The Science Journal of the American Association for Respiratory Care

2002 OPEN FORUM Abstracts

A Comparison of Gas Sources and I:E Ratios and Their Effects on Aerosol Deposition During Conventional Ventilation

Brian Smith, RRT, Jason Higgins, BS RRT, Anthony Dal Nogare, MD
Parkland Health and Hospital System, Dallas, Texas Department of Respiratory Care

Background: Several factors are identified in the current literature as contributors to aerosol deposition in the small airways. The effect of the gas source, whether it is continuously by a flowmeter or intermittently from a ventilator, as well as the set I:E ratio on the ventilator are of particular interest in our study. We sought to determine if either gas source is more efficient and whether greater I:E ratios with each method has an effect on optimal deposition.

Method: An in-vitro lung model with in-line bacteria filters was designed for the purpose of this study. We compared aerosol deposition when generated by a Bear 1000 ventilator during inspiration only versus continuously by a wall source at I:E ratios of 1:3 and 1:6. Ten albuterol nebulizers each containing 3 mls of albuterol was delivered in-line using the traditional port on the inspiratory side of a ventilator circuit for each aerosol generator at each I:E ratio. The nebulized aerosols generated from the wall were delivered at 8 liters/minute for 7 minutes. Nebulized aerosols generated from the ventilator were driven during inspiration only for a time period of 30 minutes. After each nebulizer was completed, filter samples were collected 6 cm to the right and left of a 90° bifurcation representing distal airways. The filters were then saturated with 7 mls of ethanol in a sterile container for a period up to 12 hours. Samples from each container were analyzed with a spectrophotometer set at 278 nanometers in order to calculate albuterol absorption amounts.

Results: Absorption amounts were converted to mg/ml:

  I:E ratio 1:3 Right I:E ratio 1:3 Left I:E ratio 1:6 Right I:E ratio 1:6 Left
Ventilator Mean- .1015
SD- .0166
Range- .078-.121
Mean- .1245
SD- .0215
Range- .095-.160
Mean- .0640
SD- .0136
Range- .040-.080
Mean- .0579
SD- .0141
Range- .045-.095
Wall Outlet Mean- .0814
SD- .0466
Range- .054-.109
Mean- .0813
SD- .0169
Range- .054-.107
Mean- .0641
SD- .0126
Range- .053-.088
Mean- .0640
SD- .0119
Range-.054-.088

Conclusion: With this study, we attempted to isolate two factors that have an effect on aerosol deposition. We demonstrated that intermittent nebulization (inspiration) along with longer inspiratory times provided notably improved aerosol deposition. Results also indicated that when shorter inspiratory times were used, there did not appear to be a noticeable difference between nebulization from the wall outlet versus nebulization from the ventilator. We feel that this data can be useful clinically with those patients who are intubated and requiring bronchodilator therapy.

OF-02-081

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