Physiological Effects on Lung Aeration of High Frequency Percussive Ventilation in Hypersecretive Tracheostomized Patients: a Physiological Observational Study

The incidence of pulmonary complications such as pulmonary atelectasis, pneumonia (including ventilator-associated pneumonia), and acute respiratory failure is high in critical care patients. The incidence of ventilator-associated pneumonia can be as high as 27% amongst mechanically ventilated patients. Studies have shown that 16% of critically ill patients have been reported to develop acute respiratory failure, which is associated with prolonged intensive care unit stay, resulting in significantly higher mortality than non-respiratory failure patients. Increased morbidity and mortality contribute to the burden on the health care system and lead to poor health-related outcomes. Multimodal physiotherapy plays a role in the management of these critically ill patients. High frequency percussive ventilation (HFPV) is used in patients with underlying pulmonary atelectasis, excessive airway secretions, and respiratory failure. HFPV is a non-continuous form of high-frequency ventilation delivered by a pneumatic device that provides small bursts of sub-physiological tidal breaths at a frequency of 60-600 cycles/minute superimposed on a patient's breathing cycle. The high-frequency breaths create shear forces causing dislodgement of the airway secretions. Furthermore, the HFPV breath cycle has an asymmetrical flow pattern characterized by larger expiratory flow rates, which may propel the airway secretions towards the central airway. In addition, the applied positive pressure recruits the lung units, resulting in a more homogeneous distribution of ventilation and improved gas exchange. In acute care and critical care settings, HFPV intervention is used in a range of patients, from spontaneously breathing patients to those receiving invasive mechanical ventilation where HFPV breaths can be superimposed on a patient's breathing cycle or superimposed on breaths delivered by a mechanical ventilator. The most common indications for HFPV use are reported as removal of excessive bronchial secretions, improving gas exchange, and recruitment of atelectatic lung segments. This study aims to assess the lung physiological response to HFPV in terms of aeration and ventilation distribution.