The Science Journal of the American Association for Respiratory Care

2000 OPEN FORUM Abstracts

AEROSOL DELIVERY DURING PRESSURE CONTROLLED VENTILATION (PCV)

Christine Dillman, BA RRT, Robert M. Kacmarek PhD RRT FAARC, Dean Hess PhD RRT FAARC. Respiratory Care, Massachusetts General Hospital and Harvard Medical School, Boston, MA

Background: Inspiratory flow with volume controlled ventilation (VCV) can be either constant or decelerating. With PCV, inspiratory flow varies with lung compliance and resistance. We investigated the effect of these flow-related factors on aerosol delivery during mechanical ventilation.

Methods: We used an in-vitro model with a Puritan Bennett 7200ae ventilator and adult circuit (dry), a jet nebulizer (Hudson RCI Micro-Mist), and a test lung (Michigan Instruments TTL). A filter (Puritan-Bennett D/Flex) was placed between the ventilator Y-piece and the lung model to collect aerosolized albuterol. A 4 mL solution containing 5 mg of albuterol was placed into the nebulizer cup. The nebulizer was powered by the ventilator for one cycle of 30 min. Albuterol was washed from the filter and analyzed by ultraviolet spectrophotometry at 276 nm (Beckman DU 520). We evaluated 2 inspiratory times (1 & 2 s), 3 inspiratory flow patterns (constant flow, decelerating flow, & PCV), 2 compliance settings (0.02 L/cm H2O & 0.05 L/cm H2O) and 2 resistance settings (5 cm H2O/L/s & 50 cm H2O/L/s). The ventilator was set to deliver a tidal volume of 0.6 L, PEEP 5 cm H2O, and respiratory rate of 15/min for all evaluations. The experiment was repeated 3 times for each set of experimental conditions (n=3).

Results: With a 1 s inspiratory time, albuterol delivery was not different between flow patterns (P=0.35). Albuterol delivery increased with a longer inspiratory time (P=0.001), but this was less pronounced with PCV. For PCV, albuterol delivery was significantly affected by resistance and compliance - particularly for the 2 s inspiratory time (P<0.001).

Conclusions: Albuterol delivery by nebulizer and mechanical ventilation was affected not only by inspiratory time, but also by the inspiratory flow pattern. For PCV, the inspiratory flow is affected by the resistance and compliance of the lungs. Nebulizer flow stops when the inspiratory flow decelerates to zero during PCV and thus lung characteristics that produce a rapid deceleration in flow (e.g., low resistance & low compliance) result in no increase in albuterol deliver with increased inspiratory time. This effect should be considered when nebulizers are used with PCV. (See Original for Figure)

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