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

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.

Keywords: analgesia; antinociceptive; cat; epidural; locoregional anaesthesia; ovariohysterectomy; pain.

Figure 1

Heart rate (HR) in cats undergoing ovariohysterectomy with (SCC-E group) or without (CTR group) sacrococcygeal epidural (n = 10 in each group). Times: T_BASELINE, prior to skin incision; T_OPEN, abdominal skin incision; T_OV1, from traction to removal of left ovary; T_OV2, from traction to removal of right ovary; T_UTERUS, traction and ligation of the uterus; T_CLOSE, during celiorraphy until the end of surgery. The horizontal line inside the boxes denotes the median value, while the upper and lower whisker bounds denote the maximum and minimum values. The boxes show the interquartile ranges. ^a Significant difference compared with T_BASELINE (p-values were <0.0001, <0.0001, and <0.0001 respectively). ^b Significant difference compared with SCC-E group (p-values were =0.0001, =0.0001, <0.0001, and =0.014 to T_OV1, T_OV2, T_UTERUS, and T_CLOSE, respectively).

Figure 2

Systolic arterial pressure (SAP) in cats undergoing ovariohysterectomy with (SCC-E group) or without (CTR group) sacrococcygeal epidural (n = 10 in each group). Times: T_BASELINE, prior to skin incision; T_OPEN, abdominal skin incision; T_OV1, from traction to removal of left ovary; T_OV2, from traction to removal of right ovary; T_UTERUS, traction and ligation of the uterus; T_CLOSE, during celiorraphy until the end of surgery. The horizontal line inside the boxes denotes the median value, while the upper and lower whisker bounds denote the maximum and minimum values. The boxes show the interquartile ranges. ^a Significant difference compared with T_BASELINE (p-values were 0.009 and 0.006 for T_OV1 and T_OV2, respectively). ^b Significant difference compared with the SCC-E group (p-values were 0.040 and 0.037 for T_OV1 and T_OV2, respectively).

Figure 3

Mean arterial pressure (MAP) in cats undergoing ovariohysterectomy with (SCC-E group) or without (CTR group) sacrococcygeal epidural (n = 10 in each group). Times: T_BASELINE, prior to skin incision; T_OPEN, abdominal skin incision; T_OV1, from traction to removal of the left ovary; T_OV2, from traction to removal of the right ovary; T_UTERUS, traction and ligation of the uterus; T_CLOSE, during celiorraphy until the end of surgery. The horizontal line inside the boxes denotes the median value, while the upper and lower whisker bounds denote the maximum and minimum values. The boxes show the interquartile ranges. ^a Significant difference compared with T_BASELINE (p-values were 0.018 and 0.012 for T_OV1 and T_OV2, respectively). ^b Significant difference compared with group SCC-E (p-values were 0.021 and 0.019 for T_OV1 and T_OV2, respectively).

Figure 4

UNESP-Botucatu-MCPS pain scale recorded for 8 h after surgery in cats undergoing ovariohysterectomy with (SCC-E group) or without (CTR group) sacrococcygeal epidural (n = 10 in each group). Times: T_BEFORE, prior to premedication, T₁, T₂, T₃, T₄, T₆, and T₈ = 1 h, 2 h, 3 h, 4 h, 6 h, and 8 h after surgery completion, respectively. The horizontal line inside the boxes denotes the median value, while the upper and lower whisker bounds denote the maximum and minimum values. The boxes show the interquartile ranges. ^a Significant differences compared with T_BEFORE (p = 0.0045, 0.0004, and 0.0034 for T₁, T₂, and T₃, respectively). ^b Significantly superior compared to the SCC-E group (p = 0.027).

Figure 5

Median and standard deviation of perianesthetic values of mechanical nociceptive thresholds (MNT) in cats undergoing ovariohysterectomy with (SCC-E group) or without (CTR group) sacrococcygeal epidural (n = 10 in each group). Times: T_BEFORE, prior to premedication, T₁, T₂, T₃, T₄, T₆, and T₈ = 1 h, 2 h, 3 h, 4 h, 6 h, and 8 h after the end of the surgery, respectively. The horizontal line inside the boxes denotes the median value, while the upper and lower whisker bounds denote the maximum and minimum values. The boxes show the interquartile ranges. ^a Significant differences compared with T_BEFORE (p = 0.0002, 0.0008, 0.0018, 0.0161, 0.0007, 0.0011 for T₁, T₂, T₃, T₄, T₆, and T₈, respectively). ^b Significant differences compared with the SCC-E group (p = 0.0001, 0.0009, 0.0025, 0.0284, 0.0121, 0.0412 for T₁, T₂, T₃, T₄, T₆, and T₈, respectively).