Which device in asthma?

The ideal way to deliver drugs in asthma or chronic obstructive pulmonary disease (COPD) is by inhalation. A standard dose of salbutamol for inhalation is 100 micrograms compared with 2 or 4 mg in tablet form.

Hence, if drugs can be delivered directly to the lung they will act faster and at a lower dose (20- to 40-fold in the case of salbutamol) which will reduce the incidence of side-effects. However, if the device fails to deliver the drug to the correct place it is of no value at all.

Devices¹²

Delivery systems for inhaled asthma medications include:

• Pressured metered dose inhalers (pMDIs).

  • pMDIs hold medication in a pressurised canister. They contain propellants, which have a high carbon footprint.

  • pMDIs require good coordination between activating the device and inhaling the drug, unless a spacer is used.

  • They require a slow and steady inhalation over 3-5 seconds, unless a spacer is used.

  • Even with perfect inhalation technique, only around 20% of each emitted dose reaches the lower airways, with the remainder deposited in the oropharynx.³

  • pMDIs should be used with spacers. Children should always use spacers with pMDIs, and spacer use should also be strongly encouraged in adults as well.

    • Spacer use is particularly helpful in people with poor inhaler technique,⁴ but reduce oropharyngeal drug deposition even in people with 'perfect' technique.³

  • Breath-actuated pMDIs are available, which are triggered by inhalation and do not require the user to coordinate device activation with inhalation.

  • Most pMDIs do not have a dose counter.

• Dry powder inhalers (DPIs).

  • DPIs are breath-actuated devices which release a dose of dry powder when the user takes a deep, quick inhalation.

  • Users therefore have to be capable of taking a quick, deep breath in to use them. This may make them less suitable for children and some older people.

  • They do not contain a propellant, and have a much lower carbon footprint than pMDIs.

  • DPIs are not used with spacers.

  • Most DPIs have a dose counter.

• Soft mist inhalers (SMIs).

  • SMIs produce a fine mist that is inhaled.

  • They require a slow, gentle inhalation over a few seconds.

  • They require some coordination between device activation and inhalation.

  • They do not contain a propellant, and have a lower carbon footprint than pMDIs.

  • SMIs have a dose counter.

Inhaler choice should be based on:⁵¹

• The ability of the patient to use the device. Factors include age, dexterity, coordination, and inspiratory flow.

• The patient's preference.

• The environmental impact of the device.

• The cost of the device.

• Whether or not the device has a dose counter.

Where possible, the same type of device should be prescribed if more than one inhaler is needed.

Children should be prescribed a pMDI with a spacer. Older children (from age 11 onwards) may be able to use a DPI.

The Medicines and Healthcare products Regulatory Agency (MHRA) have received reports of patients who have inhaled objects into the back of the throat. In some cases objects were aspirated, causing airway obstruction. Patients should be reminded to remove the mouthpiece cover fully, shake the device and check that both the outside and inside of the mouthpiece are clear and undamaged before inhaling a dose, and to store the inhaler with the mouthpiece cover on.⁶

Technique ⁷

Good technique is essential in ensuring optimum use of inhaler devices:

• Only prescribe the inhaler after the person (or their carer) has received training in its use and has demonstrated an acceptable technique.

• Repeated checks are essential, as poor technique, even after training, is common. Reassess inhaler technique as part of a structured clinical review during follow-up.

Generic prescribing of inhalers should be avoided as this can lead to people with asthma being given an unfamiliar inhaler device with resultant problems of usage and compliance.

Spacers⁷

Spacers are plastic devices with a mouthpiece at one end and a hole for a pressurised metered-dose inhaler (pMDI) to be inserted at the other. They increase the proportion of the drug delivered to the airways and reduce the amount of drug deposited in the oropharynx, reducing local adverse effects and reducing the amount of systemic absorption.

• Each brand of spacer is different. Some are specifically licensed for use with particular inhalers. Others are not licensed for use with particular pMDIs, but still compatible with them. In general, different spacer devices are usually compatible with most pMDIs, but not necessarily all of them. Ensure that the spacer device prescribed is compatible with the pMDI used. RightBreathe.com has a tool for checking this.⁸

• The drug is administered by single-dose actuations from the pMDI into the spacer, with each actuation followed by inhalation.

• There should be minimal delay between inhaler actuation and inhalation, as the drug aerosol is very short-lived.

