Overcoming the adverse effect of humidity in aerosol delivery via pressurized metered-dose inhalers during mechanical ventilation

The well-known problem of reduced drug delivery that occurs when heated, hu mid air is used with pressurized metered-dose inhalers (pMDIs) and spacers in intubated settings is carefully studied with Airomir using an in vitro m odel under controlled conditions of temperature and humidity. A better unde rstanding of the physical processes leading to the aforementioned drop in p erformance is obtained, and a method is devised to circumvent the problem w ithout having to reduce the temperature or humidity of the ventilator circu it. The present study shows that the mole fraction of water vapor in the ve ntilation air (and not the temperature) is the major factor behind the shar p drop in the amount of drug delivered to the lung. However, the presence o f water vapor does not affect performance because of hygroscopic growth. In stead, it influences the initial atomization process and the early stages o f aerosol generation. Removal of these negative effects can be achieved by using a larger spacer that allows longer times for the aerosol to evaporate , as is demonstrated in the present study.