"At-risk extubation" defines a situation where there is some uncertainty as to whether or not the patient will stay extubated for any prolonged period of time. This state is characterised by the expectation of difficult reintubation or by the presence of incompletely met criteria for extubation, be it a full stomach, haemodynamic instablily, poor neurological performance or metabolic derangement.
"Difficult extubation" has no formal definition as such. Cavallone et al (2013) are the authors of the most sensibles-sounding article on this topic, and even they were unable to define it beyond using specific examples. It seems to be the inverse of difficult intubation, i.e. there is some sort of crude mechanical barrier to getting the tube out. In lay terms, the tube is stuck. This is weird and rare. Historically, case reports have included accidental stitching of the ETT into the trachea, transfixation of the ETT by a skeletal traction wire, failure of the cuff to deflate, formation of barbs along a lacerated tube, and the total disappearance of a shortened ETT into the depths of the patient's airway. Lang et al (1989) chronicle these and numerous other hilarious tracheal tube mishaps, completing the collection with the first case report of a nasotracheal tube being permanently affixed to the patient with a Luhr plate screw.
Both Question 11 from the second paper of 2011 and Question 2a from the second paper of 2004 asked the candidates to assess for extubation a 45 year old "intellectually handicapped man" who was intubated for the evacuation of an airway-obstructing dental abscess. Similarly, Question 26 from the second paper of 2020 presented the candidates with a borderline-awake cardiac arrest survivor. This sort of question takes emphasis away from normal ventilator weaning, but on the preparation for extubation failure, and for the possibility that reintubation will be difficult.
A good literature resource to answer these sorts of SAQs is the "Difficult Airway Society Guidelines for the management of tracheal extubation" ( Mitchell et al, 2012). This statement has informed most of the ensuing summary. The time-poor candidate could safely limit their reading to Lang et al (2013), who have published an excellent review of at-risk extubation and extubation failure.
The perils of extubation
Why do we make such a big deal of this reversible airway manipulation?
- Airway reflexes may be exaggerated. The intubated patient may cough uncontrollably or develop laryngospasm. Increased intracranial pressure and possibly post-extubation pulmonary oedema may develop as a consequence.
- Airway reflexes may be depressed. Obesity, residual effect of opiates and residual neuromuscular blockade can result in airway failure. Prolonged tracheal intubation depresses airway reflexes.
- The airway can be injured by extubation, particularly uncontrolled self-extubation (with the cuff up). The latter can lead to arytenoid dislocation, vocal cord oedema and post-extubation stridor.
- Derecruitment: Loss of PEEP and subsequent basal collapse tends to disadvantage the respiratory function. A patient who is reintubated following a prolonged period of derecruitment is potentially several days behind on their respiratory wean; you have to start all over again.
The normal criteria for extubation readiness are outlined below.
Assessment of the Readiness for Extubation
- Resolution of the condition which had required the intubation and ventilation
- Patient-directed mode of ventilation (eg. PSV)
- Haemodynamic stability (the patient is unlikely to need massive fluid resuscitation in the near future, and their cardiac function is satisfactory to endure the increased demand from hard-working respiratory muscles)
- Adequate muscle strength
|Airway protection assessment
- Good cough reflex on tracheal suctioning
- Good gag reflex on oropharyngeal suctioning
- Adequate neurological performance (obeying commands, or at whatever cognitive baseline previously permitted spontaneous breathing)
|Gas exchange criteria
- Adequate oxygenation: SpO2 over 90% on FiO2 under 40%
- Normal acid base status (pH >7.25), i.e. no significant respiratory acidosis
|Lung mechanics criteria
- Adequate oxygenation: FiO2 40%
- PEEP less than 8 cmH2O
- Satisfactory tidal volume: VT > 5ml/kg
- Satisfactory vital capacity: VC > 10ml/kg
- Satisfactory MIP: less than 20-25 cmH2O (i.e pressure trigger)
- Satisfactory RSBI: an fR/VT less than 105 breaths.min-1L-1
"Borderline" patients at risk of peri-extubation complications
The extubation criteria are not carved in stone. On occasion, one may be tempted to extubate what might be described as a "borderline" patient, who may not be a hundred percent cooperative, or who may have impaired airway reflexes, or whose disease state may not have completely resolved.
In short, there are situations where intensivist has made the extubation difficult by virtue of their impatience.
