Preparation for the difficult airway

A plan of management for a difficult intubation is (fairly) expected of senior ICU trainees, and has come up several times over the last few years. It can be expected to remain a routine part of the exam process. As such, the savvy candidate will memorise a certain management algorithm, and will be ready to regurgitate it at the appropriate moment.

Historical SAQs on this topic have generally followed the same sort of pattern. The patient is usually a “known difficult intubation” and is deteriorating rapidly, usually due to severe airflow obstruction. The candidate is invited to outline their plan of management, or to “identify priorities” in management. The list of past paper questions include the following:

• Question 19 from the first paper of 2022
• Question 19 from the first paper of 2020
• Question 22 from the second paper of 2012
• Question 1c from the first paper of 2004
• Question 3 from the first paper of 2002

This is the pattern seen in and . may also be described as a “difficult airway”, but not in the classical sense: rather, the candidates were expected to describe the crash intubation of a patient who was having melaena and likely had a stomach full of blood. This matter falls more neatly into the “rapid sequence induction” category and is discussed elsewhere. Then, there's , which presented the candidates with a stridorous patient recently returned from thyroidectomy.

In the past paper SAQs, the patients are all “known difficult intubation”, which places them into the 7% of difficult intubations which are recognised beforehand. Nørskov et al (2015) have recently published a retrospective survey of 3391 reported difficult intubations, 93% of which were not expected to be difficult. As such, the discussion below is mainly directed towards the preparations for an anticipated difficult airway, rather than the reaction to a failed intubation (which is discussed elsewhere).

As far as important literature goes, the statement from the American Society of Anaesthesiologists Task Force (Apfelbaum et al, 2013) was my primary resource for this summary. ANZCA also have a statement on the equipment which should be available to manage a difficult airway, but apparently no algorithm of their own. The time-poor candidate who just wants to pass may wish to limit their reading to this excellent LITFL page.  The person with infinite patience may also wish to explore the Difficult Airway Society’s 2015 guidelines – however, these refer to the unexpected  93% of difficult intubations, and therefore aren’t strictly applicable to the abovementioned SAQs.

Equipment for difficult airway management

• A selection of oropharyngeal airways
• A selection of nasopharyngeal airways
• Macintosh laryngoscope blades size 3 and 4.
• Alternative laryngoscope blades (eg. a Kessel blade)
• A short laryngoscope handle (for fat or big-breasted people)
• An endotracheal tube introducer
• A malleable blunt atraumatic stylet.
• Normal LMAs of different sizes
• Intubating LMA kids, eg. Fastrach
• A selection of specialised ETTs, eg. long flexometallic, nasal, etc.
• A long airway exchange catheter.
• A surgical cricothyroidotomy kit
• A kink resistant cricothyroidotomy cannula and jet ventilation kit
• A capnograph, capnometer or colorimetric end-tidal CO₂ detector.

Preparation for a difficult intubation

History

• Why is the patient a difficult intubation?
  Look through previous anaesthetic records, if time permits.
• Why does the patient need intubation?
  This step helps assess the likely complications (eg. in Question 1c from the first paper of 2004 the patient is having emergency gastroscopy for an upper GI bleed, and the likely complications inevitably include aspiration).

Examination

• Assess for difficulty of intubation, to determine which specific features were problematic.
• Assess for difficulty of bag-mask ventilation.
  This is all discussed in the chapter on recognising the difficult airway.
• Look at the most recently available ABG or venous biochemistry: specifically, the PaCO₂ helps determine the dose of anaesthetic induction agent, and the serum K⁺ level helps select the muscle relaxant.

Planning

• Decide beforehand what the algorithm is going to be, depending on what is available locally.
• Have a plan for intubation
• Have a plan for oxygenation
• Have a backup plan (or two) for each
• Have a clear idea of what the locally available cricothyroidotomy kit looks like and roughly how long it takes to set up (given that pretty much all of the algorithms lead to cutting the throat).

Preparation of the staff

• Choose a competent assistant to assist with the airway: somebody who knows what BURP is and how to correctly do cricoid pressure
• Choose a competent assistant to give drugs
• Assign a staff member to act as “access”, i.e. somebody to run around and get equipment
• Inform standby staff to be ready (eg. inform ENT surgeon, senior anaesthetist)
• Discuss the plan with the team to ensure everyone is aware of what is going to happen (eg.  “OK people, Plan A is videolaryngoscopy with bougie, Plan B is Fastrach”).

