Time-controlled adaptive ventilation (TCAV) accelerates simulated mucus clearance via increased expiratory flow rate

BACKGROUND: Ventilator-associated pneumonia (VAP) is the most common nosocomial infection in intensive care units. Distal airway mucus clearance has been shown to reduce VAP incidence. Studies suggest that mucus clearance is enhanced when the rate of expiratory flow is greater than inspiratory flow. The time-controlled adaptive ventilation (TCAV) protocol using the airway pressure release ventilation (APRV) mode has a significantly increased expiratory relative to inspiratory flow rate, as compared with the Acute Respiratory Distress Syndrome Network (ARDSnet) protocol using the conventional ventilation mode of volume assist control (VAC). We hypothesized the TCAV protocol would be superior to the ARDSnet protocol at clearing mucus by a mechanism of net flow in the expiratory direction. METHODS: Preserved pig lungs fitted with an endotracheal tube (ETT) were used as a model to study the effect of multiple combinations of peak inspiratory (I(PF)) and peak expiratory flow rate (E(PF)) on simulated mucus movement within the ETT. Mechanical ventilation was randomized into 6 groups (n = 10 runs/group): group 1—TCAV protocol settings with an end-expiratory pressure (P(Low)) of 0 cmH(2)O and P(High) 25 cmH(2)O, group 2—modified TCAV protocol with increased P(Low) 5 cmH(2)O and P(High) 25 cmH(2)O, group 3—modified TCAV with P(Low) 10 cmH(2)O and P(High) 25 cmH(2)O, group 4—ARDSnet protocol using low tidal volume (LTV) and PEEP 0 cmH(2)O, group 5—ARDSnet protocol using LTV and PEEP 10 cmH(2)O, and group 6—ARDSnet protocol using LTV and PEEP 20 cmH(2)O. PEEP of ARDSnet is analogous to P(Low) of TCAV. Proximal (towards the ventilator) mucus movement distance was recorded after 1 min of ventilation in each group. RESULTS: The TCAV protocol groups 1, 2, and 3 generated significantly greater peak expiratory flow (E(PF) 51.3 L/min, 46.8 L/min, 36.8 L/min, respectively) as compared to the ARDSnet protocol groups 4, 5, and 6 (32.9 L/min, 23.5 L/min, and 23.2 L/min, respectively) (p < 0.001). The TCAV groups also demonstrated the greatest proximal mucus movement (7.95 cm/min, 5.8 cm/min, 1.9 cm/min) (p < 0.01). All ARDSnet protocol groups (4–6) had zero proximal mucus movement (0 cm/min). CONCLUSIONS: The TCAV protocol groups promoted the greatest proximal movement of simulated mucus as compared to the ARDSnet protocol groups in this excised lung model. The TCAV protocol settings resulted in the highest E(PF) and the greatest proximal movement of mucus. Increasing P(Low) reduced proximal mucus movement. We speculate that proximal mucus movement is driven by E(PF) when E(PF) is greater than I(PF), creating a net force in the proximal direction.