Airway Assessment & Plan
When making an airway plan, it is important to consider the following questions [23]:
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Is there a history of difficult intubation?
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Are there predictors of difficult intubation:
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Mallampati score >2
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Reduced neck mobility (<90 degrees maximal anterior plus posterior flexion)
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Thyromental distance <6cm
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Inter-incisor distance <3cm
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Reduced temporomandibular joint mobility
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Are there predictors of difficult mask ventilation (MOANS) [24]:
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Mask seal: Facial features such as beards, saliva or blood, anatomical disruptions such as facial fractures or retrognathia
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Obesity (BMI > 26), parturient or at-term mothers
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Age > 55 years
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No teeth (edentulous)
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Snoring or stiff: OSA, bronchospasm, neck radiation changes
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Will you be able to ventilate the patient using a supraglottic airway (RODS):
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Reduced mouth opening
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Obstruction at or below the level of the glottis
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Distorted airway
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Stiff neck or lungs (eg rheumatoid arthritis, asthma)
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What are the cardiorespiratory reserves?
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Will there be a safe apnoeic oxygenation period?
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Is there an aspiration risk?
mallampati grade 3-4 5
apnoea / osa suspected 2
cervical spine limited 1
open mouth limited <3cm 1
coma or agitation 1
hypoxaemia 1
non-anaesthetist/intensivist 1
The MACOCHA score has been validated to predict difficult intubation in the ICU setting [25]. This considers factors related to the patient, pathology and operator to determine when senior assistance should be recruited. A score of 3 or greater predicts difficult intubation with a sensitivity of 76% and negative predictive value of 97%.
The introduction of pre-intubation checklists was one of the strongest recommendations of the NAP4 audit. It serves as a final check, or “time out”, to ensure things such as suction and end-tidal CO2 have not been forgotten. The checklist consists of a number of challenge-response questions (“yes / no”) and should take less than 60 seconds to complete. An example of a pre-intubation checklist is presented below (with thanks to Dr Peter Garrett):
Rapid Sequence Induction
Rapid sequence induction and intubation (RSI) has been considered the gold standard in emergency airway management when there is a need to urgently secure an airway. The essential elements are rapid induction of anaesthesia and paralysis with the goal to achieve optimal intubating conditions and minimise aspiration risk as fast as possible.
There are multiple variations of the originally described RSI - sometimes termed “modified RSI” – and include substitution of sedative or paralysing agents, ventilation during the apnoea period or removal of cricoid pressure. This may be necessary depending on the circumstances of the critically ill patient, environment or resources [26]. Importantly, cumulative evidence now favours the use of mask ventilation during the apnoeic period. Not only does this prevent desaturation, but it also allows the operator to determine whether the patient is able to be mask ventilated should they encounter difficulty with inserting a definitive airway.
Common errors on embarking upon RSI are:
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Incomplete airway assessment
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Suboptimal preparation (i.e. equipment, positioning)
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Not having formulated an appropriate airway plan
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Insufficient pre-oxygenation
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Not anticipating hypotension and not having any fluid, inotrope and or vasopressors ready
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Not having EtCO2 ready to confirm placement of the ETT
The Physiologically Difficult Airway
Optimise before you Compromise
- Chris Nickson
The "difficult airway" has traditionally been used to describe anatomic challenges that may make visualisation of the vocal cords or passing a tube difficult, and is often the focus of a pre-intubation assessment. However, critically ill patients present additional challenges in the form of physiologic derangements which lead to rapid deterioration following induction. There are four clinically important physiologically difficult airways, with recommendations below on how to optimise the patient prior to induction.
Awake Intubation
An important option within an anaesthetist’s airway management armamentarium is awake intubation. It should be considered in patients who have known difficult supraglottic airways. It is a complex procedure and requires thorough topicalization, patient co-operation, and planning regarding failure. It should be conducted in a controlled operating room environment by an experienced operator. The key advantage is maintenance of upper airway tone, spontaneous ventilation and the ability to abandon the procedure.
Important considerations are:
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Preparation time and topicalisation - needs assessment and preparation by a senior and experienced clinician; it is very rarely done as an only option in a time pressured emergency
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Device selection - can be performed using either a slim fibreoptic bronchoscope or video laryngoscopy with a hyperangulated blade
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Patient selection is paramount - co-operation is essential
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Back-up planning – i.e. an ENT surgeon equipped to provide emergency front-of-neck access if required
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Contraindications - supraglottic obstruction (“cork in bottle” effect), patient refusal, operator inexperience, local anaesthetic allergy, airway bleeding
The 2020 Difficult Airway Society guidelines for awake tracheal intubation (ATI) in adults advocate the following technique [27]:
Extracorporeal Membrane Oxygenation
VV-ECMO is increasingly available throughout Australia. It should be considered in the event of an anticipated difficult airway and where there is appropriate cardiac anaesthesia, intensivist, and surgical support.
