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Clinical decision making
Midline versus flank approach for spaying cats – is one less painful than the other?
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  1. Bree Merritt and
  2. Abi Collinson
  1. Royal Veterinary College, London, UK
  2. Centre for Evidence-based Veterinary Medicine, University of Nottingham, Sutton Bonington, UK

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This is an updated version of a clinical decision making article originally published in Vet Record in June 2018.7

Bottom line

  • There is no clear evidence that a flank incision is more or less painful than a midline incision when spaying cats. However, the surgeon’s preference and individual patient circumstances should be considered when choosing which approach to take.

Clinical scenario

Dr Perry brings her five-month-old female domestic shorthair kitten, Kylie, in to be spayed. She has read on the internet that cats can be spayed using either a midline or a flank incision. She is very concerned about Kylie being in pain and asks you which is the least painful surgical option for Kylie. You wonder if one approach is less painful than the other.

The question

In [female cats that are being neutered] does [a midline approach compared with a flank approach] [decrease pain following surgery]?

Search parameters

The search strategy can be viewed at https://bestbetsforvets.org/bet/567, and it is also available as a supplement to this article on Vet Record’s website at https://veterinaryrecord.bmj.com/content/186/17/565

Supplemental material

Search outcome

  • One hundred and thirty-three papers were found in the Medline search.

  • One hundred and twenty-six were excluded because they did not answer the question.

  • One was excluded because it was a review article, in vitro research or conference proceedings.

  • In total, six relevant papers were obtained.

  • Two hundred and twenty-nine papers were found in the CAB search.

  • Two hundred and twenty-two were excluded because they did not answer the question.

  • Two were excluded because they were review articles, in vitro research or conference proceedings.

  • In total, five relevant papers were obtained.

  • Overall, six relevant papers were identified.

Search last performed: 24 April 2020

Only five of the six papers identified were evaluated for this evidence summary. Coe et al1 contains the same data set as Grint et al,2 but Grint et al2 was selected for inclusion as it was more relevant to the question being investigated.

Summary of evidence

Paper 1: Prospective evaluation of postoperative pain in cats undergoing ovariohysterectomy by a midline or flank approach3

Patient group: Twenty female cats undergoing ovariohysterectomy.

Study type: Randomised controlled trial.

Outcomes: Pain was assessed using a modified version of the Cambridge SDS (simple descriptive scale) score system. It was assessed before surgery and at 30 minutes, one, two, four, eight, 12 and 24 hours after surgery. Duration of surgery was also recorded.

Key results: No significant difference in postoperative pain was seen between the two approaches (P=0.05). The midline approach was associated with a significantly longer surgery time than the flank approach (13.6 minutes versus 11.1 minutes, P=0.006). Longer surgery time was significantly associated with reduced postoperative pain (P=0.01). However, the midline approach and postoperative pain were not significantly independently correlated. Cats reached their preoperative pain score (or lower) by 24 hours after surgery.

Study weaknesses: The study only included a small group of cats, it was not blinded and the previously optimised pain score had been modified. In addition, multiple statistical tests were performed on a small data set.

Paper 2: Assessment of the influence of surgical technique on postoperative pain and wound tenderness in cats following ovariohysterectomy2

Patient group: A total of 66 female cats undergoing ovariohysterectomy. Most of the cats were domestic shorthairs, and the mean bodyweight was 2.71 kg. The median age of cats undergoing the flank approach was nine months, while the median age of those undergoing the midline approach was 10.5 months. At the preoperative examination, none of the cats were found to be pregnant, lactating or in oestrus.

Study type: Randomised controlled trial.

Outcomes: Pain was observed using a previously described visual analogue scale. Wound tenderness was assessed by digital palpation and scoring on a visual analogue scale, and the number of cats requiring rescue analgesia was documented.

Key results: No significant difference in postoperative pain was seen between the two approaches (P=0.516). However, wound tenderness was significantly higher for flank incisions (mean pain score=381) than for midline incisions (mean pain score=256) (P=0.007). Two cats in each group required rescue analgesia.

Study weaknesses: Only a small number of cats were enrolled in the study, although this number was chosen based on a sample size calculation. Also, the study was not blinded. Blinding was attempted, but this proved to be unfeasible as the cats did not tolerate having bandages on their abdomens.

Surgery was performed by final year veterinary students with variable levels of experience and ability, so the effect observed may be due to the surgeons’ inexperience. There was also subjectivity in the scoring of the outcomes.

Paper 3: Pain assessment in cats undergoing ovariohysterectomy by midline or lateral celiotomy through use of a previously validated multidimensional composite pain scale4

Patient group: A total of 14 healthy female cats from a shelter undergoing ovariohysterectomy. Cats were aged three years or under.

Study type: Randomised controlled trial.

Outcomes: Pain was assessed using the Botucatu multidimensional composite pain scale at one, two, four and six hours after surgery. Duration of surgery, the number of cats needing rescue analgesia and when this was needed were also recorded.

Key results: No significant differences were observed between the two surgical approaches for each individual item of the Botucatu pain scale. However, flank incisions resulted in a higher total pain score (excluding blood pressure – a physiological variable of the pain scale – which was not measured) (P=0.023) and also a higher score for the psychomotor changes subdivision of the scale (P=0.047).

