BackgroundThe effect of antithrombotic drugs on intraoperative operative blood loss volume in patients undergoing emergency surgery for generalized peritonitis is not well defined. The purpose of this study was to investigate the effect of antithrombotic drugs on intraoperative blood loss in patients with generalized peritonitis using a nationwide surgical registry in Japan.MethodThis retrospective cohort study used a nationwide surgical registry data from 2011 to 2017 in Japan. Propensity score matching for the use of antithrombotic drugs was used for the adjustment of age, gender, comorbidities, frailty, preoperative state, types of surgery, surgical approach, laboratory data, and others. The main outcome was intraoperative blood loss: comparison of intraoperative blood loss, ratio of intraoperative blood loss after adjusted for confounding factors, and variable importance of all covariates.ResultsA total of 70,105 of the eligible 75,666 patients were included in this study, and 2947 patients were taking antithrombotic drugs. Propensity score matching yielded 2864 well-balanced pairs. The blood loss volume was slightly higher in the antithrombotic drug group (100 [10–349] vs 70 [10–299] ml). After adjustment for confounding factors, the use of antithrombotic drugs was related to a 1.30-fold increase in intraoperative blood loss compared to non-use of antithrombotic drugs (95% CI, 1.16–1.45). The variable importance revealed that the effect of the use of antithrombotic drugs was minimal compared with surgical approach or type of surgery.ConclusionThis study shows that while taking antithrombotic drugs is associated with a slight increase in intraoperative blood loss in patients undergoing emergency surgery for generalized peritonitis, the effect is likely of minimal clinical significance.