Surface oximetry for intraoperative assessment of colonic viability in horses

Jack R. Snyder From the Departments of Surgical and Radiological Sciences (Snyder, Pascoe, Meagher) and Medicine (Thurmond), School of Veterinary Medicine, University of California, Davis, CA 95616.

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John R. Pascoe From the Departments of Surgical and Radiological Sciences (Snyder, Pascoe, Meagher) and Medicine (Thurmond), School of Veterinary Medicine, University of California, Davis, CA 95616.

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Dennis M. Meagher From the Departments of Surgical and Radiological Sciences (Snyder, Pascoe, Meagher) and Medicine (Thurmond), School of Veterinary Medicine, University of California, Davis, CA 95616.

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Mark C. Thurmond From the Departments of Surgical and Radiological Sciences (Snyder, Pascoe, Meagher) and Medicine (Thurmond), School of Veterinary Medicine, University of California, Davis, CA 95616.

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Summary

Surface oximetry was used to evaluate viability of the ascending colon in 60 horses with naturally occurring colonic volvulus or displacement. Tissue surface oxygen tension (Pso2) was measured on the serosal surface of the pelvic flexure after anatomic correction of the colonic obstruction. Horses with Pso2 > 20 mm of Hg were predicted to have viable colon; whereas, horses with Pso2 ≤ 20 mm of Hg were predicted to have nonviable colon. Results of surface oximetry were compared with final outcome. For surface oximetry, sensitivity (ability to accurately identify colon that was nonviable) was 53%, but specificity (ability to accurately identify bowel that was viable) was 100%. Negative predictive value (probability that a horse with Pso2 > 20 mm of Hg truly had viable bowel) was 87%, and positive predictive value (probability that a horse with Pso2 ≤ 20 mm of Hg truly had nonviable bowel) was 100%. The overall accuracy was 88%. Of the 45 horses that had a colonic Pso2 > 20 mm of Hg and survived, 7 had been given, on the basis of subjective assessment of visual criteria, a good prognosis, 28 had been given a guarded prognosis, and 10 had been given a poor prognosis. Of the horses that had a colonic Pso2 > 20 mm of Hg but died after surgery because of further colonic infarction, confirmed at necropsy, 4 had been given a poor prognosis, and 3 had been given a guarded prognosis. Of the 8 horses that had a colonic Pso2 ≤ 20 mm of Hg and died after surgery, 7 had been given a poor prognosis, and 1 had been given a guarded prognosis. We concluded that surface oximetry, a relatively noninvasive technique, provided a better prediction of survival in horses with colonic volvulus or displacement than did visual inspection alone.

Summary

Surface oximetry was used to evaluate viability of the ascending colon in 60 horses with naturally occurring colonic volvulus or displacement. Tissue surface oxygen tension (Pso2) was measured on the serosal surface of the pelvic flexure after anatomic correction of the colonic obstruction. Horses with Pso2 > 20 mm of Hg were predicted to have viable colon; whereas, horses with Pso2 ≤ 20 mm of Hg were predicted to have nonviable colon. Results of surface oximetry were compared with final outcome. For surface oximetry, sensitivity (ability to accurately identify colon that was nonviable) was 53%, but specificity (ability to accurately identify bowel that was viable) was 100%. Negative predictive value (probability that a horse with Pso2 > 20 mm of Hg truly had viable bowel) was 87%, and positive predictive value (probability that a horse with Pso2 ≤ 20 mm of Hg truly had nonviable bowel) was 100%. The overall accuracy was 88%. Of the 45 horses that had a colonic Pso2 > 20 mm of Hg and survived, 7 had been given, on the basis of subjective assessment of visual criteria, a good prognosis, 28 had been given a guarded prognosis, and 10 had been given a poor prognosis. Of the horses that had a colonic Pso2 > 20 mm of Hg but died after surgery because of further colonic infarction, confirmed at necropsy, 4 had been given a poor prognosis, and 3 had been given a guarded prognosis. Of the 8 horses that had a colonic Pso2 ≤ 20 mm of Hg and died after surgery, 7 had been given a poor prognosis, and 1 had been given a guarded prognosis. We concluded that surface oximetry, a relatively noninvasive technique, provided a better prediction of survival in horses with colonic volvulus or displacement than did visual inspection alone.

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