Obesity Attenuates the Association Between the Modified Five-Item Frailty Score and Mortality in Septic Surgical Patients

Introduction Obesity is an independent predictor of mortality in septic surgical patients, likely associated with underlying physiologic frailty, measured by the modified 5-item frailty index (mFI-5). This study aimed to determine the prevalence of frailty among obese and nonobese surgical patients and evaluate the impact of frailty on mortality in these populations. Methods We performed a single-center retrospective cohort study of surgical intensive care unit patients admitted with sepsis (sequential organ failure assessment, SOFA ≥2). Individual mFI-5 scores (range 0–5) were calculated and the prevalence of prefrailty (mFI <2), moderate-frailty (mFI = 2), and severe-frailty (mFI ≥3) across body mass index (BMI) categories (underweight, nonobese, class I-III obesity) was compared. BMI <18.5 kg/m 2 was excluded. Characteristics associated with mFI ≥2 were evaluated. Factors independently associated with frailty, incorporating demographic, socioeconomic, and clinical variables were identified. Four cohorts were made: obese (BMI ≥30 kg/m 2 , n = 766) and nonobese (18.5–29.9 kg/m 2 , n = 574), further divided into frail (mFI≥2) and prefrail (mFI <2). In-hospital mortality, cumulative 90-day mortality, and 90-day survival were compared across groups. Results Severe frailty was highly associated with increasing BMI class, occurring in 37% of morbidly obese patients versus 19% of nonobese patients ( P < 0.005). Increasing BMI independently predicted moderate-to-severe frailty (odds ratio [OR]: 1.04, 95% confidence interval [CI]: 1.02–1.05). Frailty significantly increased 90-day mortality in nonobese patients (17.4% versus 36.4%, P < 0.005) but not in obese patients (34% versus 35%). Nonfrail nonobese patients demonstrated superior 90-day-survival. Conclusions Obesity is highly associated with higher mFI-5 scores, though its prognostic impact appears attenuated in obese versus nonobese cohorts, suggesting the need for more discriminatory frailty tools in the obese population.