Antinociceptive Effect of a Sacro-Coccygeal Epidural of Morphine and Lidocaine in Cats Undergoing Ovariohysterectomy

SIMPLE SUMMARY: Few studies are reporting the use of lumbosacral epidural administration of lidocaine in cats for ovariohysterectomy (OHE). The 2020 global pain council guidelines of the World Small Animal Veterinary Association (WSAVA) also recommended an epidural with lidocaine for ovariectomy as a substitute analgesic method. However, unlike dogs, the spinal cord in cats extends more caudally (first sacral vertebra) and the dural sac terminates at the level of the third sacral vertebra. To reduce the risk of dural sac perforation and intrathecal injections, the sacrococcygeal (SCC) space has been proposed by some authors as a reasonable alternative approach to epidural space, since it prevents the existence of adverse effects related to the volume of solution administered in case of inadvertent intrathecal injection, considering the recommended volumes for the latter are significantly lower compared with those for epidural administration. Intraoperative heart rate, systolic blood pressure, and postoperative UNESP-Botucatu multidimensional composite pain scale (MCPS) and mechanical nociception thresholds (MNT) were used to access the antinociceptive effect of epidural sacrococcygeal administration of lidocaine with morphine in cats submitted to OHE. This study indicates that the implementation of SCC-E could be a simple and effective technique to control perioperative pain in cats submitted to OHE. ABSTRACT: Background: A commonly described analgesic protocol for ovariohysterectomy (OHE) combines systemic opioids, sedatives, and non-steroidal anti-inflammatory drugs. However, systemic analgesia does not fully prevent perioperative visceral and somatic pain triggered by the surgical stimulus. Objectives: To compare the analgesic effects and quality of recovery of systemic analgesia with those of a sacrococcygeal epidural injection of lidocaine and morphine in cats undergoing elective OHE. Methods: Twenty domestic female cats were premedicated with dexmedetomidine (0.01 mg kg(−1) IM) and alfaxalone (1.5 mg kg(−1) IM) and randomly assigned to one of two analgesic protocols: methadone (0.2 mg kg(−1) IM) in the control group CTR (n = 10) and methadone (0.1 mg kg(−1) IM) + epidural lidocaine 2% (0.3 mL kg(−1)) + morphine 1% (0.1 mg kg(−1)) diluted with NaCl 0.9% to a total volume of 1.5 mL in the SCC-E group (n = 10). General anaesthesia was induced with alfaxalone (1 mg kg(−1) IV) and maintained with sevoflurane in 100% oxygen. Non-invasive blood arterial pressure and cardiorespiratory variables were recorded. The quality of recovery was assessed using a simple descriptive scale. Before surgery and 1, 2, 3, 4, 6, and 8 h post-op pain was assessed using the UNESP-Botucatu multidimensional composite pain scale (MCPS) and mechanical nociception thresholds (MNT). The repeated measures analysis of variance (ANOVA) was used to compare groups over time. Comparison between groups was performed using independent samples t-test if the assumption of normality was verified, or the Mann–Whitney test. The chi-square test of independence and exact Fisher’s test were used to compare groups according to recovery quality. Results: Heart rate and systolic arterial pressure increased significantly from baseline values in the CTR group and did not change in the SCC-E group. In the CTR group, MNT and UNESP-Botucatu-MCPS scores increased significantly from baseline for all assessment points and the first 3 h, respectively, whereas this did not occur in the SCC-E group. Conclusions and clinical relevance: Based on our results, the SCC-E administration of lidocaine 2% with morphine 1% is a reasonable option to provide perioperative analgesia in cats submitted to OHE, compared to a systemic protocol alone.