The volume of gas emitted from five metered dose inhalers at three levels of fullness.

UNLABELLED: We conducted this study to determine the volume of gas emitted from five commonly used metered dose inhalers (MDIs).

MATERIALS &

METHODS

We used the following MDIs: Alupent (Boehringer Ingelheim), Atrovent (Boehringer Ingelheim), Beclovent (Allen & Hanburys), Intal (Fisons), and Ventolin (Allen & Hanburys). The test system consisted of plastic bag, MDI adapter, 4-way stopcock, and 60-mL calibrated syringe. This system was glued together, and absence of leaks was confirmed by underwater testing. Each evaluation consisted of 10 puffs from the MDI into the bag, after which the volume in the bag was determined using the syringe, and the volume/puff was calculated by dividing by 10. Each MDI was evaluated at 3 levels of fullness: nearly full, partially empty, and nearly empty. Five measurements were made with each MDI brand, using a new MDI for each set of measurements.

RESULTS

Although there was a significant difference in the volumes emitted between MDI (p less than 0.001) and the levels of fullness (p = 0.001), the volume of gas emitted from these MDIs was small (approximately 15-20 mL). A significant interaction existed between MDI brand and level of fullness (p = 0.001).

CONCLUSIONS

Based on prior studies of propellant toxicity coupled with our findings on the volumes of gas emitted from MDIs, we conclude that the volumes of gas emitted are too small to be clinically important in the care of adult patients. The volume of gas emitted from an MDI is only potentially important if MDIs are used with very small tidal volumes in a closed system (eg. infants).