Many people have learned about chest percussion and have heard of the active cycle of breathing, but what they most want cleared up in practice is: what exactly are the steps of ACBT? Which of the three parts comes first, how many times is each done, and when does the cycle start again? This page concentrates on answering these practical questions.
ACBT (the active cycle of breathing technique) is an airway clearance method that the patient can carry out independently, and it is a cycle of three parts: breathing control, then thoracic expansion exercises, then the forced expiration technique (huff). Research confirms that the technique is safe, helps to clear secretions in the short term and temporarily improves lung function (Zisi 2022), but it is only a short-term aid and cannot cure lung disease. The sections below go through how each part is done and how they are combined. To see where chest percussion, cough assist machines, suctioning and ACBT fit on the whole ladder of airway clearance, read the overview of airway clearance and chest percussion techniques first.
What ACBT is and when it is used
ACBT needs no equipment, and the patient can do it alone to clear secretions. It suits patients who can understand instructions and can still blow out an airflow (for example patients with bronchiectasis or stable COPD, or older adults with a lot of sputum but a cough that still has some strength). The advantage of the technique is that it is both gentle on the body and safe. Through rhythmic breathing, secretions deep in the lungs are loosened gradually and moved toward the large airways, and finally cleared easily with a huff, which spares the exhaustion of continuous violent coughing.
A systematic review of 11 studies (Zisi 2022) found that ACBT has a "short-term improvement" effect on clearing airway secretions and on lung function. It increases the amount of secretions cleared, reduces the viscoelasticity of secretions and eases breathlessness. The quality of the included studies was rated moderate to good, but the focus was on short-term and not long-term effects. A Cochrane review of stable bronchiectasis (Lee 2015) likewise showed that airway clearance techniques "appear safe" with no adverse events, but all conclusions about effectiveness were of low-quality evidence. In other words, the reasonable expectation of this technique is that it is safe and helps to clear more secretions in the short term, and it does not cure disease.
First tell apart whether the patient has secretions or is too weak to cough them up. If the patient has secretions and has enough strength to blow out air on request, ACBT can help. If the patient clearly lacks the strength to cough (for example a patient with neuromuscular disease) and cannot cough up secretions alone, ACBT by itself may not be enough and other methods are needed, as explained at the end of the article.
The three parts of ACBT: breathing control, thoracic expansion and huffing
ACBT is made up of three elements, each with a different role, and none can be left out. The British Thoracic Society physiotherapy guideline (Bott 2009) set a practical standard for carrying out these three steps in adult patients who are breathing spontaneously. Each part is described in detail below:
The biggest difference between a huff and a violent cough is that during a huff the glottis stays open, a medium to low lung volume is used and the force is controlled, so the airway is irritated less and the patient is not coughing to exhaustion. For more on the choice of lung volume and the breathing rhythm during a huff, see the page on the huff and forced expiration technique.
How to do a full cycle and how many times to repeat it
The three parts are not simply repeated many times each. They are combined in a set order into one "cycle", and carried out set by set in turn. The usual sequence is shown below (the actual numbers and order should be adjusted by the physiotherapist to the patient's condition, Bott 2009):
Start with breathing control, move forward step by step, and then come back:
- Step 1 · Breathing control—Take a few relaxed abdominal breaths to settle the breathing. This is also the rest period between each set of movements.
- Step 2 · Thoracic expansion ×3 to 4—Take 3 to 4 deep, slow breaths in a row. At the deepest point, gently hold the breath for about 3 seconds, then relax and breathe out, so that air reaches behind the secretions.
- Step 3 · Breathing control (again)—After the thoracic expansion, take a few more breaths of breathing control to settle the breathing, so that continuous effort does not cause breathlessness.
- Step 4 · Huff ×1 to 2—Do 1 to 2 forced expirations (huffs). Only when the patient feels that the secretions have reached the large airways, give a gentle cough or another huff to clear them.
- Start the cycle again—After some secretions have been coughed up, go back to Step 1 to start the next cycle. If there are a lot of secretions (for example on waking in the morning), one or two more cycles can be done, but breathing control must be done in between for rest.
In short, the rhythm of one cycle is rest, expand, rest, huff. How many cycles to do each time has no fixed rule clinically, and the studies pooled in Zisi 2022 mostly used individualised programmes. The main principle is to clear secretions smoothly without causing breathlessness or dizziness.
