Measuring tissue oxygen saturation in the orad intestinal segment during equine colic surgery may aid in predicting the occurrence of postoperative ileus.

Overview

• This study investigates the use of tissue oxygen saturation (tSO2) measurement in the small intestine segment upstream of a strangulation during equine colic surgery to predict the likelihood of postoperative ileus, a common complication after surgery.
• The research evaluates the relationship between tSO2, blood flow, histological intestinal injury, and postoperative outcomes in horses undergoing surgery for small intestinal strangulation.

Background

• Colic surgery in horses often involves addressing small intestinal strangulation, where parts of the intestine are twisted or compressed, cutting off blood supply.
• Postoperative ileus (POI), or postoperative reflux (POR), is a complication characterized by impaired intestinal motility and can lead to a poor prognosis.
• Assessing intestinal tissue viability intraoperatively is challenging but important for predicting complications and guiding surgical decisions.
• Laser Doppler flowmetry and spectrophotometry (LDFS) are techniques that allow real-time measurement of tissue blood flow (tBF) and oxygen saturation (tSO2), reflecting tissue perfusion and oxygenation status.

Objective and Methods

• The prospective clinical trial aimed to measure tSO2 and tBF in the intestinal segment orad (upstream) to the strangulation site after surgical release in horses undergoing colic surgery.
• Measurements were made using LDFS in 18 horses after strangulation release.
• Postoperative outcomes, specifically the occurrence of postoperative reflux (POR), were monitored and compared between groups based on tSO2 levels.
• Histological injury was assessed through intestinal biopsies collected either during intestinal resection or euthanasia (28 horses total).
• The study compared tSO2 and tBF measurements between injured and non-injured intestinal segments using statistical tests (Mann-Whitney U or t-test), and postoperative reflux incidence using Fisher’s exact test.

Key Findings

• Both tissue oxygen saturation (tSO2) and tissue blood flow (tBF) in the intestinal segments orad to strangulation were lower than values previously reported for healthy horses, implying compromised perfusion and oxygenation in these areas.
• Horses with low tissue oxygen saturation (< 35%) had a significantly higher incidence of postoperative reflux (6 out of 6 cases) compared to those with high tSO2 (> 69%), where only 1 out of 6 experienced POR.
• Survival rates until hospital discharge did not differ significantly between low and high tSO2 groups (2/6 vs. 6/6 respectively), indicating that low tSO2 was more predictive of POR than survival.
• All horses presenting mucosal injury on histology developed postoperative reflux, which was significantly more frequent compared to horses without mucosal injury (6/6 vs. 3/13 cases).
• No statistically significant difference was found in tSO2 or tBF between intestinal segments that showed histological injury and those that did not within the sampled population.

Interpretation and Conclusions

• The study suggests that measuring tissue oxygen saturation in the portion of the intestine upstream to the strangulation can serve as a useful intraoperative indicator to predict postoperative ileus in horses.
• Lower tSO2 values (<35%) are associated with a higher risk of postoperative reflux, which is an important clinical complication.
• The lack of significant difference in tBF and tSO2 between histologically injured and non-injured segments may indicate that these measurements reflect functional changes in perfusion and oxygenation not directly mirrored by histological injury or that tissue damage is patchy and difficult to capture with limited biopsies.
• Overall, tSO2 measurement by LDFS during surgery could help veterinarians make more informed decisions about prognosis and postoperative management in equine colic cases involving strangulation.

Clinical Implications

• Intraoperative tSO2 monitoring might become a valuable tool for predicting postoperative complications, allowing early intervention strategies for horses at high risk of postoperative ileus.
• This technique may complement current diagnostic methods and provide real-time assessment of intestinal viability beyond visual inspection.
• Further research might explore integrating tSO2 measurements with other markers and refining thresholds to improve accuracy and clinical utility.