Compensating Artificial Airway Resistance via Active Expiration Assistance

Artificial airway resistance as provided by small-lumen tracheal tubes or catheters increases the risk of intrinsic PEEP (PEEPi). We hypothesized that by active expiration assistance, larger minute volumes could be generated without causing PEEPi compared with conventional mechanical ventilation when using small-lumen tracheal tubes or a cricothyrotomy catheter.

We investigated the active expiration assistance in a physical model of the respiratory system and estimated its hypothetical performance in terms of maximal flow generated with endotracheal tubes ranging from 3.0 to 8.0 mm inner diameter (ID); with microlaryngeal tubes of 4.0, 5.0, and 6.0 mm ID; and with a cricothyrotomy catheter. Furthermore, we determined the minute volumes that could be achieved without generating PEEPi by ventilating a physical lung model using conventional mechanical ventilation or using active expiration assistance.

The inspiratory and expiratory flow during active expiration assistance increased with increasing supply flow and decreased with decreasing ID of the connected endotracheal tubes (both P < .001). With small-lumen tracheal tubes, the active expiration assistance generated similar or higher minute volumes than conventional ventilation. Conventional mechanical ventilation with PEEPi <1 cm H₂O was not achievable via a microlaryngeal tube of 4.0 mm ID and smaller lumen tubes.

For mechanical ventilation via small-lumen tubes or thin catheters, active compensation of airway resistance might be a necessary means to generate adequate minute ventilation without causing PEEPi. Active expiration assistance can generate reasonable respiratory minute volumes via small-lumen tubes or thin catheters.