Safety points and common mistakes
ACBT itself is quite safe (Lee 2015), but if the details of the technique are ignored, the effort is wasted and the patient may become dizzy. The most common points to note are as follows:
- Use a huff instead of repeated hard coughing. A huff takes less effort and irritates the airway less (Bott 2009).
- Always rest with breathing control between each set of movements. If the patient feels breathless or dizzy, stop at once and settle the breathing.
- Sit upright with the upper body leaning slightly forward. This position makes it easier to blow air out than lying flat.
- It is best done 1 to 2 hours after a meal, to reduce the chance of choking or feeling sick.
- Do not start with a forceful deep breath. Many older adults become dizzy this way. Start with breathing control to let the breathing settle.
- If the secretions have not yet loosened, do not keep coughing hard and dry. This brings up no secretions and also tires the patient out quickly.
When teaching older adults and carers ACBT at home, the first and most important lesson is often the rest step of "breathing control". Many older adults are impatient and start with a hard deep breath, which makes them dizzy. Using a few relaxed abdominal breaths as a buffer between each set of movements is in fact what decides whether the whole technique can be kept up, and lets the patient manage it at home with confidence.
When to seek a physiotherapist, and why ACBT does not suit everyone
ACBT is not a cure-all. In some situations it is not enough alone, and carrying on with it regardless may delay appropriate treatment. The clearest dividing line is cough strength. For patients with a weak cough (for example neuromuscular disease), the American Association for Respiratory Care guideline (AARC, Strickland 2013) states that a cough assist device should be considered when the peak cough flow (PCF) is below 270 L/min, rather than relying on ACBT alone to clear secretions. For the use of mechanical insufflation-exsufflation (MI-E) in patients with neuromuscular disease, the Cochrane review (Morrow 2013) pooled data from 5 short-term studies with 105 participants and concluded that the "evidence is not enough to support or oppose its use". This means that it cannot be assumed that the device is bound to work, and each case must be assessed individually.
The public should also hold realistic expectations of the overall effect. On whether chest physiotherapy can lower mortality or raise the cure rate in adult pneumonia, the Cochrane review (Chen 2022, 8 RCTs, 974 participants) reached a conclusion described as "very uncertain", with very low certainty of evidence. Whether it is ACBT or any other airway clearance technique, its clinical role therefore remains that of a safe short-term aid, and it should not be regarded as a treatment that cures lung disease.
If any of the following occur, do not rely on ACBT alone. Have a healthcare professional assess the patient as soon as possible: a clearly weak cough, blood in the sputum, fever, sudden worsening breathlessness, or being unable to bring up secretions even after ACBT. A physiotherapist or doctor should examine the patient. The registered physiotherapists at Nova Health can visit and measure the patient's peak cough flow to see whether ACBT alone is enough, or whether other airway clearance methods such as breath stacking, manually assisted coughing or a cough assist machine are needed.
Arranging ACBT practice at home
The greatest advantage of ACBT is that it needs no equipment, so the patient can easily practise at home. In practice, an older adult can sit upright on a chair with a back 1 to 2 hours after a meal, to avoid vomiting from practising straight after eating, and the carer only needs to watch whether the older adult becomes breathless or dizzy. Practice is usually most effective in the early morning after getting up and at times in the day when secretions collect more easily. If there are a lot of secretions, one or two more cycles can be added as appropriate. Once the patient has learned through home physiotherapyhow to tell the "breathing control rest" from the "huff to clear secretions", the patient can complete the cycle step by step alone even when no therapist is present on ordinary days.
If the patient cannot get the knack when practising alone, or the family wants to confirm whether ACBT suits the patient's condition, a chest physiotherapy assessment is advisable. Among local community resources, the Rehabaid Society (復康資源協會) offers chest physiotherapy services covering percussion, vibration, postural drainage, coughing and breathing exercises. Its address is G/F, 7 沙灣徑, Pok Fu Lam, Hong Kong, and the enquiry telephone number is (852) 2364 2345. The Hospital Authority also keeps a list of allied health (physiotherapy) clinics, and patients can be referred by a doctor for chest physiotherapy. If assessment confirms that the patient has a weak cough and ACBT alone is not enough to clear secretions, the next step is usually to move on to more advanced techniques such as breath stacking and a cough assist machine. These are covered on pages for specific conditions such as secretion clearance in bronchiectasis.