Onset and quality of sedation after intramuscular administration of dexmedetomidine and hydromorphone in various muscle groups in dogs.

Objective: To compare onset time and quality of sedation achieved by IM injection of hydromorphone and dexmedetomidine into either the semimembranosus, cervical, gluteal, or lumbar muscle groups in dogs.

Design: Prospective, randomized, crossover study.

Animals: 7 dogs.

Procedures: Each dog was assigned to receive each treatment in random order, and at least 1 week elapsed between treatments. Dogs were sedated with dexmedetomidine and hydromorphone combined and injected IM into the assigned muscle group. An observer unaware of group assignments assessed physiologic variables every 5 minutes for 30 minutes, and a videographic recording was obtained. Recordings were evaluated by 16 individuals who were unaware of group assignments; these reviewers assessed time to onset of sedation and assigned a sedation score to each dog every 5 minutes.

Results: Resting pulse and respiratory rates did not differ among injection site groups. The semimembranosus site had a significantly higher sedation score than all other sites, and the cervical site had a significantly higher sedation score than the lumbar and gluteal sites. The semimembranosus and cervical sites had significantly shorter time to onset of sedation than did the gluteal and lumbar sites.

Conclusions And Clinical Relevance: When the combination of dexmedetomidine and hydromorphone was used to induce sedation in dogs, rapid and profound sedation was achieved with IM injection into the semimembranosus muscle.