Difficult Airway: Assessment

HOSAM M ATEF

Difficult Airway: Definitions

Difficult airway:

trained anaesthesiologist experiences difficulty with mask ventilation, difficulty with tracheal intubation or both

Difficult airway: spectrum

Difficult : spontaneous/mask ventilation

laryngoscopy

tracheal intubation

Definitions (Contd.)

Difficult mask ventilation: A clinical situation when either,

unassisted anaesthesiologist to maintain the SpO2 > 90% using 100% O2 and positive pressure mask ventilation in a patient whose SpO2 was > 90% before the anaesthetic intervention

Difficult laryngoscopy

can not see any portion of the vocal cords after multiple attempts at conventional laryngoscopy (3, ASA)

Difficult tracheal intubation

more than three attempts or ten minutes using conventional laryngoscopic techniques

Definitions (Contd.)

Optimal attempt at laryngoscopy – can be defined as

Reasonably experienced laryngoscopist

The use of the optimal sniffing position

The use of OELM

One change in length/type of blade

Definitions (Contd.)

Assessment of Difficult Airway

History

General physical examination

Specific tests for assessment

– Difficult mask ventilation

– Difficult laryngoscopy

– Difficult surgical airway access

Radiologic assessment

History

Congenital airway difficulties: e.g. Pierre Robin, Down’s syndromes

Acquired– Rheumatoid arthritis, Acromegaly, Benign and malignant

tumors of tongue, larynx etc.

Iatrogenic– Oral/pharyngeal radiotherapy, Laryngeal/tracheal surgery,

TMJ surgery

Reported previous anaesthetic problems– Dental damage, Emergency tracheostomy

General Examination

Adverse anatomical features: e.g. small mouth, receding chin, high arched palate, large tongue, morbid obesity

Mechanical limitation: reduced mouth opening, post-radiotherapy fibrosis, poor cervical spine movement

Poor dentition: Prominent/loose teeth Orthopaedic/neurosurgical/orthodontic

equipment Patency of the nasal passage

Specific Tests

Basic categories

Evaluation of tongue size relative to pharynx

Mandibular space

Mobility of the joints

– TMJ

– Neck mobility

Inter-incisor Gap

Inter-incisor distance with maximal mouth opening

Minimum acceptable value > 4 cm

Significance :

Positive results: Easy insertion of a 3 cm deep flange of the laryngoscope blade

< 3 cm: difficult laryngoscopy

< 2 cm: difficult LMA insertion

Affected by TMJ and upper cervical spine mobility

Mandibular Protrusion Test

Class A: able to protrude the lower incisors anterior to the upper incisors

Class B: lower incisors just reach the margin of upper incisors

Class C: lower incisors cannot reach the margin of upper incisors

Significance

Class B and C: difficult laryngoscopy

Upper Lip Bite Test

Class I: Lower incisors can bite the upper lip above vermilion line

Class II: can bite the upper lip below vermilion line

Class III: can not bite the upper lipSignificance Assessment of mandibular movement and

dental architecture

Mallampati Test

Patient in sitting position

Maximal mouth opening in neutral position

Maximal tongue protrusion without arching

No phonation

Class I: faucial pillars, soft palate, uvula visible

Class II: faucial pillars, soft palate visible

Class III: only soft palate visible

Somsoon-Young’s modification

Class IV: soft palate not visible

Significance of MMP Score

Class III or IV: signifies that the angle between the base of tongue and laryngeal inlet is more acute and not conducive for easy laryngoscopy

Limitations– Poor interobserver reliability

– Limited accuracy

Good predictor in pregnancy, obesity, acromegaly

Correlation between MMP score and laryngoscopy grade

MMP class

Cormack and Lehane grade

Grade 1 Grade 2 Grade 3 Grade 4

Class I (73%) 59% 14% - -

Class II (19%) 5.7% 6.7% 4.7% 1.9%

Class III & IV (8%)