• Tidal breathing can be used, as it is as effective as single breaths.

• Spacers should be washed monthly in detergent and allowed to dry in air.

• Plastic spacers should be replaced at least every 12 months. Some manufacturers advise changing at 6 months.

People requiring large doses of inhaled corticosteroids may require a specialised nebuliser, which is initiated by a respiratory specialist.

Nebulisers⁶

A nebuliser converts a solution of a drug into an aerosol for inhalation. It is used to deliver higher doses of drug to the airways than is usual with standard inhalers.

In England and Wales nebulisers and compressors are not available on the NHS (but they are free of VAT). Some nebulisers (but not compressors) are available on form GP10A in Scotland.

Home nebuliser use should be reserved for people with severe asthma, and only under the advice of an asthma specialist.

Before prescribing a nebuliser, a home trial should be undertaken to monitor response for up to 2 weeks on standard treatment and up to 2 weeks on nebulised treatment. If prescribed, patients must:

• Have clear instructions on the use of the nebuliser (including maintenance and cleaning) and on peak-flow monitoring.

• Be instructed not to treat acute attacks at home without also seeking help.

• Have regular follow up (initially after about 1 month and then annually).

The main indications for use of a nebuliser are to deliver:

• A beta2 agonist or ipratropium bromide to a patient with an acute exacerbation of asthma or of chronic obstructive pulmonary disease.

• A beta2 agonist, corticosteroid, or ipratropium bromide on a regular basis to a patient with severe asthma or reversible airways obstruction when the patient is unable to use other inhalational devices.

• An antibiotic (such as colistimethate sodium) or a mucolytic to a patient with cystic fibrosis.

• Budesonide or adrenaline/epinephrine to a child with severe croup.

• Pentamidine isetionate for the prophylaxis and treatment of pneumocystis pneumonia.

Solutions for nebulisation used in severe or life-threatening asthma attacks are administered over 5–10 minutes from a nebuliser, usually driven by oxygen. Patients with a severe attack of asthma should preferably have oxygen during nebulisation since beta2 agonists can increase arterial hypoxaemia. However, the absence of supplemental oxygen should not delay treatment.

Home use of nebulisers for the treatment of acute asthma in children should be initiated and managed by an appropriate specialist.

The proportion of a nebuliser solution that reaches the lungs depends on the type of nebuliser and although it can be as high as 30%, it is more frequently close to 10% and sometimes below 10%. The remaining solution is left in the nebuliser as residual volume or is deposited in the mouthpiece and tubing.

The extent to which the nebulised solution is deposited in the airways or alveoli depends on the droplet size, pattern of breath inhalation, and condition of the lung. Droplets of 1–5 microns are deposited in the airways and are therefore appropriate for asthma.

NHS England and NHS Improvement have issued a national patient safety alert (NPSA) regarding the inadvertent use of piped medical air via a flowmeter to drive the administration of nebulised medication.⁹

Jet nebulisers

Jet nebulisers are more widely used than ultrasonic nebulisers. Most jet nebulisers require an optimum gas flow rate of 6–8 litres/minute and can be driven by air or oxygen (in acute asthma the nebuliser should be driven by oxygen). Domiciliary oxygen cylinders do not provide an adequate flow rate and so an electrical compressor is required for domiciliary use.

For patients at risk of hypercapnia, such as those with chronic obstructive pulmonary disease, oxygen can be dangerous and the nebuliser should be driven by air. If oxygen is required, it should be given simultaneously by nasal cannula.

Tubing

The correct grade of tubing must be used when connecting a nebuliser to a medical gas supply or compressor.

Ultrasonic nebulisers

Ultrasonic nebulisers produce an aerosol by ultrasonic vibration of the drug solution and, therefore, do not require a gas flow. They are not suitable for the nebulisation of some drugs (for example, dornase alfa) and for nebulised suspensions.

Vibrating mesh nebulisers

Vibrating mesh nebulisers produce an aerosol of consistently small sized particles by using the vibration of the mesh to act as a pump to push the liquid drug through the holes of the mesh. They do not require a compressed air source, can be battery operated, and are silent, small, and portable.

Nebuliser diluent

Nebulisation may be carried out using an undiluted nebuliser solution or it may require dilution beforehand. The usual diluent is sterile sodium chloride 0.9% (saline).