In-Vitro Comparison of Six Continuous Nebulizers*

BACKGROUND: Continuous nebulization has become popular for treating patients with severe reversible airway disease. Continuous nebulization therapy has been shown to be safe, effective, and labor efficient as compared to other traditional medication aerosol treatments 1-11 . Although numerous studies have been done evaluating the clinically efficacy of continuous nebulization, little work has been done on comparing the various continuous nebulizers available. In this study, six continuous nebulizers, EZflow, HEART, MiniHEART, UniHEART, IVHEART, and Hope, are evaluated for medication delivered to patient and particle size. METHODS: Each nebulizer was set up and used as described on the product insert accompanying each nebulizer. Each nebulizer was mixed to provide 10 mg/hour of albuterol sulfate based on the nominal output of each nebulizer. Reservoirs were filled to their maximum volume or enough for five hours of nebulization, whichever was less. Airflow was set initially to the nominal airflow specification of the nebulizer and than adjusted incrementally, up or down, until the mean output of the nebulizer, as indicated on the graduations of the nebulizer reservoir, matched the nominal output listed for the nebulizer. Each nebulizer was connected to an aerosol mask as described in the product insert. An inhalation flow of 10 L/ min was simulated; entrained air was humidified. A cascade impactor was used to sample aerosol every hour. Medication delivered and particle size were determined using a spectrophotometer operating at 279 nm. RESULTS: In spite of the fact that each nebulizer was mixed to provide the same amount of medication, there were significant differences in the quantity of medication delivered to the patient. The EZflow Continuous Nebulizer was shown to deliver significantly more medication than the others (p <0.01). The UniHEART and IVHEART delivered the least amount of medication. The HEART had an MMAD of 3.6 microns, which was significantly more than the other nebulizers which had particle sizes ranging from 2.0 to 2.5 microns (p < 0.01). CONCLUSION: Clinically important differences exist between different continuous nebulizers. When comparing the performance of nebulizers it is important to conduct testing under identical conditions which simulate actual clinical use.