Decannulation of tracheostomy

The topic of what one does with a tracheostomy once it has outlived its utility has never come up in the Part 2 exam until Question 17 from the first paper of 2019. For something that is a common part of the intensivists' responsibilities, this is quite surprising. It does not need to be mentioned that the procedure itself is not the interesting part (you basically just pull the tube out). The real skill is in the assessment of readiness for decannulation. The college answer to this question was fortunately quite well laid out with clear points and transparent expectations:

"To pass the candidate needed to demonstrate awareness of the requirement for all of:
1.    Patent upper airway
2.    Ability to clear secretions with a mention of cuff deflation
3.    Adequate level of consciousness
4.    Adequacy of spontaneous ventilation"

The best practical resource for this would probably be Christopher (2005) or O'Connor & White (2010). Heffner (1995) is the most classical article on this topic, and ends up quoted by virtually all the other papers, but is unfortunately paywalled. 

In summary:

• Determine that the condition which called for the tracheostomy had resolved
• Establish that mechanical ventilation is no longer required
• Establish that the cough is strong enough and that secretions are manageable
• Establish that the upper airway is patent and with intact reflexes
  • Test gag and cough, or alternatively perform a "blue dye test".
  • Perform a cuff deflation trial for ~ 72 hours
  • Endoscopic evaluation should be performed if the patient has failed the cuff-down trial 
  • Tracheostomy may be downsized to assist the cuff-down trial, or exchanged for a fenestrated tracheostomy
• If there is still uncertainty, a trial of decannulation may be undertaken using a tracheal spacer device

Benefits and adverse consequences of decannulation

Why not just leave the tracheostomy where it is, one might ask? Well. There are multiple benefits:

• Improved force/quality of cough and improved secretion clearance
• Decreased airway irritation and inflammation
• Decreased secretions - tracheostomy may stimulate bronchorrhoea
• Improved swallowing
• Better humidification of inspired air
• Speech becomes possible, which improves quality of life and clinical assessment
• Pursed-lip breathing becomes possible, which provides some relief in a PEEP-like fashion

From a purely pragmatic non-patient-centred perspective:

• Care for a tracheostomy requires specialised nursing expertise
• Care for a patient who is unable to speak is more difficult, from a nursing perspective
• Complications of prolonged tracheostomy are frequently serious, requiring prolonged hospital admission or specialist intervention (eg. tracheal stenosis or tracheomalacia)
• Long-term tracheostomy promotes respiratory infections (particularly in COPD patients) which increases their lifetime healthcare costs (Enrico et al, 1999)

Physiological effects of decannulation

So, you've decided to take out the tracheostomy. How will this look from a respiratory mechanics point fo view? Turns out, there won't be much difference, unless the tracheostomy tube was laughably small. There will be some minor changes to the patient's respiratory physiology, mainly due to the fact that the tracheostomy eliminates a lot of anatomical dead space by diverting air away from the upper airway.  When breathing through a tracheostomy tube was compared by Chadda et al (2002) to breathing through a normal upper airway, the following changes were observed:

• Tidal volume increases by about 25%
• This increase is mainly due to the increase in the anatomical dead space 
• Work of breathing increases slightly (by about 25-30%)
• Respiratory resistance and compliance remain unchanged

Thus, the patient must be able to tolerate some increase in their work of breathing, which is purely due to the fact that now they need to move approximately 25% more air to achieve the same rate of CO₂ elimination.

"What happens to the hole" is a frequently asked question by junior doctors.  Following decannulation, the stoma usually closes by secondary intention over 5-7 days, analogous to a hole for a piercing that has been removed. If the stoma is well-established and epithelialised, the healing may be delayed, in which case the hole may still narrow as wound contraction takes place. That outcome is still usually unsatisfactory for the patient (for one, mucus leaks constantly from the opening) and so various surgical approaches to the closure of a persistent stoma have been described (eg. Shen et al, 2003). 

Pre-conditions to decannulation

Following from the above, its stands to reason that the first step before you can even consider taking out the tracheostomy tube is to assure yourself that the patient will be able to breathe without ventilator support in spite of the additional increase in the respiratory workload. In addition to this, several other conditions must be met for the decannulation to be successful. One usually needs to o through these in a stepwise fashion.

1) Establish that mechanical ventilation is no longer required. This is continuous with the process of ventilator weaning, i.e. it represents the final stages thereof. Slowly you withdraw ventilator support by decreasing the airway pressure and increasing the periods of ventilator deprivation until the patient is able to maintain normal gas exchange without ventilator support for a sustained period. How long is a "sustained period"? Technically, one would have to say that this would be the rest of their natural life. The college examiners give a minimum period of 24 hours.  Rumbak et al (1997) used 48 hours of spontaneous unassisted breathing in their study. 

2) Establish that the level of consciousness is adequate.  Again, "adequate" is defined inconsistently in the literature. Singh et al (2017) and Ceriana et al (2003) waited until all the delirious patients completely recovered their marbles before attempting decannulation, whereas Enrichi et al (2017) accepted any GCS over 8 in their cohort of brain-injured patients. . Generally, logic dictates that if decannulation is non-palliative (i.e. expected to lead to recovery), then in order for the patient to participate in their own rehabilitation (and to get the maximum psychological benefits from decannulation) their level of consciousness should be relatively normal.

3) Establish that the load of secretions is manageable. This is some sort of a competition between the patient's capacity to produce sputum and the patient's ability to cough it out. Put in a different way, the greater the volume of secretions, the more effective and forceful the cough mechanism has to be in order to expectorate them. There is probably no scientific method to determine this parameter without obsessing over precise measurements of sputum viscosity and volume. As a compromise, most authors use frequency of documented suctioning events - for example Singh et al (2017) recommend that the frequency of suctioning should be less than 4 over the previous 24 hours. 

