Infant aerosol holding chamber face masks: not all are born equal!

Face masks are used for many respiratory care applications, such as anesthesia, resuscitation, and aerosol therapy. In pediatric practice, particularly with infants and toddlers, aerosol therapy is usually administered by means of a small-volume nebulizer and face mask. Because of their convenience, speed of administration, versatility, dose accuracy, reproducibility, near-optimal mass median aerodynamic diameter, and relatively low per-treatment cost, pressurized metered-dose inhalers have become an increasingly popular alternative for providing most therapeutic aerosols, even to very small infants and neonates.1 In children, pressurized metered-dose inhalers are commonly used with valved holding chambers (VHCs) via a mouthpiece. In infants and children too young to use a mouthpiece, the face mask serves as the interface between the patient and the VHC. Face masks attached to VHCs have greatly advanced our ability to effectively and more economically treat even the youngest infants.2 Aerosol therapy via VHC and face mask is a relatively recent development, and many physicians, especially pediatricians who have been in practice for many years, may thus have little experience with this approach to aerosol delivery. Although the mask interface is arguably the single most important factor determining the dose of medication delivered from the VHC (or any aerosol source) to the nose/mouth of the infant or toddler, its role in the aerosol-delivery chain has not previously been very well characterized, and studies comparing various face masks are lacking. Most studies dealing with VHC performance have paid relatively little attention to the characteristics of the mask and the seal between the mask and the infant’s face. For example, in previous studies of VHCs with masks,3,4 parents were instructed to hold the mask tightly against the infant’s face, and this was monitored and reinforced during the study, thus minimizing possible leaks. However, in daily home use, and without repeated emphasis on achieving a mask-face seal, some mask designs appeared to be inherently more leaky than others.5–7 Only relatively recently has there been a scientific focus on mask-infant interaction. It was less than a decade ago that it was occasionally reported that the mask could be an obstacle to adequate aerosol delivery.5,8 Zak et al7 measured mask pressures in some 200 children and found them to be highly variable and much lower than those measured when ventilation was accomplished with a simulated-breathing-programmed respirator, which suggested frequent air leaks around the mask in these children. A study published in Pediatrics in 2001 emphasized that an effective mask seal is crucial for adequate therapy with VHCs.6 In that study the amount of leakage that occurred with 3 commonly used VHC masks was compared to that with the Hans Rudolph anesthesia mask (Hans Rudolph, Kansas City, Missouri). The Babyhaler (Glaxo, Germany), Aerochamber (Trudell Medical, London, Ontario, Canada), and Nebuchamber (AstraZeneca, Lund, Sweden) masks were evaluated. Of these, the Nebuchamber performed most poorly. Ventilation measured through the Nebuchamber, when applied to the face of young children under simulated real-life conditions, was significantly less than the other 3, indicating a greater leak. The Aerochamber mask performed best and was similar to the Hans Rudolph mask, which is considered the gold standard. Furthermore, the coefficient of variation of ventilation was greatest with the Nebuchamber mask, although ventilation through the other masks was also quite variable, amounting to 25%, even with the best-performing (Aerochamber) mask.