Case Study: Pre-operative Airway Assessment Before ENT Surgery

Patient Presentation

Why Airway Assessment Is Especially Critical in ENT Surgery

Step 1: History - The First Layer of Airway Assessment

Key questions to ask:

Teaching point: Past anaesthetic records should always be reviewed. Patients may relay verbal or written warnings from a previous anaesthetist. Difficulty may also be inferred from a history of displaced front teeth, bruised lips, excessive post-operative sore throat, or an unexpected stay in ITU. (Scott-Brown's, Vol. 1)

Step 2: Physical Examination - The Bedside Battery

2a. Mouth Opening

• Measure the inter-incisor gap. A distance of ≥3 cm (approximately 3 fingerbreadths) is desirable in an adult.
• Less than 3 cm suggests difficult laryngoscope blade insertion.
• In Mr. Ahmed: reduced mouth opening is possible given prior neck radiotherapy causing progressive fibrosis/trismus.

2b. Mallampati Classification

Mallampati Classification - Classes I to IV. (Morgan & Mikhail's Clinical Anesthesiology, 7e, Fig. 19-5A)

• Class III or IV predicts a difficult intubation (Grade III/IV laryngoscopic view). (Morgan & Mikhail's)
• Note: Although the presence of these findings is not highly sensitive alone, the absence of all these findings is reassuring. Any patient's airway may prove surprisingly difficult despite a normal bedside assessment. (Morgan & Mikhail's)

2c. Thyromental Distance (TMD)

• Desirable: ≥3 fingerbreadths (approximately 6-8 cm).
• A short TMD reflects reduced neck mobility, retrognathia, and predicts difficult tongue displacement during laryngoscopy.
• In this patient with prior neck radiotherapy, TMD may be reduced.

2d. Neck Circumference

2e. Upper Lip Bite Test (ULBT)

• Class I: Lower incisors bite above the vermilion border of the upper lip - easy intubation likely
• Class II: Lower incisors bite below the vermilion border - moderately difficult
• Class III: Lower incisors cannot bite the upper lip at all - difficult intubation predicted

2f. Neck Mobility / Atlanto-occipital Extension

• Previous radiotherapy and diabetes both reduce this.
• Assess by asking the patient to maximally extend the neck and estimating the angle of excursion.

2g. Dentition

• Prominent central incisors obstruct the laryngoscopic view.
• Poor or restored dentition increases risk of dental trauma.
• Edentulous patients are harder to mask-ventilate. (Barash's Clinical Anesthesia, 9e)

Summary Physical Examination Table

Step 3: Imaging and Indirect Laryngoscopy

• CT scan of the neck/larynx: Defines the size, location, and degree of luminal narrowing caused by the mass. Reviews whether the mass is supraglottic, glottic, or subglottic, and whether there is tracheal deviation or subglottic extension.

  "Reviewing the results of a preoperative computed tomography (CT) scan or an indirect laryngoscopy in selected patients can be particularly helpful." (Miller's Anesthesia, 10e)

• Indirect/flexible laryngoscopy (nasendoscopy): Often performed by the ENT surgeon in clinic pre-operatively. Directly visualises the mass, vocal cord mobility, and the degree of supraglottic obstruction. This is arguably the most important single investigation before proceeding to intubation.
• Nasendoscopy findings in Mr. Ahmed: A 2 cm supraglottic mass on the right aryepiglottic fold with partial vocal cord fixation and approximately 50% reduction in glottic lumen on inspiration.

Step 4: Recognising Conditions with Heightened Risk

• History of failed or traumatic airway management
• History of head/neck surgery or radiation therapy ✓
• Supraglottic pathology: airway cyst or tumour ✓
• Stridor ✓
• Obstructive sleep apnoea ✓
• BMI >35 ✓
• Cervical spine disease or limited range of motion ✓
• Temporomandibular joint disease

Step 5: Anaesthetic Decision - Awake Intubation vs Intubation After Induction

1. The likelihood and clinical impact of basic management problems (difficult mask ventilation, difficult SGA placement, difficult laryngoscopy, difficult intubation, difficult surgical airway)
2. The feasibility of awake intubation vs intubation after induction of general anaesthesia
3. Non-invasive vs invasive techniques
4. Preservation vs ablation of spontaneous ventilation
5. Video-assisted laryngoscopy as an initial approach

"Awake intubation vs. intubation after induction of general anesthesia" is a core decision node in the ASA algorithm. (Morgan & Mikhail's, 7e)

In Mr. Ahmed's case:

• A supraglottic mass with stridor and partial vocal cord fixation means that induction of general anaesthesia may cause complete airway obstruction - loss of spontaneous ventilation removes the safety net.
• ATI with a flexible bronchoscope is well-tolerated, gentle on the airway, and does not require force to obtain glottic exposure. (Miller's Anesthesia, 10e)
• The patient can be topicalised and sedated with dexmedetomidine or low-dose remifentanil while maintaining spontaneous breathing.

