1995 OPEN FORUM Abstracts
Pattern Of Deposition And Aerosol Particle Size In A Dry Vs Humidified Ventilator Circuit Using Metered Dose Inhaler And Spacer
J. Fink, MS RRT, R. Dhand MD, J. Grychowski PhD, M.J. Tobin MD. Hines VA Hospital and Loyola Univ. Chicago, Hines IL.
To determine the role of heat and humidity on deposition and particle size during aerosol administration to ventilated patients, we administered albuterol by metered dose inhaler (MDI) with spacer chamber into the inspiratory limb of a dry (27ºC,< 30% RH) or wet (35ºC, >99% RH) ventilator circuit. A trachea and bronchi model was ventilated through an 8 mm ET tube during control mode (CMV). The mean mass aerodynamic diameter (MMAD)(QCM cascade impactor with Plenum chamber) and albuterol deposition (246nm) measured distal to the spacer chamber (site A), entering the ET tube (site B) and at the bronchi (site C) were:
Site ASite B Site C
WetDry Wet Dry Wet Dry
MMAD µm 1.61.3 1.1 1.3 1.0 1.1
Deposition % 60.5 44.829.835.016.030.3
At site A there was a significant difference between wet and dry conditions in both MMAD (p < 0.007;ANOVA) and deposition (p < 0.001), while at site C deposition differed (p < 0.003) but MMAD did not (p=0.16). In summary, during CMV with heat and humidity a larger fraction of albuterol leaves the spacer chamber with a larger particle size, compared to a dry circuit. Humidification lead to a three-fold increase in the ventilator circuit resulting in a decreased albuterol at the bronchi. The deposition of drug in the ventilator circuit under both wet and dry conditions was greater in the ventilator circuit than the ET tube (p < 0.001).
In conclusion, compared to a dry ventilator circuit, humidification resulted in a larger MMAD with reduction in bronchial deposition.