Pratt CL, Balakrishnan A, et al. A prospective randomized, double-blinded clinical study evaluating the efficacy and safety of bupivacaine versus morphine-bupivacaine in caudal epidurals in cats with urethral obstruction. J Vet Emerg Crit Care (San Antonio). 2020 Feb 26.
Lower urinary obstruction is one of the most common emergency presentations in feline medicine. Cats with a lower urinary obstruction require urinary catheterization, a procedure that necessitates heavy sedation or anesthesia. These patients also lack cardiovascular stability, making these procedures higher risk. There is also longer-term pain associated with obstruction and catheterization, making the need for post de-obstruction analgesia important. A technique to help lower sedation/anesthesia requirement, provide intra- and post procedure analgesia, and potentially aid in catheterization has been administration of a caudal epidural (ie, local anesthesia administered at the sacro-coccygeal space). This provides maximal urethral relaxation and analgesia with minimal side effects.
The purpose of this study was to investigate the use of a caudal epidural in cats with lower urinary obstruction. It was designed as a prospective, placebo controlled, partially blinded trial investigating the use of bupivacaine 0.22mg/kg, bupivacaine 0.22mg/kg with morphine 0.1mg/kg, or placebo in cats with lower urinary obstruction. Cats were recruited from the group of cats with lower urinary obstruction presenting to a university teaching hospital over a 2-year period.
Caudal epidurals were administered at either than SC or first intercoccygeal space with a 25g, 1.5” needle after clipping and sterile preparation of the area. Tail and perineal tone were assessed before and after administration. A second epidural was administered if tone was still present. Cats in the placebo group did not receive any injection; as such providers were blinded to the bupivacaine vs morphine-bupivicaine group, but not to placebo. Time to place an epidural and time to catheterize were recorded, as were required volume of propofol, subjective presence of urethral spasm, and ease of catheterization. Pain scoring was performed every 2h after the procedure. After discharge, follow up questionnaires to owners were administered at 1 and 4 weeks.
Eighty-eight cats were recruited in the study; 30 to the BUP group, 28 to BUP-MOR, and 30 to placebo. Median age was 4 years, and all cats were male. No difference in signalment or physical exam findings were present between groups.
Thirty-four percent of cats had one epidural attempt while 66% had two attempts. Body condition score did not affect number of attempts. Median time to perform the epidural was 2 minutes (0.2-13min). 70% of cats had an effective epidural based on loss of tail and perineal tone; 24% had no response, and 6% could not be assessed due to absent initial tail tone. There was no trend to increased success over the length of the study and no difference between administrators.
The median amount of propofol administered was lower in BUP and BUP-MOR groups than in placebo, but no difference was seen between the BUP and BUP-MOR groups.
There was no difference noted in difficulty of catheterization, urethral spasm, or median time to place the catheter between the treatment groups, nor were differences seen in these parameters between successful and unsuccessful epidurals.
There was a significantly greater time to rescue analgesia in the BUP and BUP-MOR cats compared to placebo, but no difference between epidural groups.
No epidural or catheter associated complications occurred over the course of the study.
A potential limitation of this study is the lack of full blinding. As providers were aware of the placebo group of cats, some bias may have been introduced. There are other combinations of anesthetics that may have been evaluated, such as lidocaine containing epidurals, which may have differing affects and should be investigated. While reasonable sample sized for a feline study were used, larger numbers of cats and different doses and combinations of drugs may lead to more information on this topic.
The findings of this study suggest that caudal epidural placement reduced the need for general anesthesia and increased the time until rescue analgesia in cats with urinary obstruction. It did not seem to affect the ease of catheterization. No difference was noted between bupivacaine or bupivacaine-morphine combinations. Ease of catheterization does not appear to be affected, though more data is needed in this area. (MRK)