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Inhaler devices: How do you choose?
- Patient adherence to inhaler therapy varies widely between 22 to 78%? (1)
- Less than half of the patients demonstrate correct inhaler technique (2)
- The effective dose that actually reaches where it needs to be is only 10 to 30% of the inhaled dose (3).
- Poor adherence and poor inhaler technique signal poor symptom control, frequency of exacerbations and hospitalisations (4).
Put all this together and you will quickly see how important it is to get the inhaler technique right!
So, how can we do this?
Inspiratory Flow Rate
One of the key factors is the choice of inhaler device. We pick the device based on the inspiratory flow rate that a given individual can generate.
What is the inspiratory flow rate, I hear you ask? (psst… it’s the same thing that helps us choose between oxygen delivery devices!)
It is the speed at which air rushes past your nostrils to get into the lungs. It is measured in litres/minute. Our inspiratory flow rate at rest is roughly 20-30L/min. This does not imply that we breathe 30 litres per minute. We only take in the normal 500ml of tidal volume per breath. The flow rate is the ‘speed’ at which air gets in. When we exercise, this can go up to 60-90L/min (in really fit individuals up to 300L/min)!
What does this have to do with inhaler devices?
There are four types of inhaler devices: pMDI (pressurised metered dose inhaler), BA-MDI (breath actuated MDI), DPI (dry powder inhaler) and soft mist inhalers (think respimat).
Every device has an intrinsic resistance which is generally in the order of DPI > pMDI/ BA-MDI > SMI. In order to overcome this resistance, the patient has to generate a peak inspiratory flow rate to ensure that the dose required gets into the lungs as shown in table 1 (5).
Table 1
| Inhaler Device | Optimum flow rate required |
|---|---|
|
pMDI |
30 – 60 L/min (slow) |
|
BA-MDI |
20 – 30 L/min (slow) |
|
DPI |
30 – 90 L/min (fast) |
|
Soft mist inhalers |
No flow rate required to generate the aerosol |
MDIs have a self-propelled delivery mechanism- point and press (figure 1). Therefore the aerosol that jets out has a velocity of its own. This is why the inspiratory flow rate for an MDI is lower than a DPI.
DPIs need a ‘minimum’ inspiratory flow rate to disperse the dry powder (figure 2). This varies with the device with some devices having medium and some high resistance. This is the reason why DPIs have a wider range for the flow rates required. It is worth looking at the references given in this blog, especially number 5 to see some examples under each category.
Soft mist inhalers have a spring that squeezes the liquid through a fine nozzle which then generates an aerosol. The aerosol generation lasts longer and has a slower speed, therefore drug deposition is greater with respimat.
Almost all devices have suboptimal drug delivery at flow rates > 120 L/min. Therefore discourage this in your patients.
Patients should be assessed to ascertain the flow rates they can achieve. This should be taken together with their ability to co-ordinate their hand movements with inhaling (pMDIs). If co-ordination is a problem this can be remedied with haleraid (e.g. with osteoarthritis or rheumatoid arthritis) or a spacer. With a spacer we just press one spray into it and breathe normally (using tidal volume breathing), no co-ordination needed. The larger particles stick to the inside of the spacer leaving only the finer particles to be inhaled. Therefore spacers obviate flow rate problems, although they can only be used with a pMDI.
Obviously cognitive issues can affect the ability to follow instructions, co-ordination and more importantly remembering to take their inhaler.
The next time you see a patient with chronic airways disease...
- First get an idea of their inspiratory flow rates and their ability to co-ordinate. Take the help of your nursing colleagues to ascertain this. There are commercially available devices which can be used to check the flow rates. They also serve as visual aids to teach patients the ideal flow rate they should aim for.
- Once this is determined, check if the patient is happy with the device being offered e.g. pMDI.
- Finally, look at the class of drugs that you want to prescribe based on international guidelines for asthma or COPD: inhaled corticosteroids/ LABA/ LAMA or SAMA or a combination. Prescribe the drug in the device that has been selected. Remember the fewer the inhalers, better the adherence.
LABA – long acting ß2 agonist, LAMA – long acting muscarinic antagonist, SAMA – short acting muscarinic antagonist and SABA – short acting ß2 agonist
References:
- Mäkelä MJ, Backer V, Hedegaard M, Larsson K. Adherence to inhaled therapies, health outcomes and costs in patients with asthma and COPD. Respir Med. 2013 Oct;107(10):1481–90.
- Molimard M, Raherison C, Lignot S, Depont F, Abouelfath A, Moore N. Assessment of handling of inhaler devices in real life: an observational study in 3811 patients in primary care. J Aerosol Med. 2003;16(3):249–54.
- Capstick TGD, Clifton IJ. Inhaler technique and training in people with chronic obstructive pulmonary disease and asthma. Vol. 6, Expert Review of Respiratory Medicine. 2012. p. 91–103.
- AL-Jahdali H, Ahmed A, AL-Harbi A, Khan M, Baharoon S, Bin Salih S, et al. Improper inhaler technique is associated with poor asthma control and frequent emergency department visits. Allergy, Asthma Clin Immunol. 2013 Mar 6;9(1).
- Haidl P, Heindl S, Siemon K, Bernacka M, Cloes RM. Inhalation device requirements for patients’ inhalation maneuvers. Vol. 118, Respiratory Medicine. W.B. Saunders Ltd; 2016. p. 65–75.