Intraoperative peritoneal fluid culture in horses undergoing emergency laparotomy: a retrospective study investigating associations with short-term complications and survival

Bacteriology of intraoperative peritoneal fluid (PF) from horses undergoing abdominal surgery is not commonly performed and the evidence supporting this practice is currently lacking. PF analysis has been used as an indicator of intestinal injury and to direct treatment decisions in colic patients. In human gastrointestinal tract surgery, culture results have been positively correlated with development of incisional complications. This retrospective study includes data extracted from the clinical records of horses that underwent colic surgery between January 2013 and January 2023 and from which a sample of PF was collected at the end of surgery. Data were analysed with Poisson and logistic regression. The first objective of this study was to investigate which factors were significantly associated with positive PF cultures. The second objective was to investigate the potential value of positive PF cultures as predictor for survival to discharge and short-term postoperative complications in horses undergoing emergency exploratory laparotomy. A total of 450 horses were included. A positive PF culture was recorded in 212/450 (47.1 per cent) of the horses. The vast majority of positive results were obtained after enrichment (195/212, 92.1 per cent). Surgical time had a significant positive effect on PF culture (OR = 1.01; 95 per cent CI, 1.001 to 1.01). Positive PF culture results were associated with a higher occurrence of postoperative fever [Incidence Rate Ratio (IRR) = 1.47; 95 per cent CI, 1.23 to 1.76] and increased odds of developing surgical site infection (SSI) (OR = 3.19; 95 per cent CI, 1.59 to 7.59). Enterobacterales, staphylococci and anaerobes were associated with higher odds of developing SSI. Positive PF had no statistically significant effect on survival. The associations we found between longer surgical time and a positive PF culture and between positive PF culture and SSIs are novel findings. This might be explained by the larger sample size in our study compared to previous ones. Another explanation might be the enrichment methodology for PF cultures used, which increases the sensitivity but might also result in false-positive results. The results reported are from a single institution, and the conclusions may not be applicable to a different hospital population. Finally, data was collected retrospectively, and not all the clinical records were complete. Longer surgical times were associated with increased odds of obtaining a positive PF culture, and positive PF cultures were significantly associated with increased odds of developing SSI, although bacterial isolates from abdominal incision rarely matched those from PF. Further research is needed to identify which mechanism is behind these associations and to investigate the nature and clinical relevance of the bacterial contamination observed.