The Difficult Airway (EAM part 3)

Although the vast majority of emergency airways will go smoothly using the above technique of rapid sequence intubation, everyone, regardless of experience, is bound to have problems sometime. It is important to recognize which airways may give you problems before you begin down the road to a possibly failed airway attempt. It is important to choose the most appropriate technique for each particular airway situation before disaster occurs. I suggest that several simple questions be asked in every airway situation: If my intubation attempt does not succeed, will I be able to ventilate the patient with a bag-valve-mask? If I can not ventilate the patient with a BVM, what should be done next and what is my back up plan? Am I prepared to provide a surgical airway?

Some estimation of the degree of difficulty of an airway is made possible from the following observation and simple maneuvers.
Facial hair- facial hair (beards and moustache) in men make it difficult to form a tight seal with a mask. If you need to provide ventilation with a BVM, you will get an air leak which may prevent you from providing adequate ventilation. Simply smearing a water soluble lubricant (like K-Y jelly) on the beard may make bagging easier and more effective.
C-spine mobility- C- spine immobilization makes most airway management more difficult as the neck can not be extended to provide visualization of the cords on laryngoscopy. It also affects performance of the Sellick’s maneuver. Some cervical collars will have holes in the front to access the cricoid cartilage for either a cricothyrotomy or Sellick’s maneuver. In reality, these holes do not provide enough access to make a real difference. In the C-spine immobilized patient, it is often best to remove the collar and have a colleague hold in-line stabilization of the head and neck during intubation which makes intubation easier. It has been said in the past that blind nasotracheal intubation was the airway of choice in the C-spine immobilized patient. However, the complication rate is higher in blind intubation and the movement of the C-spine with blind nasotracheal intubation is as much or more than with in line traction. The success rate for blind nasotracheal intubation is 40-50% compared to nearly 99% with oral intubation combined with RSI. Another example where the C-spine interferes with intubation is in the patient with arthritis of the C-spine or ankylosing spondylitis of the C-spine. Not only will this interfere with extension of the neck but the C-spine can actually be fractured if extended.
Mouth opening- an adult with normal TMJ will be able to open the mouth to accommodate 3 or 4 fingers between the incisors. TMJ disease or rheumatoid arthritis may limit mouth opening and thus oropharyngeal and laryngeal visualization. Rheumatoid arthritis can affect the stability of the atlanto-axial joint causing subluxation and instability.
Physical characteristics- Patients with small mandibles or receding mandibles have tongues that will obstruct access to the airway during intubation. All children basically fall into this category as they all have tongues proportionately larger than their developing mandibles. A good rule of thumb is that if you can look into the mouth without a tongue blade and visualize the uvula, peritonsillar area and posterior pharynx easily, you should be able to visualize the larynx on intubation. If you struggle with visualization of the posterior aspects of the throat before intubation, you will struggle during the intubation. The length of the neck and the position of the larynx is important.
The larynx in the adult should be at the C5-6 level. A larynx that is higher will be difficult to visualize. Typically, there should be 2 fingerbreaths between the top of the thyroid cartilage and the base of the neck in the normal adult.
Teeth- All false teeth should be removed prior to intubation. Large upper incisors may obstruct visualization of the larynx because they elongate the AP axis of the mouth. Jagged teeth may lacerate balloons on the ET tubes. [If the patient can eat an apple through a picket fence - you are in for trouble.]
Oral dimensions- patients with narrow facial features and high arched palates may have difficult airways. Access will be limited because of reduced space side to side in the mouth.

Reference
Advanced Emergency Airway Management Walls RM, Luten RC, Murphy ME, Schneider, 1997