Difficult airway-assessment
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Difficult Airway: Assessment
HOSAM M ATEF
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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
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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
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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.)
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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.)
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Assessment of Difficult Airway
History
General physical examination
Specific tests for assessment
– Difficult mask ventilation
– Difficult laryngoscopy
– Difficult surgical airway access
Radiologic assessment
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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
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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
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Specific Tests
Basic categories
Evaluation of tongue size relative to pharynx
Mandibular space
Mobility of the joints
– TMJ
– Neck mobility
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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
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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
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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
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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
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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
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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%
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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
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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
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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
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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
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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°
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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
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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.)
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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
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“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
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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
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Predictors of Difficult Mask Ventilation
Age > 55 years
BMI > 26 kg/m2
History of snoring
Beard
Edentulous
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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
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Specific Tests for Assessment: Statistical significance
Predicted difficult airway
Truly difficult airway
Yes No
Yes TP FP
No FN TN
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Sensitivity = TP / TP + FN
Specificity = TN/TN+FP
Positive predictive value = TP/TP+FP
Negative predictive value = TN/TN+FN
Statistical significance (Contd.)
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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%
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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
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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
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Difficult airway : specific subgroups
Pediatrics
Obstetrics
Obesity
Systemic diseases with airway implications, e.g. rheumatoid arthritis, diabetes, ankylosing spondylitis.
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Pediatric difficult airway
History:
Past difficult intubation
Airway problems associated with feeding
Syndromes related to pediatric difficult airway
Stridor
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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).
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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.
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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
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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.
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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.
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Difficult airway: neurosurgical perspective
Diseases of the cervical spine
Trauma
Pituitary disease, e.g. acromegaly
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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
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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
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Down’s Syndrome
Atlanto-axial instability
Macroglossia
Sleep apnea
Associated multisystem anomalies
Subglottic stenosis
Hypotonia
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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
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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
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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
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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)
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LMA in ASA DA algorithm
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Airway management in trauma Challenges
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