Delivery efficiency of metered dose aerosols given via endotracheal tubes

The authors studied the efficiency of delivery of the inhaled bronchodilator metaproterenol when delivered via an endotracheal tube (ETT) using a metered dose inhaler (MDI). They found that the percentage of drug exiting the ETT varied with tube size, ranging from 3.0 +/- 1.9 for a 6.0 mm ETT to 6.5 +/- 4.4 for a 9.0 mm ETT (mean +/- SEM, P less than 0.05). The efficiency of delivery was also affected by whether the MDI was activated before or after initiation of gas flow through the ETT, with activation into a flowing stream significantly more efficient. The authors conclude that an MDI can deliver a dose of drug to the trachea, but delivery efficiency is lower than reported for MDI delivery in spontaneously breathing patients.