SpHb Group (N=170) Standard Care Group (N=157)   Differencea   95% CI Intraoperative   Total*   Total*     Received RBC transfusions, N (%) 1 (0.6) 170 7 (4.5) 157 -0.04 (-0.07, -0.004)                 By procedure type, N Spine Surgery,1   Spine Surgery, 3 Hip Surgery, 3 Knee Surgery, 1       RBC units transfused, Median (Range) 0 (0-2) 170 0 (0-5) 157 0.00 (0.00, 0.00) Estimated blood loss (mL), Median (Range) 100 (0-2,000) 170 100 (0-1,500) 157 0.00 (0.00, 50.00) Received laboratory Hb test, N (%) 18 (10.6) 170 22 (14.0) 157 -0.03 (-0.11, 0.04) Postoperative Received RBC transfusions, N (%) 0 (0.0) 170 1 (0.6) 157 -0.01 (-0.02, 0.01) Laboratory Hb value (g/dL), Mean (SD) 11.8 (1.5) 128 11.7 (1.5) 115 -0.02 (-0.40, 0.36) Suffered complications within 28 days, N (%) 15 (15.2) 99 22 (24.2) 91 -0.09 (-0.20, 0.02)

*Total refers to the number of patients for whom relevant data was available (e.g. responded to follow up). aFor categorical variables, difference refers to the risk difference. For normally distributed continuous variables, difference refers to the difference in means. For skewed continuous variables, difference refers to the difference in medians.

Table 2: Intraoperative and postoperative outcomes among the Standard Care Group (control) and SpHb Group (intervention).