BackgroundFlowable hemostatic agents have the advantage of being able to be applied to irregular wound surfaces and difficult to reach areas. We sought to compare the effectiveness and safety of the flowable hemostatic sealants Collastat® (collagen hemostatic matrix, [CHM]) and Floseal® (gelatin hemostatic matrix, [GHM]) during off-pump coronary artery bypass (OPCAB).MethodsIn this prospective, double-blind, randomized controlled trial, 160 patients undergoing elective OPCAB surgery were enrolled between March 2018 and February 2020. After primary suture of the aortocoronary anastomosis, an area of hemorrhage was identified, and patients received either CHM or GHM (n = 80, each). Study endpoints were the following: proportion of successful intraoperative hemostasis and time required for hemostasis overall postoperative bleeding, proportion of transfusion of blood products, and surgical revision for bleeding.ResultsOf the total patients, 23% were female, and the mean age was 63 years (range 42–81 years). Successful hemostasis proportion within 5 min was achieved for 78 patients (97.5%) in the GHM group, compared to 80 patients (100%) in the CHM group (non-inferiorityp= 0.006). Two patients receiving GHM required surgical revision to achieve hemostasis. There were no differences in the mean time required to obtain hemostasis [GHM vs. CHM, mean 1.49 (SD 0.94) vs. 1.35 (0.60) min,p= 0.272], as confirmed by time-to-event analysis (p= 0.605). The two groups had similar amounts of mediastinal drainage for 24 h postoperatively [538.5 (229.1) vs. 494.7 (190.0) ml,p= 0.298]. The CHM group required less packed red blood cells, fresh frozen plasma, and platelets for transfusion than the GHM group (0.5 vs. 0.7 units per patient,p= 0.047; 17.5% vs. 25.0%,p= 0.034; 7.5% vs. 15.0%,p= 0.032; respectively).ConclusionsCHM was associated with a lower need for FFP and platelet transfusions. Thus, CHM is a safe and effective alternative to GHM.Trial registration: ClinicalTrials.gov, NCT 04310150.