Management of the Difficult Airway
supraglottic airway device (SAD) placement and ventilation
emergency surgical airway (including cannula cricothyroidotomy and surgical techniques).
CICV is an abbreviation for ‘Can’t intubate, can’t ventilate’.
BEFORE MANAGING THE DIFFICULT AIRWAY
The key to safe management of the difficult airway is preparedness.
Organizational Preparedness
Guidelines: Organizational preparedness requires that those events which might reasonably be anticipated to occur can be managed appropriately in the organization. This in turn requires guidelines (or policies) and equipment. As a minimum, the guidelines should cover the following:
management of unanticipated difficult tracheal intubation
management of unanticipated CICV
triggers and mechanisms for getting assistance when airway difficulty is anticipated or unexpectedly encountered
information to provide to a patient after a difficult airway event.
Equipment: Logic dictates that the equipment needed to satisfy institutional preparedness is that which is needed for all the guidelines to be carried out in their entirety. This equipment should be procured, stored, maintained and checked appropriately to ensure that it is readily available whenever and wherever it is required. Difficult airway equipment (perhaps better described as advanced airway equipment) is usually maintained in an airway trolley (Fig. 22.1). It is advisable for all airway trolleys in an organization to have the same content and layout; this includes areas such as ICU and the emergency department. Organizing the airway trolley so that the layout of the equipment matches the flow of the airway guideline may improve compliance with the guideline and patient care; an example based on the DAS guideline is shown in Figure 22.2.
Communication and Training: The final aspect of institutional preparedness is communication and training. Guidelines are of limited value if they are not understood, accepted and practised by the relevant staff. Many hospitals have access to training in advanced airway management. Guidelines should be distributed widely. Training should involve the use of local guidelines and locally available equipment to ensure relevance. Where possible, those individuals who work together in teams should be trained together so that the chances of the team working well in an emergency are enhanced. The ‘team’ need not be limited to the anaesthetist and anaesthetic assistant, and some training (rather like a trauma team) allocates specific roles to surgeons, scrub nurses and other anaesthetists who attend to help in a crisis. While there is no evidence that such an approach improves outcome in real airway emergencies, it probably enables an organized, systematic approach and has the value of enabling a ‘team leader’ to oversee the management of the crisis, perhaps avoiding ‘task fixation’ and promoting ‘situation awareness’.
Personal Preparedness
Assessment and Planning a Strategy: While it is accepted that not all cases of airway difficulty can be anticipated (perhaps 50% are unanticipated), many can be. Airway assessment is discussed in detail in Chapter 21. Only principles are discussed here.
obesity (BMI > 30 kg m− 2) and morbid obesity (BMI > 40 kg m− 2).
previous radiotherapy to the neck/floor of mouth
high risk of aspiration (this will severely restrict many options).
MANAGEMENT OF THE DIFFICULT AIRWAY
Before Approaching the Difficult Airway
Will delivery of oxygen be difficult?
Will face-mask ventilation be difficult?
Will SAD placement be difficult?
Will tracheal intubation be difficult?
Will direct access to the trachea be difficult?
Will there be problems with patient consent or co-operation?
Consider the relative merits of:
securing the airway with the patient awake or anaesthetized
making the initial approach to tracheal intubation direct or indirect
maintaining spontaneous ventilation or ablating it during airway management.
Securing the Airway Awake
awake fibreoptic intubation via oral or nasal routes
topical anaesthesia of the oral route followed by:
awake direct laryngoscopy (standard laryngoscope)
awake indirect laryngoscopy (rigid fibreoptic laryngoscope/videolaryngoscope)
awake intubation via an intubating LMA
Administration of Muscle Relaxants in the Patient with a Difficult Airway
The subject remains controversial but can be summarized as follows:
neuromuscular blockade often makes difficult mask ventilation easier
this is not universal and is uncertain in anatomically abnormal patients
administration of a neuromuscular blocker removes the possibility of waking the patient
if neuromuscular blockade is used to manage difficult mask ventilation, the anaesthetist must be adequately prepared to secure the airway, including managing a CICV situation
even if it was not part of the initial airway management strategy, if CICV occurs and waking the patient is not an option, a muscle relaxant should be given before determining the need to proceed to a surgical airway.
