Face masks for aerosols—there is more science…

The role of inhaled medications in treating various airways and pulmonary diseases is well established. For example, the place of inhaled corticosteroids (ICS) in the treatment of asthma is appreciated, and it is considered the cornerstone of the therapy. However, when it comes to children the role of aerosol therapy continues to be debated. Part of the reason is a paucity of studies in the pediatric age group. The problem is magnified when it comes to infants and young children. Many clinicians still believe that results from adults’ studies can be extrapolated to children. An important example of this is the role of ICS in infants. While there is a consensus about its effects in adults and even in older children—the place of ICS in infants and toddlers up to age 3–4 years has been recently questioned. Based on a few recently published studies it was suggested that ICS may not be efficacious for treating wheezy infants. A major shift resulted with respect to the recommendations for ICS therapy in wheezy infants and young children in general, and it was subsequently stated—‘‘We believe that doctors should not rush into the treatment of intermittent infantile wheeze with ICS. ’’ These studies, however, did not take into account features that are characteristic of infants in regard to aerosol drug delivery that may have significantly reduced the potential benefits of ICS because of anatomical, physiological, and behavioral issues. Clearly, there is a need to conduct more studies on inhaled therapy in infants and toddlers before providing evidence-based therapeutic recommendations for the treatment of wheezy infants and children under age 3–4 years. The study by Chavez et al. in this issue is a welcome addition in this regard. As the authors suggest in their introduction, infants cannot inhale aerosols from a mouth piece and thus require the addition of an interface between the face and valved holding chamber (VHC) or nebulizer—such as a face mask. However, as emphasized previously—‘‘not all masks are born equal. ’’ It is therefore, important to understand the various factors that are crucial to the performance of face masks. Chavez studied well known and previously studied factors that affect aerosol delivery such as a tidal volume (Vt) and respiratory rate (RR). It is intuitive and was demonstrated previously that a greater Vt inhalation will deliver a greater mass of small drug particles from a VHC, to the mouth. Similarly, greater RR will result in overall greater minute ventilation and thus increase the total dose of drug delivered to the mouth. It should, however, be emphasized that this may not necessarily translate into better clinical efficacy as an increase in Vt and/or RR results in increased inspiratory flow velocity of the aerosol particles with an increased probability of their impaction in the upper respiratory tract (URT) thus reducing the lower respiratory tract (LRT) dose. The Chavez study did not measure the dose of albuterol that penetrated beyond the upper airway into the LRT nor did they measure the size distribution of the particles which is known to have a profound effect on lung deposition and clinical efficacy. In this study, what is new and particularly welcome is their focus on airway dead space or the ‘‘static dead volume (SDV). ’’ This issue is particularly relevant to infants and is a potentially important consideration with all aerosol delivery systems that use a face mask. It is not an issue with adults or children over 5 years of age who inhale directly from a mouthpiece. The Chavez results emphasize that, if possible, we should try and avoid the use of masks, to maximize aerosol delivery to the LRT. Thus, a mouthpiece for a VHC (with minimal dead space) is the target to aim for with all VHC users. However, a mouthpiece is not an option with young children less than 3–4 years of age. In this age group, in whom a mask must usually be used, it is obvious that the smallest possible dead space would be optimal since more drug will then be delivered to the respiratory tract.