Preparation of the equipment

• Plan A equipment should be ready for use
• Plan B equipment should be available within 60 seconds (which means, in the room, within arm’s reach, and wherever possible unwrapped and lubricated).
• Drugs should be drawn up, including a couple of adrenaline ampoules in case CPR becomes a part of the rapid sequence induction.
• An end-tidal CO2 monitor should be within reach
• The equipment should be checked, and its operability ensured (i.e. those CMAC batteries better be charged).

Preparation of the patient

• Explain to the patient what the plan is (if they are conscious and capable of processing this information, it would be helpful to have them on your side).
• Commence high flow oxygen
• Preoxygenate for a minimum of 3 minutes. 
• During this time, either position the patient for intubation, or (if they cannot tolerate that position) prepare equipment and assistants to put them into that position as soon as the induction is commenced.

Algorithms for anticipated difficult intubation

LITFL has an excellent Difficult Airway Algorithm page, full of algorithms. Of these, several are applicable to the anticipated difficult airway - i.e 7% of them, the one predicted to be difficult (that turns out to be totally easy in 75% of cases).

Strayer difficult airway algorithm (anticipated difficulty)

• Decide early, whether you wil go ahead with awake fiberoptic intubation or with laryngoscopy (decision will be based on patient cooperation and aspiration risk)
• Unsuccessful laryngoscopy attempts are repeated, with the following changes for each attempt:
  • Change equipment (eg. get a different blade)
  • Change operator (get a more experienced person)
  • Change patient position (eg. elevate the head/shoulders)
  • Change modality (eg. try videolaryngoscopy)
• Those attempts can be repeated only while you are able to ventilate. This is very similar to the “just keep having a go at it” suggestion from ASA.
• If you aren’t able to ventilate, you need to insert an LMA and try to ventilate that way.
• If you aren’t able to ventilate with LMA, it’s a CICO and you need to cut the throat.
• If LMA ventilation is successful, the algorithm is somewhat unclear. Reuben Strayer’s 2010 lecture on this topic seems to suggest that the LMA is really just a temporary option. With the LMA in situ,  you make a decision whether to  wake the patient up, or to proceed with cricothyroidotomy. For some reason, the use of an intubating LMA or similar device is not considered in this approach.
• The difference of the Strayer approach from the 2008 Wall et al approach is the focus on the use of early effective ventilation, and the reassurance that a lifesaving cricothyroidotomy should be performed before the patient is actually dead of hypoxia.

ACMEAM (Wall and Murphy, 2008) algorithm

• The Manual of Emergency Airway management separates the algorithm into several. There is an Emergency Airway Algorithm, a Crash Airway Algorithm, a Difficult Airway Algorithm and a Failed Airway Algorithm.
•  Essentially, all of them have three major stages.
• First, direct laryngoscopy is attempted (perhaps even a few times) while oxygenation can be maintained.
• If oxygenation can be maintained and there is still no success with intubation, the operator is invited to select among a host of options, which include fiberoptic intubation, videolaryngoscopy, or the use of a lighted stylet.
• If oxygenation is impossible, a cricothyroidotomy needs to be  performed.
• This is a reasonable algorithm (or series of algorithms), and it resembles the others insofar as a failure of bag-mask ventilation and LMA oxygenation is treated as an indication for cricothyroidotomy. If the LMA fails to produce an effect, the operator is not invited to pull it out and try the face mask again (as the ASA seem to do) – sensibly, Walls et al advise you to go straight for the throat.

CICM (Lim et al, 2003) algorithm

• Our own college published this thing in Critical Care and Resuscitation
• It hinges on the suggestion that the first attempt should be a “best laryngoscopy” attempt, involving several simultaneous adjustments to the technique, including:
  • Longer laryngoscope blade
  • BURP
  • A bougie
  • Using a smaller ETT
• If this fails, and an “alternate airway device” is ineffective, a needle cricothyroidotomy is used to oxygenate the patient while other techniques are being organised.
• The college offers “alternative intubating technique” as the solution, without being particularly specific about what that means. This is suggested alongside percutaneous and surgical tracheostomy as the solution to a failed intubation with a rapidly decreasing oxygen saturation in spite of a needle in the cricothyroid membrane. The casual onlooker may suggest that this needle might now be used to introduce a guidewire of a Melker emergency cricothyrotomy kit, so that the already established hole may be dilated and converted into a 5-6mm cricothyroid airway. Though the Griggs tracheostomy technique can apparently be performed in around 30 seconds, the only operators who can confidently do this seem to be the people who developed this technique.
• Another  criticism of this approach is the redundant commentary about “best intubation”, as it implies that the intubation has failed because the first attempt was somehow haphazard and “not best”. Sure, it was probably a crap attempt, but a failed intubation algorithm should not imply that the same operator can court triumph by simply upping their game.  Your first attempt is usually your best attempt.

