Physiologic correlates of in-hospital weight loss in acute heart failure: insights from bioimpedance analysis

Background

Acute heart failure (AHF) accounts for 5% of emergency admissions in the UK, with up to 20% of patients re-hospitalised within 30 days (1). Fluid congestion is the primary presentation, yet accurate quantification remains challenging. Residual congestion at discharge is associated with adverse clinical outcomes (2). Body weight, a surrogate for decongestion, may not accurately reflect changes in fluid status, as redistribution of body water and alterations in body composition can occur despite minimal or disproportionate weight change (3). Bioimpedance analysis (BIA) offers a non-invasive assessment of body fluid distribution which could complement management.

Purpose

We aimed to correlate in-hospital weight loss with BIA-derived parameters in AHF patients.

Methods

We analysed paired BIA measurements and weight obtained at admission and discharge in patients admitted with AHF. The patient cohort was derived from a randomised controlled study evaluating BIA-guided fluid management compared with standard care.

BIA was performed within 48 hours of admission, and at discharge, after patients were stepped down to oral diuretic therapy. Body weight was recorded within 4 hours of BIA measurement.

Changes in body weight (kg) were compared to BIA-derived parameters, including total body water (TBW), extracellular water (ECW), intracellular water (ICW), extracellular water fraction (ECW%=ECW/TBW), and fat-free mass (FFM). These were assessed using Pearson correlation coefficients following visual confirmation of monotonic relationships. Statistical analyses were performed using SPSS version 30, with statistical significance defined as p < 0.05.

Results

Over 11 months, 250 paired BIA and weight measurements from 125 patients admitted with AHF were analysed. 62% were male and median body mass index was 27.37 (IQR 24.34–32.44) kg/m². Mean left ventricular ejection fraction was 36 (SD ±14.1)%, and median NT-proBNP was 4911 (IQR 2683–9596)ng/l.

Weight loss correlated moderately with reductions in TBW (r = 0.67, p < 0.001) and ECW (r = 0.66, p < 0.001), but weakly with ICW loss (r=0.30, p < 0.001), suggesting weight change predominantly reflected extracellular fluid loss. Weight loss also correlated moderately with changes in FFM (r = 0.53, p < 0.001), suggesting a contribution from non-fluid mass loss. The association between weight loss and ECW% was weak (r = 0.41, p < 0.001), suggesting weight loss did not reliably reflect normalisation of fluid distribution.

Conclusion

In-hospital weight loss is a heterogeneous marker correlating with absolute fluid loss but does not reliably reflect extracellular fluid redistribution or euvolaemia. BIA-derived measures, particularly ECW%, may provide complementary insights to aid clinical decision making in AHF.For image description, please refer to the figure legend and surrounding text.Correlation of weight loss with ECW lossFor image description, please refer to the figure legend and surrounding text.