Perioperative predictors of colonic ischemia after ruptured abdominal aortic aneurysm

Purpose: Colonic ischemia and colonic resection occur frequently after rupt ured abdominal aortic aneurysm (rAAA). The purpose of this study was to ide ntify the perioperative risk factors that might help to determine earlier i n the postoperative period which patients are at risk for colonic ischemia and colonic resection. Methods: The medical records of the 43 patients who underwent repair of rAA A from January 1989 to November 1997 were reviewed. The data were reviewed for the following factors: acidosis, presser agents, lactate levels, guaiac status, cardiac index, coagulopathy, early postoperative bowel movement, t he lowest intraoperative pH level, the temperature at the conclusion of the case, the location and duration of aortic cross clamping, the amount of fl uid boluses administered after surgery, the amount of packed red blood cell s administered during the case, and the average systolic blood pressure It admission and during surgery Univariate analysis was performed with Fisher exact test, chi(2) test, and Student t test. Multivariate analyses also wer e performed with the variables that were found to be significant on the uni variate analysis. Results: Thirteen of the 43 patients (30.2%) had colonic ischemia, and seve n of the 13 underwent colonic resection (53.8%). The overall mortality rate was 51.2% (22/43)-five of the deaths were intraoperative and excluded from the study. In a comparison of the patients who had colonic ischemia Frith those who did not, statistically significant differences were found in the following variables: average systolic blood pressure at admission 90 mm Hg or less, hypotension of more than 30 minutes' duration, temperature less th an 35 degrees C, pH less than 7.3, fluid boluses administered after surgery 5 L or more, and packed red blood cells 6 units or more. Multivariate anal ysis indicated that the number of these variables present correlated signif icantly with the positive predicted probability of colonic ischemia occurri ng. No patient with two factors or fewer had an ischemic bowel, and the pos itive predictive probability of colonic ischemia for those patients with si x factors was 80%. Conclusion: The results of this study show that: (1) colonic ischemia after rAAA may be predicted with the presence of two or more specific perioperat ive factors, (2) the lack of a guaiac-positive bowel movement may be mislea ding for the early diagnosis of colonic ischemia, and (3) more than 50% of the patients with colonic ischemia will require a colonic resection. We rec ommend that any patient with rAAA with more than two perioperative factors undergo sigmoidoscopy every 12 hours after surgery for is hours to rule out colonic ischemia without waiting for early or guaiac-positive bowel moveme nt.