Dissociative anesthesia using ketamine combined with midazolam, dexmedetomidine, or both, with or without reversal, for orchiectomy in guinea pigs (Cavia porcellus)

The increasing popularity of guinea pigs as pets and their high reproductive capacity have heightened demand for orchiectomy procedures. This study aimed to evaluate the effects of different anesthetic drug combinations on this species. Eighteen male Cavia porcellus (641 ± 135 g) were randomly assigned to three groups (n = 6) after baseline blood glucose measurement: ketamine (15 mg kg -1) combined with midazolam (1 mg kg -1) (M), dexmedetomidine (10 µg kg -1) (D), or half-doses of each (0.5 mg kg-1 midazolam and 5 µg kg -1 dexmedetomidine) (DM). After intramuscular administration, sedation was scored using two systems that assessed posture, response to stimuli, and muscle relaxation. Orchiectomy was then performed under aseptic conditions, with all animals receiving standardized supportive care, including thermal support via a heating mattress and continuous monitoring of vital parameters. A single veterinarian performed all surgeries to ensure consistency. Anesthesia was maintained with isoflurane (1 vol%) via face mask, adjusted by ± 0.25 vol% in response to manipulation and vital signs. Postoperatively, blood glucose was re-measured, and three animals from each group received antagonists: flumazenil (0.1 mg kg -1) in group M, atipamezole (50 µg kg -1) in group D, or half-doses of both drugs in group DM. Recovery was assessed using the blink reflex, time to ventral recumbency, and time to ambulation, with blood glucose levels measured again at the end of recovery. On one sedation scale, group D (score 19, range 18–19) exhibited significantly deeper sedation than group M (14.5, range 7–18), while group DM (18, range 9–19) did not differ significantly from either. Mean heart rate was highest in group M (249 ± 29) compared with groups D (184 ± 16) and DM (180 ± 21). Isoflurane concentration was lowest in group D (0.8 ± 0.2 vol%) compared with groups M (1.5 ± 0.4 vol%) and DM (1.4 ± 0.4 vol%). Antagonists reduced recovery time by 66% in group M, 30% in group D, and 48% in group DM, with significantly shorter times to ambulation observed in groups M and DM. Blood glucose levels did not differ significantly across groups. In conclusion, ketamine combined with dexmedetomidine provided deeper sedation, reduced isoflurane requirements, and, in the groups receiving dexmedetomidine, lowered heart rate compared with midazolam, whereas antagonist administration accelerated recovery in protocols containing midazolam.