"Endotracheal intubation in an awake patient (awake tracheal intubation [ATI]) with a flexible bronchoscope is commonly used when intubation following induction of general anesthesia is predicted to be difficult or impossible." (Miller's Anesthesia, 10e)

"When an airway disorder is so extensive that awake endotracheal intubation is too risky or impractical, tracheostomy performed using local anesthesia (with or without judicious intravenous sedation) is usually the best alternative." (Miller's Anesthesia, 10e)

Step 6: Planning for Equipment and Contingencies

Various specialty organisations produce algorithms that discourage repeated performance of the same failed technique to secure the airway. Rather, they suggest continually attempting new approaches and proceeding to front-of-neck airway access once a "can't intubate, can't oxygenate" event is recognised. (Morgan & Mikhail's, 7e)

ENT-Specific Tube Considerations (Miller's Anesthesia, 10e):

• A microlaryngeal tube (MLT) will be used - smaller diameter allows better surgical access to the larynx.
• If a laser is involved: a laser-safe ETT must be selected matched to the laser type; cuff can be filled with saline dyed with methylene blue to detect cuff leaks immediately.
• Wire-reinforced (armoured) tubes prevent kinking during head manipulation in ENT procedures.
• Cuff pressure must be kept <25 mm Hg to prevent ischaemic tracheal mucosal damage - especially important in long cases.
• If nitrous oxide is used, diffusion into the cuff will gradually increase cuff pressure and requires monitoring.

Communication with the Surgeon:

• Whether bronchoscopy is planned pre- or post-intubation
• How the tube will be secured during head manipulation
• Whether neuromuscular blocking drugs can be used (facial nerve monitoring during some ENT procedures precludes their extended use)
• Whether tracheostomy under LA needs to be planned as a primary strategy

Step 7: Special Considerations in This Case

Post-Radiotherapy Airway

• Restricted mouth opening (trismus)
• Reduced neck mobility
• Friable mucosa prone to bleeding and oedema
• Distorted anatomy with absent landmarks
• Reduced tissue compliance making mask ventilation difficult

Obesity and OSA

• Both predict difficult mask ventilation.
• Morbidly obese patients (BMI ≥35) may have redundant pharyngeal tissue and increased neck circumference.
• Not only may these patients prove difficult to intubate - routine bag-mask ventilation may also be problematic. (Morgan & Mikhail's, 7e)
• Pre-oxygenation in the 20-30° head-up (ramped) position significantly extends safe apnoea time.

Stridor

• Inhaled foreign bodies
• Bilateral vocal cord palsy
• Airway oedema / angioedema
• Epiglottitis
• Subglottic stenosis
• Airway tumours (as in this patient)

"Regardless of the aetiology, the initial assessment should focus on whether endotracheal intubation or a surgical approach to the airway is immediately necessary to rescue the patient from death or injury." (Miller's Anesthesia, 10e)

For patients with stridor but satisfactory gas exchange, a helium:oxygen (heliox) blend via non-rebreathing mask or high-flow nasal oxygen can improve airflow temporarily while assessing and managing the cause. (Miller's Anesthesia, 10e)

Step 8: Documentation and Handover

• Document the difficulty encountered in the medical record and add it to the problem list.
• Use a structured tool such as the Intubation Difficulty Scale (IDS) (Adnet et al.) which scores: number of supplementary attempts, additional operators, alternative techniques used, laryngoscopic grade, subjective lifting force, use of external laryngeal manipulation, and vocal cord characteristics. (Miller's Anesthesia, 10e)
• Provide the patient with a written difficult airway alert card.
• Ensure the anaesthetic record flags this for any future procedures.

Summary: The LEMON Mnemonic for Pre-operative Airway Screening in ENT

Key Learning Points

1. ENT surgery carries the highest rates of difficult intubation of any surgical specialty - up to 12.3% in ENT cancer cases vs 2% in general surgery. Never underestimate the head and neck airway. (Scott-Brown's Otorhinolaryngology)
2. Pre-operative assessment must be multi-layered: history (prior anaesthetic records, XRT, current pathology) + physical exam (LEMON/bedside tools) + indirect laryngoscopy + imaging review.
3. Mallampati alone is insufficient - it is one component of a multivariable risk index. No single test is sensitive enough to exclude a difficult airway.
4. Stridor and supraglottic pathology demand awake intubation - inducing general anaesthesia before securing the airway in a patient with partial glottic obstruction risks total airway loss.
5. Always plan four steps ahead: Plan A (preferred technique), Plan B (alternative non-invasive), Plan C (SGA bridge), Plan D (front-of-neck access). Never repeat a failed technique without escalating.
6. Communication between anaesthetist and ENT surgeon is essential before the case, not during a crisis.
7. Document every difficult airway and alert the patient - the next anaesthetist will thank you.