Odds Ratio (95% CI) P Tranexamic Acid used 0.36 (0.15 to 0.82) 0.016 Surgeon 3.01 (1.53 to 5.92) < 0.001 Female 5.15 (1.95 to 13.56) < 0.001 Weight (kg) 0.97 (0.94 to 1.0) 0.043 Levels Fused 1.23 (1.03 to 1.47) 0.02 Estimated Blood Loss * 1.07 (1.02 to 1.12) 0.01 Total Intravenous Anesthesia 0.53 (0.26 to 1.10) 0.09

Table 5: Logistic Regression summary for outcome of any transfusion Considered for the model and were found not to be confounders or have independent relationship with transfusion were: Surgery time, deliberate hypotension, volume of crystalloid, use of 5% albumin, inotropic medications used, and use of cell saver. *Estimated Blood Loss was transformed via square root to fit assumptions of normality. This odds ratio represents the odds of transfusion for each increase of 10cc of EBL. Model fit was assessed by the Hosmer-Lemeshow test. Resultant model fit was appropriate (P=0.15).