The Accumulating Deficits Model for Postoperative Mortality and Readmissions: Comparison of Four Methods Over Multiple Calendar Year Cohorts

OBJECTIVE: To assess 4 measures of the accumulating deficits model of frailty for postoperative mortality and readmissions including their stability over time. BACKGROUND: Frailty has been assessed by multiple methods. It is unclear whether variation in how frailty is measured is important and would be stable over time. METHODS: Rockwood's 57-item frailty index was mapped onto 14,568 ICD9 diagnosis codes from Healthcare Cost and Utilization Project State Inpatient Database for the state of Florida (HCUP-SID-FL) for calendar years 2011 to 2015, inclusive, with 962 ICD9 codes matching onto 42 items. This became the modified frailty index (mFI) used. Three measures of the mFI were differentiated: the number of admission diagnoses, number of chronic conditions upon admission, and number of increased deficits accumulated during the admission. The Charlson Co-Morbidity Index was a fourth measure of frailty. The mFI of patients who survived or died and were readmitted or not were compared. RESULTS: Across all years, 4,796,006 patient observations were compared to the number of diagnoses matched on the 42 items of the mFI. The median mFI scores for each method was statistically significantly higher for patients who died compared those that survived and for patients readmitted compared to patients not readmitted for all years. There was little-to-no variation in the year to year median mFI scores. CONCLUSIONS: The 4 methods of calculating frailty performed similarly and were stable. The actual method of determining the accumulated deficits may not be as important as enumerating their number.