Evaluation of xylazine, butorphanol and propofol for short-term intravenous anesthesia in horses.

The purpose of this study was to evaluate selected physiological and behavioral responses to xylazine (XYL)–butorphanol (BUTOR) supplemented propofol (PROP) anesthesia in horses and the influence of BUTOR dose on outcome. Eight horses [13 ± 2 (mean ± SE) year], weighing 524 ± 9 kg were anesthetized three times with at least 3 weeks between each anesthesia. After collecting pre-drug data, horses were always medicated with 0.5 mg kg[sup -1] XYL IV. Five minutes later, BUTOR was administered IV according to a randomized order of three doses: 0.025, 0.05, and 0.075 mg kg[sup -1] ; all horses received the complete dose set. Five minutes after BUTOR, anesthesia was induced with PROP, 2 mg kg[sup -1] IV. The resultant data were grouped by treatment and parameter and analyzed by RM anova; p < 0.05 considered significant. The pre-drug values within a treatment group were not significantly different. The combined pre-drug values were heart rate (HR) = 32 ± 1 beats minute[sup -1] , respiratory frequency (f ) = 11 ± 1 breaths minute[sup -1] , PaO[sub 2] = 66.6 ± 1.5 mm Hg (Mexico City is 2240 m above sea level; yearly average P[sub BAR] = 582 mm Hg), PaCO[sub 2] = 36.2 ± 0.7 mm Hg and pH[sub a] = 7.42 ± 0.01. During 20 minutes of anesthesia HR, f and PaCO[sub 2] were not significantly different from pre-drug values. The PaO[sub 2] decreased by an average of 12 mm Hg during anesthesia but returned to the pre-drug values within 15 minutes after the horses stood. The quality of anesthetic induction varied and brief paddling limb movements occurred occasionally after recumbency regardless BUTOR dose. Recovery from anesthesia was subjectively graded good to excellent. The BUTOR dose did not significantly influence recumbency time (33 ± 2 minutes for all studies). The BUTOR dose did not markedly influence study results. However, some physiological effects likely were confounded by the notably low PaO[sub 2] that was influenced... [ABSTRACT FROM AUTHOR]