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Updated: Sep 26, 2026
Evaluation of Fluid Overload by Bioelectrical Impedance Vectorial Analysis
Published on: August 17, 2022
The Fluid Overload Ultrafiltration Percentage (FOUP): a novel metric that contextualizes fluid removal to initial
Dong Li1, Xiaowei Xiong1, Chunxiao Wang1
1Department of Critical Care Medicine, Chongqing Key Laboratory of Pediatric Metabolism and Inflammatory Diseases, Children's Hospital of Chongqing Medical University, National Clinical Research Center for Child Health and Disorders, Chongqing, China.
Background:
Optimal fluid removal during pediatric continuous renal replacement therapy (CRRT) remains challenging. Conventional metrics-net ultrafiltration rate (NUFR) and net fluid balance (NFB)-do not assess removal efficiency relative to initial fluid overload (FO). We hypothesized Fluid Overload Ultrafiltration Percentage (FOUP)-cumulative NFB normalized to initial FO-would reveal clinically meaningful patterns.
Methods:
We studied 220 children receiving CRRT for ≥72 h. FOUP, NUFR, and NFB were calculated over three 24-h intervals. Subgroup analyses were performed within survivors stratified by FO (<5% vs. ≥5%), capillary leak index (CLI < 3.3 vs. ≥3.3), and body weight.
Results:
Non-survivors (n = 84) had higher baseline FO (6.6% vs. 2.4%, p < 0.001) and received higher NUFR at all time points (all p < 0.01), yet achieved similar NFB and FOUP. NUFR trajectories diverged: survivors decreased (p = 0.003), and non-survivors increased (p = 0.013). In survivors, FOUP revealed a biphasic pattern in high-risk patients (FO ≥ 5% or CLI ≥ 3.3): vigorous early removal (-43.3% at 24 h) followed by a plateau (-2.0% to -4.1% at 48-72 h, p< 0.001), despite continued high NUFR. Hemodynamic stability was maintained.
Conclusions:
FOUP normalizes fluid removal to the initial FO, revealing a biphasic pattern in high-risk patients-early rapid removal followed by a plateau, signaling diminishing returns. These findings support a response-adaptive, FOUP-guided approach.
Impact:
This study introduces FOUP, a metric normalizing fluid removal to initial overload. Unlike weight-dependent NUFR or absolute NFB-which require baseline FO for interpretation-FOUP directly quantifies removal relative to initial burden. This enables FOUP to reveal clinically meaningful patterns: in patients with FO ≥ 5% or CLI ≥ 3.3, FOUP shows a biphasic trajectory-vigorous early removal followed by a plateau at 48-72 h-indicating that continued high-intensity ultrafiltration yields diminishing returns. By contextualizing removal to initial overload, FOUP provides a rational basis for response-adaptive fluid management.
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