The recovery of horses from inhalant anesthesia: A comparison of halothaneand isoflurane

Objective-Recovery is one of the more precarious phases of equine general a nesthesia. The quality and rate of recovery of horses from halothane and is oflurane anesthesia were compared to determine differences in the character istics of emergence from these commonly used inhalant anesthetics. Experimental Design-Prospective. randomized blinded clinical trial. Sample Population-A total of 96 Thoroughbred and 3 Standardbred racehorses admitted for elective distal forelimb arthroscopy. Methods-All horses were premedicated with intravenous xylazine, induced wit h guaifenesin and ketamine, and maintained on a large animal circle system fitted with an out of the circle, agent specific vaporizer. Recoveries were managed by a blinded scorer with a standardized protocol. A 10 category sc oring system was used to assess each horse's overall attitude, purposeful a ctivity, muscle coordination, strength and balance from the time of arrival in recovery to standing. Times to extubation, sternal recumbency and stand ing were recorded. Median recovery scores and mean times to extubation, ste rnal and standing were compared using the Mann-Whitney U test and student's t test, respectively. Results-The median score for horses recovering from halothane was lower (20 .0; range, 10 to 57) than that for horses recovering from isoflurane (27.5; range, 10 to 55). Horses in the two groups were extubated at similar mean times (halothane, 11.3 +/- 5.5 and isoflurane? 9.5 +/- 5.2 minutes) but hor ses recovering from isoflurane achieved sternal recumbency (halothane, 37.7 +/- 12.1 and isoflurane, 24.7 +/- 8.8 minutes) and stood (halothane, 40.6 +/-: 12.9 and isoflurane, 27.6 +/- 9.6 minutes) sooner than those recoverin g from halothane. Conclusions-The recovery of horses from isoflurane anesthesia was mon rapid but less composed than that from halothane. Clinical Relevance-The quality of recovery following isoflurane was worse t han after halothane anesthesia using the criteria chosen for this study. Ho wever, the range of recovery scores was similar for both groups and all hor ses recovered without significant injury. (C)Copyright 2000 by The American College of Veterinary Surgeons.