Recovery from sevoflurane anesthesia in horses: comparison to isoflurane and effect of postmedication with xylazine.
OBJECTIVE
To compare recovery from sevoflurane or isoflurane anesthesia in horses.


METHODS
Prospective, randomized cross-over design.


METHODS
Nine Arabian horses (3 mares, 3 geldings, and 3 stallions) weighing 318 to 409 kg, 4 to 20 years old.


METHODS
Horses were anesthetized on three occasions with xylazine (1.1 mg/kg), Diazepam (0.03 mg/kg intravenously [i.v.]), and ketamine (2.2 mg/kg i.v.). After intubation, they were maintained with isoflurane or sevoflurane for 90 minutes. On a third occasion, horses were maintained with sevoflurane and given xylazine (0.1 mg/kg i.v.) when the vaporizer was turned off. Horses were not assisted in recovery and all recoveries were videotaped. Time to extubation, first movement, sternal, and standing were recorded as was the number of attempts required to stand. Recoveries were scored on a 1 to 6 scoring system (1 = best, 6 = worst) by the investigators, and by three evaluators who were blinded to the treatments the horses received. These blinded evaluators assessed the degree of ataxia present at 10 minutes after each horse stood, and recorded the time at which they judged the horse to be ready to leave the recovery stall.


RESULTS
Mean times (+/- SD) to extubation, first movement, sternal, and standing were 4.1 (1.7), 6.7 (1.9), 12.6 (4.6), and 17.4 (7.2) minutes with isoflurane; 3.4 (0.8), 6.6 (3.1), 10.3 (3.1), and 13.9 (3.0) minutes with sevoflurane; and 4.0 (1.2), 9.1 (3.3), 13.8 (6.5), and 18.0 (7.1) with sevoflurane followed by xylazine. Horses required a mean number of 4 (2.3), 2 (0.9), and 2 ( 1.6) attempts to stand with isoflurane, sevoflurane, and sevoflurane followed by xylazine respectively. The mean recovery score (SD) for isoflurane was 2.9 (1.2) from investigators and 2.4 (1.1) from blinded evaluators. For sevoflurane, the mean recovery score was 1.7 (0.9) from investigators and 1.9 (1.1) from evaluators, whereas the recoveries from sevoflurane with xylazine treatment were scored as 1.7 (1.2) from investigators and 1.7 (1.0) from blinded evaluators.


CONCLUSIONS
Recoveries appeared to vary widely from horse to horse, but were significantly shorter with sevoflurane than isoflurane, although sevoflurane followed by xylazine was no different from isoflurane. Under the conditions of the study, recoveries from sevoflurane and sevoflurane followed by xylazine were of better quality than those from isoflurane.


CONCLUSIONS
Sevoflurane anesthesia in horses may contribute to a shorter, safer recovery from anesthesia.
Matthews
N S
NS
Department of Small Animal Medicine and Surgery, Texas A&M University, College Station 77843-4474, USA.
Hartsfield
S M
SM
Mercer
D
D
Beleau
M H
MH
MacKenthun
A
A
D000759:Adjuvants, Anesthesia; D000316:Adrenergic alpha-Agonists; D000769:Anesthesia, Inhalation / Q000662:veterinary*; D000778:Anesthetics, Dissociative; D018685:Anesthetics, Inhalation; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D018592:Cross-Over Studies; D003975:Diazepam; D005260:Female; D006736:Horses / Q000502:physiology*; D007530:Isoflurane; D007649:Ketamine; D008297:Male; D008738:Methyl Ethers; D011446:Prospective Studies; D000077149:Sevoflurane; D016037:Single-Blind Method; D013997:Time Factors; D014743:Videotape Recording; D014991:Xylazine
D000759:Adjuvants, Anesthesia; D000316:Adrenergic alpha-Agonists; D000778:Anesthetics, Dissociative; D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D014991:Xylazine; D000077149:Sevoflurane; D007649:Ketamine; D007530:Isoflurane; D003975:Diazepam