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

Abstract

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 ₂O and P _High 25 cmH ₂O, group 2—modified TCAV protocol with increased P _Low 5 cmH ₂O and P _High 25 cmH ₂O, group 3—modified TCAV with P _Low 10 cmH ₂O and P _High 25 cmH ₂O, group 4—ARDSnet protocol using low tidal volume (LTV) and PEEP 0 cmH ₂O, group 5—ARDSnet protocol using LTV and PEEP 10 cmH ₂O, and group 6—ARDSnet protocol using LTV and PEEP 20 cmH ₂O. 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.