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Behavioral responses following eight anesthetic induction protocols in horses
Ann E Wagner1, Khursheed R Mama1, Eugene P Steffey2
1Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, USA.
Objective:
To compare behavioral characteristics of induction and recovery in horses anesthetized with eight anesthetic drug protocols.
Study Design:
Randomized prospective experimental study.
Animals:
Eight horses, 5.5 ± 2.4 years (mean ± SD) of age, and weighing 505 ± 31 kg.
Methods:
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 kg-1; THIO 6 mg kg-1 + PRO 0.5 mg kg-1; THIO 4 mg kg-1 + PRO 1 mg kg-1; THIO 2 mg kg-1 + PRO 1.5 mg kg-1; KET 2 mg kg-1; KET 1.5 mg kg-1 + PRO 0.5 mg kg-1; KET 1 mg kg-1 + PRO 1 mg kg-1; KET 0.5 mg kg-1 + PRO 1.5 mg kg-1. 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.
Results:
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). The best recovery scores were associated with combinations comprised mainly of propofol.
Conclusions:
Combining propofol with either ketamine or thiopental modifies behaviors associated with use of the individual drugs.
Clinical Relevance:
Quality of early anesthesia recovery in horses may be improved by some combinations of propofol with either thiopental or ketamine.