Three main types of inhaler device are available: 'press-and-breathe' pressurised metered dose inhalers (pMDIs), breath-actuated pressurised metered dose aerosol inhalers, and dry powder inhalers (DPIs). In addition, press-and-breathe pMDIs can be used in conjunction with spacer systems, and pMDIs use either chlorofluorocarbon (CFC) or CFC-free, hydrofluoroalkane (HFA) propellants.
Over 70 individual inhaler products (including different drugs and doses), together with at least five further spacer device attachments, are licensed in the UK for use by children aged 5–15 years. Innovation is continuing and new devices are emerging into the market. The majority of research on asthma therapy concentrates on the effect of drugs rather than that of the delivery device. Consequently there is a shortage of independent and evidence-based information for clinicians and patients choosing devices.
Around 60% of childhood asthma inhaler medication is delivered by press-and-breathe pMDIs. These comprise a small plastic construction carrying a metal aerosol canister, often containing 200 doses. Both branded and generic press-and-breathe pMDIs are available. The inhaler is prepared by shaking. Users should remove the mouthpiece cap, breathe out, then take a slow deep breath through the mouth, actuating the device (i.e. pressing the canister) as inhalation begins, and then hold their breath.
Individuals may experience a number of problems with press-and-breathe pMDIs that can affect adherence to therapy and adequacy of delivery of drug to the lungs, and therefore effectiveness. It is estimated that at least 50% of press-and-breathe pMDI users have less than optimal technique. Problems include difficulty in co-ordinating device actuation and inhalation, oropharyngeal deposition of the drug, and, in the case of CFC devices, the 'cold freon effect', when the temperature of the propellant causes some individuals briefly to stop inhaling.
The use of various spacer systems, which attach directly to the inhaler device, is one approach to alleviating some of the problems associated with pMDI use.
Two general types of spacer are available:
Detachable chambers (small, medium or large volume): this type of spacer is attached to a press-and-breathe pMDI when required, and acts as a holding chamber for the aerosol and drug, allowing a number of breaths to be taken. Most spacers of this type incorporate a valve system, and inhalation techniques need to be taught. Five such spacers are currently available on NHS prescription.
Small-volume extended mouthpiece spacers: these provide increased distance between the point of aerosol release and the oropharyngeal area. They are available for use with some press-and-breathe and breath-actuated pMDIs.
Many spacers are designed in conjunction with specific press-and-breathe pMDIs. However, some are designed to allow attachment to a wider range of press-and-breathe pMDIs, and in these cases there may be some uncertainty about their performance with different inhalers compared with those spacers designed for use with an individual inhaler.
Detachable plastic spacers are prone to developing an electrostatic charge, which causes adhesion of the drug to their surface, so reducing delivery. Careful washing and air-drying (i.e. leaving to dry) of spacers at appropriate intervals reduces this problem. A metal spacer, which aims to avoid problems with electrostatic charge, has also been developed.
Other shortcomings associated with spacers are portability and inconvenience, and feelings of stigma, which children may experience with their use.
Breath-actuated pMDIs also deliver a pressurised aerosol metered dose of drug, but are automatically actuated when the user inhales through the mouthpiece. Automatic actuation removes the difficulty of actuation-inhalation co-ordination that is associated with press-and-breathe pMDIs. However, the sound of some devices and the different sensation of automatic actuation may hamper use in some children. Oropharyngeal deposition can be a problem in breath-actuated pMDIs. Two breath-actuated pMDIs are currently available.
DPIs deliver the micronised drug, and generally a carrier powder, using the individual's own inspiratory flow. This is another approach to overcoming the problem of actuation–inhalation co-ordination associated with pMDIs. Many newer DPIs also incorporate approaches to counting doses used or the amount of drug remaining, which can be used to aid monitoring of adherence to treatment.
Some children (generally younger ones) may not reliably generate inspiratory flows that are high enough for effective delivery. These problems may present difficulty during acute exacerbations, and a press-and-breathe pMDI and spacer may be required for back-up.
There is greater variation in the design of DPIs than in other device types. A child may find one DPI device easier to use than another, or express a preference because of the appearance of a particular device. Seven DPIs are currently available for children.
The benefit gained from inhaled therapy is a unique combination of the drug, device and the individual (i.e. physical, cognitive, psychological and lifestyle characteristics). Consequently the following factors require consideration when choosing a device.
Inhaler technique – Poor technique, resulting either from poor training or from choosing a device poorly suited to the child, can significantly reduce the amount of drug delivered to the lungs and result in poor asthma control. Some children, especially the younger ones in the age range being considered, may have difficulty with actuation–inhalation co-ordination with a press-and-breathe pMDI, while others may have inconsistent inspiratory flow, which causes problems in using a DPI, or find the automatic actuation of some breath-actuated devices off-putting.
Adherence to treatment – Even where good technique is possible, children may not use their devices appropriately. Device use may be influenced by a range of factors, including convenience, ease of device use, portability, the stigma of having asthma, and personal or peer preference for a specific device. The relative importance of these factors changes as children get older and so the choice of device should be reviewed frequently.
Availability of drugs – Some drugs are only available in particular devices.