp/dt/IP (peak dp/dt/IP). Systemic vascular resistance (SVR) was unchanged during either anesthesia. The correlations between the percent change of circulatory indices and the logarithm of the blood anesthetic concentrations were expressed by correlation coefficients (r): mAP, r = -0.718 (H), and -0.650 (E): HR, r = -0. 329 (H), and -0.352 (E): CI, r = -0.597 (H), and - 0.596 (E): SI, r = -0.389 (H), and -0.449 (E): SVR, r = -0.161 (H), and -0.030 (E): peak dp/dt/IP, r = -0.708 (H), and -0.871 (E). Using several indices of anesthetic depth including MAC, MAC-EI and MAC-BAR, the percent changes of mAP, CI and peak dp/dt/IP were calculated at the same anesthetic depth using halothane or enflurane. These results indicate that enflurane depresses these circulatory indices more than halothane. The differences were: mAP, 14.51 +/- 1.46%: CI, 8.14 +/- 1.86%: peak dp/dt/IP, 7.38 +/- 3.95% (mean +/- SD).