The Science Journal of the American Association for Respiratory Care

2004 OPEN FORUM Abstracts

COMPARISON OF AEROSOL MEDICATION DELIVERY USING DIFFERENT LENGTH EXPIRATORY RESERVOIRS

Ruben D Restrepo MD RRT, Douglas S Gardenhire MS RRT, Arzu Ari MS RRT, Joseph L Rau PhD RRT . Department of Cardiopulmonary Care Sciences. Georgia State University. Atlanta, GA.




Background: Most hand-held nebulizers that provide constant aerosol generation during inspiration and expiration have a T-piece that fits on top of the unit to allow attachment of a mouthpiece. An optional 6-inch corrugated tube extension is usually placed at the distal end of the T-piece (expiratory reservoir). There is no report in the literature on the impact of using different expiratory reservoir tubing lengths on the amount of drug available for inhalation.

Objective
: To measure the effect of expiratory tubing of various lengths on the inhaled dose of a constant output nebulizer.

Methods
: An in vitro model was used to evaluate delivery of nebulized bronchodilator to simulated spontaneously breathing adults. The Airlife Misty-Neb was the nebulizer used as it represents an example of a traditional constant output nebulizer. Eight trials of three system configurations were run: a nebulizer with T-piece adapter without an expiratory reservoir; a 6-inch (50 mL) length of large-bore corrugated tubing attached to the expiratory outlet of the T-piece, and a 12-inch (100 mL) expiratory reservoir. The amount of aerosol drug in the filter that was attached to the proximal end of the T-piece, between the nebulizer and the breathing simulator, was used as an indicator of the amount of drug available to the patient on each inspiration. Drug amounts collected at the filter were expressed as a percent of the nominal dose.

Measurement of Drug:
All drug amounts were analyzed using a spectrophotometer at a wavelength of 276 nm.

Data Analysis:
Means and standard deviations were calculated for each series measured. Differences across configurations were compared using repeated measures ANOVA. Pairwise comparisons were used to identify differences between configurations at a 0.05 level of significance.

Results:
As illustrated in the bar graph, there was only a significant difference in the amount of drug measured at the inspiratory filter between the configuration with no reservoir and the 12 inch reservoir (p= 0.01).

Conclusion:
Attachment of a 12-inch reservoir to the T-piece used with small volume nebulizers may improve the clinical response to aerosolized medications. However, pulmonary function testing before and after aerosol delivery with this configuration, as well as quantification of carbon dioxide rebreathing from a longer expiratory reservoir should be evaluated before the results of this study are extrapolated to clinical practice.

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