- 0.5% 5% 2.5%

Class Zero Mallampati

Visualisation of any part of epiglottis during MMP test

Associated with easy laryngoscopy

Contrasting View Class zero MMP: difficult airway possible

large epiglottis hinder laryngoscopic view as well as ventilation

Evaluation of Mandibular Space

Thyromental distance (Patil test)

Distance from the tip of thyroid cartilage to the tip of mandible

Neck fully extended

Minimal acceptable value – 6.5 cm

Significance

Negative result – the larynx is reasonably anterior to the base of tongue

Limitations Little reliability in prediction Variation according to height, ethnicity

Modification to improve the accuracy Ratio of height to thyromental distance

(RHTMD) Useful bedside screening test RHTMD < 25 or 23.5 – very sensitive

predictor of difficult laryngoscopy

Thyromental Distance

Sternomental Distance (Savva Test)

Distance from the upper border of the

manubrium to the tip of mandible, neck fully

extended, mouth closed

Minimal acceptable value – 12.5 cm

Evaluation of Neck Mobility

Clinical methods

Patient is asked to hold the head erect, facing directly to the front maximal head extension angle traversed by the occlusal surface of upper teeth

Grade I : > 35°

Grade II : 22-34°

Grade III : 12-21°

Grade IV : < 12°

Neck Mobility: Clinical Assessment

Flexing the head on the neck immobilize the

lower cervical spine full head extension

angle traversed by the vertex or forehead

Significance

Angle > 90°

Specific test for atlanto-occipital joint

extension

Placing one finger on the patient’s chin One finger on the occipital protuberance

Result

Finger on chin higher than one on occiput normal cervical spine mobility

Level fingers moderate limitation

Finger on the chin lower than the second severe limitation

Neck mobility (contd.)

Combination of Predictors

Wilson Score

5 factors

– Weight, upper cervical spine mobility, jaw movement, receding mandible, buck teeth

Each factor: score 0-2

Total score > 2 predicts 75% of difficult intubations

“LEMON” Assessment

L - Look externally (facial trauma, large incisors,

beard, large tongue)

E - Evaluate 3-3-2 rule

3 - inter incisor gap

3 - hyomental distance

2 - hyoid to thyroid distance

M - MMP score

O - Obstruction (epiglottitis, quinsy)

N - Neck mobility

Cormack-Lehane Grading of Laryngoscopy

Grade 1: Full exposure of glottis (anterior +

posterior commissure)

Grade 2: Anterior commissure not visualised

Grade 3: epiglottis only

Grade 4: Visualization of only soft palate

Predictors of Difficult Mask Ventilation

Age > 55 years

BMI > 26 kg/m2

History of snoring

Beard

Edentulous

Predictors of Problems with Back-Up Techniques

LMA Insertion Mouth opening < 2 cm Intraoral/pharyngeal masses (e.g. lingual tonsils)

Direct Tracheal Access Gross obesity Goitre Deviated trachea Previous radiotherapy Surgical collar

Specific Tests for Assessment: Statistical significance

Predicted difficult airway

Truly difficult airway

Yes No

Yes TP FP

No FN TN

Sensitivity = TP / TP + FN

Specificity = TN/TN+FP

Positive predictive value = TP/TP+FP

Negative predictive value = TN/TN+FN

Statistical significance (Contd.)

Statistical Significance of Bedside Predictors

Diagnostic test Sensitivity Specificity

MMP class 49% 86%

TMD 20% 94%

Sternomental distance

62% 82%

Mouth opening 22% 97%

Wilson risk score 46% 89%

MMP + TMD 56% 97%

Radiographic Predictors

X-Ray neck (lateral view) :

Atlanto-occipital gap

C1-C2 gap

Posterior depth of mandible- distance between

the bony alveolar margin just behind 3rd molar

tooth and lower border of mandible.

Tracheal compression

Radiologic Predictors

CT Scan:

Tumors of floor of mouth, pharynx, larynx

Cervical spine trauma, inflammation

Mediastinal mass

Helical CT (3D-reconstruction):

Exact location and degree of airway

compression

Difficult airway : specific subgroups

Pediatrics

Obstetrics

Obesity

Systemic diseases with airway implications, e.g. rheumatoid arthritis, diabetes, ankylosing spondylitis.

