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Airway clearance: active cycle of breathing technique (ACBT)

Patient information A-Z

This information leaflet is designed to introduce the stages of ACBT to those who need to clear secretions from their chest, such as people who have chronic obstructive pulmonary disease (COPD), bronchiectasis or another respiratory condition. It should act as a guide and be used in conjunction with advice from a respiratory physiotherapist, who may make modifications based on your individual needs.

Why ACBT might help

Some people with chronic lung conditions find that they have secretions that can be difficult to clear. The active cycle of breathing technique (ACBT) is a form of airway clearance that can be performed at any time, without the need for equipment.

If you perform ACBT regularly it may:

  • reduce your need to cough throughout the day
  • improve your feelings of breathlessness
  • help to reduce the number of infections, especially those requiring hospitalisation
  • reduce any further damage to your lungs


Although coughing is the most common way of clearing secretions, it is also quite hard work and can lead to fragile airways becoming irritated and collapsing. Where possible try to limit the amount of coughing you do. It is much more effective to move secretions up through your lungs by using ACBT and only have to do a small number of effective coughs.

The three stages of ACBT

Breathing control (relaxed breathing)

The first stage of ACBT is designed to aid recovery from breathlessness and promote good quality breathing, using the correct muscles.

  1. Get into a comfortable position, with your shoulders and arms relaxed. Sitting upright or side lying may be the best positions to use initially
  2. Breathe in through your nose, at a comfortable speed
  3. Breathe out through your mouth, at a comfortable speed
  4. Avoid letting your shoulder rise up
  5. You should feel your tummy softly moving in and out with your breathing
  6. Maintain this relaxed breathing for one to two minutes, or as guided by your therapist

Thoracic expansion exercises (deep breathing)

The second stage of ACBT is designed to improve air entry to all parts of your lungs and loosen the secretions from where they may be stuck.

  1. Take a long slow breath in through your nose to fill your lungs as much as possible.
  2. Hold your breath in for up to five seconds.
  3. Breathe out through your mouth, at a comfortable speed.
  4. Avoid rushing the next breath in as this may push secretions further down into your airways

Forced expiratory technique (Huff)

The third stage of ACBT is designed to move the secretions from the smaller airways upwards to where it is easier to cough and clear. This is the stage that requires most practice and should be checked by a respiratory physiotherapist to ensure that you are being as effective as possible.

It may not be necessary to perform a forced expiratory technique on every cycle of ACBT. However, you should try to do one or two towards the end of each session of airway clearance to ensure that any secretions are cleared.

  1. Take a slow breath in through your nose, a little deeper than a normal breath, but not as large as during a thoracic expansion exercise.
  2. Open your mouth to an ‘O’ shape and huff the air out, as if you are trying to steam up a mirror.
  3. You should feel your tummy muscles working to push out the air.
  4. The secretions should move upwards so that you can cough them up or perform a short, sharp huff to move them into your mouth.
  5. Avoid huffing too hard. Excessive force may make you wheezy.
  6. If done correctly you should hear crackles on the breath out. These may be quite subtle and quiet if there are not many secretions or louder and more coarse if there are a lot of secretions.
  7. Limit the number of huffs to one or two to reduce the chance of becoming wheezy or starting a ‘coughing fit’.

The full cycle

The separate parts of ACBT are combined into a cycle that can be repeated as many times as needed, and as often as needed through the day. Generally it is best to start with breathing control, followed by thoracic expansion exercises, and then, if needed, the forced expiratory technique.

Diagram showing the full ACBT cycle

Putting it all together

Airway clearance is most effective when used in combination with your inhalers or nebulisers.

It is advisable to use your bronchodilator (also known as a reliever, usually blue in colour eg Salbutamol, Ventolin) about 10 to 15 minutes before you try to clear your secretions. This will help open your airways, allowing air and secretions to move more easily, and prevent you from feeling wheezy.

If you have a nebulised antibiotic then use this after your airway clearance. This will ensure that the nebulised antibiotic can get into the smallest airways and be more effective.

Find a time and place where you can comfortably complete the full session and make your airway clearance part of your daily routine.

How long for and how many times?

Your respiratory physiotherapist will advise you on how many sessions you should do a day. This will depend upon the amount of sputum that you usually produce. Each session should usually take 10 to 20 minutes.

During an exacerbation (a worsening of your symptoms) you may find it beneficial to increase the number of times you perform ACBT through the day. This may be because you have more secretions, they may be thicker and so more difficult to clear, or you may be getting more short of breath and not able to tolerate doing your usual airway clearance in one session.

Your personalised ACBT routine:


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