Face Mask Leak Determines Aerosol Delivery in Noninvasive Ventilation

BACKGROUND: Aerosol transport during noninvasive ventilation follows the flow of pressurized gas through the noninvasive ventilation circuit, vented via leak port and face mask, and inhaled by the patient. Recommendations for nebulizer placement are based on in vitro models that have focused primarily on aerosol losses via the leak port; face mask leaks have been avoided. This study tested aerosol delivery in the setting of controlled face mask leak. METHODS: Three nebulizer technologies were studied on a bench model using a lung simulator with a face mask placed onto a manikin head. Radiolabeled aerosol delivery (ie, inhaled mass) was determined by mass balance using filters and a gamma camera that tested the effects of nebulizer location and face mask leak. Low (15–20 L/min) and high (55–60 L/min) mask leaks were used to mimic realistic clinical conditions. RESULTS: Inhaled mass (% nebulizer charge) was a function of nebulizer technology (with the nebulizer at ventilator outlet position: Aerogen 22.8%, InspiRx 11.1%, and Hudson 8.1%; P = .001). The location of the nebulizer before or after the leak port was not important (P = 0.13 at low leak and P = 0.38 at high leak). Aerosol delivery was minimal with high mask leak (inhaled mass 1.5–7.0%). Aerosol losses at the leak port at low mask leak were 28–36% versus 9–24% at high mask leak. Aerosol losses via the mask leak were 16–20% at low mask leak versus 46–72% at high mask leak. Furthermore, high face mask leak led to significant deposition on the mask and face (eg, up to 50% of the nebulizer charge with the Aerogen mask). CONCLUSIONS: During noninvasive ventilation, nebulizer placement at the ventilator outlet, which is a more practical position, is effective and minimizes deposition on face and mask. Aerosol therapy should be avoided when there is high face mask leak.