Surface oximetry for intraoperative assessment of colonic viability in horses.

The research article explores the use of surface oximetry to assess the viability of the ascending colon in horses suffering from colonic volvulus or displacement. The study revealed a commendable success rate of predicting nonviable and viable bowels using the PsO2 levels.

Study methodology

• The research was conducted on 60 horses that had naturally occurring colonic volvulus or displacement. This ensured that the results were not biased by experimentally induced conditions.
• To evaluate the viability of the horses’ colon, tissue surface oxygen tension (PsO2) was measured on the serosal surface of the pelvic flexure. This was done after the anatomic correction of the colonic obstruction.
• Based on the test values, if a horse had the PsO2 level greater than 20 mm of Hg, the colon was predicted to be viable. Conversely, if PsO2 was less than or equal to 20 mm of Hg, the colon was suspected to be nonviable.

Study outcomes and findings

• The study findings were compared with the final outcome in terms of viability to determine sensitivity (53%) – the capacity to accurately identify a nonviable colon.
• The research also evaluated specificity (100%), the ability to accurately identify a viable colon.
• The test also considered the negative predictive value (87%), the percentage indicative of a horse with PsO2 less than or equal to 20 mm of Hg truly having a nonviable bowel.
• The positive predictive value considering the same PsO2 criteria was found to be 100%, pointing to a highly accurate prediction in identifying nonviable bowels.
• The overall accuracy of the surface oximetry to determine the state of the colon was measured as 88%.
• Among the horses that survived with a colonic PsO2 greater than 20 mm of Hg the study considered the discrepancy between the prognosis based on visual criteria and the PsO2 measurement. Seven out of 45 horses were visually given a good prognosis, as opposed to the 28 who were given a guarded prognosis and the 10 horses which were given a poor prediction.
• Among the horses that eventually died due to further colonic infarction, despite having a PsO2 greater than 20 mm of Hg, four were visually given a poor prognosis and three were given a guarded prognosis. This further highlights the superiority of surface oximetry over visual analysis.

Implications and conclusions

• The findings of this research suggest surface oximetry as a useful tool in assessing the health of the ascending colon in horses and can prove to be a determining factor in predicting the animal’s survival chances during surgeries for colonic volvulus or displacement.
• It also reveals the superiority of the oximetry results over traditional visual prognosis which may not always be accurate.
• The outcomes of the study open the door for more intensive research on the subject.