Ratio of Overhydration and Extracellular Water Versus Ratio of Extracellular Water and Body Cell Mass in the Assessment of Fluid Status in Patients With Acute Kidney Injury Requiring Kidney Replacement Therapy: A Cohort Study

The aim of this study is to analyze the association between the ratio of overhydration and extracellular water (OH/ECW) and the ratio of extracellular water and body cell mass (ECW/BCM) measured by bioelectrical impedance and outcomes of patients with acute kidney injury (AKI) requiring kidney replacement therapy (KRT).Patients with severe AKI treated with KRT in our hospital between September 2016 and August 2018 were enrolled. These patients were assessed using a body composition monitor before KRT, and on the 3rd day and the 7th day after initiation of KRT. The predictors mainly included OH/ECW and ECW/BCM. The association between all-cause mortality and predictors were analyzed using Cox regression.A total of 152 patients were included in this study with a median follow-up of 39 (interquartile range 8-742) days. The 28-day mortality, 90-day mortality, and 1-year mortality were 46.7%, 54.6%, and 60.5%, respectively. A high ratio of OH/ECW (adjusted hazard ratio per standard deviation, 1.45; 95% confidence interval = 1.15-1.82, P = .002) and a high ratio of ECW/BCM (adjusted hazard ratio per standard deviation, 1.33, 95% confidence interval = 1.07-1.64, P = .009) before KRT were associated with all-cause mortality during follow-up. Higher ECW/BCM rather than OH/ECW at 7th day was associated with poorer outcomes. Furthermore, a reduction of OH/ECW with an increase of ECW/BCM had higher 1-year mortality as compared to others (85.7% vs. 51.2%, P = .004) in patients who survived 7 days after KRT initiation.ECW/BCM performed better than OH/ECW in assessment of fluid status in AKI patients requiring KRT. This study suggested that a simple reduction of OH/ECW without decreasing ECW/BCM may not improve outcomes.