When suctioning a patient with a tracheostomy or tube at home, it is common to see the oxygen saturation reading fall and then recover after suctioning. Many carers wrongly think this is because the suction was too weak or the phlegm was not cleared, and so suction for longer or insert the catheter deeper. In fact, a fall in oxygen saturation is an inevitable physical result of negative pressure suction and has nothing to do with whether the suctioning was thorough.
The essentials of safe suctioning are: wash hands and wear gloves, suction only after confirming there is phlegm, keep each suction under 15 seconds, use shallow insertion and intermittent suction while withdrawing, monitor oxygen saturation throughout, and let the patient recover the breath afterwards. These are clinical practice standards (AARC, Restrepo et al. 2010) and not evidence from randomised controlled trials. Suctioning can clear secretions safely, but there is no evidence that it improves hard outcomes such as mortality. This page does not repeat the indications and basic procedure already covered in safe suctioning steps at home. It goes further into the physical and physiological mechanisms behind each technique parameter, so that carers fully understand the reason for every step.
Why each suction is limited to 15 seconds
To understand why oxygen saturation drops after suctioning, the physics of negative pressure suction must be understood first. A suction catheter works by negative pressure, but the suction itself cannot tell "phlegm" from "air". Once negative pressure is connected, everything around the catheter opening is drawn away, including the oxygen-containing gas in the airway and alveoli. When oxygen is removed, some alveoli collapse briefly (alveolar derecruitment) and cause low oxygen saturation. This is the real reason oxygen saturation falls after suctioning, and it is not weak suction.
For this reason the AARC suctioning guideline requires each suction to be under 15 seconds (Restrepo et al. 2010). The longer the suction, the more oxygen is removed, and the greater the fall in saturation and the degree of alveolar collapse. Besides limiting the time of a single suction, the patient must be given enough time to recover the breath afterwards. Time-limited suction and breath recovery afterwards are in effect two necessary responses to the same physical phenomenon.
Once carers understand that "15 seconds" is "the upper limit of how long the body can cope with oxygen being drawn away" and not "the target time for clearing the phlegm completely", they will know when to stop. Suctioning for longer only leaves the patient with less oxygen and does not make the airway cleaner.
How to control the depth of catheter insertion
The AARC guideline recommends shallow and not deep suctioning (Restrepo et al. 2010). Shallow suctioning means advancing the catheter only as far as the end of the endotracheal tube (or tracheostomy tube)and then stopping. Deep suctioning means pushing the catheter in until it touches the carina at the bifurcation of the trachea. The difference between the two is not as simple as "the deeper it goes, the more phlegm comes out".
| Shallow suctioning (recommended) | Place the catheter at the end of the artificial airway, then apply negative pressure and withdraw. This touches a smaller area of airway lining and causes less irritation. Carers can measure a suitable catheter length first and make a mark, to make sure it always goes to the same safe depth. |
| Deep suctioning (not recommended as routine) | This means pushing the catheter in until it touches the carina before drawing back. The lining at the carina is very sensitive, and touching it easily causes violent coughing, changes in heart rate and blood pressure and even injury and bleeding of the lining, yet the clearing effect is no better than shallow suctioning. |
- 1Measure the length and mark itHealthcare staff first work out how deep the catheter should go from the length of the patient's artificial airway, and then put a mark or note the scale on the catheter as the upper limit of insertion depth each time.
- 2Stop at the markEach time you suction, stop as soon as the catheter reaches the mark and never push further down. Marking beforehand is the most direct way of putting "shallow suctioning" into practice at home.
- 3Pull back a little if you feel resistanceIf the catheter meets clear resistance before reaching the mark, or the patient coughs violently, withdraw the catheter a little before starting to suction, and never force it in. Resistance usually means the catheter has hit the airway lining or the carina.
Controlling negative pressure and the suction movement
The core rule of the suction technique is "no suction going in, apply pressure only on the way out". When the catheter is advanced into the airway, the negative pressure control port should be left open (zero suction on insertion). If suction is turned on while the catheter is advancing, the catheter opening scrapes the airway lining along the way and keeps drawing away oxygen, which does only harm. The right way is to cover the port only when the catheter has reached the set depth and is ready to come out, and to rotate the catheter and suction intermittently (not continuously) as it is withdrawn.
Rotating while withdrawing spreads the suction evenly around the wall and avoids the catheter opening sticking to one spot for long and damaging the lining. Intermittent suction (pressing and releasing the port with a finger) stops the airway being under continuous negative pressure and reduces the degree of oxygen shortage. As for what the negative pressure should be set at, it depends on the suction machine model and the individual patient. The AARC guideline does not set a single mmHg value, and carers at home should strictly follow the setting that healthcare staff have adjusted beforehand and never turn up the pressure to speed up suctioning.
Turning up the negative pressure oneself is one of the most common dangerous practices in suctioning at home. The greater the negative pressure, the more oxygen is drawn away each second and the stronger the pull on the airway lining. The result is that the phlegm is not cleared better, and oxygen saturation drops sharply and the lining is badly hurt. The negative pressure must be decided by healthcare staff, and carers must never change it themselves.
