Cardiovascular, antinociceptive and electroencephalographic effects of epidural and unintentional spinal anaesthesia in pigs: an observational prospective trial.

Objective 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.Study Design Prospective, observational, experimental study.Animals 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).Methods 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.Results 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%.Conclusions And Clinical Relevance 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.