Study maps expected peritoneal fluid changes after equine colic surgery: full analysis

Version 2

A new prospective study in Veterinary Surgery offers a clearer picture of what “normal” postoperative peritoneal fluid can look like in horses after colic surgery. In 26 horses undergoing exploratory laparotomy for naturally occurring gastrointestinal lesions, investigators found that peritoneal lactate and total protein remained elevated for up to seven days after surgery, regardless of whether the original lesion was strangulating or non-strangulating. That matters because those same markers are often used before surgery to help assess intestinal compromise. (pmc.ncbi.nlm.nih.gov)

The question comes out of a familiar clinical problem in equine practice: abdominocentesis is a standard tool in colic workups, and peritoneal fluid color, protein, cell counts, and lactate can help distinguish surgical from medical disease. But the evidence base for interpreting those values after surgery has been much thinner. Earlier literature established that postoperative laparotomy itself can trigger inflammatory changes in peritoneal fluid, and more recent reviews have emphasized that fluid characteristics must be interpreted in clinical context rather than as stand-alone answers. (pubmed.ncbi.nlm.nih.gov)

In the new study, horses were sampled repeatedly after surgery, and the authors compared fluid findings between 14 horses with strangulating lesions and 12 with non-strangulating lesions. According to the publication record, the team used linear mixed models to account for repeated measures. Their main finding was that postoperative peritoneal lactate and total protein stayed high for one week in both groups, while cellular inflammatory markers also increased over time. The practical takeaway is that abnormal postoperative fluid values may reflect expected postoperative change, not necessarily a worsening lesion or failed surgery. (pmc.ncbi.nlm.nih.gov)

That conclusion is especially useful because preoperative literature has sometimes encouraged heavy reliance on lactate. For example, a 2018 study in the Journal of Equine Veterinary Science found that peritoneal fluid lactate alone did not significantly distinguish non-strangulating from strangulating small intestinal lesions, while the peritoneal fluid-to-blood lactate ratio performed better. A 2025 retrospective study in Animals also linked some peritoneal fluid variables, including lactate and protein, with lesion type and survival, but that work focused on broader diagnostic and prognostic associations rather than defining expected postoperative trends. (sciencedirect.com)

The new paper also carries some early field validation. It was presented at the 2025 ACVS Surgery Summit in Seattle and received a highest clinical impact award in the Large Animal Resident’s Forum, suggesting the work resonated with surgeons dealing with postoperative decision-making in real cases. No separate institutional press release or formal outside commentary was readily available in the sources reviewed, but the topic aligns closely with ongoing interest in improving postoperative monitoring while avoiding unnecessary alarm over expected inflammatory changes. (pmc.ncbi.nlm.nih.gov)

Why it matters: For veterinary professionals managing horses after exploratory laparotomy, this study may help reduce false-positive concern when peritoneal fluid remains abnormal during the first postoperative week. If lactate and protein stay elevated even in recovering horses, then serial fluid analysis should be weighed alongside pain level, reflux, cardiovascular parameters, ultrasound findings, incisional status, and overall clinical trajectory, rather than treated as a trigger on its own. That could support more confident monitoring decisions, better communication with pet parents, and potentially fewer unnecessary interventions. This is an inference based on the study findings and the broader literature on equine peritoneal fluid interpretation. (pmc.ncbi.nlm.nih.gov)

The study’s limitations are also worth keeping in mind. It was a pilot-sized cohort of 26 horses, from a single academic setting, and the findings describe aggregate postoperative trends rather than a validated cutoff for identifying complications. That means the work is best viewed as a reference point, not a rule-out tool for postoperative peritonitis, recurrent ischemia, or anastomotic problems. (pmc.ncbi.nlm.nih.gov)

What to watch: The next step will likely be larger prospective studies that connect serial postoperative peritoneal fluid patterns with specific complications and outcomes, helping clinicians distinguish expected postoperative inflammation from the horses that need earlier escalation or repeat intervention. (pmc.ncbi.nlm.nih.gov)