Principal indication is central airway obstruction which cannot be bypassed via oral or front-of-neck airway establishment. It is important to recognise that ECMO serves as a bridge to recovery, in the sense that an intervention to resolve the obstruction must be available prior to considering this modality.
Emergency Cricothyroidotomy
A CICO declaration is made when optimal attempts at all three non-surgical airway techniques have failed, and mandates progression to emergency front-of-neck access (FONA).
There are three methods for achieving trans-tracheal oxygenation:
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Cannula cricothyroidotomy
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Melker seldinger airway
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Surgical (scalpel-bougie-tube) cricothyroidotomy
You can watch each of these techniques demonstrated below. Please note, in the case of impalpable neck anatomy, a modified scalpel bougie technique should be used and can be viewed here.
Scalpel bougie technique in CICO emergencies | Airway Management
Needle Cricothroidotomy and Melker conversion in CICO emergencies | Airway Management
NAP4 audit provided commentary that, although cannula cricothyroidotomy was favoured by anaesthetists over surgical techniques, approximately 60% of attempts using this technique were unsuccessful. FONA attempts in an out-of-theatre environment (ED and ICU) were more likely to be surgical cricothyroidotomy and were more consistently successful. A simulation study in Western Australia also demonstrated that cannula cricothyroidotomy performed poorly when faced with difficult neck anatomy [29].
We advocate a surgical (scalpel-bougie-tube) cricothyroidotomy as the default FONA technique. This is consistently the fastest and most reliable method of securing the airway in the emergency setting and is endorsed by the DAS [30]. A vertical neck incision and digital blunt dissection should be used in case of difficult to palpate neck anatomy.
Principles of Safe Extubation
Extubation is an underappreciated period of airway related risk and one third of critical anaesthesia incidents occur during extubation and recovery [28].
Examples of ‘at-risk’ extubation scenarios include:
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Pre-existing airway factors - initial difficult airway, anatomical abnormalities, obesity, OSA
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Airway deterioration - distorted anatomy due to surgery, haematoma, oedema, trauma, local infection
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Restricted airway access - C-spine fixation, HALO, mandibular wiring
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General factors - limited ventilatory reserve, neuromuscular impairment, cardiovascular instability, fluid overload, acidosis
Extubation of patients in ED and ICU is performed with the patient awake - in OT, patients may have a “deep extubation” under anaesthesia, though this requires a specific skill set. Use of an extubation checklist helps to determine whether patients are low-risk, and may continue along a standard extubation pathway, or “at-risk” and need consideration for other techniques including laryngeal mask exchange, trans-tracheal catheters and airway exchange catheters, or even tracheostomy. Remember, extubation can always be deferred.
If a patient for extubation has been deemed “at-risk”, they may benefit from continuous airway access, which can be achieved with an airway exchange catheter (AEC) or a staged extubation kit. The AEC is inserted into the trachea through the ETT prior to extubation. The AEC is supplied with a 15mm or luer-lock connector for use with jet ventilation or oxygen tubing, however this approach is strongly discouraged due to risk of barotrauma and deaths attributed to the practice [31].
If the AEC is utilised for reintubation, an AIC may be used to stiffen the catheter and prevent snagging of the ETT on the corniculate or arytenoid cartilages [32].
Post-Extubation Stridor
Laryngeal oedema can cause airway obstruction following extubation in the at-risk patient, manifesting clinically as respiratory distress and inspiratory stridor – this may require reintubation in between 1-4% of all patients extubated in ICU.
Predictors of PES include:
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ETT factors – large ETT, high cuff pressures
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Airway – small airway, females, short neck, pre-existing airway pathology
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Trauma – airway injury or surgery, difficult intubation, reintubation, self-extubation, agitation
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Patient – older age, overweight
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Disease factors – prolonged intubation, higher illness severity score
The cuff leak test, developed by Miller and Cole in 1996, can assist in predicting PES by using a cuff leak volume cut-off of 110mL. A leak below this value predicts PES with 98% negative predictive value and 67% sensitivity [33]. It is important to consider confounders: a small ETT, low tidal volumes and high PEEP can alter the sensitivity and NPV of this test.
As a general rule, you can also employ the 10-20% rule. A leak of >20% (difference between inspiratory and expiratory tidal volumes) means it is highly unlikely the patient will develop PES, whilst a leak of 10-20% is indeterminate, and a leak <10% predicts PES.
Corticosteroids are beneficial in reducing PES in patients with a positive cuff leak test. Methylprednisolone 20mg 12 hours before extubation, repeated every 4 hours until extubation, reduces the risk of PES from 22% to 3%, and halves the reintubation rate [34].