How good does the cough need to be? Bach et al (1994) found that patients with a voluntary cough peak flow of more than 160L/min were more likely to succeed. To accommodate the fact that their (often profoundly unconscious) patients might not cough voluntarily, Enrichi et al (2017) gave them nebulised citric acid for their spirometry. 

4) Establish that the upper airway is patent. There are several ways of doing this, ranging from highly scientific to purely subjective. In essence, one needs to demonstrate somehow that there is sufficient unrestricted airflow through the upper airway to support normal breathing after decannulation. Methods of doing this include the cuff deflation trial which is included in the college answer to Question 17 from the first paper of 2019 as an essential part of the answer. This basically consists of deflating the cuff of the tracheostomy and observing what happens.

Some people also occlude the tracheostomy tube ("capping" or "corking" is what that's called), which is an interesting manoeuvre because it markedly increases the airway resistance. In essence, the capped tracheostomy becomes an airway obstruction, taking up 10-12mm of the internal tracheal diameter. Logically, as a test of respiratory wherewithal this makes sense, because surely if the patient is able to breathe effectively past this obstruction, they will surely breathe even better when it is removed. How long do you keep them like that? Enrichi et al (2017) suggested that 72 hours would be enough. 

If the patient fails this trial (i.e. develops respiratory distress or stridor), it is unclear whether this happens because of increased airway resistance or because the upper airway is somehow abnormal. Most authors recommend to perform an endoscopic assessment of the upper airway to ensure that there isn't some weird flap of granulation tissue growing in there. Some people do thi routinely to see examine the upper airway before decannulating any patient, but Rumbak et al (1997) had demonstrated that this is not necessary (i.e. if you pass 

If the upper airway appears normal, one might conclude that the capped tracheostomy created too much of an obstruction, and might instead opt to downsize it (i.e. exchange it for a tube of a smaller external diameter).  With a smaller tracheostomy tube, the patient may find it easier to breathe and phonate. The disadvantage of downsizing the tube is the very real possibility that the tube will be too small for its cuff to occlude the trachea without a leak, making it impossible to properly ventilate the patient with positive pressure. At the same time, with the inner tube diameter now much smaller, the patient will find it much more difficult to breathe spontaneously.

As both spontaneous and supported ventilation is made more difficult by downsizing, the practice represents an interesting trial of survival for the patient. An alternative to downsizing is the use of a fenestrated tracheostomy which allows one to open the upper airway for vocalisation by removing the non-fenestrated inner cannula. This is also not without its disadvantages: for example, tissue may herniate into the fenestration, occluding the airway, or the inner cannula may inappropriately exit the fenestration. 

5) Establish that airway-protective reflexes are adequate,  i.e. assure yourself that the patient - if decannulated - will not immediately aspirate. There are several ways of doing this. For a low-tech solution, one could give the patient an oral food bolus composed of ice chips coloured with a non-irritant blue dye such as Evans Blue, and then observe for blue-stained tracheal aspirates. With the cuff down, the aspirating patient will develop a blue discolouration of their tracheal secretions. First described by Cameron et al in 1973, this test has had a history of patchy acceptance, with many people complaining about its poor accuracy. A more recent study by Belafsky et al (2010) reported that the sensitivity of this test is 82%, or 100% if the patient is mechanically ventilated. This was good enough to make it a part of the protocol developed by Enrichi et al (2017).

An even more low-tech solution would be to demonstrate that the patient has an intact cough and gag reflexes by testing them clinically, which is what most people seem to do in their routine practice. 

Failure to decannulate

Let's say the patient fails the assessment, or they are so borderline that it is impossible to commit confidently to one course of action. What would one do? O'Connor et al describe the options, which include:

• Approach surgical specialities for the management of upper airway obstruction, in case there is some available operative management for the obstruction
• Try to decannulate anyway, but using a tracheal spacer device (analogous to a staged extubation)
• Use a nasopharyngeal airway to suction the patient if their secretion clearance is inadequate
• Place a mini-tracheostomy for secretion clearance
• Give up and place a long-term tracheostomy with an inner cannula

A practical approach to the decannulation assessment

This list, which suffers from incompleteness as does any other such list, is offered here not as a means of educating an already educated readership, but rather as a means of offering a handy alternative answer to Question 17 from the first paper of 2019.

• Adequate gas exchange while off mechanical ventilator support:
  • Surviving off the ventilator for at least 24 hours
  • Requiring minimal oxygenation support:
    • "blow over" of humidified gas, i.e. a T-piece trial
    • HME with room air or minimal supplemental oxygen, eg a "Swedish Nose". 
  • No planned procedures in the near future which may require mandatory mechanical ventilation
• Preconditions for a decannulation trial: 
  • Secretion volume
    • Fewer than 4 suction episodes in the last 24 hours
    • No intercurrent suppurative lung disease
  • Intact airway reflexes
    • Gag reflex present
    • Cough reflex present
  • Intact sensorium
    • Level of consciousness should be high enough to sustain cooperation with physiotherapy and nursing staff in the post-decannulation period
  • Satisfactory muscle power
    • Maximum expiratory peak flow of over 160 L/min with cough
  • If the patient does not meet these preconditions, the cuff deflation trial will need to be delayed
• Cuff deflation trial 
  • Deflate the tracheostomy cuff
  • Ensure adequate oxygenation and ventilation with the tracheostomy still patent
  • Then, occlude the tracheostomy
  • Observe for 72 hours 
    • If unsuccessful, perform videoendoscopy or CT imaging of the upper airways to determine the cause
  • Test for aspiration during this time (blue dye test)