When a person with bronchiectasis has thick phlegm that is hard to cough up, family members often ask whether buying a nebuliser and spraying saline mist could loosen the phlegm and help the patient cough it up. To answer this, it is not enough to ask whether it works. It is also necessary to be clear about which concentration to use, when to use it, and whether it may have the opposite effect.
A clear conclusion first: it does help to a degree, but only as a supporting measure, and the medical evidence is of low quality. The British Thoracic Society (BTS) suggests that humidification with sterile water or saline can be considered to help clear phlegm, but this is only the lowest level of evidence (Grade D). The role of humidification and isotonic saline nebulisation is to moisten the airway and thin phlegm before airway clearance. Hypertonic saline may increase the amount of phlegm cleared, but it can provoke coughing or narrowing of the airway, so it has to be assessed case by case and does not suit everyone (Hill 2019; Lee 2015).
How moistening the airway helps to clear phlegm
To understand what nebulisation and humidification really do, it is first necessary to understand why phlegm builds up. The surface of a normal airway is covered by a layer of mucus. The cilia beat regularly and push the mucus, together with foreign particles, upwards to a point where it can be coughed out. This physiological mechanism is called mucociliary clearance. Once the mucus becomes too dry and thick, the resistance against which the cilia push rises sharply, clearance becomes less efficient, and phlegm is left behind in the airway (this is a consensus of respiratory physiology).
Humidification and isotonic saline nebulisation target exactly this step. Before clearing movements such as chest percussion or the active cycle of breathing, water is added to the airway to thin thick phlegm and reduce the difficulty of the cilia pushing it, so that phlegm loosens more easily and can be coughed up. A small study supports this direction, finding that breathing warm, saturated humidified air through the nose for a period each day helped to improve measures of mucociliary clearance (Hasani 2008). It must be recognised, though, that this only thins and moistens, and does not clear the phlegm for the patient. Real clearance of phlegm still depends on an effective cough and on the airway clearance techniques themselves (teaching on ACBT and PEP).
The BTS guideline position: humidification can be considered, but at Grade D low-level evidence
Where do international clinical guidelines put humidification therapy? The attitude is in fact quite cautious. The BTS guideline for bronchiectasis in adults suggests that humidification with sterile water or saline can be considered in clinical practice to help clear the airway, and that mucoactive treatment can be tried for patients who find it hard to cough up phlegm. Both recommendations are also graded at the lowest evidence level, Grade D, which means they are based mainly on expert consensus and limited research data and not on rigorous randomised controlled trials (Hill 2019).
In other words, the attitude of clinical guidelines is that it is worth a try and worth considering, and not that every patient must use it. Keeping this sense of proportion is very important. Treating humidification as an optional preparatory step in the phlegm clearance routine fits the medical evidence far better than treating a nebuliser as equipment that must be bought.
Isotonic saline compared with hypertonic saline
Once saline nebulisation is chosen, the next question is the concentration. The most commonly used in practice is 0.9% isotonic normal saline, followed by hypertonic saline of higher concentration (for example 7%). In short, hypertonic saline may make phlegm easier to cough up and increase the amount cleared, but at the cost of more coughing and airway narrowing, so it is not the first choice and is usually reserved for particular patients.
A crossover study of 24 people with stable bronchiectasis compared the two. It showed that 7% hypertonic saline increased the amount of phlegm cleared significantly more than isotonic saline (P=0.002), and also lowered phlegm viscosity significantly (linear trend P=0.0002). Even so, the authors were cautious in their conclusion, positioning it only as an adjunct to physiotherapy for selected patients, and called for longer clinical trials to assess more important clinical measures such as infection rate and quality of life (Kellett 2005). The same research team later carried out a 3-month single-blind crossover study with 32 participants. It also reported improvement in some measures, but a recent pooled analysis points out that this study has a high risk of bias (the reporting on blinding, missing data and allocation concealment was inadequate), a reminder not to over-interpret the data (Kellett 2011).
- Close in concentration to body fluid; its main role is to moisten the airway and thin phlegm
- Generally better tolerated, and less likely to cause strong coughing or airway narrowing
- Suits routine moistening before clearing, without aiming for the largest amount of phlegm
- More phlegm cleared and lower phlegm viscosity (Kellett 2005)
- More likely to cause coughing, throat irritation, breathlessness and even airway narrowing
- A test dose under monitoring is needed first, and it is kept for selected people who find it hard to cough up phlegm
Results of small studies of humidification at home
For humidification at home alone, the existing evidence is likewise “positive in direction but small in scale”. In interpreting it, particular attention should be paid to the size of the effect and the nature of the data. Because the samples are very small, the results can only show a trend and are not yet enough to be conclusive.
Note the p value of the first figure. 0.07 has not crossed the conventional threshold of statistical significance, and the authors themselves described the result only as a “trend” towards better mucociliary clearance, calling for more clinical trials to confirm it (Hasani 2008). This shows that humidification at home is a reasonable supporting measure worth considering, but it is still some way from being “proven effective”.
What humidification and nebulisation actually do, and their limits
What family members care about most is often whether the patient will get better after using it. To answer responsibly, both the real benefit and the clinical limits must be explained together, to help the family hold reasonable expectations.
Humidification and nebulisation help to clear phlegm, and they do not cure the disease. On the whole, using airway clearance techniques together with humidification or saline nebulisation is safe in the short term and can help to bring up a little more phlegm. The quality of evidence that it improves quality of life and lung function is still low, though (Lee 2015), and how useful mucoactive treatment really is has not been settled either (Wilkinson 2014). The most realistic goal is therefore to use moisture to loosen thick phlegm, so that clearing goes more smoothly and comfortably. It is not to expect that breathing in a mist alone will cure the disease or prevent lung infection.
