Multimodal analgesia is an essential part of a modern, balanced anesthetic technique. Local anesthetics are effective tools in the management and prevention of surgical pain. Bupivacaine is conserved a long acting local anesthetic that has been shown to be effective in controlling surgical pain in cats. It must be administered at the source of pain, and so intraoperative administration is required.
The purpose of this study was to determine the efficacy of bupivacaine for post-operative pain control in cats undergoing ovariohysterectomy. This study was designed as a prospective double blinded case control trial.
267 female cats presenting for routine, elective OHE to a high volume spay-neuter practice were recruited into the study. Cats were >2m age and 0.9kg body weight. Cats that were pregnant, in heat, or had an intraoperative complication were excluded from the study. Cats were block randomized by day to receive either bupivacaine, placebo, or sham.
Cats were pre medicated with buprenorphine, ketamine, and dexmedetomidine, intubated and maintained on isoflurane. OHE was performed by experienced high-volume surgeons via a midline approach. Two of the surgeons utilized a pedicle ligation technique and one used a pedicle tie. The times to administer interventions were recorded.
Cats in the treatment group received bupivacaine 2mg/kg total dose divided into the left and right suspensory ligaments and mesovarium of the ovary, the uterine body just cauda to the bifurcation, and the SQ tissue between the closed linea and skin using a 25g needle. The placebo group received saline at these sites, and in the sham group the sites were simply identified.
Pain was assessed by a veterinary technician trained in pain scoring techniques. Pain was scored at 1h post op and just before discharge (<7h post op). Initially, a modified UNESP
Botucatu multidimensional composite pain scale (MCPS) was used to score cats pain, in conjunction with a 0-10 numerical scale. As the study progressed, the MCPS was replaced with a modified version of the Colorado scale due to difficulty and time constraints performing the MCPS.
A total of 267 cats were enrolled in the study, of which 212 met all inclusion criteria. 71 cats were included in the bupivacaine group, 58 in the saline group, and 83 in the sham group. Cats were stratified by weight into 0.9–1.5 kg, >1.5–2.7 kg and >2.7 kg groups for the purposes of analysis.
In the lower two weight categories there was no significant difference in pain score at both time points between groups (while the pain scores were numerically lower in the other groups this did not attain statistical significance). In the higher weight class, the bupivacaine group had lower pain scores at both time points. No cat included in the study required rescue analgesia.
Surgical times were measured and averaged 5.5 minutes. The median time to administer bupivacaine was 69s, of which 30s was due to calculating dose and drawing up the drug.
Some drawbacks to this study were present. One of these was the change in pain scoring technique partway through the study, with the use of a non-verified pain scale limiting interpretation of results. Rescue analgesia was given to any cat with moderate to severe pain.
The authors of this study concluded that a targeted bupivacaine block reduced post-operative pain in cats. This block may provide a safe and inexpensive option for pain control in cats presenting for routine spay. The authors also concluded that the MCPS was not an ideal pain scoring system for a high volume spay setting.
Oliveira JP, Mencalha R, Santos Sousa CA, et al. Pain assessment in cats undergoing ovariohysterectomy by midline or lateral celiotomy through use of a previously validated multidimensional composite pain scale. Acta Cir Bras 2014; 29: 633–638.