Selecting an Appropriate Size of Tracheal Tube
passes though some narrow lumens which a larger tracheal tube will not passlarger tracheal tube will not pass
passes through a narrow lumen with greater ease and with less risk of trauma to the airway
is easier to ‘railroad’ over a bougie or exchange catheter with less risk of ‘hold-up’ during insertion.
DIFFICULT AIRWAYS AND THEIR MANAGEMENT
The first guidelines were published in 1993 by the ASA. The introduction of guidelines in the USA has been demonstrated to have led to a reduction in death and brain damage claims (and therefore probably critical incidents) related to airway management, most notably at the time of induction of anaesthesia. Many European countries developed their own guidelines in subsequent years. While all these claim to be evidence-based, the paucity of robust evidence means that most guidelines differ significantly from each other, often reflecting local preferences. The UK guidelines were published by the Difficult Airway Society in 2004. The major differences between the guidelines published by the ASA and DAS are summarized in Table 22.1. Both emphasize the most important principles in airway management:
TABLE 22.1
Comparison between the American Society of Anesthesiologists’ and Difficult Airway Society’s Guidelines Dealing with Management of the Difficult Airway
ASA Guidelines 2012 | DAS Guidelines 2004 | |
Breadth of ‘difficult airway’ management covered | A clinical situation in which a conventionally trained anesthesiologist experiences difficulty with face mask ventilation of the upper airway, difficulty with tracheal intubation or both | A Cormack and Lehane grade 3 or 4 view despite optimal direct laryngoscopy, using an alternative laryngoscope and external laryngeal manipulation |
Evaluation of the airway | 11 non-reassuring findings | Not covered |
Number of attempts at laryngoscopy allowed before moving to a different technique | > 3, multiple attempts | Up to 4 during routine intubation and 3 during RSI. A further single attempt if a more experienced anaesthetist arrives. |
Techniques recommended for difficult intubation | Multiple including AFOI, blind, retrograde, LMA used as conduit and invasive airway access | Optimal laryngoscopy with gum elastic bougie (Plan A), then LMA/ILMA as conduit using fibreoptic control (Plan B)* then invasive airway access (Plan D) |
Order of techniques | None given | Clear flow chart |
Recommendations for extubation | Yes | Published separately (2012) |
Recommendations on training | None given | Should form part of all anaesthetist training |
to have devised a plan for airway management in the eventuality of it proving difficult, and a backup plan(s) which has been prepared for and practised
priority must be given to ensuring oxygenation and preventing iatrogenic trauma to the airway at all times.
The ASA guidelines cover airway assessment and a number of different difficult airway situations. They offer the user a wide choice of options at each point of airway difficulty. They recommend multiple different techniques and it is likely that not all will be within the competence of all anaesthetists. They offer ‘choices’. In contrast, the DAS guidelines are didactic and present a single recommended pathway arranged in plans A to D and differentiating between the patient undergoing routine intubation or rapid sequence induction. They do not prescribe any advanced techniques but recommend simple procedures using equipment that should be familiar to all anaesthetists in training. They also strongly emphasize the need for regular practice of the recommended techniques using simulators and manikins where appropriate. The DAS guidelines are shown in Figures 22.3–22.5.
FIGURE 22.3 Difficult Airway Society guideline for unanticipated difficult tracheal intubation during routine induction of anaesthesia in an adult patient. (Adapted from Henderson JJ, Popat MT, Latto IP, Pearce AC. Difficult Airway Society guidelines for management of the unanticipated difficult intubation. Anaesthesia 2004; 59:675–964, with permission from Blackwell Publishing Ltd. LMA, laryngeal mask airway; ILMA, intubating laryngeal mask airway.)
FIGURE 22.4 Difficult Airway Society guideline for unanticipated difficult tracheal intubation during rapid sequence induction of anaesthesia in a non-obstetric adult patient. (Adapted from Henderson JJ, Popat MT, Latto IP, Pearce AC. Difficult Airway Society guidelines for management of the unanticipated difficult intubation. Anaesthesia 2004; 59:675–694, with permission from Blackwell Publishing Ltd.)
