Airway Pressure Release Ventilation with a Time-Controlled Adaptive Ventilation Strategy (APRV-TCAV) Reverses Endotracheal Secretion Movement Compared with Volume-Control Ventilation: A Bench Study

Background/Objectives: Retained airway secretions are a common complication of mechanical ventilation and a major contributor to ventilator-associated pneumonia. Airway Pressure Release Ventilation following a Time-Controlled Adaptive Ventilation protocol (APRV-TCAV) has been anecdotally observed to improve secretion clearance, but the mechanism is not well established. Because TCAV sets the release time (TLow) from each patient’s own expiratory flow decay, we hypothesized that the resulting expiratory-dominant flow profile would generate a net antegrade force on secretions. This bench study compared secretion movement between APRV-TCAV and conventional Volume-Control Continuous Mandatory Ventilation (VC-CMV), with and without an in-line oscillatory device. Methods: A critical care ventilator was connected to a 3 L test lung via a 7 mm endotracheal tube (ETT). Simulated mucus (1% guar gum) was instilled into the ETT, and secretion movement was measured under VC-CMV (positive end-expiratory pressure (PEEP) 5, 10, 15 cmH2O) and APRV-TCAV (PHigh 20, 25, 30 cmH2O; PLow 0 cmH2O). Each condition was repeated with an in-line oscillatory device. Results: All VC-CMV settings produced retrograde secretion movement toward the test lung; all APRV-TCAV settings produced antegrade movement. The largest antegrade movement was observed at the widest PHigh-to-PLow differential. Adding the oscillatory device raised peak expiratory flow above peak inspiratory flow in every condition, yet abolished antegrade movement under APRV-TCAV. Conclusions: In this bench study, APRV-TCAV reversed the direction of secretion movement within the ETT, with larger antegrade movement at wider PHigh-to-PLow differentials. This suggests a potential mechanism by which the ventilator flow profile itself may influence secretion movement. The directional effect depended on the intact release-phase waveform and was abolished by in-line oscillatory therapy despite preserved peak flow asymmetry.