A 45-year-old intellectually handicapped man is admitted to your Intensive Care Unit for airway management. He is currently nasally intubated following an evacuation of a large dental abscess that had caused airway compromise. Describe how you would assess his readiness for extubation.

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College Answer

Readiness for extubation requires an assessment of factors that necessitated intubation in the first place and standard criteria.


Standard criteria would include:
• Adequacy of oxygenation (usually on FiO2 ~ 0.4 and PEEP 5)
• Ventilation (minimal respiratory support eg low level of PS £ 10). Some other ventilatory indices may be used (eg rapid shallow breathing index, negative inspiratory force, P0.1, CROP, Vt 4-6 ml/kg, Vmin 10-15 L/min)
• Protection of airway (adequate cough ± gag)
• Ability to clear secretions
• Appropriate neurological state (obeys command, orientated)
• Stable haemodynamics not requiring support
• Sepsis controlled
• Metabolic / biochemical parameters normal


Specifics for this man would also include:
• Assessment of airway swelling with direct/indirect visualization
• Discussion with treating surgical team regarding timing and management of ongoing swelling
• Adjust criteria for neurological state given his intellectual handicap

Discussion

This is a straightforward question about criteria for extubation. A curveball is thrown in the form of an intellectual handicap, but it is not anything too extraordinary.

The normal criteria for extubation readiness are outlined below.

Assessment of the Readiness for Extubation
Basic pre-conditions
  • 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

... in the model answer, one may also want to mention that 30% of patients who DONT satisfy these criteria can still be successfully extubated.

The Specific criteria for this patient

  • Direct laryngoscopy to visually assess airway oedema should reveal an improvement in the swelling and predict the difficulty of reintubation laryngoscopy.
  • There should be a surgical plan for ongoing management of swelling
  • The neurological criteria for extubation should be adjusted (one cannot expect everybody to obey commands and be orientated)

Things to consider before a difficult extubation:

  • Perform a cuff leak test. The cuff leak is a good indicator: if it is present, 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:
    • Dexamethasone
    • 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 long 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.

References

References

Andrew D Bersen wrote chapter 27 of the Oh's Manual, which regards mechanical ventilation.

Table 27.3 on page 363 of the 6th edition of Ohs Manual is a nice list of the various indices meantioned above (eg. the rapid shallow breathing index).

On page 362, Bersen references this Chest article from 2001, where the evidence for extubation criteria is summarised.
MacIntyre NR (chairman), Evidence-based guidelines for weaning and discontinuing ventilatory support: a collective task force facilitated by the American College of Chest Physicians; the American Association for Respiratory Care; and the American College of Critical Care Medicine. CHEST December 2001 vol. 120 no. 6 suppl 375S-396S.

Recommendations regarding which conditions favour extubation has been put forward in a 2007 practice guidelines statement by the AARC:
AARC GUIDELINE: REMOVAL OF THE ENDOTRACHEAL TUBE; RESPIRATORY CARE •JANUARY 2007 VOL 52 NO 1 

Karmarkar, Swati, and Seema Varshney. "Tracheal extubation." Continuing Education in Anaesthesia, Critical Care & Pain 8.6 (2008): 214-220.

Mitchell, V., et al. "Difficult Airway Society Guidelines for the management of tracheal extubation." Anaesthesia 67.3 (2012): 318-340.

Kriner, Eric J., Shirin Shafazand, and Gene L. Colice. "The endotracheal tube cuff-leak test as a predictor for postextubation stridor." Respiratory care 50.12 (2005): 1632-1638.

Loudermilk, Eric P., et al. "A prospective study of the safety of tracheal extubation using a pediatric airway exchange catheter for patients with a known difficult airway." CHEST Journal 111.6 (1997): 1660-1665.