Predicting a Difficult Airway

Written on 10/10/2024
jombuatapp

There are multiple tools and mnemonics that can be used to evaluate the potential for a difficult airway before intubation.

  • LEMON: Predicts overall intubation difficulty.
  • MOANS: Predicts difficult BVM ventilation.
  • ROMAN: Predicts difficult laryngoscopy.
  • RODS: Predicts difficult supraglottic airway (SGA) placement.
  • SMART: Predicts difficult cricothyrotomy.

 

LEMON

The LEMON mnemonic is a widely used method to assess airway difficulty. It stands for:

 

LOOK externally:

Assess for physical features that may predict difficulty.

  • Facial trauma
  • Large tongue or short neck  
  • Beard or mustache  
  • Obesity    
  • Neck masses or radiation changes    
  • Dentures, loose or large teeth    

 

 EVALUATE: 3-3-2 Rule:

  • Mouth opening: At least 3 fingerbreadths between upper and lower teeth.
  • Thyromental distance: At least 3 fingerbreadths between the chin and the hyoid bone (mentum to thyroid notch).    
  • Neck mobility: At least 2 fingerbreadths between the floor of the mouth and the top of the thyroid cartilage.

 

MALLAMPATI score: Assess the visibility of structures in the oropharynx.  

  • Class I: Full view of soft palate, uvula, tonsillar pillars (easy).  
  • Class II: Soft palate and part of uvula visible.    
  • Class III: Soft palate only, base of the uvula (moderate difficulty).    
  • Class IV: Only hard palate visible (high likelihood of difficult intubation).

 

OBSTRUCTION: Identify potential obstructions.    

  • Upper airway tumors or masses    
  • Infections (e.g., epiglottitis, abscess)  
  • Foreign bodies    
  • Anaphylaxis or swelling (angioedema)

 

NECK MOBILITY: Assess range of motion.    

  • Restricted neck extension or flexion:
    • ​Trauma, arthritis, or congenital issues
    • May predict difficulty in aligning airway axes for intubation.

 

 

2. Predicting a Difficult Bag-Valve-Mask (BVM) Ventilation

The MOANS mnemonic helps assess difficulty in BVM ventilation:

 

MASK SEAL: Assess for factors that may hinder mask seal.    

  • Facial hair    
  • Obesity    
  • Edentulous (lack of teeth)

 

OBESITY / OBSTRUCTION:

  • Obese patients or those with airway obstruction may have difficulty with BVM due to increased tissue or airway resistance.

 

AGE:

  • Patients >55 years old often have reduced tissue elasticity, making mask ventilation more difficult.

 

NO TEETH:

  • Edentulous patients (missing teeth) may require adjustments to the mask to achieve a proper seal (consider using gauze to fill spaces or applying tegaderm).

 

SNORES / STIFF:

  • Snoring or stiff lungs can indicate obstructive sleep apnea or reduced lung compliance (e.g., pulmonary edema, ARDS).

 

 

3. Predicting a Difficult Laryngoscopy

The ROMAN mnemonic assesses factors predicting difficult laryngoscopy:

 

RADIATION:

  • History of radiation therapy to the neck or face can lead to fibrosis and difficulty in airway visualization.​

 

OBESITY / OBSTRUCTION:

  • Obesity or anatomic airway obstructions can hinder laryngoscope placement and visualization of the vocal cords.

 

MALLAMPATI SCORE:

  • Higher classes (III and IV) predict a more difficult airway.

 

AGE:

  • Older patients may have decreased neck mobility, increased tissue stiffness, and comorbidities that make intubation more challenging.​

 

NECK MOBILITY:

  • Reduced neck mobility from trauma, arthritis, or cervical spine precautions can make it difficult to align the airway axes during intubation.​

 

 

4. Predicting a Difficult Supraglottic Airway (SGA) Placement

The RODS mnemonic helps in predicting difficulty with supraglottic airway (SGA) placement:

 

RESTRICTED MOUTH OPENING:

  • Limited ability to open the mouth can make SGA insertion difficult.​

 

OBSTRUCTION:

  • Upper airway obstruction (e.g., tumors, epiglottitis, foreign bodies) may prevent SGA use.​

 

DISTORTED AIRWAY:

  • Abnormal anatomy due to trauma, tumors, or surgical scars can complicate SGA placement.​

 

STIFF LUNGS (or cervical spine):

  • Conditions that reduce lung compliance (e.g., pulmonary fibrosis, ARDS) or neck immobility can limit the efficacy of an SGA.

 

 

5. Predicting a Difficult Cricothyrotomy

The SMART mnemonic assesses the likelihood of a difficult cricothyrotomy:

 

SURGERY:

  • Previous neck surgery can alter anatomy and cause scarring, making identification of landmarks difficult.

 

MASS:

  •    Neck masses or tumors may obscure landmarks and limit space for cricothyrotomy

 

ACCESS / ANATOMY:

  • Obesity, trauma, or congenital abnormalities may hinder access to the cricothyroid membrane.

 

RADIATION:

  • Prior radiation therapy can cause fibrosis, altering neck landmarks and making dissection more difficult.

 

TRAUMA:

  • Severe neck trauma may distort anatomy and lead to bleeding, complicating cricothyrotomy.

 

 

6. Recognizing a Difficult Airway During Intubation

Even with a thorough assessment, airway difficulty may still be encountered unexpectedly during intubation. Some key signs of a difficult airway include:

 

A. Poor view on laryngoscopy:

  • Failure to visualize the glottis (Cormack-Lehane Grade III or IV views).

 

B. Multiple failed intubation attempts:

  • More than two attempts without success can increase the risk of trauma and hypoxia

 

C. Difficulty advancing the endotracheal tube:

  • Resistance or difficulty navigating the tube past the vocal cords may indicate anatomic variations.

 

D. Inability to ventilate via BVM:

  • If you are unable to ventilate adequately, consider calling for help and moving to alternate airway strategies (e.g., SGA, cricothyrotomy).

 

 

7. Planning for a Predicted Difficult Airway

If a difficult airway is predicted, it is important to prepare:

        

i. Optimize preoxygenation:

  • Ensure adequate preoxygenation to prolong the safe apneic window during intubation (use NODESAT, high-flow oxygen, or BVM with PEEP if necessary).

 

ii. Call for help early:

  • If available, ensure airway experts (e.g., anesthesiologist, intensivist) or a backup team is present.

 

iii.  Prepare for difficult airway algorithms:

  • Have equipment for alternate intubation strategies (e.g., video laryngoscopy, bougie, SGA) ready at the bedside.

 

iv. Consider awake intubation:

  • For patients with high-risk airways, an awake intubation using topical anesthesia and minimal sedation may allow better airway control.

 

v. Prepare for a cricothyrotomy:

  • Always have cricothyrotomy equipment ready in the event of a can't intubate, can't oxygenate (CICO) scenario.