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Syringe-Actuated Metered Dose Inhalers

A Quantitative Laboratory Evaluation of Albuterol Delivery Through Nozzle Extensions

Robert A. Peterfreund, MD, PhD^*, Ralph W. Niven, PhD, MR PharmS, and Robert M. Kacmarek, PhD, RRT^*

^*Department of Anaesthesia, Harvard Medical School at the Massachusetts General Hospital, Boston, Massachusetts Amgen Incorporated, Thousand Oaks, California

The metered dose inhaler (MDI) is a device that can be used to supply aerosolized bronchodilators to the tracheobronchial tree of patients requiring endotracheal intubation. Because direct actuation of the MDI into the breathing circuit is inefficient, a technique of extending the MDI nozzle with small-bore, long, intravenous catheters has been devised. To facilitate connecting the MDI to the extension and actuating the release of aerosol, insertion of the MDI cannister into the barrel of a large syringe attached to the Luer hub of the extension has been proposed but not quantitatively evaluated. The purpose of this study was to test, in a laboratory model, the performance of syringe-actuated MDIs attached to nozzle extensions. The deposition of the bron-chodilator albuterol in the delivery device and distal to the extension was quantified spectrophotometrically. Maximum distal delivery of drug from nozzle extensions fashioned from small-bore (19-gauge) catheters was 80% of the actuated release. Loss of drug to the inner surface of the syringe plus extension varied inversely with the number of successive actuations. Syringes from two manufacturers in two sizes were compared and found to perform comparably. Syringes could be attached to the Luer connector of the secondary sampling channel of special pediatric-sized endotracheal tubes (ETTs) and the channels were evaluated as nozzle extensions, with distal delivery >80% as efficient as the 19-gauge intravenous catheter. We conclude that syringe actuation of MDIs through nozzle extensions is an efficient method for supplying the aerosol distal to the tip of the ETT. Luer-hubbed sampling lumina of specialized ETTs are also efficient nozzle extensions and may be convenient to use for enhanced delivery of aerosol in the clinical setting. (Anesth Analg 1994;78:554–8)