Effects of hydromorphone alone and combined with medetomidine-vatinoxan or dexmedetomidine on alfaxalone induction dose and mean arterial pressure in dogs anesthetized with sevoflurane.

OBJECTIVE

To evaluate the dose of alfaxalone needed for induction of anesthesia following sedation with medetomidine-vatinoxan plus hydromorphone (MVH), dexmedetomidine plus hydromorphone (DH), or hydromorphone (H) alone. A secondary objective included evaluating selected cardiopulmonary variables before, during, and after sedation and general anesthesia with sevoflurane in healthy dogs.

STUDY

DESIGN

Prospective, randomized, masked, crossover.

ANIMALS: Eight healthy Beagle dogs, 3-4 years old.

METHODS

All dogs received three intramuscular (IM) treatments: H (0.1 mg kg-1), DH (0.005 mg kg-1 + 0.1 mg kg-1, respectively), or MVH (0.01 mg kg-1 + 0.2 mg kg-1 + 0.1 mg kg-1, respectively) at least 6 days apart. General anesthesia was induced with alfaxalone 20 minutes after treatment administration and maintained for 60 minutes with 2.8% sevoflurane (expired). Sedation scores, selected cardiopulmonary variables, and recovery scores were measured before, during, and after anesthesia at selected timepoints. Mixed-effects ANOVA and ANOVA on ranks were used to evaluate differences between treatments, time, and their interaction, and Tukey-Kramer method was used for post hoc analysis (p < 0.05). Data are presented as mean ± SD or median (range).

RESULTS

Dogs given MVH required a lower dose of alfaxalone for induction of anesthesia (0.77 ± 0.4 mg kg-1) compared to DH and H (1.16 ± 0.34 mg kg-1; p = 0.02, 1.13 ± 0.18 mg kg-1; p = 0.02), and had a higher incidence (50%; p = 0.038) and longer duration [median; 10 (0-35) minutes] of hypotension during sevoflurane anesthesia compared to H [0%; 0 (0-0) minutes; p = 0.040] but not DH (p = 0.272).

CONCLUSIONS AND CLINICAL RELEVANCE: Premedication with MVH provided the greatest alfaxalone-sparing effect. However, this treatment was associated with lower arterial pressures and clinically relevant hypotension. Off-label use of medetomidine-vatinoxan before sevoflurane-based anesthesia should be used with caution due to a high incidence of hypotension.