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A look at spacer use with inhaled therapy
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For almost 70 years, patients have been using pressurized metered-dose inhalers (pMDI) that deliver inhaled therapy to manage their obstructive airway disease. However, it is commonly recognized that these devices are often used incorrectly or suboptimally, which may affect efficacy, safety and patient compliance. Even in patients using optimal technique aided by advanced hydrofluoroalkane propellants, only ~20% of the emitted dose is delivered to the lower airways, leaving ~80% in the oropharynx. With poor technique, this percentage is further reduced—potentially to zero.
Professional guidelines recommend that pMDIs be used with a spacer or valved holding chamber (VHC) but actual use is lagging, with estimates varying from 10% in the UK in 1990 to 46% in Canada in 2008. In this review article, Spacer devices for inhaled therapy: why use them, and how?1, the advantages and potential disadvantages of using spacers/ VHCs with pMDIs are addressed, including spacer size, type, material, patient interface, and feedback mechanism; the potential impact of spacers/VHCs on drug delivery; and universal recommendations on how patients should use these devices. A few of these findings are highlighted here:
Spacer size and volume
Volume is among several considerations when choosing a spacer/VHC because it determines the number of breaths needed to empty it. This is especially important with small children. Size may also influence the aerosol profile and the variability in the particle content of the emitted dosage over time. In a small-volume device, the particle cloud remains turbulent and may deliver an initial “burst” of concentrated aerosol followed by comparatively aerosol-free air. In a large-volume device, the particle cloud becomes static, providing an evenly distributed aerosol delivery throughout inhalation. Thus, a large-volume device may target the entire bronchial tree in a more uniform fashion.
Device material of manufacture
Devices made from plastics/polycarbonates/polymers are electrostatic, which attracts aerosol particles. This may considerably reduce by up to 50% the aerosol dosage that the patient actually inhales. Priming the spacer/VHC with multiple dosages from a pMDI can reduce the electrostatic charge, but is a wasteful use of medications. Steel or aluminum spacers/VHCs and plastic ones with antistatic inner linings do not accumulate electrostatic charge, and can increase fine-particle mass and lung deposition of aerosolized drugs.
Patient interfaces and feedback mechanisms
Spacers/VHCs with a facemask interface rather than a mouthpiece might work better for children under 3 years of age, and for those who cannot take slow and measured breaths while using a mouthpiece. The challenge of using facemasks is achieving a tight yet comfortable seal with the face in order to prevent variable drug delivery. In addition, feedback mechanisms, such as a whistle that sounds if a patient inhales too quickly, help insure correct breathing techniques.
How spacers/VHCs might impact drug delivery
The clinical goal of adding spacers/VHCs to pMDIs is to maximize the fraction of respirable aerosol that is delivered to the airways. This requires careful consideration of precise pMDI-spacer/VHC combinations; spacer/VHC priming and maintenance; inhaler technique that’s not influenced by spacer/VHC usage; and patient compliance in general.
Here’s a brief summary of the advantages/disadvantages of spacers/VHCs
Advantages
Disadvantages
Conclusions There are advantages to using spacers/VHCs with pMDIs. The authors recommend using these devices for all patients, and call on healthcare professionals to teach patients how to use inhalers and spacers properly. Currently, only ~10% of health workers know how to train patients properly on these devices. The authors also recommend further research on the clinical benefits of spacers/VHCs to determine their cost effectiveness.
Resources
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1 Vincken W, Levy ML, Scullion J, et al. Spacer devices for inhaled therapy: why use them, and how? ERJ Open Res 2018; 4: 00065-2018