The influence of butorphanol dose on characteristics of xylazine-butorphanol-propofol anesthesia in horses at altitude.
OBJECTIVE
To characterize behavioral and physiological responses to short-term, unsupplemented intravenous (IV) anesthesia in healthy horses at high altitude (2240 m), and to test the hypothesis that the dose of butorphanol modifies the response of the horse to propofol anesthesia following xylazine pre-medication.


METHODS
Randomized prospective butorphanol dose cross-over experimental design. Animals Eight healthy horses, 13 +/- 6 (mean +/- SD) years of age, and weighing 523 +/- 26 kg.


METHODS
Each horse was anesthetized three times with at least 3 weeks between each anesthesia. After collecting pre-drug data, xylazine (0.5 mg kg(-1)) was given IV. Five minutes later butorphanol was given IV according to a randomized order of three doses: 0.025, 0.05 and 0.075 mg kg(-1). Five minutes later, anesthesia was induced with propofol, 2 mg kg(-1) IV. Data on heart rate (HR) and respiratory rate (f(r)), mean arterial blood pressure, P(a)O(2), P(a)CO(2) and pH(a) were collected before, during and for 60 minutes following anesthesia, and quality of induction and recovery was scored.


RESULTS
The pre-drug values for the three butorphanol groups did not differ. The combined pre-drug values from the 24 studies were HR, 33 +/- 7 beats minute(-1); f(r), 11 +/- 3 breaths minute(-1); P(a)O(2), 67 +/- 7 mmHg; P(a)CO(2), 36 +/- 4 mmHg; and pH(a), 7.42 +/- 0.04. Five minutes after anesthetic induction P(a)O(2) decreased and P(a)CO(2) increased 14.5 +/- 7.7 and 5.1 +/- 4.9 mmHg, respectively, but returned to pre-drug levels within 15 minutes of anesthetic recovery. There were no significant butorphanol dose-related differences in physiological results, anesthetic induction and recovery quality scores or recovery time.


CONCLUSIONS
Dose of butorphanol did not markedly influence study results. Notably, low P(a)O(2) values related to geographic location of study and general anesthesia indicates a narrow margin of error for hypoxemia-related complications in anesthetized horses breathing unsupplemented air at high altitude.
Garcia Lascurain
Alma A
AA
Department of Medicine and Surgery in Equines, School of Veterinary Medicine of the National Autonomous University of Mexico, Mexico City, Mexico.
Sumano Lopez
Hector
H
Steffey
Eugene P
EP
Santillán Doherty
Patricio
P
Hernandez
Enrique Núñez
EN
D000531:Altitude; D000762:Anesthesia Recovery Period; D000771:Anesthesia, Intravenous / Q000662:veterinary; D018686:Anesthetics, Intravenous / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure; D002077:Butorphanol / Q000008:administration & dosage* / Q000494:pharmacology*; D002245:Carbon Dioxide / Q000097:blood; D004305:Dose-Response Relationship, Drug; D006339:Heart Rate / Q000187:drug effects; D006736:Horses; D010100:Oxygen / Q000097:blood; D015742:Propofol / Q000494:pharmacology*; D014991:Xylazine / Q000494:pharmacology*
D018686:Anesthetics, Intravenous; D002245:Carbon Dioxide; D014991:Xylazine; D002077:Butorphanol; D010100:Oxygen; D015742:Propofol