Popular tests for airway assessment

Different Tests for airway assessment to find difficult intubation

There are multiple tests for assessment of the airway preoperatively which are discussed below one by one with pictures.
Before we talk about the tests let me introduce a general term for flexion and extension of neck is called as sniffing position.
Now let’s discus the tests one by one

1.Delikan test

A normal range of head/neck flexion and extension is necessary for an easy laryngoscopy and tracheal intubation.

In this test you have to put your left hand index finger on chin of the patient and right index on the back of neck at the tuberosity of occipital bone.
Now ask the patient to look sealing  of the roof/ceiling now check if the left index is above your right index then it will be normal and if left index finger is below the right one then its consider as abnormal or difficult airway. You can check it in below picture

2. Upper lip bite/catch test

This test is use for assessment of the mandibular movement and tooth architecture. This test have the following three classes.

Class1:

Patient can bite the upper lip above vermillion line.

Class2:

Patient can bite the upper lip below the vermillion line.

Class3:

Patient cant  even bite the upper lip.

as shown in this picture below, the green line shows the vermillion line.

3.Inter incisors gap distance 

The normal inter incisors gap is greater than 5cm or 3 fingers.

But if the distance is below 3cm it shows difficult laryngoscopy.

If the distance between incisors is less than 2cm so it shows difficult LMA insertion.

4.Patils tests/Thyromental distance 

With fully extended head the distance from upper edge of thyroid cartilage/adams apple to the chin is called as thyromental distance.

It has the following three scenarios

• If the distance is >6.5cm:

        So there is no problem with laryngoscopy and intubation.

• If the distance is 6 to 6.5cm:

        Both the intubation and laryngoscopy will be difficult.

• If the distance is <6cm:

        Laryngoscopy may possible.

Ratio of height to the thyromental distance>23.5cm is very sensitive predictor of difficult  laryngosocpy.

 

5.SAVVA test/ sternomental distance

Distance from the upper border of manubrium to the tip of the omentum with neck fully extended and mouth closed is called as the sternomental distance.

 always remember this point both for exam point of view and for assessment that the SAVVA test is the single best predictor of difficult laryngoscopy and intubation with good sensitivity and specificity.

Normal distance is 12.5cm but below this will predict the difficult intubation.

Note: check out the difference between sterno and thyro mental distance

Tests for assessment of TMJ function

1. Mandibular protrusion or calder test

there are three classes in this test

Class A

Lower incisors can protrude anterior to the upper incisors

its mean that patient can move his lower incisors forward to upper incisors as shown in the picture.

Class B

Lower incisors can be brought edge to edge with upper incisors.

Class C

Lower incisors cant be brought edge to edge with upper incisors

2. Another test for TMJ assessment or subluxation of the lower jaw

1) Place the index finger in front of the tragus and thumb in front of the lower part of the mastoid process behind the ear.

2) Now ask the patient to open his mouth wide. As the condyle of the mouth slides forward, the index finger in front of the tragus can be intended (move in)  in its space and the thumb can feel the sliding of the condyle. This shows the good sliding function of mandible.

8. Mallampati grading

This test is used for the assessment of adequacy of the oropharynx for the intubation and laryngoscopy.

This is probably the most commonly applied test for predicting the airway management difficulty.

This tests indicates the amount of the space within the oral cavity to accommodate the laryngoscope and ETT. Performing this test is meticulously difficult to correct prediction. This is performed by having the patient mouth open as wide as possible and stick out the tongue without phonation like saying 'ah'   this lowers the grade by one step mean from grade 2 to grade 1.

one should also ensure that patient is in sitting position with head protruding forward, making the sniffing position for laryngoscopy and intubation.

The observer eye should be at the level of the patient open mouth.

Now observe the degree to which faucial pillars, uvula, soft and hard palate are visible.

This test has the following four grades on basis of the above structures.

Grade1

Following structures can be seen

1. faucial pillars
2. uvula
3. soft palate
4. hard palate

Grade2

Following structures can be seen

1. Uvula
2. soft palate
3. hard palate

Grade3

Following structure can be seen

1. Base of uvula or none
2. soft palate
3. hard palate

Grade4

Only hard palate visible 

Tests for direct laryngoscopy

1. Cormack and lehane grading of direct laryngoscopy

there are four grades in this test 

Grade1

 visibility of entire vocal cord (A in picture below)

Grade2

Visibility of posterior part of the laryngeal aperture (B in picture below)

Grade3

Visibility of epiglottis (C in this picture below)

Grade4

No glottic structure can be seen (D in picture below)

Cook has further subdivided the cormack classification  of Grade 2 and 3 as 2a, 2b, 3a and 3b where we have visualization of  posterior vocal cords. arytenoids only, epiglottis liftable, and epiglottis adherent or only tip of epiglottis visible.

As per cook, grade 1 and 2a patients can be directly intubated, 2b and 3a would require bougie while 3b and 4 cannot be intubated using conventional  laryngoscope and bougie but would required an alternative special technique.

2.POGO scoring

pogo( percentage of glottic opening) during direct laryngosocpy.

 its divided on basis of percentage structures visibility

100% mean entire glottic  structure is visible/

33% mean only lower third of vocal cords and arytenoid are visible.

0% mean no glottic structure is visible.

This test is use for new intubating devices.

9.palm print tests

This test is use for the diabetic patients, in this test the palm and fingers of the dominant hand of the patient is painted with black ink using paint brush.

the patient presses the hand firmly against a white sheet of paper on a hard surface. Then acordingly it is divided into 4 grades

Grade0

All phalanges are visible

Grade1

Defiency in the inter phalangeal areas of 4th and 5th digits

Grade2

Defiency in the inter phalangeal areas of 2nd and 5th digits

Grade3

only the tips of the digits are seen.

10. Lemon trial test.

LEMON trial test which includes five things as discused below

L

Look externally which includes the beared, facial hairs, obesity, facia trauma, piercing, large incisors, large tongue, dentures shape of face.

E

Evaluate 3,3 and 2

its mean the following three things

first is interincisors distance which should be 3 fingers 

Second the thyrohyoid distance which should be also 3 fingers

third is the hyomental distance which should be 2 fingers.

M

mean Malampati classes

O

means obstructions or any mass, swelling of foreighn body in airway

N

neck mobility with the following angles

Neck extension > 80 to 85 degrees

Neck flexion > 25 to 30 degrees

Rotation > 70 to 75 degrees

4Ds for predicting difficult airway

last but not the least is to remember these 4ds for difficult airway

1. Dentition

prominant upper incisors and receding chin

2. Distortion

oedema, blood in vomiting, tumors and  infection

3.Disproportion

short distance from larynx  to  chin, bull neck , large tongue and small mouth

4.Dysmobility

tmj and cervical spine dysmobility.

I hope this article has helped you in finding the tests you can comment your questions and suggestions below.

you can also visit the pubmed.com for  improving your knowledge more about airway assessment for difficult intubation.