Oxygen saturation monitoring and recovery time before and after suctioning
The basic principle of monitoring oxygen saturation is "check the baseline before, watch the change during, and watch the recovery after". Because every suction draws oxygen out of the airway, safety depends not only on keeping a single suction within 15 seconds but also on letting the patient recover fully between two suctions until oxygen saturation returns to its level. If suctions follow one another without giving the patient a chance to rest (several passes in a row), low oxygen builds up pass by pass. As for whether to give extra oxygen before suctioning, the AARC guideline advises raising oxygen beforehand only for patients who show a clinically significant fall in saturation during suctioning, with no need to add oxygen routinely each time (Restrepo et al. 2010).
- Before suctioning: note the patient's usual oxygen saturation reading, breathing rate and colour for comparison
- During suctioning: watch the reading on the oximeter closely, stop after 10 to 15 seconds, and never go over the time to clear a little more phlegm
- After suctioning: give the patient enough time to recover the breath, and decide whether another suction (the next pass) is needed only once oxygen saturation is back to the usual level
- Only if the patient's oxygen saturation tends to fall markedly should oxygen be given before suctioning, as the healthcare staff have instructed
- Never suction several times in a row (several passes) before the patient has recovered the breath, so that low oxygen does not get worse and worse
If one suction does not clear the phlegm, it is better to pause and let the patient recover the breath fully before reassessing, and never force repeated suctions in a row. Whether suctioning at home is safe often depends on whether the carer "knows when to stop" more than on how good the hand movements are.
Why saline is not recommended routinely before suctioning
Many people are used to instilling saline into the airway before suctioning, thinking it "thins the phlegm" and makes thick secretions easier to remove. Clinical evidence, however, does not support this. A pooled analysis of 5 randomised controlled trials with 337 patients showed that routine instillation of saline before suctioning does not thin secretions and in fact causes a significant fall in oxygen saturation 5 minutes after suctioning, with no clear difference in heart rate or blood pressure (Wang et al. 2017). The AARC guideline likewise states that routine instillation of saline before suctioning is not recommended (Restrepo et al. 2010).
To deal with phlegm that is too thick, the right direction is to make sure the patient takes enough fluids, to strengthen humidification of the airway, and to have a doctor assess whether a phlegm-thinning medicine is needed, and not to instil saline routinely before suctioning. For a fuller picture of ways to clear secretions beyond suctioning, see the assessment criteria on the page about when suctioning is really needed.
Infection control and clean practice for suctioning at home
Suctioning at home generally uses a clean technique and not the fully sterile technique of a hospital operating theatre. This is a practical approach that fits the home setting and is not a lowering of the safety standard. The one-hand-clean rule applies when working: one hand stays clean and is only for holding the suction catheter, and the other hand deals with the contaminated parts and the connector of the suction machine, with clear division of work to avoid cross-contamination. In fact the gaps in infection control at home often do not come from complicated technique but from bad habits taken for convenience.
- Work with the two hands separately: one hand stays clean and only holds the catheter, and the other touches the contaminated parts and switches the machine
- Use the catheter once: a single-use suction catheter must be thrown away after use and never washed and reused
- Keep catheters separate: the catheter used for the mouth and the one used for the artificial airway must be kept apart and never be the same catheter
- Wash and disinfect regularly: empty the collection bottle on time, wash it thoroughly and disinfect it, and never leave phlegm in it overnight
Evidence on suctioning and other secretion-clearance techniques
Even with the right suction technique, carers still need to understand objectively what suctioning really does. Suctioning can safely and immediately help clear secretions retained in the airway, and for patients who cannot cough up phlegm on their own it is an important supporting measure. However, the clinical research on respiratory physiotherapy is generally of low-certainty evidence, so suctioning must not be exaggerated as a treatment that cures disease, lowers mortality, reduces hospital admissions or prevents infection.
To see how cough assistance techniques fit into the overall strategy for secretion management, and to understand the PCF assessment threshold and how to use it, see the page on cough assistance for people with neuromuscular disease.
When to stop and call a nurse for help
However skilled the suction technique, carers must know how to recognise danger situations. If any of the following warning signs appear during suctioning, the current suction (this pass) must be stopped at once.
If the patient's face turns blue, oxygen saturation drops sharply, the heartbeat is irregular, or the phlegm brought up has fresh blood, stop suctioning at once and withdraw the catheter, then let the patient recover the breath or give oxygen as healthcare staff have instructed, and watch closely whether oxygen saturation recovers. These situations usually mean a single suction went on too long, the negative pressure was too high, or the catheter was inserted too deep. If the problem keeps recurring, do not carry on regardless. Stop at once and contact the community nurse or the treating healthcare staff for help.
Suctioning at home is often done by a family member alone late at night with no healthcare staff on hand, so knowing beforehand "when you must call for help" is just as important as learning "how to suction correctly". Under the present healthcare system, the Hospital Authority's Community Nursing Service can be arranged through referral by the treating doctor in a public hospital or the discharge department, with nurses visiting to provide tracheostomy care, suctioning and technical guidance for carers (enquiries can be made to the original treating hospital or on the Hospital Authority hotline 2300 6555, and details are also on www.ha.org.hk under community health services). Carers can also call the Social Welfare Department Carers Hotline on 182 183 for respite and related support services. When Nova Health's registered physiotherapists provide home physiotherapy, they use the patient's own suction machine at home to demonstrate to carers on the spot how to mark the insertion depth of the catheter, the intermittent suction technique and when to watch for the oxygen saturation recovering, and they turn each danger sign into a large-print reminder card in Cantonese stuck at the bedside, so that family members can still respond safely by the instructions at a tense moment.