Comparison of Two Isoflurane Delivery Systems for Maintaining Anesthesia in Horses: End-Tidal Closed-Loop Target-Controlled Versus Out-Of-Circuit Vaporizer

The purpose of this study was to compare two different isoflurane (Iso) delivery systems: (1) end-tidal closed-loop target-controlled infusion (ETCLo-TCI) system and (2) out-of-circuit vaporizer (VOC)-in horses undergoing surgery. Twenty-four horses undergoing scheduled surgery were enrolled in this study. Anesthesia was maintained using Iso delivered either by a calibrated TEC 4 VOC (group V, n = 14) or an ETCLo-TCI system (group I, n = 10). Data were collected within the first hour of anesthesia on the consumption of Iso, the number of anesthetist drug delivery adjustments (modifing the vaporizer setting or the FE'Iso target in the software), the number of fresh gas flow changes, and the time taken to reach the first FE'Iso target (1.5%) after induction. The median consumption of Iso and the median consumption of Iso per kilogram of body weight during the first hour of anesthesia were significantly lower in group I compared with group V (20.5 [9.3-31.4] vs. 29.1 [21.5-43.0]) mL (P = .003) and 0.042 (0.028-0.052) versus 0.062 (0.037-0.094) mL kg−1 (P = .009). The median number of anesthetist drug delivery adjustments was significantly lower in group I compared with group V (1.5 [0-3] vs. 4 [3-9]; P = .0002). No significant difference was found in FGF changes and in the time taken by both systems to reach the end-tidal target.