In addition, the airway may be difficult, thus making this a "difficult re-intubation". The Difficult Airway Society propose the following problem domains to describe such an "at-risk" extubation:
- Pre-existing airway difficulty (i.e. the patient is known to have a difficult airway, eg. they are known to have ankylosing spondylitis or macroglossia)
- Recent airway deterioration (i.e. a previously normal airway is now difficult, eg. when it is distorted by haematoa following a haemorrhagic complication of carotid endarterectomy)
- Restricted airway access (the airway is difficult because the patient is in a fixed position where intubation becomes impossible, eg. where the head or neck movements are restricted by external fixation, or where the jaw is wired).
Additional considerations for at-risk extubation
One might view the following as an "extended" list of extubation criteria, specificaly relevant to the situation where one is concerned about post-extubation airway patency, and where one is not confident in one's ability to reintubate the patient in a hurry. A classical example is the head-and-neck radiotherapy patient who gets intubated for an elective occipitocervical spinal fusion, and is then discovered to have a rip-roaring dental infection which they failed to mention at the pre-admission clinic.
- Perform a quantitative cuff leak test. The cuff leak is a good indicator: if it is present (>110-120ml), there is little likelihood of post-extubation stridor . Sure, the patient may fail for a hundred other reasons, but at least they will not br stridorous. In fact, failing the cuff leak test does not preclude a successful extubation (Kriner et al, 2006), but in a patient with a difficult airway one would want to be extra careful.
- See the airway before extubation. This is particularly important in cases where some sort of primary airway problem was the main reason for intubation. An excellent example of such a scenario is the a 45 year old "intellectually handicapped man" from the college SAQs (Question 11 from the second paper of 2011 and Question 2a from the second paper of 2004). The man had a large dental abscess which affected his airway. Before extubating him, the wise candidate would ask for direct laryngoscopy in order to
- Scan the airway before extubation. This is an extension of direct laryngoscopy, which can only ever show you the intubated larynx. If there is some sort of sublaryngeal pathology (eg. subglottic stenosis) a CT would reveal it, whereas laryngoscopy or bronchoscopy would not.
- Prepare for management of post-extubation stridor: these techniques are discussed in greater detail elsewhere, but briefly listed they consist of the following:
- Adrenaline nebs
- Extubation on to NIV
- Extubation on to heliox
- Extubation in the operating theatre with ENT on standby
- Extubate over an airway exchange catheter. These are ong hollow polyurethane tubes. You can extubate the patient, leaving one in situ (or just the guidewire from one, sitting above the carina). If the patient gets into respiratory trouble, the end of the catheter can be attached to a standard 15mm conector, and the patient may be ventilated by this method while a definitive airway is beign established. Historically, they seem to improve reintubation success rates in cohorts of difficult airway patients. For example, Loudermilk et al (1997) reported a high rate of successful first-time reintubation with these devices.
- Postpone extubation. Extubation, as the DAS point out, is an entirely elective procedure. There is no such thing as a "crash extubation". There is never any rush. A delay may improve the degree of airway oedema, or allow for expert staff to assemble so that the best chance of reintubation is afforded.
- Electively convert to tracheostomy. In some circumstance, it is clear that the upper airway problem is persisting and is unlikely to resolve of the medium-term. Prolonged intubation has its own numerous disadvantages and will cause vocal cord oedema eventually, so to keep the patient intubated for an excessively long time is not an option either. In some cases, extubation to you own airway will be impossible and a tracheostomy is inevitable.
Exotic tests of upper airway function
There are a few strange bedside tests and investigations which may be considered in specific circumstances, but which do not form a part of even the "extended" list of pre-extubation assessments. These were largely scraped together from Table 3 in the 2013 article by Lang et al.
- Fiberoptic laryngoscopy and bronchoscopy: this is an extension of direct or videolaryngoscopy, and serves to confirm that the airway is indeed clear of any swelling, and that there is
- Directly visualised cuff leak test: while performing direct or flexible fiberoptic laryngoscopy, one may deflate the cuff and directly observe how much (or how little) space there is.
- Extubation over bronchoscope: the patient can be extubated while the bronchoscope keeps a close eye on the vocal cords. This may be useful if there was concern regarding vocal cord paralysis.
- Laryngeal ultrasound: This may play a role in situations where the cuff leak test is for whatever reason unreliable or impossible (eg. if you are using an uncuffed tube in a paediatric setting). Ding et al(2006) reported good reliability in a small cohort, but over ten years have now passed without wide adoption of this practice.
- Recurrent laryngeal nerve neurophysiology is an alternative to laryngoscopy as a means of diagnosing cord paralysis, but is infrequently resorted to.