b'Scientific Session Abstracts SUNDAY APRIL 21, 2024 33: IMPACT OF ANEMIA AND TRANSFUSION ON PATIENTS UNDERGOING INFRAINGUINAL BYPASSAlexander D. DiBartolomeo, MD, Helen A. Potter, MD, Li Ding, MD MPH, Michelle Manesh, MD, Gregory A. Magee, MD, MScUniversity of Southern CaliforniaObjectives: Liberal use of red blood cell (RBC) transfusion has been proposed to reduce major adverse events associated with preoperative anemia in patients undergoing vascular procedures. However, the benefits and optimal transfusion threshold have not been well defined in patients with peripheral vascular disease. This study evaluates the impact of preoperative anemia andtransfusion on major adverse cardiac events (MACE), major adverse limb events (MALE) and mortality in patients undergoing infrainguinal bypass.Methods: The Society for Vascular Surgeons Vascular Quality Initiative registry was queried for patients who underwent infrainguinal bypass. Emergent cases and patients with hemoglobin (Hgb) 7 were excluded. Patients were grouped by preoperative Hgb level (7-10 vs 10-12 vs 12 g/dL) then stratified by RBC transfusion status. The primary outcome was MACE and secondary outcomes were MALE, in-hospital mortality and 1-year survival. Multivariable analysis was performed for MACE and MALE.Results: In total, 55,884 patients were analyzed of which 16% had Hgb 7-10, 26% had Hgb 10-12, and 58% had Hgb12. On univariate analysis MACE, MALE, in-hospital mortality and 1-year survival were worse in the most anemic group. However, after stratification, patients who received transfusion had a significantly higher rate of MACE, MALE, and in-hospital mortality for eachHgb group. Multivariable analysis showed patients who received transfusion compared to those that did not had increased risk of MACE and MALE for all preoperative Hgb levels (MACE: OR 2-4, P.0001; 2.8, P.0001; 4.5, P.0001, respectively and MALE: OR 2.1, P.0001; 1.8, P.0001;2.6, P.0001, respectively). Transfusion had a larger negative impact on mortality than anemia or blood loss.Conclusions: Preoperative anemia in patients undergoing infrainguinal bypass is associated with increased risk of MACE and MALE. However the risk of MACE, MALE, and in-hospital mortality was 2-3 fold higher for transfusion than anemia or blood loss at all Hgb levels 7 g/dL. These data suggest that rather than attenuating the risks of anemia, transfusion is an independent riskfactor. A randomized trial is warranted to determine the optimal transfusion threshold for these patients.86SOUTHERN CALIFORNIA VASCULAR SURGICAL SOCIETY'