Calculation of the Electronic Frailty Index (eFI)

Construction of the eFI has been previously described.²² Briefly, the eFI quantifies the proportion of age-related health deficits present within a particular individual, as with other frailty indices.¹⁷ Our eFI comprises 54 total deficits, constructed from diagnosis codes, vital signs, laboratory measurements, information on smoking history and medications, and functional assessments (when available) from Medicare Annual Wellness Visits (Supplementary Figure S1). To calculate the eFI, we required that a patient had at least two outpatient encounters with a measured blood pressure in the 2 years before surgery, and 30 or more of the 54 items measured. For this analysis, we set the reference date for eFI calculation at 2 days before surgery. eFI scores range from 0 to 1, with higher scores indicating greater frailty. We categorized frailty status as fit (eFI ≤ 0.10), pre-frail (0.10 < eFI ≤ 0.21), and frail (eFI > 0.21).^22,23