A difficult airway is an airway in which oxygenation and ventilation cannot be achieved in a desired manner within a desired amount of time.

In terms of Bag-valve Mask ventilation. A difficult airway is defined as one in which a proper seal cannot be achieved and/or a desired O2 saturation cannot be maintained.

In intubation a difficult airway is one in which it is not possible to visualize the cords with conventional laryngoscopy or proper ET tube insertion takes more than 10 minutes/more than three attempts.

Our ability to rapidly identify a patient who may have a difficult airway allows us to formulate a plan of action before we attempt airway management.
This allows us to better prepare for the unknown and can reduce the amount of time it takes to achieve effective airway management.
Airway prediction is currently an inexact science and there is no method that is both highly sensitive and highly specific.

In spite of this fact, airway assessment is STILL a valuable practice and can help us anticipate and appropriately plan for unforeseen difficulties.

When using a Bag-Valve-Mask to ventilate a patient proper technique is paramount in achieving adequate ventilation.

That said there are several patient factors that can make this goal harder to accomplish.

When you need to BVM a patient be on the lookout for "B-O-N-E-S", these patient characteristics can help you predict a difficult BVM and help you adjust your management to achieve desired ventilation.

BONES-

B- Beard
O- Obese
N- No teeth
E- Elderly
S- Sleep Apnea/snoring

A beard can prevent you from achieving a proper seal with a BVM leading to inadequate oxygenation.

Potential solutions to this problem include-

1) Applying large amounts of lubricating jelly to the portion of the beard in contact with the BVM

2) Using a large occlusive dressing over the patient's face with a hole cut in it for their nose.

A BMI of >26 is a predictor of BVM difficulty.
The obese patient presents a problem for a number of reasons. It is difficult to find a mask that fits creating seal issues. It is also difficult to ventilate them even with a good seal due to their habitus (increased chest wall weights with reduced compliances, redundant supraglottic tissue etc.).

Ways to improve your BVM include-

1.Using the best fitting mask.

2. keep the patient in an upright sitting position.

3. Using a 2-3 person BVM technique with bilateral support of the jaw

A patient having no teeth or missing a large number of teeth causes difficulty due to missing supporting structures needed to properly seat and seal the mask.
It can also lead to a loss of vertical dimension causing the patient to over-close their mouth which can result in an airway that collapses more readily

Age >57 is a predictor of difficulty.

Older patients tend to be harder to BVM due to loss of connective tissue and bony structure on their face. Making a good seal more difficult to achieve.

Patients with a history of Sleep Apnea/Snoring can be difficult to BVM.
This history may be difficult to ascertain in an unresponsive/altered patient, but is always an important question to ask the awake and aware patient or family member.
A patient with these conditions is more likely to have a collapsing airway.

Intubation is an essential skill for every EM physician.
The TTI (Time to intubate) is a very important prognostic factor for patient morbidity and mortality.
Therefore it is essential that EM physicians not only learn the proper technique but also learn how to predict a difficult intubation. This will help reduce TTI and thus patient hypoventilation.

So when preparing to intubate always consider- 'L-E-M-O-N'.

L- Look
E- Evaluate (3-3-2 method)
M- Mallampati score
O- Obstruction/obesity
N- Neck Mobility

This is a quick external assessment of your patient.

There may be some physical clue, condition or foreign object that could result in a difficult intubation.

Evaluate using the 3:3:2 finger method.

3- Can you fit three fingers between the patient's incisors? If not this indicates poor temporomandibular joint mobility and is a sign of a potential difficult intubation

3- Is the distance between the patients Hyoid bone and mentum approximately three fingers? If this distance is longer OR shorter than 3 fingers it can make ventilation and intubation more challenging.

2- Is the distance between the Hyoid bone and the thyroid cartilage at least 2 fingers? This is an indicator of neck length and a distance

A mallampati score can really only be done in a cooperative alert patient as it requires them to open their mouth and stick out their tongue voluntarily so you can examine their airway.
However, if it can be performed it is useful to help predict a difficult intubation and will help determine what equipment should be used.

A higher Mallampati score is correlated with a higher degree of intubation difficulty.

Look inside the patients airway for any signs of objects or injuries that might get in your way and prevent a successful intubation. Evaluate for stridor and other signs of supraglottic and subglottic obstruction.
Some of the more common causes of obstruction are soft tissue swelling from smoke inhalation, broken necks, burns, tumor abscess, expanding hematomas, foreign bodies in the airway, and excessive supraglottic tissue in the obese patient.

Good neck mobility is desirable for intubation.
In the emergency setting it is very common for a patient to arrive in a neck brace due to c-spine injury/precaution or have limited neck mobility for other reasons (previous injury, arthritis).
This may prevent you from manipulating their head/neck into the optimal position for intubation, creating a degree of difficulty.

"...And Knowing is half the battle!!!" - G.I JOE (1983-86)

Using these two Mnemonics to quickly assess a patient when preparing to ventilate can allow you to predict and prepare for a difficult airway.

References-

https://www.acep.org/content.aspx?id=33992

http://www.ncems.org/pdf/AppIDifficultAirwayEvaluation.pdf

http://www.uptodate.com/contents/the-difficult-airway-in-adults?source=sear...

http://lifeinthefastlane.com/ccc/airway-assessment/

https://books.google.com/books?id=wISHCgAAQBAJ&pg=PA416&lpg=PA416&dq=why+ar...

http://gijoeclub.com