Am. J. Respir. Crit. Care Med.,
Volume 161, Number 5, May 2000, 1614-1618
Overcoming the Adverse Effect of Humidity in Aerosol
Delivery via Pressurized Metered-Dose Inhalers during
Mechanical Ventilation
CARLOS F.
LANGE
and
WARREN H.
FINLAY
Aerosol Research Laboratory, Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta, Canada
The well-known problem of reduced drug delivery that occurs
when heated, humid air is used with pressurized metered-dose inhalers (pMDIs) and spacers in intubated settings is carefully studied with Airomir using an in vitro model under controlled conditions of temperature and humidity. A better understanding of the
physical processes leading to the aforementioned drop in performance is obtained, and a method is devised to circumvent the
problem without having to reduce the temperature or humidity of
the ventilator circuit. The present study shows that the mole fraction of water vapor in the ventilation air (and not the temperature) is the major factor behind the sharp drop in the amount of
drug delivered to the lung. However, the presence of water vapor
does not affect performance because of hygroscopic growth. Instead, it influences the initial atomization process and the early
stages of 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.
