Karen Heslop, MSc, PG Dip Cognitive Behavioural Therapy, BSc, is respiratory nurse consultant, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne
Heslop, K. (2008) How to use pressurised metered dose inhalers. Nursing Times; 104: 47, 78–80.
Karen Heslop outlines the reasons for using inhaled medicines with patients who have respiratory disorders, and the technique required to use metered dose inhalers. Part 2 will provide an update on other inhaler devices.
An inhaler is a medical device used for delivering medication directly into the lungs. Inhalation is the preferred route of administration of drugs in the treatment of many respiratory disorders such as asthma and COPD. Inhalation enables drugs to be delivered to the required site of action. The onset of action is rapid and lower doses can be given, which reduces the risk of systemic side-effects.
Inhalation therapy dates back more than 2,000 years, when aromatic fumes and vapours were used to treat respiratory problems (Education for Health, 2007).
The pressurised metered-dose inhaler (pMDI) was the first inhaler device, and was introduced in 1956 (Brocklebank et al, 2001).
The anatomy of the airways is such that particles tend to be filtered out before they reach the lungs. The ideal particle size for lung deposition is between 1µm and 5µm in diameter. Larger particles will be deposited at the back of the throat.
The aims of inhaled therapy in asthma and COPD are to:
- Deliver drugs such as bronchodilators (which open the airways);
- Deliver drugs such as corticosteroids (which help reduced inflammation).
Choosing a device
Before prescribing treatment, healthcare professionals need to consider which inhaler would be most appropriate for individual patients. There are many different inhaler devices available in a range of colours, shapes and sizes. There are several methods of delivering inhaled medication. These are listed in Box 1.
Box 1. Methods of delivering inhaled medicines
To select an appropriate inhaler, the healthcare professional needs to know:
- What drugs are available in each device;
- Practical knowledge on how the devices work;
- How to clean each device;
- Possible side-effects.
Other important considerations when choosing a device are:
- Patient preference – if patients do not like the device, they may not use it. The inhaler needs to be acceptable to the patient, reliable, easy to use and clean, and portable;
- The patient’s ability to learn to use the device;
- The patient’s lifestyle and circumstances such as where and when is it going to be used;
- Whether a combination inhaler is appropriate –some contain a combination of drugs and this can be important if patients pay for their prescriptions as only one inhaler is required instead of two;
- Whether an inhaler that indicates when it is running out of medication is required – some have a dose counter but not all inhalers contain the same number of doses;
- The age of the patient – for example, young children and some older patients may find certain inhalers difficult to use;
- Whether the device can be used in an exacerbation of asthma or COPD – for example, pMDIs with a large volume spacer are as effective as a nebuliser at treating mild and moderate exacerbations of asthma (British Thoracic Society and Scottish Intercollegiate Guidelines Network, 2008);
- The cost of the device – costs should be considered but if patients are happy with a particular inhaler, they are more likely to use it. This means the cheapest device may not be the most cost-effective one, especially if the patient will not use it.
Pressurised metered dose inhalers
pMDIs are widely prescribed for the delivery of drugs because of their small size and portability. They are often (but not always) cheaper than dry powder devices and simple in that no drug preparation is required (Dolovich et al, 2000).
pMDIs are also called aerosol inhalers or ‘puffers’. The device consists of a plastic case with a mouthpiece, a pressurised metal canister containing a drug and propellant, and a cap to protect the mouthpiece. To activate the inhaler, the canister is pushed down and a valve delivers a measured dose of drug in a fine mist. The propellant evaporates quickly, leaving the drug particles which are inhaled.
Chlorofluorocarbon propellants (CFCs) have been used for many years but are known to deplete the ozone layer. In 1987, the Montreal Protocol was signed and there has been a global agreement to stop using CFCs as propellants. Alternative CFC-free propellants such as hydrofluoroalkane 134a have been developed and are now replacing CFC inhalers (Education for Health, 2007).
Patients must have excellent coordination of inspiration with inhaler activation to achieve optimum drug delivery to the lungs (Melani et al, 2004). To use the inhaler correctly, the patient needs to coordinate breathing in with depressing the canister to release the medication.
Devices may seem simple to use but are often used incorrectly by patients, and physicians, nurses and pharmacists have been shown to be unable to demonstrate their proper use (Hanania et al, 1994; Kesten et al, 1993). An incorrect technique will result in decreased delivery of the drug to the lungs and potentially reduce its effectiveness.
Inhalers should only be prescribed after patients have received training in the use of their device and have a demonstrated a satisfactory technique (British Thoracic Society and Scottish Intercollegiate Guidelines Network, 2008). The technique is outlined in Box 2.
box 2. The Technique for using a pMDI
Several problems can be encountered when using pMDIs:
- Poor coordination of breathing and activating the inhaler can reduce drug delivery;
- Inhaling too quickly or too slowly can affect the amount of drug deposited in the lungs;
- The teeth or tongue can obstruct the flow of the medication from the inhaler;
- The spray from the inhaler can cause coughing;
- Side-effects such as hoarse voice (dysphonia) or thrush (candidiasis) can occur with some inhaled steroids. This can be reduced by using a spacer device and gargling with water after use. The water should be discarded rather than swallowed to prevent systemic absorption of steroids.
pMDIs and spacer devices
pMDIs are often used with a spacer or holding chamber device. These ‘hold’ the medication and allow sufficient time for it to be breathed in through the one-way valve of the spacer. Spacers are useful when:
- The patient has poor coordination when using an inhaler;
- High doses of inhaled corticosteroids are needed;
- Infants and toddlers require inhaled medicines.