Besta algorithm (Caldiroli et al, 2011)

• This algorithm relies on using the El-Ganzouri multivariate preoperative risk index to identify patients at risk of having a difficult intubation
• The patients who score high (over 7) should undergo awake fiberoptic intubation, whereas the others in this study were intubated using a commercially available videolaryngoscope.
• The safety of this technique is admirable, but it has no place in the ED or ICU. It is another one of the algorithms which lead to the patient waking up and being sent home from their elective list.

“Own Approach”

• Prior to the attempt, try to dodge the airway catastrophe:
  • Can I confidently perform an emergency cricothyroidotomy on this patient? If not, then it may be safer to move this show to the operating theatre.
  • Is there an immediate need for intubation here? If the situation does not call for an immediate definitive airway, organise for an urgent awake fiberoptic intubation instead.
• First attempt is the best attempt. Therefore, make all possible optimising adjustments before this attempt.
• Maximise periprocedural oxygenation by using apnoeic oxygenation via nasal cannula (15L/min)
• Approach with videolaryngoscopy as the first attempt. This approach embraces the Zaouter et al (2015) conclusion, that “videolaryngoscopes should replace direct laryngoscopes as smart phones have replaced standard cell phones; they should be used for all intubations”.
• Use the bougie pre-emptively loaded with an appropriately sized tube, or (if using an unusually shaped videolaryngoscope blade) a stylet bent into a D-shape
• If videolaryngoscopy has failed, go back to bag-mask ventilation (if you can do it) or progress to LMA (if they have a massive messiah-like beard).
• If the LMA has bought you some time to think, reoxygenate the patient and decide whether you need ENT to come and do a tracheostomy, or whether you can do your own, or whether more attempts to intubate are appropriate. This decision will depend on what went wrong during the intubation.
• If the LMA has not had the desired effect, go ahead with the cricothyroidotomy.

Additional considerations for COVID

Question 19 from the first paper of 2022 gave the candidates a patient with (probable) COVID pneumonitis who needed to be urgently intubated for respiratory failure, and who had history of ankylosing spondylitis.  The best resource for this that probably crosses the most international boundaries is the NEJM video from 2021 by Shrestha et al. To narrow things even more, for COVID patients with difficult airways, this 2021 set of guidelines from the Society of Airway Management spells out all the issues that need to be considered. One can probably split these considerations into "what's different in COVID intubation" and "whats also different when the COVID patient has a difficult airway". 

• Additional infection control measures
  • Move the patient into a single-bed negative pressure room
  • Minimise staff in the room (four should be enough), bring only essential equipment
  • Keep a runner outside the room to fetch equipment
  • PPE for all staff (N95, hat, goggles, face shield, gloves, gown)
  • No bag-valve-mask ventilation after relaxant
  • And/or: viral filter on the BVM apparatus
  • Clamp ETT following intubation, unclamp when connected to the ventilator
• Differences in the management of the difficult airway
  • ​​​​​​​Well-sealed face mask with viral filter and EtCO₂ module is recommended for preoxygenation. Preoxygenation on NIV and apnoeic oxygenation with HFNP is an alternative, but thought to be the inferior option and is not routinely recommended, considering especially the risk of generating aerosols
  • Awake fibreoptic intubation would be the ideal gold standard for the difficult airway, but is a highly aerosol-generating procedure, and should be avoided if possible in COVID patients. Videolaryngoscopy is preferred. For patients with fixed neck deformities like that ank spond patient from Question 19  would benefit from a "hyperangulated" blade, like a CMAC "D" blade.
  • The videolaryngoscope should ideally have a detached screen, allowing the operator to put some distance between their own face and the patient's mouth
  • For a rescue procedure in a CICO situation, the scalpel-bougie-tube technique is recommended mainly because it is very quick and has a high rate of success in the non-COVID population, benefits which the SAM expected to translate.