Can assessment of small airway dysfunction support the diagnosis or management of asthma exacerbations in children? A systematic review

Background: Asthma exacerbations are acute episodes associated with worsening symptoms and lung function decline. In children, diagnosis and monitoring rely largely on clinical judgment and measures of large airway function, which may overlook peripheral airway involvement. Tests of small airway function, such as forced expiratory flow between 25% and 75% of vital capacity (FEF25–75) and impulse oscillometry (IOS), may offer additional physiological insights. The aim of this systematic review is to evaluate the evidence supporting the use of small airway tests during pediatric asthma exacerbations.

Main body: The protocol was registered on PROSPERO, and this systematic review followed established methodology. Electronic databases searched included MEDLINE (Ovid), EMBASE (Ovid), CINAHL (EBSCOhost), and CENTRAL (Cochrane Library). The search strategy combined subject headings and keywords relating to asthma exacerbations and small airway function (e.g.,‘asthma exacerbation’, ‘small airway dysfunction’, ‘impulse oscillometry’). Eligible studies included observational studies and randomised controlled trials assessing small airway tests during paediatric asthma exacerbations (aged <18 years). Risk of bias was assessed using appropriate validated tools according to study design.

Thirty-five studies met inclusion criteria. Thirty-one studies reported FEF25–75; four studies reported IOS parameters, including one that also included multiple-breath washout (MBW). Most studies found that small airway indices were impaired during exacerbations and improved after treatment. In many cases, FEF25–75 and IOS parameters (R5–R20, AX) showed greater relative change than forced expiratory volume in one second (FEV1), and small airways dysfunction persisted longer despite clinical recovery. All IOS studies achieved high feasibility in acute settings. No study evaluated whether small airway tests could be used to direct clinical management.

Conclusion: Physiological tests of small airway function appear feasible during acute paediatric asthma exacerbations and may detect abnormalities not captured by FEV1. However, no included studies evaluated whether incorporating these indices altered management or improved outcomes. While these tests show promise for future diagnostic or monitoring use, further validation in larger cohorts is needed before routine implementation.

Systematic review registration: PROSPERO 2025 CRD42025623062. Available from: https://www.crd.york.ac.uk/PROSPERO/view/CRD42025623062.