The efficiency of beta 2-agonist delivery through tracheal tubes with the metered-dose inhaler: an in vitro study

To study the delivery efficiency of procaterol aerosols administered through the tracheal tube (ETT) with a metered-dose inhaler (MDI) during apnea.

First, in a normal room air environment (at ambient temperatures of 24 degrees to 26 degrees C), we measured the amount of aerosol delivered through the ETT by comparing the weight of a 2-l bottle before and after firing the MDI directly into the 15-mm adapter of the ETT. The distal half of the ETT was inserted in the bottle. This procedure was repeated using five different ETTs with an internal diameter of 4-8.5 mm. The delivery efficiency was obtained by dividing the amount of aerosol delivered through the ETT by the total aerosol output per MDI puff. Next, we investigated whether the connector attached to the 15-mm ETT adapter could reduce the delivery, by repeating the same procedure with 4-mm and 5-mm ETTs. Finally, we compared the efficiencies of aerosol delivery through the 5-mm ETT and the 7.5-mm ETT in a normal room air environment with results obtained under a humidified condition (100% humid air at 37 degrees C).

The percentages of aerosol delivered through the ETTs in a normal room air environment were 40%-60%, except for the 4-mm ETT, for which the percentage was 32.7% +/- 6.6% ( P < 0.05 vs that with the 5-mm ETT or the 6-mm ETT). A connector attached to the 15-mm ETT adapter significantly decreased the delivery efficiencies (19.0% +/- 5.8% vs 32.7% +/- 6.6% with the 4-mm ETT, 24.6% +/- 11.8% vs 51.7% +/- 10.8% in the 5-mm ETT) when compared with those without a connector. The delivery efficiencies under the humidified condition in the 5-mm ETT and the 7.5-mm ETT were 65.5% ( P < 0.05) and 89.8% of those in the normal room air environment, respectively.

The efficiency of delivery of procaterol aerosol through the ETTs was unexpectedly high (approximately half of the total aerosol output per MDI puff in the 5-mm to 8.5-mm ETTs, and one third of the total aerosol output per MDI puff in the 4-mm ETT). A connector attached to the 15-mm ETT adapter noticeably decreased the delivery efficiency. In the smaller-sized ETT, delivery efficiency was significantly lower under the humidified condition than in the normal room air environment.