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Table 2 Key considerations

From: Outcome measures for airway clearance techniques in children with chronic obstructive lung diseases: a systematic review

Outcome measure

Indications, advantages

Limitations

Pulmonary function

- Suitable for long-term studies.

- Conventional PFT (i.e. spirometry, body plethysmography): valid measures, reference equations and extensive guidelines available.

- Inappropriate to detect acute changes related to ACTs.

- Pulmonary function is measured as a single unit (‘black box’ principle). No regional abnormalities or changes can be detected.

- Conventional PFT: insensitive to mild lung disease.

- Age appropriate approach required.

- The potential of PFT in infants and preschoolers remains unclear.

Expectorated sputum

- Sputum quantity gives an impression of mucus transport in short-term studies.

- Sputum quantity: inaccurate, unreliable, unsuitable for uncooperative children.

Oxygen measurements

- Provides information about the presence of a ventilation-perfusion mismatch.

- ABG analysis is the ‘gold standard’ method to measure blood oxygenation status.

- Pulse oximetry is suitable for continuous monitoring and is simple to perform.

- ABG analysis requires invasive sampling.

- Pulse oximetry is too imprecise for research purposes to detect small changes.

- Oxygenation as an outcome is not suitable for children with mild lung disease in stable conditions.

Exercise capacity

- Adequate for long-term studies focused on pulmonary rehabilitation.

- Exercise capacity cannot be measured in children <6y.

- Inappropriate to evaluate short-term effects of airway clearance.

- Inadequate to measure solely the effects of airway clearance.

Imaging

- Detailed regional information of the lungs.

- Hyperpolarized MRI is sensitive to changes in ventilation distribution.

- RAT technique is the most direct technique to quantify acute changes in mucus transport.

- Chest X-rays lack sufficient sensitivity.

- CT imaging is associated with radiation exposure.

- Subjectivity of scoring methods.

- Limited availability and high cost of most techniques.

Disease exacerbation parameters

- Demonstrate the impact on pulmonary exacerbations, which is a direct clinical endpoint.

- No complex testing material is required to achieve this information.

- Only relevant for long-term studies.

Patient-reported outcomes

- The inclusion of PROs promotes a patient-centered model of care.

- The perception and preference of the patient will influence adherence to the therapy, which emphasizes the importance of PROs for the evaluation of ACTs.

- There are a large number of PROs available, but not all PROs are validated and therefore results should be interpreted with caution.

- High risk of bias if subjects are not blinded to the therapy.