The duration of surgery was not significantly different between the two approaches, with a mean of 24.5 minutes for the midline approach and 28 minutes for the flank approach. Six of the seven cats receiving a flank incision and three of the seven cats receiving a midline incision required rescue analgesia.

Study weaknesses: The anaesthesia and analgesia protocol used in the study is unconventional in UK practice, and the pain score was modified but not revalidated. It was also unclear if the assessors were successfully blinded to the location of each cat’s incision. Although many cats required rescue analgesia, it was not clear when it was given.

Only a small number of cats were enrolled in the study, and basic data of the groups were not explained. Multiple statistical tests on a small data set were performed, increasing the chance of a result being statistically significant by chance.

Paper 4: Assessment of postoperative pain in cats after ovariectomy by laparoscopy, median celiotomy or flank laparotomy5

Patient group: A total of 60 healthy female domestic shorthaired cats.

Study type: Randomised controlled trial.

Outcomes: Pain was assessed at one, two, four, six and 12 hours after endotracheal extubation, using the 4A-Vet pain scale. The duration of anaesthesia, surgery and recovery were also recorded.

Key results: Laparoscopic ovariectomy was found to be the least painful procedure, although it took significantly longer to perform. No significant difference in pain scores between the midline and flank approaches were seen.

Cat undergoing ovariohysterectomy via a midline incision

Study weaknesses: A small number of cats were enrolled in the study, and no sample size calculation was performed. There was also no blinded investigator to measure outcomes. All procedures were performed with the assistance of veterinary students, and this may have affected the results, particularly the duration of surgery. It should also be noted that the 4A-Vet scale has been validated for use in dogs but not for use in cats.

Paper 5: Prospective comparison of perioperative wound and pain score parameters in cats undergoing flank vs midline ovariectomy6

Patient group: Seventy-five healthy female cats presented for elective ovariectomy. Cats showing signs of oestrus, pregnancy or lactation at the preoperative examination were excluded.

Study type: Randomised controlled trial.

Outcomes: Pain was measured before surgery using the Colorado State University feline acute pain scale (FAPS). Pain was then reassessed one hour after surgery, at the time of discharge and at three and 10 days after surgery using the FAPS, a dynamic and interactive visual analogue scale (DIVAS) and a simple descriptive scale of pain response to wound pressure (SDSwound). Also recorded at these times were any swelling of the surgical wound, discharge or periwound erythema.

Duration of surgery and anaesthesia, as well as any intraoperative complications (including hypotension, haemorrhage, slipping of ligatures or break in aseptic technique), were also recorded.

Key results: Duration of surgery, duration of anaesthesia and the requirement for an intravenous fluid bolus did not vary significantly between the two surgical approaches.

FAPS scores for cats in both groups were significantly higher one hour after surgery than before surgery (P=0.0002). However, FAPS, SDSwound and DIVAS scores for cats in the flank group were significantly higher than those for cats in the midline group one hour after surgery and at the time of discharge (P=0.0004 for FAPS).

Three days after surgery, cats in the midline group had significantly higher FAPS, SDSwound and DIVAS scores than the flank group (P=0.016 for FAPS). At 10 days after surgery, cats in the midline group still had significantly higher FAPS scores than cats in the flank group (P=0.045), but there were no significant differences in the SDSwound and DIVAS scores between the two groups.

Study weaknesses: The FAPS has not been validated, and only moderate to good inter-rater reliability was found in this study. In addition, low numbers of cats were presented for postoperative assessment, with only 68 per cent returning for examination three days after surgery and 46.7 per cent returning for examination 10 days after surgery.

Cats underwent an ovariectomy, but the majority of cats in the UK will undergo ovariohysterectomy. Also, all procedures were performed by veterinary students under supervision, and this may have affected the results obtained, particularly with regard to the duration of surgery.

Comments

The studies are difficult to compare as each of them used a different pain scale, analgesia protocol and timings of postoperative pain scoring. The pain scales that were used were also of variable validity.

In addition, the experience of the surgeons and the actual surgery being performed varied. Ovariectomies were carried out in two studies, whereas the majority of cats spayed in the UK will likely undergo an ovariohysterectomy. Therefore, the findings of these studies should be interpreted with care.

All pain scales involve interpretation of a cat’s behavioural expression of pain, which can be variable, and interpretation is subjective and requires training. The nature of the question also makes it difficult to blind the trial. It is impossible to blind the surgeon to the intervention, and it is very difficult to blind the assessor, which is especially problematic as the assessment is subjective.

Two of the studies found the flank approach to have a significantly higher pain score on the day of surgery. However, the cats in one of these studies4 did not receive analgesia routinely used in the UK, so this difference may not be clinically significant in UK patients.

In the second study,6 this effect was reversed at three and 10 days after surgery, with the midline group demonstrating significantly higher pain scores. This was the only study to score pain for more than 24 hours after surgery. However, there were low numbers of cats presented for postoperative assessment, which makes the significance of these results difficult to definitively translate to clinical practice.

Critically Appraised Topics (CATs) are a standardised, succinct summary of research evidence organised around a clinical question, and a form of evidence synthesis used in the practice of evidence-based medicine (EBM) and evidence-based veterinary medicine (EBVM). Access to CATs enables clinicians to incorporate evidence from the scientific literature into clinical practice. CATs will be published regularly in the Clinical Decision Making section of Vet Record.

References

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