Airway clearance techniques and evidence
| ACT | Physiological principles | Evidence | Pragmatic approach in LAC |
| ACBT | Flexible three phase cyclical technique of breathing control, TEE and FET Enhances tidal volumes, collateral ventilation and expiratory airflow Modification for use in LAC to ensure FET is optimised | Physiological background [32] Bronchiectasis [34] Cystic fibrosis [25] | No direct evidence • Clinical experience in LAC demonstrates that caution may be required in FET to ensure balance of airway calibre with creation of equal pressure points |
| PEP | A flow-regulated technique that has three effects: to increase lung volume (functional residual capacity and tidal volume (VT)), to reduce hyperinflation and to improve airway clearance. Positive pressure is then achieved by augmenting expiratory flow against this resistance | Physiological background [35] COPD [39] Cystic fibrosis [38] TBM (improve expiratory airflow) [40] | No direct evidence • Use in LAC to reduce airway closure during expiration and modify FET • Caution to prevent airway collapse but not to cause limitation to expiratory airflow |
| OPEP | PEP is applied by blowing out against a variable resistance that produces an oscillation in flow Individuals breathe out to expiratory reserve volume (ERV) enabling a modulation of both pressure and flow | Physiological background [22] Bronchiectasis [42] Cystic fibrosis [45] COPD [43] | No direct evidence • Use in LAC with caution as oscillations may cause airway collapse and irritation in some patients • If used comfortably, may have similar benefits to OPEP |
| HFCWO | Patient wears an inflatable vest attached to a machine that creates positive and negative pressure changes through high-frequency air pulses at a set pressure and frequency. Displacement of the airway walls additionally disengages secretions, enhancing airflow and ciliary beating | Physiological background [22] Bronchiectasis [47] Cystic fibrosis [49, 50] COPD [48] | No direct evidence • Clinical experience suggests this technique must be combined with FET (with relevant principles discussed for patients with LAC) |
| CPAP | Creates a “pneumatic splint”, helping to prevent dynamic airways collapse as flow and effort increase | Paediatric TBM [51] | Extrapolation of knowledge from paediatric TBM although caution required as different conditions • Clinical expertise/extrapolation of knowledge from use of PEP/high PEP • Caution required as underlying pathology may be different |
ACT: airway clearance technique; ACBT: Active Cycle of Breathing Technique; TEE: thoracic expansion exercise; FET: two forced expiration technique; LAC: large airway collapse; TBM: tracheobronchomalacia; PEP: positive expiratory pressure; OPEP: oscillating expiratory pressure; HFCWO: high-frequency chest wall oscillation; CPAP: continuous positive airway pressure.