FIGURE 22.5 Difficult Airway Society guideline for management of failed intubation, increasing hypoxaemia and difficult ventilation in the paralysed, anaesthetized patient, with rescue techniques for the ‘can’t intubate, can’t ventilate’ situation. (Adapted from Henderson JJ, Popat MT, Latto IP, Pearce AC. Difficult Airway Society guidelines for management of the unanticipated difficult intubation. Anaesthesia 2004; 59:675–694, with permission from Blackwell Publishing Ltd.)
Difficult Mask Ventilation
The first problem encountered in any difficult airway situation is often difficulty with face-mask ventilation. This is a vital step because it represents the basic and least invasive way of ensuring oxygenation of the patient. For mask ventilation to occur, a clear, sealed and patent airway from face mask to the lower airway is required. Difficulty can be diagnosed when there is inadequate chest movement despite high airway pressures (in the case of obstruction) or very low airway pressures (due to a leak during inspiration). Capnography and spirometry, both of which are available on most modern anaesthetic machines, can also identify poor ventilation before hypoxaemia occurs (Fig. 22.6).
FIGURE 22.6 (A) A normal capnograph trace. (B) A flow-volume loop from a patient with an unobstructed airway.
Difficulties with Mask Ventilation can be due to:
failure to maintain a patent upper airway (by far the most common problem)
laryngeal obstruction (either spasm or pathology)
obstruction below the larynx, in the trachea, bronchi or in patients with reduced pulmonary compliance.
Face-mask ventilation requires the combination of: establishing a seal between the mask and the face; maintaining a clear upper airway; and ventilation of the lungs. Flexion of the lower cervical spine, extension of the upper cervical spine and mandibular protrusion are required, ideally with good quality facial soft tissues to enable an adequate seal with the mask. Using a ‘C-grip’, the thumb and first finger are used to hold the mask pushing downwards while the remaining three fingers pull the chin, jaw and soft tissues into the mask while also maintaining head and neck positions (Fig 22.7). Manual ventilation is performed with the anaesthetist’s other hand. Problems with the upper airway can often be predicted by prior airway assessment. Patients for whom obtaining an adequate mask seal is often problematic include the edentulous elderly, bearded patients and those who require high ventilation pressures, such as the morbidly obese.
FIGURE 22.7 Mask ventilation with one person. Note the C-grip of the fingers over the mask and the three fingers supporting the airway.
insertion of an appropriately sized oropharyngeal airway
consideration of a nasopharyngeal airway
a two-person technique (Fig. 22.8)
a three-person technique (Fig 22.9).
MANAGEMENT OF UNPREDICTED DIFFICULT INTUBATION
Every anaesthetist should have a strategy prepared for dealing with problems with intubation, including plans for the more serious situation of CICV. The DAS algorithm is a suitable approach and is shown in Figures 22.3–22.5. This, or another equally valid strategy, should be familiar to all anaesthetists who are practising without direct supervision.
Plan A: Primary Intubation Attempt
There is no necessity to use the same laryngoscope blade for all attempts at intubation. Alternative blades include a long (size 4) Macintosh blade, the McCoy (levering laryngoscope) blade and a number of straight-bladed laryngoscopes (e.g. Miller, Henderson). Arguably, at least one attempt should be with a McCoy blade (Fig. 22.10) because it is recognized to move the fulcrum of the force applied to the airway distally and to improve the view when laryngoscopy is awkward. Use of a straight blade may offer the benefit of using an alternative approach to the laryngoscopy, such as a retromolar approach (Fig. 22.11), and this may be helpful, particularly if there is a small mandibular space.
Plan B: Secondary Intubation Attempt
Intubation Via a SAD: The cLMA is recommended because it is a device with which all anaesthetists are familiar. The cLMA does have several important limitations for such a use.
The tube lumen is relatively narrow. To intubate through a size 3 cLMA requires a tracheal tube of maximum internal diameter of 6 mm (size 4, 6.5 mm; size 5, 7.0 mm).
The LMA aperture bars can obstruct the passage of the tube.