Body mass index and mortality in patients receiving Extracorporeal Membrane Oxygenation: an analysis of the Chinese extracorporeal life support registry

Background The prognostic significance of body mass index (BMI) in patients receiving extracorporeal membrane oxygenation (ECMO) remains uncertain, particularly in Asian populations. Methods We conducted a nationwide, multicenter, retrospective cohort study of adults receiving ECMO in China from 2014 to 2025. Patients were classified as underweight (< 18.5 kg/m²), normal weight (18.5 to < 24.0 kg/m²), overweight (24.0 to < 28.0 kg/m²), or obesity (≥ 28.0 kg/m²). The primary outcome was in-hospital mortality. Multivariable logistic regression and restricted cubic splines were used to evaluate categorical and nonlinear associations between BMI and mortality. Results Among 13,636 patients, 13,585 with known hospital outcomes were included in mortality analyses; 5,530 died (40.7%). In the fully adjusted model, overweight (adjusted OR, 1.15; 95% CI, 1.06–1.24; P < 0.001) and obesity (adjusted OR, 1.26; 95% CI, 1.10–1.44; P = 0.001) were associated with higher odds of in-hospital mortality compared with normal weight, whereas underweight was not statistically significant (adjusted OR, 1.16; 95% CI, 0.98–1.38; P = 0.084). The BMI–mortality association was nonlinear (P for nonlinearity = 0.006), with the lowest estimated odds at approximately 21.47 kg/m². No significant effect modification was detected across major clinical subgroups. Conclusions In this nationwide Chinese ECMO cohort, BMI was nonlinearly associated with in-hospital mortality. Overweight and obesity were independently associated with higher mortality odds, supporting BMI as one component of multidimensional ECMO risk stratification rather than an isolated selection criterion.