The incidence of post-operative colic in adult equine patients undergoing elective non-abdominal surgery at SLU and potential risk factors

Abstract: Post-operative colic (POC) is a well-recognised complication in horses undergoing abdominal surgery but there are few studies describing the prevalence and incidence of colic in horses after non-abdominal surgery. Recently, the benefits of fasting horses pre-operatively have been questioned. A future randomised prospective study is planned to investigate the beneficial or negative effects of fasting horses prior to surgery. This retrospective pilot study was performed to evaluate the incidence of post-operative colic after non- abdominal elective surgery, with the current feeding regimen at SLU. Is there a problem that needs further investigation? Are specific procedures associated with increased risk of POC? Can we identify any common risk factors that should be included and separately studied in a prospective larger case-controlled study? Can we identify possible risk factors in the management pre- and post-surgery that can be applied and changed to decrease the risk of colic post-surgery? We performed a retrospective study including elective non-abdominal procedures performed at SLU between October 2021 and October 2022. The inclusion criteria were: all adult horses >1 year of age, monitored in the hospital for a minimum of 24h following anesthesia, starved before the surgery according to the pre-surgery feeding regimen at SLU, and not known to have a medical history of colic within 6 months before surgery. In addition, we briefly investigated the incidence of post�operative colic following surgical procedures performed under standing sedation and when two procedures were performed in close succession. Data was analysed using descriptive statistics, hypothetical association tests and binary logistic regression analysis. 297 horses were included in the main study. We found an incidence of POC after non-abdominal surgery of 13.5% (40/297) within 3 days post general anesthesia. The incidence of POC within 7 days post general anesthesia was 14.5% ((43/297). These results are markedly higher compared to the previous described incidence of 2.5% (Bailey et al.2016) to 10.5% (Jago et al.2015). The incidence of colic following standing surgery during CRI-sedation was 14.5% (10/69) within 3 days post-operative. The incidence of colic following two separate anesthesia events performed close to each other was 10.7% (3/28) within 3 days post the second surgical event. The results indicate that pre- and especially post-operative management of the horse may alter the risk of POC. We found that hand-walked exercise during hospitalization decreased the odds of development of POC within our study population, an event to our knowledge not described before. Our result also indicates that systemically administration of morphine given either intravenously or intramuscularly during anesthesia may increase the risk to develop of POC. As previous reported by Ekstrand et al. (2022), atropine treatment was associated with higher risk of colic. Higher age was found associated with higher risk to develop POC. Comparing orthopaedical and non-orthopaedical procedures, no association was found between procedure and increased risk for POC within our study population. Neither did we find any association with breed type nor positioning during surgery nor lidocaine constant rate infusion during anesthesia. We conclude that a larger prospective study under controlled conditions needs to be performed, to further investigate if it is possible to decrease the risk of POC following the finding of an uncommon high incidence. The result of literature review in combination with the results from our pilot study indicates that different pre- and post-operative feeding regimens should be included and evaluated.