Interaction between peri-operative blood transfusion, tidal volume, airway pressure and postoperative ARDS: an individual patient data meta-analysis.

Background: Transfusion of blood products and mechanical ventilation with injurious settings are considered risk factors for postoperative lung injury in surgical Patients. Methods: A systematic review and individual patient data meta-analysis was done to determine the independent effects of peri-operative transfusion of blood products, intra-operative tidal volume and airway pressure in adult patients undergoing mechanical ventilation for general surgery, as well as their interactions on the occurrence of postoperative acute respiratory distress syndrome (ARDS). Observational studies and randomized trials were identified by a systematic search of MEDLINE, CINAHL, Web of Science, and CENTRAL and screened for inclusion into a meta-analysis. Individual patient data were obtained from the corresponding authors. Patients were stratified according to whether they received transfusion in the perioperative period [ red blood cell concentrates (RBC) and/or fresh frozen plasma (FFP)], tidal volume size [<= 7 mL/kg predicted body weight (PBW), 7-10 and > 10 mL/kg PBW] and airway pressure level used during surgery (<= 15, 15-20 and > 20 cmH(2)O). The primary outcome was development of postoperative ARDS. Results: Seventeen investigations were included (3,659 patients). Postoperative ARDS occurred in 40 (7.2%) patients who received at least one blood product compared to 40 patients (2.5%) who did not [ adjusted hazard ratio (HR), 2.32; 95% confidence interval (CI), 1.25-4.33; P=0.008]. Incidence of postoperative ARDS was highest in patients ventilated with tidal volumes of > 10 mL/kg PBW and having airway pressures of > 20 cmH(2)O receiving both RBC and FFP, and lowest in patients ventilated with tidal volume of <= 7 mL/kg PBW and having airway pressures of <= 15 cmH(2)O with no transfusion. There was a significant interaction between transfusion and airway pressure level (P=0.002) on the risk of postoperative ARDS. Conclusions: Peri-operative transfusion of blood products is associated with an increased risk of postoperative ARDS, which seems more dependent on airway pressure than tidal volume size.