Association between input/weight ratio and acute kidney injury in obese critical ill patients: a propensity analysis of multicenter clinical databases.

Rehydration volume may be underestimated in obese critically ill patients, which can lead to acute kidney injury (AKI). This study aimed to investigate the association between input/weight ratio (IWR) and AKI risk in obese critical patients. This retrospective observational study analyzed data from three large open databases. Patients were divided into lean and obese groups and matched 1:1 based on age, sex, APACHE II score, SOFA score, sepsis status, mechanical ventilation status, renal replacement therapy status, and hospital type. The exposure of interest was the mean IWR during the first three ICU admission days. The primary outcome was the incidence of AKI within 28 days after ICU admission. Cox regression analysis was used to evaluate the association between IWR and AKI risk. A total of 82,031 eligible patients were included in the study, with 25,427 obese patients matched with 25,427 lean patients. The IWRs were significantly lower in the obese groups in both the unmatched cohort (35.85 ± 19.05 vs. 46.01 ± 30.43 ml/kg, p < 0.01) and the matched cohort (36.13 ± 19.16 vs. 47.34 ± 31.13 ml/kg, p < 0.01). An increase in IWR was significantly associated with decreased creatinine levels, increased urine output and a lower AKI risk. The interaction terms of IWR and obesity were significantly associated with decreased AKI incidence in both the unmatched cohort (hazard ratio [HR] = 0.97, 95% CI 0.96-0.97, p < 0.01) and the matched cohort (HR = 0.97, 95% CI 0.96-0.97, p < 0.01). Inadequate rehydration of patients with obesity may contribute to an increased risk of AKI in patients with obesity. These results highlight the need for better rehydration management in patients with obesity.