Association between fluid status and small airway dysfunction in hemodialysis patients: A prospective paired study

Fluid overload is a major cause of dyspnea in patients with end-stage kidney disease (ESKD). However, the mechanistic links between volume status, changes in small airway function, and dyspnea remain poorly understood. We hypothesized that fluid overload impairs small airway function and contributes to dyspnea, and that impulse oscillometry (IOS) can detect dialysis-induced improvements in airway mechanics.

This prospective, paired pre- and post-intervention study evaluated patients on maintenance hemodialysis before and after a single session. Assessments included modified Medical Research Council (mMRC) dyspnea scale, spirometry, IOS, and bioimpedance analysis.

Fifty-four patients were enrolled. The proportion of patients with notable dyspnea (mMRC ≥ 2) decreased after hemodialysis, from 31.5% to 18.5% (P = 0.001), accompanied by a reduction in extracellular water (ECW). While spirometry indices remained unchanged, IOS parameters, including Z₅, R₅, R₅-R₂₀, and AX, decreased significantly after dialysis. These changes were negatively correlated with predialysis ECW/total body water (TBW) ratio. A higher predialysis ECW/TBW ratio was associated with greater reductions in R₅-R₂₀ and AX after hemodialysis, reflecting that patients with greater baseline fluid overload experienced more improvement in small airway function. Patients with mMRC ≥ 2 at baseline demonstrated greater impairment of small airway function prior to dialysis.

Fluid overload contributes to impaired small airway function and dyspnea in patients with ESKD. IOS-derived parameters, including R₅-R₂₀ and AX, are more sensitive than spirometry in detecting subtle changes in small airway mechanics following fluid removal.