Spacers also help to reduce local side-effects, such as dysphonia or candidiasis, from inhaled corticosteroids. There are a number of spacers on the market which vary in design, material, shape, size and how they are assembled. While smaller spacers may be more compact, it is important to remember that deposition to the lungs may be reduced. The procedure for using a large-volume spacer is outlined in Box 3.
Box 3. How to use a Large-Volume Spacer Device
Using a multiple-breath technique
It is important to use the spacer device correctly and the spacer should be compatible with the pMDI being used. According to the British Thoracic Society and Scottish Intercollegiate Guidelines Network (2008):
- The drug should be administered by single actuations of the pMDI into the spacer followed by an inhalation. Multiple presses of medication into the spacer can reduce the medication delivered to the lung as this will make more of the drug adhere to the inside of the spacer;
- There should be minimal delay between inserting the medication into the chamber and inhaling it, as delays can reduce the amount of drug available by 80% (Barry et al, 1993);
- Patients can take a slow single breath to retrieve the medication or take tidal breaths from the chamber (Global Initiative for Asthma, 2006).
Either technique can be used – often young children and older patients find the tidal breathing (multiple breathes) method easier;
- Large-volume spacers should be cleaned monthly rather than weekly following manufacturers’ recommendations or performance is adversely affected. They should be washed in detergent (soapy water) and allowed to dry in air (British Thoracic Society and Scottish Intercollegiate Guidelines Network, 2008; Pierart et al, 1999);
- All plastic spacer devices are susceptible to static charge. This attracts medication to the side of the spacer device and reduces the amount of drug available for inhalation. This would limit the effectiveness of the drug. The mouthpiece should be wiped clean of detergent before and after use.
It is important to check that the one-way valve is clean and moves freely. Metal and other antistatic spacers are not affected by static;
- Plastic spacers should be replaced at least every 12 months or if the valve becomes damaged. Some may need to be changed every six months (British Thoracic Society and Scottish Intercollegiate Guidelines Network, 2008).
Patients with physical impairment
Patients with physical impairments, for example rheumatoid arthritis, may be prescribed inhalers but their physical problems may affect their ability to use them properly.
A number of aids are available that can help patients to grip the pMDI. The Haleraid device fits on to the plastic pMDI casing and enables it to be ‘squeezed’ rather than ‘pressed’. It can also be used with a spacer. Two sizes are available, with choice depending on the size of the inhaler as inhalers provide 120 or 200 doses.
If the patient struggles to use the pMDI with or without the spacer, an alternative device should be considered.
Good practice points
It is very important to check patients’ inhaler technique regularly. It is also important to ensure that patients know how to recognise when their inhaler is empty, how to clean it and how to reduce the risk of oral side-effects. Each department or general practice should have an agreed inhaler technique protocol so that patients receive consistent advice.
National Institute for Clinical Excellence guidance on inhaler systems in children under five with chronic asthma.
Barry, P.R. et al (1993) Optimum use of a spacer device. Archives of Disease in Childhood; 69: 6, 693–694.
British Thoracic Society and Scottish Intercollegiate Guidelines Network (2008) British guideline on the management of asthma. Thorax; 63: 5 (Supp IV), iv 1–iv 121.
Brocklebank, D. et al (2001) Comparision of the effectiveness of inhaler devices in asthma and chronic obstructive airways disease: a systematic review of the literature. Health Technology Assessment; 5: 26.
Dolovich, M. et al (2000) Consensus statement: aerosols and delivery devices. Respiratory Care; 45: 6, 589–596.
Gabriuo, B.J. et al (1999) A new method to evaluate plume characteristics of hydrofluoroalkane and chlorofluorocarbon metered dose inhalers. International journal of pharmaceutics; 186: 1, 3–12.
Education for Health (2007) Simply Devices. A Practical Pocket Book. Warwick: Education for Health.
Ernst, P. (1998) Inhaled drug delivery: a practical guide to prescribing inhaler devices. Canadian Respiratory Journal; 5: 3, 180–183.
Global Initiative for Asthma (GINA) (2006) Instructions for Inhaler and Spacer Use.
Hanania, N.A. et al (1994) Medical personnel’s knowledge of and ability to use inhaling devices: metered dose inhalers, spacing chambers and breath-actuated dry powder inhalers. Chest; 105, 111–116.
Kesten, S. et al (1993) Pharmacist knowledge and ability to use inhaled medication delivery systems. Chest; 104, 1737–1742.
Pierart, F. et al (1999) Washing plastic spacers in household detergent reduces electrostatic charge and greatly improves delivery. European Respiratory Journal; 13: 3, 673–678.