Comparison of High Frequency Oscillatory Ventilation to Conventional Ventilation in Delivery of Medical Aerosols to a Test Lung ♦ 225

Abstract

It has previously been established that only 1% to 3% of albuterol placed in a small volume nebulizer (SVN) is delivered to an intubated infant receiving conventional mechanical ventilation (CMV). We hypothesized that in high frequency oscillation (HFO) even less drug would be delivered due the very small tidal volumes. To demonstrate this we nebulized green food coloring in an HFO circuit attached via an endotracheal tube (ETT) to a test lung with a white filter at the opening. However, the filter quickly turned green, se we formed a new hypothesis to the effect that the ouput of an SVN was as likely to reach an intubated lung when used with HFO as it was in CMV. To test this a cotton ball was placed in an adapter at the opening of a neonatal test lung. A 3.0 mm ETT was attached to the adapter containing the cotton ball, and placed in brackets which held it in a curved shape. This ETT was in turn attached to the circuit of an actively cycling ventilator in which a nebulizer containing 2.5 mg of albuterol in 3 mL of solution was driven with 8 L/min flow until the nebulizer was exhausted. The cotton ball was then removed, placed in a cup, washed with 20 mL of saline solution, and agitated for one minute. The concentration of albuterol present in the resulting solutions was determined by spectrophotometry. Five repetitions of three different ventilator configurations were performed. In trial A HFO was performed using a Sensormedics 3100a operated at a rate of 15 Hz, a mean airway pressure of 15 cm H2O, a ΔP of 33 cm H2O, and the SVN placed on the inspiratory side of the patient circuit in the temperature monitoring port. In trial B HFO was performed in the same way but the SVN was placed directly on the ETT. In trial C the SVN was placed in the inspiratory side of the patient circuit in the temperature monitoring port with a Sechrist 1000 IV providing CMV at a rate of 60, a peak inspiratory pressure of 30 cm H2O, a continuous positive airway pressure of 4 cm H2O, and an inspiratory time of 0.40 seconds. Results: Trial A- 0.18 mg ± 0.059; Trial B- 0.225 mg ± 0.107; Trial C- 0.172 mg±0.009. Results for all three trials were not significantly different from one another (P-value >.4 by both Kruskal-Wallis H and ANOVA.) We therefore have concluded that an SVN is not more inefficient in albuterol delivery to the lung in HFO that it is in CMV. As a result, we are now investigating particle size and dose effect when the SVN is used in HFO.