Ventilator Hyperinflation for intensive care patients: Influence of Pressure versus Volume controlled settings to optimise expiratory flow rate bias.

Ventilator hyperinflation (VHI) is a technique used in Intensive Care Units by physiotherapists. VHI aims to assist in the removal of secretions from the lungs in patients who are intubated and receiving mechanical ventilation by adjusting the patient's mechanical ventilator settings to deliver breaths of a larger size in a slow controlled manner. While the use of VHI in Australia is increasing, different VHI protocols (i.e. ventilator setting adjustments) are utilised between hospitals. This study will be conducted in the intensive care unit of a major tertiary hospital. A single Physiotherapist with >10 years experience will administer VHI to two groups of patients. Group 1: Low Positive End Expiratory Pressure (PEEP) 5-9 cmH2O Group 2: High PEEP 10-15 cmH2O Patients will be allocated to Group 1 or 2 according to the level of PEEP they are receiving as part of their clinical management (i.e. their ventilator settings including PEEP level prescribed by the medical staff as part of the management of their clinical presentation). The effect of VHI will be analysed within these groups. Each group will have three ventilator hyperinflation protocols applied. The protocols will vary the mode of ventilation and target pressures used. Group 1: Low PEEP 5-9 cmH2O VHI Protocols 1. Pressure support ventilation (PSV) with Pressure Support set so that PIP equals 35cmH2O 2. Synchronised Intermittent Mandatory Ventilation - Volume Control (SIMV-V) with maximum tidal volume to a peak inspiratory pressure (PIP) limit of 35cmH2O 3. SIMV-V with maximum tidal volume resulting in a driving pressure limit of 20cmH2O Group 2: High PEEP 10-15 cmH2O VHI Protocols 1. SIMV-V with maximum tidal volume resulting in a driving pressure limit of 20cmH2O 2. SIMV-V with maximum tidal volume to a PIP limit of 35cmH2O 3. BiLevel mode with High PEEP to low PEEP range equals 20cmH2O (driving pressure limit) The order that the VHI protocols are applied within each group will be randomised. Each protocol will be applied for 2 minutes. For each patient, when each VHI method is applied, the settings will be documented and reported to assess the fidelity to the described protocols. After the application of a VHI protocol, the patient’s ventilator settings will be returned to their baseline settings for a period of 10 minutes, before the next VHI protocol will be performed.