SURFACE OXIMETRY FOR INTRAOPERATIVE ASSESSMENT OF COLONIC VIABILITY IN HORSES

Surface oximetry was wed to evaluate viability of the ascending colon in 60 horses with naturally occurring colonic volvulus or displacement . Tissue surface oxygen tension Ps(O2) was measured on the serosal sur face of the pelvic flexure after anatomic correction of the colonic ob struction. Horses with Ps(O2) > 20 mm of Hg were predicted to have via ble colon; whereas, horses with Ps(O2) less than or equal to 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 Ps(O2) > 20 mm of Hg truly had viable bowel) was 87%, and positive predictiv e value probability that a horse with Ps(O2) less than or equal to 20 mm of Hg truly had nonviable bowel) was 100%. The overall accuracy was 88%. Of the 45 horses that had a colonic Ps(O2), > 20 mm of Hg and su rvived, 7 had been given, on the basis of subjective assessment of vis ual 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 colo nic Ps(O2) > 20 mm of Hg but died after surgery because of further col onic infarction, confirmed at necropsy, 4 had been given a poor progno sis, and 3 had been given a guarded prognosis. Of the 8 horses that ha d a colonic Ps(O2) less than or equal to 20 mm of Hg and died after su rgery, 7 had been given a poor prognosis, and 1 had been given a guard ed prognosis. We concluded that surface oximetry, a relatively noninva sive technique, provided a better prediction of survival in horses wit h colonic volvulus or displacement than did visual inspection alone.