Acute anemia and cardiovascular events after vascular surgery

Abstract

Introduction: Anemia is a risk factor for cardiovascular complications in vascular surgery and we believe that the acute loss of hemoglobin may be more important than the baseline level. The purpose of this study is to evaluate the relationship between perioperative hemoglobin values and Cardiovascular Events (CVE). Methods: Prospective data were collected from 285 patients scheduled for elective vascular surgery. Cardiac risk was estimated according to the American College of Physicians algorithm and patients were monitored for CVE during hospitalization, with daily troponin T, CKMB, hemoglobin and eletrocardiogram until the 3rd post-operative day, repeated as needed. The degree of acute anemia was measured as the lowest hemoglobin value after surgery (nadir Hb), post-operative Hb below 9g/dL and Hb delta (pre-operative – post-operative Hb) during the first week. Results: In total, 286 patients were submitted to the planned surgery (72% men, 66.8yrs) and 45 (15.7%) had an event: 12 myocardial infarctions, 2 unstable anginas, 15 isolated troponin elevations; 11 ischemic strokes and 5 cardiac deaths. Preoperative anemia was present in 25.5% but baseline hemoglobin level was not associated to CVE. In the univariate analysis we found that coronary artery disease, intraoperative haemodynamic instability, blood transfusion, longer duration of anesthesia and the degree of acute anemia, were all associated to CVE. In the logistic regression model, the degree of acute anemia persisted significantly associated to CVE and patients with a post-operative hemoglobin under 9g/dL had more than twice the risk of events when compared to patients with hemoglobin above or equal to 9g/dL (OR: 2.30; CI 1.07 – 4.96; P=0.03). The other independent predictors of CV event were intraoperative haemodynamic instability (OR 4.62; CI: 2.12- 10.06; P<.000) and coronary artery disease (OR 2.55; CI: 1.17 -5.52; P=0.018). When we performed the same multivariate model for the 202 patients that did not receive blood transfusion, the putative effect of acute anemia was even greater (OR 3.90; CI: 1.30 -11.71; P=0.015). We also found that in 78.9% of our patients who had myocardial infarction, unstable angina or CV death, the gap between the CV event and the nadir Hb value was lower than 24hrs. Conclusion: The degree of acute anemia appears to be more important than the isolated preoperative value toward the occurrence of CVE. Blood transfusion therapy should be individualized and considered a mitigating factor.