ALBUTEROL DELIVERY BY METERED-DOSE INHALER WITH A PEDIATRIC MECHANICAL VENTILATORY CIRCUIT MODEL

Study Objective. To determine albuterol delivery by metered-dose inhal er (MDI) in an in vitro pediatric mechanical ventilatory circuit model . The influence of a spacing device, endotracheal tube (ETT) diameter and length, and air humidity was also investigated. Design. An albuter ol MDI canister was connected to an AeroVent spacer or Airlife MDI ada pter and ETT 4.0, 5.0, or 6.0 mm at commercially available and equal l engths. The ETT tip was attached to an in-line filter holder with a 1- mum type A/E glass fiber filter. Ventilator settings were fractional c oncentration of inspired oxygen 50%, tidal volume 250 ml, inspiratory: expiratory (I:E) ratio 1:3, rate 25 breaths/minute, temperature 35-deg rees-C, and a decelerating flow pattern. Ten albuterol canisters were activated two times each (total 2000 mug) into dry (4.0-, 5.0-, and 6. 0-mm ETT) and humidified air (4.0- and 6.0-mm ETT) and repeated in tri plicate. Percentage MDI output was determined by weighing the filter b efore and after drug administration (balance sensitivity 10 mug). Sign ificant differences (p less-than-or-equal-to 0.05) among the groups wi th and without a spacer and in dry and humidified air were determined by ANOVA with Scheffe's multiple comparison test. Multiple regression was used to determine significant associations between ETT diameter an d length and delivery. Main Results. With the AeroVent spacer in humid ified air, delivery with the 4.0- and 6.0-mm ETT was approximately 2.3 % and 5%, respectively. The spacer and dry air significantly improved delivery. Conclusions. In humidified air, the dose of albuterol by MDI with an AeroVent spacer should be doubled for children intubated with 6.0-mm ETT, and four puffs administered for every one puff desired fo r 4.0-mm ETT. The results of this investigation should prove useful in initial clinical trials of albuterol MDI in ventilator-dependent infa nts and children.