MAINTENANCE OF ANESTHESIA WITH SEVOFLURANE AND OXYGEN IN MECHANICALLY-VENTILATED HORSES SUBJECTED TO EXPLORATORY LAPAROTOMY TREATED WITH INTRA-OPERATIVE AND POST-OPERATIVE ANESTHETIC ADJUNCTS

Eight healthy horses premedicated with xylazine and induced with ketam ine were used to evaluate sevoflurane in oxygen for maintenance of ana esthesia during elective exploratory laparotomy. After orotracheal int ubation, horses were hoisted, placed in dorsal recumbency on a padded surgery table, and received sevoflurane in oxygen for maintenance of a naesthesia. The horses were allowed to breathe spontaneously until ins trumented; then, they were mechanically ventilated to maintain the PaC O2 between 35 and 45 mmHg. Systolic (SAP), diastolic (DAP), and mean ( MAP) arterial blood pressures, heart rate (HR), EGG, respiratory rate, an estimation of the saturation of haemoglobin with oxygen in periphe ral arterial blood (SpO2), nasal temperature, end-tidal CO2 (ETCO2), e nd-tidal sevoflurane (ETSEVO), and vaporiser concentration were record ed every 5 min post induction; arterial blood samples were obtained so on after induction, at 30 min after induction, and every hour thereaft er until surgery was completed. Recovery data including times from the sevoflurane vaporiser being turned off to first movement, to sternal recumbency, and to standing, number of attempts to stand, and recovery score (between 1 = safe, smooth and 6 = stormy, major injury to horse ) were collected. Analysis of variance was performed using physiologic al data collected over 195 min of anaesthesia, the longest time period during which all 8 horses were instrumented. Time effects (P<0.05) fo r HR, SAP, DAP, MAP, and nasal temperature were identified. Heart rate peaked at 45 min and declined over the course of the procedure. Arter ial blood pressure generally decreased over time. Body temperature dec reased over time. From 15 to 195 min mean ETSEVO concentration ranged from 2.0 to 3.3%, while mean vaporiser settings ranged from 3.7 to 5.5 %. Three horses received intra-operative ketamine; all horses received dobutamine infusions; and 2 horses received intra-operative calcium-d extrose, Total anaesthesia time was 222-316 min (mean +/- s.d. 269 +/- 31 min). Time from aiming the sevoflurane vaporiser off to first move ment was mean +/- s.d. 18 +/- 15 min; to sternal recumbency was 54 +/- 22 min; to standing was 65 +/- 27 min; and to returning the horse to the stall in the ward was 78 +/- 24 min. Six horses stood on the first attempt; 2 horses stood on the second attempt. The median recovery sc ore was one (1-3). In conclusion, sevoflurane provided a stable, easil y controllable anaesthetic plane during prolonged exploratory laparoto mies; horses experienced smooth, safe recoveries after maintenance of anaesthesia with sevoflurane following routine anaesthetic induction a nd post operative xyalzine administration.