Pediatric difficult airway

History:

Past difficult intubation

Airway problems associated with feeding

Syndromes related to pediatric difficult airway

Stridor

Pediatric difficult airway

Mouth opening

Size of tongue

Palate- narrow, high arched, cleft

Schwartz-hyoid maneuver –

A-P distance from mentum to hyoid measured: >1.5cm. (neonates), >3cm.(children).

Difficult obstetric airway: predictors

MMP Class 3 or 4

Edema of tongue, supraglottic and glottic

areas; (history of rapid weight gain,pre-

clampsia, change in voice)

Large breasts, full dentition

Mucosal congestion of nose, pharynx,etc.

Difficult airway :obesity

Difficult spontaneous ventilation in obstructive sleep apnea

BMI >26 – predicts difficult mask ventilation

Difficult intubation predictors-

MMP Score >3

Neck circumference > 16 inches

Systemic Diseases : Airway Ramifications

Rheumatoid Arthritis:

TMJ arthritis ( inter incisor gap, MMP score )

Cricoarytenoid arthritis (dysarthria,

stridor,hoarseness )

Cervical spine mobility – ankylosis, atlanto-

axial instability.

Diabetes mellitus: stiff joint syndrome

Palm print :

Patient’s fingers and palms painted with blue ink and pressed firmly against a white paper

Grade 1- all phalangeal areas visible

Grade 2- deficient interphalangeal areas of 4th and 5th digits

Grade 3- deficient interphalangeal areas of 2nd to 5th digits

Grade 4- only tips seen.

Prayer sign.

Difficult airway: neurosurgical perspective

Diseases of the cervical spine

Trauma

Pituitary disease, e.g. acromegaly

Diseases of the Cervical Spine

Limited neck mobility– Congenital

– Acquired• Rheumatoid arthritis

• Ankylosing spondylitis

Cervical spine instability– Congenital

• Down’s syndrome

• Mucopolysaccharidosis

– Acquired• Trauma

• Rheumatoid arthritis

Klippel-Feil Syndrome

Clinical triad

– Cervical vertebral fusion

– Short neck

– Low-set hairline

Increase likelihood of airway obstruction

Cause: associated anomalies e.g.

– CNS

• Cervicomedulary junction involvement

Down’s Syndrome

Atlanto-axial instability

Macroglossia

Sleep apnea

Associated multisystem anomalies

Subglottic stenosis

Hypotonia

Assessment: Chronic Diseases of Cervical Spine

History Trauma Weakness/numbness of hands Preferred pillow height and sleeping position

Clinical examination Neck posture Neck mobility Unstable cervical spine

– Inspection and palpation of the midline alignment of the hyoid, thyroid and spinous processes

– Loss of normal cervical lordosis

Radiologic Assessment

Suspicion of CSI

3-view cervical spine X-rays– Lateral

– A-P

– Open-mouth odontoid views

Cervical spine CT scan– Findings

• Fracture spine

• Marked prevertebral edema

• Malalignment

Radiologic Assessment (Cond.)

MRI

Best technique to ascertain the integrity of cervical soft tissues for potential instability

Recommended in patients with prolonged (> 72 hrs) depressed mental status

However, MR imaging is not superior to multidetector row CT scan in detecting unstable cervical spine injuries in obtunded patients with blunt trauma

Acromegaly: Airway Implications

Macroglossia, thickened pharyngeal and laryngeal soft tissues, obstructive sleep apnea

Grades of airway involvement– Grade 1: No involvement

– Grade 2: Nasal and pharyngeal mucosa hypertrophy

– Grade 3: Glottic involvement e.g. glottic stenosis/ vocal cord paresis

– Grade 4: Grade (2+3)

LMA in ASA DA algorithm

Airway management in trauma Challenges

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