Objectives: Fluid imbalance due to sodium retention and malnutrition can be characterized by the ratio of extracellular water (ECW) to intracellular water (ICW). We investigated whether the ECW/ICW ratio is a risk factor for adverse outcomes.
Design: Retrospective cohort study.
Setting and participants: 149 patients with chronic kidney disease from 2005 to 2009, who were followed until August 2013.
Measurements: Body fluid composition was measured by bioelectrical impedance analysis. Patients were categorized according to the ECW/ICW ratio tertile. Daily nutrient intake was estimated from 24-h dietary recall and analyzed using standard food composition tables. The main outcomes were adverse renal outcomes, as defined by a decline of 50% or more from the baseline glomerular filtration rate or initiation of renal replacement therapy, cardiovascular events, and all-cause mortality.
Results: The ECW/ICW ratio increased with downward ICW slope with age and renal dysfunction besides ECW excess with massive proteinuria. Sodium intake, protein intake, and calorie intake were negatively correlated with the ECW/ICW ratios due to the steeper decreasing ICW content with the decreased dietary intake than the decreasing ECW content. During a median 4.9-year follow up, patients in the highest tertile had the worst adverse renal outcomes (15.9 vs. 5.1 per 100 patient-years, P < 0.001), cardiovascular events (4.1 vs. 0.3 per 100 patient-years, P = 0.002), and mortality (11.2 vs. 1.3 per 100 patient-years, P < 0.001). The adjusted hazard ratio (95% confidence intervals) for adverse renal outcomes, cardiovascular events, and mortality were 1.15 (1.03 - 1.26), 1.12 (0.93 - 1.31), and 1.29 (1.11 - 1.50), respectively.
Conclusions: Fluid imbalance between ICW and ECW occurring in malnourished and elderly patients with chronic kidney disease may explain the reserve capacity for volume overload and is associated with adverse renal outcomes and all-cause mortality.