Weight-Based Assessment of Fluid Overload in Patients with Acute Kidney Injury

Abstract

Introduction: Acute kidney injury (AKI) with fluid overload is associated with poor outcomes. While percentage fluid overload (PFO) using intake/output charts (PFO_i/o) has been validated as a marker of overload, accurate PFO_i/o measurements may not be possible in a general ward. We propose an alternative weight-based PFO calculation: PFO_w = [(maximum weight − baseline weight) ÷ baseline weight] × 100%. Methods: This is a prospective, observational pilot study on general ward inpatients with AKI who were referred for nephrology consult. PFO_w was compared with PFO_i/o, and both were evaluated for associations with dialysis requirement, AKI stage 2 or 3, and 90-day mortality. Results: Fifty-eight patients with a median age of 67.5 years (interquartile range 18.0) were recruited. Of which, 33 (56.9%) were males and 41 (70.7%) had preexisting CKD 3 or higher. We found no correlation between PFO_i/o and PFO_w (R² = 0.015, p = 0.531). A higher PFO_w was observed in AKI stage 2 or 3 (p = 0.005) and in patients requiring dialysis (p = 0.001). On multivariate analysis, each percentage increase in PFO_w was associated with increased odds of AKI stage 2 or 3 (odds ratio 1.37 [95% CI 1.05–1.78], p = 0.020) and dialysis need (odds ratio 1.69 [95% CI 1.20–2.39], p = 0.003). Twenty-nine patients had complete quantitative data to calculate PFO_i/o. Multivariate analysis of these 29 patients showed that PFO_w correlated with AKI stage 2 or 3 and dialysis requirement, while PFO_i/o had no correlation with these events. The area under the curve receiver operating characteristics of PFO_w was 0.706 for AKI stage 2 or 3 and 0.819 for AKI requiring dialysis. The optimal PFO_w cutoff was determined at ≥1%. Three deaths occurred within 90 days, and all had PFO_w ≥ 1%, although the log-rank test did not achieve statistical significance (p = 0.050). Conclusion: The proposed PFO_w is a potential prognostic indicator for general ward patients with AKI. PFO_w ≥ 1% is associated with poor renal outcomes.