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InFocus

Bupivacaine for midline ovariohysterectomy in cats

Is the use of local anaesthesia with bupivacaine associated with a reduction in post-operative pain score in cats undergoing midline ovariohysterectomy?

Imagine this clinical scenario: a client has decided to spay their cat and is considering an ovariohysterectomy. When assessing the breakdown of costs for this treatment, they notice the fee for a bupivacaine local anaesthetic block and question whether it is necessary.

You decide to review the evidence to find out whether the use of bupivacaine as part of a multimodal anaesthetic protocol in cats undergoing elective ovariohysterectomy reduces post-operative pain scores.

The evidence

Three papers were critically reviewed, all of which were prospective controlled clinical trials. Benito et al. (2016) and Tobias et al. (2006) implemented a blinded randomised method, while Fudge et al. (2020) used a randomised double-blinded placebo-controlled method.

Benito et al. (2016) examined 45 healthy client-owned female cats (mean weight 3.1kg) due to undergo ventral midline incision for ovariohysterectomy. The cats were split into three groups. The treatment group was given bupivacaine, the negative control group was given saline and the positive control group was given saline and meloxicam. The outcomes studied were the requirement for rescue analgesia, the pain score before and after surgery and the mean mechanical nociceptive thresholds before and after surgery.

Tobias et al. (2006) examined 52 healthy client-owned female cats estimated to be at least six months old and weighing over 2.2kg that were due to undergo midline ovariohysterectomy. Two cats were removed from the study due to unexpected complications, leaving a sample size of 50. The cats were split into four groups, with each group administered one of the following medications: carprofen, ketoprofen, butorphanol titrate or bupivacaine. The outcomes studied were the pain scores, the requirement for rescue analgesia and other outcomes irrelevant to the clinical question.

Fudge et al. (2020) studied 212 healthy female cats from a shelter that were aged over two months (weighing more than 0.9kg) and due to undergo ventral midline ovariohysterectomy.  The cats were divided into three groups: the treatment group received bupivacaine, the placebo control group received saline and the sham control group was observation-only. The outcomes studied were the pain score of the patients at two intervals after surgery and the requirement for rescue analgesia.

Limitations of the evidence

All three studies followed a reliable method and had strong study design. However, they were inconclusive in determining the superiority of bupivacaine over other analgesics

All three studies followed a reliable method and had strong study design. However, they were inconclusive in determining the superiority of bupivacaine over other analgesics. This, therefore, weakens the evidence when considered against the clinical question.

Benito et al. (2016) had the following limitations: a small sample size, unclear effects of sedation and the level of experience of the veterinary surgeon was not stated. The pain scale used was also not validated for use on cats.

Tobias et al. (2006) had the following limitations:

  • One cat was given the wrong analgesic, leading to uneven group distribution
  • The varying sedative effects of each medication was not accounted for, which may have impacted the accuracy of pain scoring
  • A lack of clarity about the impact of intravenous fluid therapy on plasma concentrations of medication(s)
  • A lack of sample size calculation
  • A small sample size

The pain scales used by Fudge et al. (2020) had shortcomings in reflecting pain complexity and were not validated for use in cats. Other limitations of this study included the facts that participants in the saline group were older than the other groups, which may have skewed results, and the induction of anaesthesia did not account for the weight of each animal, which may have blunted pain scores.

Summary of findings

All three of the studies found that bupivacaine provided some level of analgesia compared to placebo measures

All three of the studies found that bupivacaine provided some level of analgesia compared to placebo measures. However, they were inconclusive in verifying bupivacaine as a more effective option than other analgesics. These findings must also be considered against the limitations outlined above.

Benito et al. (2016) found no statistically significant difference in pain scores among treatment groups, suggesting all treatments provided a similar level of analgesia. A higher proportion of the group that received bupivacaine required rescue analgesia than the group that received saline, while the group that received meloxicam and saline had the fewest instances of rescue analgesia being required. All the differences reported on rescue analgesia were statistically significant.

Tobias et al. (2006) found that the pain scores for cats receiving bupivacaine were significantly higher one hour post-surgery compared to those receiving butorphanol. But there was no significant difference in pain scores at any time between cats receiving carprofen, ketoprofen and butorphanol.

Fudge et al. (2020) found that there was no significant difference in the pain scores across all groups for cats that weighed under 2.7kg. However, the pain scores for cats over 2.7kg in the bupivacaine group were significantly lower than in the control groups one hour post-recovery and at discharge. None of the cats studied required rescue analgesia.

Conclusion

There is insufficient evidence to support the idea that bupivacaine can cause a reduction in pain scores when used as local anaesthesia for feline ovariohysterectomy. Despite this, bupivacaine administration is cheap and simple to perform so its use as part of a multimodal analgesic protocol is supported.

Bupivacaine administration is cheap and simple to perform so its use as part of a multimodal analgesic protocol is supported

When compared to a control, pain scores for the cats studied were lower after administration of bupivacaine. However, statistical significance was only recorded in one of the studies. Additionally, other medications were found to lower the post-operative pain score to a greater degree.

Further investigation involving larger cohorts, other multimodal combinations and consistent and improved methodologies (particularly in relation to pre-medications, pain scoring systems and anaesthetic location) would be prudent to learn more about the analgesic properties of bupivacaine in cats undergoing ovariohysterectomy.

The full Knowledge Summary can be read in RCVS Knowledge’s open access journal Veterinary Evidence.

Disclaimer

The application of evidence into practice should take into account multiple factors, not limited to individual clinical expertise, patient’s circumstances, owner’s values, the individual case in front of you, the availability of therapies and resources, and the country, location or clinic where you work.

Knowledge Summaries are a resource to help reinforce or inform decision making. They do not override the responsibility or judgement of the practitioner to do what is best for the animal in their care.

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