Overview
Definition:
Airway assessment is the systematic evaluation of a patient's airway to predict the likelihood of a difficult tracheal intubation or airway management
Difficult airway refers to 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
This can lead to severe consequences including hypoxemia, brain injury, and death.
Epidemiology:
Difficult laryngoscopy occurs in approximately 5-10% of patients, with difficult intubation occurring in 1-2% of patients
Complete airway obstruction leading to failed intubation and failed ventilation (Cannot Intubate, Cannot Oxygenate - CICO) is rare, occurring in approximately 1 in 2000 to 1 in 10,000 anesthetics
Risk factors are varied and can be anatomical, physiological, or related to pathology.
Clinical Significance:
Effective airway assessment and preparedness for difficult airway management are paramount for patient safety in all surgical specialties
Failure to anticipate and manage a difficult airway is a leading cause of anesthesia-related morbidity and mortality
Surgeons, particularly those involved in head and neck procedures or emergency surgery, must be proficient in these principles.
Diagnostic Approach
History Taking:
Obtain a focused history
Ask about previous intubation difficulties, snoring, obstructive sleep apnea (OSA), rheumatoid arthritis, ankylosing spondylitis, diabetes mellitus, mucopolysaccharidoses, acromegaly, head and neck surgery or radiation, cervical spine injury or surgery, obesity (BMI > 30 kg/m²), and presence of a beard or limited jaw opening
Red flags include a history of radiotherapy to the neck, known difficult airway, or conditions affecting neck mobility.
Physical Examination:
Perform a systematic head-to-neck examination
Assess for: 1
Mouth opening (inter-incisor distance < 3 fingerbreadths)
2
Mallampati classification (Class III or IV)
3
Thyromental distance (TMD) ( < 6 cm or < 3 fingerbreadths)
4
Neck mobility (flexion/extension, < 80 degrees extension)
5
Jaw protrusion (Class III mandible)
6
Dentition (prominent upper incisors, loose teeth)
7
Presence of beard, obesity, or large tongue
The Upper Lip Bite Test (ULBT) is also useful for predicting difficult laryngoscopy.
Investigations:
Routine investigations are typically not specific for airway assessment
However, in suspected obstructive sleep apnea, polysomnography may be indicated
Imaging such as CT or MRI of the airway may be useful in selected cases with suspected anatomical abnormalities, tumor, or trauma
Fiberoptic bronchoscopy can be used for direct visualization in awake patients with suspected severe airway compromise.
Differential Diagnosis:
While direct airway assessment aims to identify difficult intubation, conditions mimicking a difficult airway can include vocal cord paralysis, laryngospasm, foreign body aspiration, anaphylaxis, severe pharyngeal or laryngeal edema, and airway tumors
These require prompt recognition and management distinct from routine difficult airway algorithms.
Difficult Airway Algorithms
Initial Assessment And Planning:
The cornerstone of difficult airway management is pre-operative assessment and planning
Based on the assessment, classify the airway as predicted easy, predicted difficult, or unknown
Develop a primary strategy (e.g., direct laryngoscopy) and backup strategies
Ensure appropriate equipment is readily available, including multiple laryngoscope blades, endotracheal tubes (ETTs) of various sizes, bougie, supraglottic airway devices (SADs), fiberoptic equipment, and cricothyroidotomy kit
Assemble a skilled team and discuss the plan.
Predicted Difficult Airway Algorithm:
If a difficult airway is predicted, consider awake intubation techniques (e.g., awake fiberoptic intubation) as the primary strategy to maintain spontaneous ventilation
If asleep intubation is chosen, aggressive use of supraglottic airway devices (SADs) should be considered
If initial attempts at intubation fail, switch to a rescue technique, such as a SAD or video laryngoscope
Avoid repeated attempts at direct laryngoscopy
If mask ventilation is inadequate, proceed to CICO management.
Unanticipated Difficult Airway Algorithm:
If a difficult airway is unanticipated during induction: 1
Maintain patient positioning and administer oxygen
2
Attempt mask ventilation
If successful, proceed with caution, consider alternative airway devices (e.g., video laryngoscope, SAD)
3
If mask ventilation fails, call for help and activate the difficult airway cart
4
Attempt intubation with a video laryngoscope or bougie
5
If intubation attempts are unsuccessful and mask ventilation remains inadequate, proceed to a supraglottic airway device
6
If the patient cannot be intubated and cannot be oxygenated (CICO), perform emergency cricothyroidotomy.
Cannot Intubate Cannot Oxygenate Cico Management:
This is a critical emergency requiring immediate intervention
The primary goal is to establish an oxygenation pathway
Perform an emergency front-of-neck access (FONA) procedure, typically a surgical cricothyroidotomy
Cannulation of the cricothyroid membrane allows for ventilation and oxygenation
This should be performed rapidly by a skilled clinician after failure of all other airway management strategies
Transtracheal jet ventilation can be a temporizing measure.
Airway Devices And Techniques
Laryngoscopy And Intubation:
Direct laryngoscopy (DL) with Macintosh or Miller blades is the gold standard
Video laryngoscopy (VL) offers an indirect view of the glottis and is often superior in cases of difficult anatomy
A bougie can be used with either DL or VL to aid tracheal tube advancement
Multiple ETT sizes should be available.
Supraglottic Airway Devices Sads:
SADs, such as the Laryngeal Mask Airway (LMA), i-gel, and King LT, are inserted into the pharynx to create a seal around the larynx
They are highly effective for ventilation and can be used as a rescue device or as a primary airway in selected patients
They are generally easier to insert than ETTs, especially for less experienced operators.
Fiberoptic Intubation:
Awake fiberoptic intubation is the preferred technique for managing a predicted difficult airway, especially when glottic visualization is expected to be poor
It allows for intubation under topical anesthesia with the patient breathing spontaneously
Sedation should be judicious to maintain spontaneous respiration.
Surgical Airway Access:
Emergency cricothyroidotomy and less commonly, tracheostomy, provide direct surgical access to the trachea
Cricothyroidotomy is an emergency procedure for CICO situations
Tracheostomy is a planned procedure for long-term airway access, typically performed in the operating room.
Key Points
Exam Focus:
Understand the key predictors of difficult airway (Mallampati, TMD, neck mobility, mouth opening)
Memorize the flowcharts for predicted and unpredicted difficult airways
Know the indications and contraindications for SADs and fiberoptic intubation
Be familiar with the steps of emergency cricothyroidotomy.
Clinical Pearls:
Always have a difficult airway cart checked and ready
Have a low threshold for calling for help
Never underestimate a patient's airway potential
always have a backup plan
Consider patient positioning carefully
Awake intubation is safer in patients with a predicted difficult airway
Recognize the limitations of SADs (e.g., do not protect against aspiration).
Common Mistakes:
Repeated, unsuccessful attempts at laryngoscopy without reassessing and changing strategy
Failure to attempt mask ventilation after failed intubation
Delayed recognition of a CICO situation
Inadequate team communication
Not having backup equipment readily available
Insufficient topicalization during awake fiberoptic intubation.