Feedback control of enflurane delivery in dogs--inspired compared to end-tidal control

A technique was studied for the rapid induction of anesthesia in a closed rebreathing circuit using feedback control of end-tidal enflurane concentration. This technique was compared to anesthetic induction using a constant inspired concentration. In one group of seven dogs, end-tidal enflurane concentration was maintained at 2.0%. Electronic feedback control automatically decreased the inspired concentration from a maximum of 3.7% to 2.1% during a 4-hr period. In the second group of seven dogs, the inspired enflurane concentration was 2.0% throughout the study. There was no statistically significant difference between the two groups with regard to enflurane uptake, heart rate, blood pressure, or cardiac output. Enflurane uptake was higher in the first group only during the first 6 min after induction. The induction technique that used feedback control to automatically adjust the inspired enflurane concentration appeared to have no adverse cardiovascular effects beyond those present during an induction using a constant inspired concentration.