In this randomized prospective experimental study, eight horses between 5.5 ± 2.4 years (mean ± SD) of age, and weighing 505 ± 31 kg, were included.
After xylazine pre-medication, each of eight horses was anesthetized on four occasions using one of eight different anesthetic induction protocols which incorporated various combinations of ketamine (KET), propofol (PRO), and thiopental (THIO):
THIO 8 mg kg1; THIO 6 mg kg1 + PRO 0.5 mg kg1; THIO 4 mg kg1 + PRO 1 mg kg1; THIO 2 mg kg1 + PRO 1.5 mg kg1; KET 2 mg kg1; KET 1.5 mg kg1 + PRO 0.5 mg kg1; KET 1 mg kg1 + PRO 1 mg kg1; KET 0.5 mg kg1 + PRO 1.5 mg kg1.
Quality of induction and recovery were scored from 1 (poor) to 5 (excellent), and time taken to achieve lateral recumbency, first movement, sternal recumbency, and standing were evaluated.
Time taken to achieve lateral recumbency after drug administration differed significantly (p < 0.0001) among the various combinations, being shortest in horses receiving THIO-8 (mean ± SD, 0.5 ± 0.3 minutes) and longest in horses receiving KET-2 (1.4 ± 0.2 minutes). The best scores for induction quality were associated with KET-1.5 + PRO-0.5, and the worst scores for induction quality were associated with KET-2, although the difference was not significant. Time to first movement varied significantly among drug protocols (p = 0.0133), being shortest in horses receiving KET-2 (12.7 ± 3.6 minutes) and longest in horses receiving THIO-8 (29.9 ± 1.5 minutes). Horses receiving THIO-8 made the greatest number of attempts to attain sternal posture (6.5 ± 4.7) and to stand (1.6 ± 0.8). Horses in the THIO-8 treatment also received the poorest recovery scores (3.3 ± 1.0 and 3.0 ± 0.7 for sternal and standing postures, respectively).
Combining propofol with either ketamine or thiopental modifies behaviors associated with use of the individual drugs.
Quality of early anesthesia recovery in horses may be improved by some combinations of propofol with either thiopental or ketamine.
Source: Wagner, AE, Mama, KR, Steffey, EP, Brevard, LF, Hellyer, PW (2002): Behavioral responses following eight anesthetic induction protocols in horses. In: Veterinary Anaesthesia and Analgesia 29 (4), pp 207-211.
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