Background A bronchodilator response (BDR) can be assessed in preschool-aged children using spirometry, respiratory oscillometry, the interrupter technique, and specific airway resistance, yet a systematic comparison of BDR thresholds across studies has not been completed.

Methods A systematic review was performed on all studies up to May 2023 measuring a bronchodilator effect in children 2-6 years old using one of these techniques (PROSPERO CRD42021264659). Studies were identified using MEDLINE, Cochrane, EMBASE, CINAHL via EBSCO, Web of Science databases, and reference lists of relevant manuscripts.

Results Of 1224 screened studies, 43 were included. Over 85% were from predominantly Caucasian populations, and only 22 studies (51.2%) calculated a BDR cut-off based on a healthy control group. Sample sizes ranged from 25-916. Only two studies (4.6%) adhered to formal recommendations for study design: at least 300 subjects, randomised for placebo response testing in healthy children, and incorporated within-session and between-session test repeatability. A relative BDR was most consistently reported by the included studies (95%) but varied widely across all techniques. A variety of statistical methods were used to define a BDR. The highest BDR feasibility was reported with oscillometry techniques in this age group.

Conclusion A BDR in 2-6-year-olds cannot be defined based on the reviewed literature due to inconsistent methodology and cut-off calculations. Precise and feasible evaluation of lung function in young children is crucial for early detection and intervention of airway diseases. A standardised approach is required to develop robust BDR thresholds.

The authors have declared no competing interest.

MDW is supported by the Thrasher Research Fund, the Queensland Health Innovation, Investment and Research Office, and The University of Queensland Faculty of Medicine.

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Funding: MDW is supported by the Thrasher Research Fund, the Queensland Health Innovation, Investment and Research Office, and the University of Queensland Faculty of Medicine.

Ethical approval: Not applicable.

PROSPERO registration: CRD42021264659 at crd.york.ac.uk/prospero/

Notation of prior abstract publication/presentation: This manuscript has been submitted as an abstract for anticipated presentation at the 2024 annual scientific meeting for the Thoracic Society of Australia & New Zealand.

Contributors’ statement: Matthew D. Wong: Conceptualization (lead); data curation (lead); formal analysis (lead); investigation (equal); methodology (lead); visualisation (lead); writing – original draft (lead); writing – review & editing (lead). Kathleena Condon: Data curation (supporting); formal analysis (supporting); investigation (equal); visualisation (supporting); writing – original draft (supporting); writing – review & editing (supporting). Paul D. Robinson: writing – review & editing (supporting). Sadasivam Suresh: Supervision (equal); writing – review & editing (supporting). Syeda Farah Zahir: Supervision (equal); writing – review & editing (supporting). Peter D. Sly: Conceptualization (supporting); supervision (equal); writing – review & editing (supporting). Tamara L. Blake: Conceptualization (lead); data curation (supporting); investigation (supporting); methodology (supporting); supervision (equal); visualisation (supporting); writing – original draft (supporting); writing – review & editing (supporting).

Conflicts of Interest: None

Data availability statement: Data are available from the corresponding author on reasonable request.

The data are available from the corresponding author on reasonable request.