Ventilator Mode Does Not Influence Blood Loss or Transfusion Requirements During Major Spine Surgery: A Retrospective Study BACKGROUND: Blood loss during adult spinal deformity surgery is multifactorial. Anesthetic-related factors, such as mode of mechanical ventilation, may contribute to intraoperative blood loss. The aim of this study was to determine the influence of ventilator mode and ventilator parameters on intraoperative blood loss and transfusion requirements in patients undergoing prone position spine surgery. METHODS: This single-center retrospective study examined electronic medical records of patients ≥18 years of age who underwent elective prone position spine surgery between May 2015 and June 2016. Associations between ventilator mode and ventilator parameters with intraoperative estimated blood loss (EBL), packed red blood cells (PRBCs), fresh-frozen plasma (FFP), cryoprecipitate and platelet transfusions, and subfascial drain output were examined using multiple linear regression models controlling for age, sex, American Society of Anesthesiologist (ASA) physical status score, body mass index (BMI), preoperative blood coagulation parameters and laboratory values, operative levels, cage constructs, osteotomies, transforaminal lumbar interbody fusions, laminectomies, reoperation, spine surgery invasiveness index, and operative time. In a secondary analysis, EBL, blood product transfusions, and postoperative drain output were compared between pressure-controlled ventilation (PCV) and volume-controlled ventilation (VCV) propensity score–matched cohorts. RESULTS: Nine hundred forty-six records were reviewed, and 822 were included in the analysis. After adjusting for confounding, no statistically significant associations were observed between mode of ventilation and intraoperative EBL (estimate, −1.77; 95% confidence interval [CI], −248.23 to 244.68; P = .99) or blood product transfusions (PRBC: estimate, −9.34; 95% CI, −154.08 to 135.40; P = .90; FFP: estimate, −2.60; 95% CI, −58.73 to 53.52; P = .93; cryoprecipitate: estimate, −13.81; 95% CI, −70.33 to 42.71; P = .63; platelets: −7.43; 95% CI, −38.84 to 23.98; P = .64). After propensity score matching (n = 27 per group), no significant differences were observed in EBL (mean difference, 525 mL; 95% CI, −15 to 1065; P = .056) or blood transfusions (PRBC: mean difference, 208 mL; 95% CI, −23 to 439; P = .077; FFP (mean difference, 34 mL; 95% CI, −17 to 84; P = .19); cryoprecipitate (mean difference, 55 mL; 95% CI, −24 to 133; P = .17); or platelets (mean difference, 26 mL; 95% CI, −12 to 64; P = .18) between PCV and VCV groups. CONCLUSIONS: In prone position spine surgery, neither mode of mechanical ventilation nor airway pressure is associated with intraoperative blood loss or need for allogeneic transfusion. Use of modern ventilation strategies using lung protective techniques may mitigate differences in blood loss previously observed between PCV and VCV modes. Accepted for publication May 30, 2019. Funding: None. Conflicts of Interest: See Disclosures at the end of the article. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s website (www.anesthesia-analgesia.org). Reprints will not be available from the authors. Address correspondence to Lauren K. Dunn, MD, PhD, Department of Anesthesiology, University of Virginia, PO Box 800710, Charlottesville, VA 22908. Address e-mail to lak3r@virginia.edu. © 2019 International Anesthesia Research Society