Aerosols in the Health Care Field

:: Section 3

Aerosol Delivery Characteristics

MDIs produce aerosols with MMAD of 3-6 µm (the respirable range), but the initial velocity and dispersion of the aerosol cause approximately 80% of the dose leaving the actuator to impact and to deposite in the oropharynx. Significant deposition on the oropharynx may result in systemic absorption of some drugs. Pulmonary deposition ranges between 10% and 20%. It is difficult to predict the exact amount of drug delivered to a patient because of high variability between patients and because of highly technique dependent of MDI drug administration.

Positioning the outlet of the MDI approximately 4 cm in front of the mouth can improve lung deposition by decreasing oropharyngeal impaction. Holding the cansiter outside the wide open month (at two finger-breadths) provides a space for the aerosols to decelerate while evaporating. This method enhances the capability of the aerosol into the inspiratory airstream and reduces the amount of propellant inhaled. Use of the open-mouth technique with a low inspiratory flow rate can improve the dose delivered to the lower respiratory tract of an adult from approximately 7% to 14%.