In other words, the core value of humidification and saline nebulisation is to add moisture beforehand when the airway is dry and then combine it with clearing movements. What improves is mainly the comfort and efficiency of the clearing process, and it does not change the course of the disease itself. Once it is put back in its place as a supplement, expectations are not disappointed.
Possible airway adverse reactions to hypertonic saline
Humidification and saline nebulisation are not risk-free, and the higher the saline concentration, the more attention must be paid to possible adverse reactions in the airway. The clinical factors below must be weighed together before deciding to use it.
When arranging saline nebulisation, especially hypertonic saline, the following approach can be followed.
- A test dose under monitoring the first time—After inhaling hypertonic saline, patients usually cough, feel the throat irritated, feel short of breath and notice a salty taste in the mouth, and a few develop narrowing of the bronchi. At the first use, healthcare staff therefore usually watch the patient try a small dose first, and decide whether to continue after observing the airway response (Kellett 2011).
- A bronchodilator first when necessary—If the patient's airway narrows easily, the doctor sometimes prescribes a bronchodilator before the nebulisation to reduce unpleasant reactions. Whether this is needed and how to arrange it is for the doctor or physiotherapist to judge.
- If it cannot be tolerated, go back to isotonic saline or plain humidification—If the patient coughs hard after inhaling, wheezes or has a clear fall in lung function, stop at once and arrange a follow-up. Changing to the gentler isotonic saline or plain humidification, which the body can tolerate, is then usually more suitable (Kellett 2005).
Safety note: watch for adverse reactions in the airway after inhaling. Hypertonic saline can cause severe coughing, wheezing and even narrowing of the bronchi, and it does not suit every patient. If there is severe coughing, difficulty breathing or a fall in lung function after inhaling, stop at once and see a doctor, and never raise the saline concentration or amount yourself.
Who needs humidification or saline nebulisation
Not every person with bronchiectasis needs nebulisation or humidification equipment. Clinical guidelines list it only as something that can be considered, and the current evidence is of low quality, so whether it suits a patient depends very much on the individual condition. Many patients can clear phlegm effectively with enough fluid in daily life and the correct airway clearance technique. The situations in which it is more worth considering and those in which it is not necessarily needed are set side by side below for family members to compare.
Situations more suitable for considering humidification or saline nebulisation
- The phlegm is very thick and dry, and moistening before clearing can clearly help thick phlegm to loosen
- In the dry autumn and winter season, or in places where the air conditioning is on all the time, phlegm easily becomes thick and very hard to cough up
- It is very hard to cough up phlegm and ordinary airway clearance techniques alone have little effect (hypertonic saline can be considered for a trial under assessment)
- After assessment by a physiotherapist, the airway is confirmed to tolerate it and the patient is willing to keep using it
Situations where it may not be needed
- There is not much phlegm usually and enough water is drunk, and correct clearing technique alone brings up the phlegm smoothly
- The body cannot tolerate hypertonic saline, and severe coughing or wheezing starts as soon as it is inhaled
- No professional has assessed it, and it is bought only with the thought that having a machine at the door gives some peace of mind
- A mistaken belief that breathing in a mist alone can replace airway clearance techniques such as chest percussion or breathing exercises
Weak cough needs better equipment: consider cough assist when PCF is below 270 L/min
One last key concept needs to be made clear. Humidification and saline nebulisation deal with phlegm that is too sticky, and not with a cough that is too weak. If the core problem of the patient is the latter, that is, not having the strength to cough so that phlegm sticks deep in the throat and cannot be cleared, moistening the airway alone does not solve the problem, and supporting equipment has to be stepped up by another route.
The only criterion with a clear number is the strength of the patient's cough. The guideline of the American Association for Respiratory Care (AARC) states that for patients who cannot cough hard enough (especially those with neuromuscular disease), cough assist techniques or devices should be considered when the peak cough flow (PCF) is below 270 L/min (Strickland 2013). This is the only indicator with a specific number for triage in the whole phlegm clearance assessment. This is because humidification and saline nebulisation only moisten the airway and thin thick phlegm, and do not give the patient the strength to cough it up.
In deciding whether more advanced equipment is needed, it is therefore not enough to look at how much phlegm there is or how sticky it is. The strength of the patient's cough must be assessed as well. For phlegm that is too sticky, stronger humidification can be considered, but for a weak cough, cough assistance has to be considered, and the two are completely different clinical problems. On a home assessment, the physiotherapist first checks the stickiness of the patient's phlegm, the strength of the cough and the airway response, and only then decides whether isotonic saline nebulisation should be added before airway clearance for moistening. This is a professional judgement made according to the individual condition, and every patient is never simply required to buy a nebuliser. If family members are looking for a professional who can assess at home, demonstrate in person and follow up continuously for an older person at home with a lot of phlegm that is hard to cough up, the home physiotherapyprovided by Nova Health's registered physiotherapists can fully assess the patient's cough ability and amount of phlegm, decide according to actual need whether to bring in humidification or saline nebulisation and which concentration to use, and avoid buying unnecessary medical equipment blindly. Cases in which the cough is clearly inadequate have another, escalated plan of management.
For public healthcare and community resources, patients can be referred through a family doctor or specialist to the respiratory or physiotherapy departments of the Hospital Authority clusters, to arrange assessment and guidance on airway clearance and humidification therapy. For enquiries, call the Hospital Authority hotline (852) 2300 6555. For community rehabilitation support for people with long-term illness, see also the community rehabilitation network of the Hong Kong Society for Rehabilitation.