Metered dose inhalers (MDIs) are frequently used to supply aerosolized drugs, particularly bronchodilators, to the tracheobronchial tree of patients with endotracheal tubes in the intensive care unit or in the operating room. The efficiency of delivery to the lungs of agents such as the beta 2-adrenergic agonists is known to be low. In an in vitro model, we evaluated a means of improving the delivery of drug released from an MDI beyond the distal tip of the endotracheal tube. Extensions of the MDI nozzle were fashioned from modified intravenous catheters or sections of small bore polyethylene tubing. A model trachea/carina was constructed and suspended above a collecting device. An albuterol MDI was actuated through the nozzle extension and into the model airway. We measured the quantity of albuterol deposited in the nozzle extension, in the trachea/carina and in the distal collecting device. Particle size distribution was determined with a cascade impactor. The results indicate an inverse relationship between the quantity of drug delivered distally and the inner diameter of the nozzle extension, with a marked increase in delivery for an inner diameter < 1 mm. Ninety percent of the actuated dose from the MDI exited a 0.76-mm inner diameter nozzle extension. From 20 to 30% of the nominal MDI dose was recovered from the distal collector, 70% of which deposited in the particle size range of 1 to 5 microns. Deposition in the trachea/carina was high, but this was reduced by introducing a flare in the tip of the nozzle extension, which did not affect the dose reaching the distal collector.(ABSTRACT TRUNCATED AT 250 WORDS)