Effect of Face Mask Design and Flow-by on Rebreathing During Noninvasive Ventilation

BACKGROUND: Noninvasive ventilation (NIV) is used to treat respiratory failure because it reduces the risks of endotracheal intubation and postextubation respiratory failure. A wide range of different interfaces is available, but concerns exist about rebreathing. This study evaluated a total face mask with a 2-limb ventilation circuit and separate access for inflow and outflow gas, which was developed to reduce rebreathing.

METHODS: In a bench test, a standard total face mask (with a single connector to the ventilation circuit) and the modified total face mask were applied to a mannequin connected to an active breathing simulator. A known CO₂flow (V̇_CO2) was delivered to the mannequin's trachea. We tested the following settings: CPAP with the mechanical PEEP valve set at 8 cm H₂O (with 60 and 90 L/min continuous flow) and pressure support of 6 and 12 cm H₂O (with 2 and 15 L/min flow-by). The settings were tested at simulated breathing frequencies of 15 and 30 breaths/min and with V̇_CO2 of 200 and 300 mL/min. The active simulator generated a tidal volume of 500 mL. Airway pressure, air flow, CO₂ concentration, and CO₂ flow as the product of air flow and CO₂ were recorded.

RESULTS: The mean volume of CO₂ rebreathed and the minimum CO₂ inspiratory concentration were significantly lower with the modified mask than with the standard mask. The 15 L/min flow-by significantly decreased rebreathing with the DiMax0 mask, whereas it had no effect with the traditional mask.

CONCLUSIONS: A face mask with a two-limb ventilation circuit and separate access for inflow and outflow gas reduces rebreathing during NIV. The addition of flow-by enhances this effect. Further studies are required to verify the clinical relevance.