The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts


Hui-Ling L. Lin1, James B. Fink3, Yue Zhou2, Yung-Song S. Cheng2

Background: On the AARC adult acute care section email listserve, a practitioner questioned whether moisture that collected in the ventilator circuit and spacer affected the delivery of aerosol from pMDIs. An in vitro model was used to quantify the impact of accumulated humidity in a pMDI spacer over time.

Methods: An AeroVent® inline chamber (Monaghan Medical) placed in the inspiratory limb of an adult ventilator circuit proximal to the Y and left in an open position. Series of 8 actuations of HFA albuterol pMDI (GlaxoSmithKline Pharmaceuticals) were performed at one, two, and three hours after the heater had been running, and immediately following the heater shut-off, with each measurement repeated (n=3). Then the AeroVent was removed from the ventilator circuit and air blow dried. Another set of measurements with a dry chamber in the wet circuit were taken An AVEA ventilator (VIASYS Inc) delivered 700 mL Vt, 12 breaths/min, 50 L/min IFR with descending flow pattern, and 5 cmH2O PEEP. An Impactor (NGI; MSP) was placed between the ETT and test lung to determine inhaled mass and mass median aerodynamic diameter (MMAD) (n=3). Samples were analyzed via spectrophotometer (224 nm) and a factorial ANOVA was performed (p<0.05).

Results: The inhaled mass as a percent of emitted dose is shown in the figure below. MMAD did not vary between conditions.

Discussion: There was no difference between an air-dried chamber and the chamber placed the humidified circuit for one hour. However, when the condensation occurred, deposition decrease by approximately 50% (p<0.005). Turning off the heated humidifier prior to dosing did not improve delivery.

Conclusion: Turning off the heated humidifier did not increase the drug delivered from an HFA pMDI during adult mechanical ventilation.

We thank the American Respiratory Care Foundation for the grants, and VIASYS Health Inc for the support of the AVEA ventilator.