Nebulizer therapy in cystic fibrosis: an overview.

Abstract

The word nebulizer comes from the Latin ‘nebula’ meaning mist, and was first used in 1872. However, the principles of nebulizer therapy date back over 4000 years. Even Hippocrates supported the use of hot vapours to help the diseases of the throat and chest.1 Nebulizer therapy has altered vastly over the years and cystic fibrosis (CF) caregivers are often bombarded with a large, and often, confusing array of nebulizer systems to choose from.2 The British Thoracic Society and European Respiratory Society formulated nebulizer guidelines in 1994 and 2001, respectively, aiming to give guidance to clinicians prescribing and delivering treatment with nebulizers.3,4 The purpose of this paper is to present practical information regarding the different nebulizer systems available. The aim is to assist the CF clinician to choose the most appropriate nebulizer device for the drug to be nebulized and the individual patient receiving therapy. Where possible information is referenced or taken from the nebulizer device handbooks. However, on occasion, observations are made based on the author's clinical experiences working with adults and children with CF. Most therapeutic aerosols are heterodisperse, consisting of a range of particle sizes.5 They can be described by the mass median aerodynamic diameter (MMAD) above and below which 50% of the mass of the drug is contained.6 The therapeutic effectiveness of an inhaled drug depends on a number of factors but in particular how much bypasses the oropharynx and deposits in the lungs. There are three main mechanisms of deposition. Inertial impaction occurs in the upper airway and in the first few generations of bronchi where airflow is faster and more turbulent. Impaction also occurs at bends and branches of the airway. Further distally, as the cross‐sectional area of the airways increases, the velocity of airflow decreases and becomes more laminar. In these peripheral airways, particularly if the tidal breath is slow and deep (increasing dwell time), gravitational sedimentation is the main method of deposition. Submicronic particles are more likely to deposit via diffusion providing they are not exhaled.7 Based on industrial hygiene models, particles greater than 10 μm in diameter are demonstrated to deposit in mouth and throat, 5–10 μm deposit in the large conducting airways and oropharanyx, and those between 1–5 μm deposit in the smaller airways and alveoli.8 However, accurately predicting aerosol deposition in real life is challenging, particularly as there are so many patient factors to consider (Table 1). Table 1 Factors determining aerosol delivery6