Buprenorphine has gained widespread popularity for use in rabbits, while much less is known about methadone. Our aim was to compare sedative, analgesic, and respiratory effects of methadone and buprenorphine as part of balanced anaesthesia. Forty-eight female New Zealand white rabbits undergoing calvaria defects were randomly equally assigned to receive either 0.03 mg kg⁻¹ of buprenorphine (group B) or 0.3 mg kg⁻¹ of methadone (group M) in combination with 15 mg kg⁻¹ of ketamine and 0.1 mg kg⁻¹ of dexmedetomidine SC. Fifteen minutes later, sedation was scored. A laryngeal mask was placed, and inhalational anaesthesia started. Rescue intraoperative analgesia was administered based on autonomic variations. Arterial blood gases were analysed intra- and postoperatively. Postoperative analgesia was administered if the Rabbit Grimace Scale (RbtGS) score was ≥4. The Mann–Whitney test, t-test, and relative risk followed by chi-square test were used to compare the treatment groups. Deeper sedation was observed in rabbits of group M than in those of group B. Rescue analgesia was administered intraoperatively to seven animals in group B and five in group M (p = 0.739) and postoperatively to three in group B and twelve in group M (p = 0.013). Rabbits of both groups showed short-term respiratory acidosis. RbtGS scores indicated better and longer analgesia in group B compared to group M.

To report rate of unintentional spinal puncture and compare intraoperative effects of a combination of morphine and ropivacaine at a volume of 0.2 mL kg^-1 in the lumbosacral epidural or subarachnoid space. Prospective, observational, experimental study. A total of 36 Edelschwein pigs (34 males and two females) 4 ± 0.5 months old, 55.6 ± 6.5 kg bodyweight (mean ± standard deviation). With pigs anaesthetized in sternal recumbency, an 18 gauge Tuohy needle was inserted at the lumbosacral intervertebral space intending to reach the epidural space. If the dural sac was accidentally punctured, the same volumes of ropivacaine 0.75% (1.45 mg kg^-1) and morphine (0.1 mg kg^-1) were administered spinally. Invasive blood pressure (IBP) and heart rate (HR) (n = 36) and electroencephalogram variables (n = 17) were recorded before and at regular intervals after injection. Differences in IBP over time and between groups were investigated with two-way repeated measures (RM) ANOVA. Remaining values were compared with RM ANOVA on ranks (over time) and U test (between groups, only for HR). p < 0.05. Need for rescue analgesia was reported in the 11 animals that underwent sternotomy before circulatory death. Rate of accidental spinal puncture was 36%. After epidural or spinal injection, IBP significantly decreased over time but mean arterial pressure did not decrease below the treatment cut-off (65 mmHg). There was no significant difference between groups. HR did not vary significantly over time, nor did electroencephalogram variables. Overall antinociceptive efficacy was 81.8%. Lumbosacral epidural or spinal administration of ropivacaine and morphine (0.2 mL kg-1) caused mild cardiovascular alterations, prevented autonomic responses during sternotomy and did not worsen electroencephalographic cortical depression. In pigs, reducing the volume injected when the dural sac is accidentally punctured does not seem necessary.