Association between obesity and kidney outcomes in critically ill patients with acute kidney injury receiving continuous renal replacement therapy: a secondary analysis of the multicenter CRRTnet study

BACKGROUND: Continuous renal replacement therapy (CRRT) is frequently utilized in critically ill adults with acute kidney injury (AKI). Outcomes among obese patients receiving CRRT, however, are poorly characterized, and the modifying effect of CRRT dose-intensity remains uncertain. This study examined the association between obesity and mortality among critically ill adults receiving CRRT and whether the method used to calculate body weight modified the association between prescribed CRRT dose-intensity and mortality.METHODS: We conducted a secondary analysis of the prospective, multicenter observational CRRTnet study, which enrolled critically ill adults with AKI receiving CRRT. Patients who received < 24 h of CRRT were excluded. Primary outcomes were in-hospital mortality, compared between obese (body mass index [BMI] ≥ 30 kg/m2) and non-obese (BMI < 30 kg/m2) patients, and by prescribed CRRT dose-intensity determined by actual body weight (ABW), ideal body weight (IBW), and adjusted-body weight (Adj-BW).RESULTS: Among 890 patients (478 obese and 412 non-obese), median BMI was 36.3 kg/m2 (interquartile range [IQR], 32.9–41.7) for obese and 25.5 kg/m2 (IQR, 23.3–27.8) for non-obese patients (p < 0.001). In-hospital mortality was similar between groups (53.8% vs. 52.4%; p = 0.74). In multivariable analysis, obesity was independently associated with increased mortality (adjusted-odds ratio [adj-OR], 1.53; 95% confidence interval [CI], 1.03–2.28; p = 0.034). Greater prescribed CRRT dose-intensity (per 5 mL/kg/h increase) was associated with greater odds of in-hospital mortality, when indexed to ABW (adj-OR, 1.17; 95% CI, 1.10–1.25; p < 0.001), IBW (adj-OR, 1.13; 95% CI, 1.09–1.18; p < 0.001), and Adj-BW (adj-OR, 1.19; 95% CI, 1.13–1.27; p < 0.001).CONCLUSIONS: Among critically ill adults with AKI receiving CRRT, obesity appears to confer greater risk of in-hospital mortality, and greater prescribed CRRT dose-intensity was consistently associated with greater mortality risk across all weight-based indices. These findings highlight the potential necessity for modifying CRRT prescription practices among obese patients and highlight the need for further research on optimal CRRT dose-intensity prescription across a broad spectrum of critically ill patients.TRIAL REGISTRATION: This study was prospectively registered on ClinicalTrials.gov (NCT02034448) on January 10, 2014.SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13054-026-05950-w.