D. C. Sutzko1, A. T. Obi1, P. K. Henke1, N. H. Osborne1 1University Of Michigan,Department Of Surgery,Ann Arbor, MI, USA
Objective: Amongst patients undergoing noncardiac surgery, major vascular surgery is associated with a high risk of perioperative MI. Currently there are no evidence based guidelines to determine appropriate transfusion thresholds in the perioperative vascular surgery patient. In a recent study on transfusion patterns and outcomes after noncardiac surgery, liberal transfusion protocols were associated with worse outcomes with the exception of patients that suffered from post-operative myocardial infarction (MI). With these results, we aimed to investigate specific risk factors for perioperative MI after major open vascular surgery to determine (1) which patients are at highest risk of MI, (2) the association of perioperative MI with intra and postoperative transfusion and (3) optimal strategies to prevent perioperative MI.
Methods: Patients undergoing major open vascular surgery (defined as open abdominal aortic aneurysm repair (oAAA repair), aorto-femoral bypass (AFB) and infrainguinal bypass (LEB)) were identified from the Michigan Surgical Quality Collaborative (MSQC) between 2008 and 2012. Rates of MI were described for each procedure. Preoperative, intraoperative and postoperative risk factors associated with MI were evaluated using univariate and multivariate statistics after adjusting for intraoperative factors including: anesthesia type, intraoperative blood loss, intraoperative transfusion and intraoperative vasopressor medications.
Results: 3,692 patients underwent major open vascular surgery, including 375 oAAA, 392 AFB, and 2,925 LEB procedures. The overall incidence of MI was 2.44% (N= 90), varying from 1.79% (N=7) for AFB, 2.36% (N=69) for LEB and 3.73% (N=14) for oAAA repair. Although pre-operative risk factors for MI included age, coronary artery disease, and preoperative hematocrit , after adjusting for intraoperative risk factors all preoperative risk factors were not significant. The only risk factors associated with MI after adjusting for intraoperative factors were the nadir hematocrit (OR=0.89, p<0.05) and postoperative transfusion (OR=2.69, p<0.05).
Conclusions: Vascular surgery is an independent risk factor for MI. Among vascular surgery patients undergoing major open vascular surgery, no preoperative risk factors were independently associated with MI. However, postoperative variables such as nadir hematocrit and postoperative transfusion were associated with MI. Taken together, this data suggests that preoperative risk stratification based on co-morbidities is unlikely to successfully predict the most at risk patients. However, minimizing excessive operative blood loss, avoiding physiologic stress and optimizing intra-operative resuscitation may mitigate risk of MI.
