Seminar Difficult Airway: Assessment and Management Algorithms

1. SeminarDifficult Airway: Assessment and Management Algorithms Presenter : Anil Agarwal Date : March 19, 2007 www.anaesthesia.co.in anaesthesia.co.in@gmail.com

2. Difficult Airway: Definitions Difficult airway: • A clinical situation in which a conventionally trained anaesthesiologist experiences difficulty with mask ventilation, difficulty with tracheal intubation or both Difficult airway: spectrum • Difficult : spontaneous/mask ventilation laryngoscopy tracheal intubation Ref. Anesthesiology, May 2003

3. Definitions (Contd.) Difficult mask ventilation: A clinical situation when either, • It is not possible for 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 or • It is not possible for the unassisted anaesthesiologist to prevent or reverse signs of inadequate ventilation during mask ventilation

4. Definitions (Contd.) Difficult laryngoscopy • It is not possibe to see any portion of the vocal cords after multiple attempts at conventional laryngoscopy (3, ASA) Difficult tracheal intubation • A clinical situation in which intubation requires more than three attempts or ten minutes using conventional laryngoscopic techniques

5. Definitions (Contd.) Optimal attempt at laryngoscopy – can be defined as • Performance by a reasonably experienced laryngoscopist • The use of the optimal sniffing position • The use of OELM • One change in length/type of blade

8. Assessment of Difficult Airway • History • General physical examination • Specific tests for assessment • Difficult mask ventilation • Difficult laryngoscopy • Difficult surgical airway access • Radiologic assessment

9. History • Congenital airway difficulties: e.g. Pierre Robin, Klippel-Feil, 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, Med-alerts, databases, previous records

10. 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

11. Specific Tests Basic categories • Evaluation of tongue size relative to pharynx • Mandibular space • Mobility of the joints • TMJ • Neck mobility

12. 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

13. 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

16. 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 lip Significance • Assessment of mandibular movement and dental architecture • Less inter observer variability Ref. Anesthesia & Analgesia, 2003

17. 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

18. 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 Anesthesia & Analgesia, February 2006

19. Correlation between MMP score and laryngoscopy grade Airway Management, Jonathan Benumof

20. Class Zero Mallampati • Visualisation of any part of epiglottis during MMP test • Associated with easy laryngoscopy Ref. Ezri et al, Anesthesia and Analgesia, 2001 Contrasting View • Class zero MMP: difficult airway possible  large epiglottis hinder laryngoscopic view as well as ventilation Ref. V. Grover, Canadian Journ Anesth, 2005

21. 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

22. Thyromental Distance 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 Anesthesiology, May 2005

23. 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

24. 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°

25. 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

26. Neck mobility (contd.) • 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

27. 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

28. “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 Ron and Walls’ Emergency Airway Management

29. 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

30. Cook’s Modification of Laryngoscopy Grade • Cormack-Lehane grade 2 & 3 2a : Posterior part of glottis visible 2b : Only arytenoids visible 3a : Epiglottis visible, can be lifted 3b : Epiglottis visible, but fixed • Easy: Grade 1 and 2a • Restricted: Grade 2b and 3a • Difficult: Grade 3b and 4 Ref. Cook et al, Anaesthesia, 1999

31. Predictors of Difficult Mask Ventilation • Age > 55 years • BMI > 26 kg/m2 • History of snoring • Beard • Edentulous Langeron et al, Anesthesiology, November 2006

32. 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

33. Specific Tests for Assessment: Statistical significance

34. Statistical significance (Contd.) Sensitivity = TP / TP + FN Specificity = TN/TN+FP Positive predictive value = TP/TP+FP Negative predictive value = TN/TN+FN

35. Statistical Significance of Bedside Predictors

36. 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

38. 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

39. Difficult airway : specific subgroups • Pediatrics • Obstetrics • Obesity • Systemic diseases with airway implications, e.g. rheumatoid arthritis, diabetes, ankylosing spondylitis.

40. Pediatric difficult airway History: • Past difficult intubation • Airway problems associated with feeding • Syndromes related to pediatric difficult airway • Stridor

42. Pediatric difficult airway • Mouth opening • Size of tongue • Palate- narrow, high arched, cleft Schwartz-hyoid maneuver – • A-P distance from middle of inside of mentum to hyoid measured: >1.5cm. (neonates), >3cm.(children). Frederic Berry’s Anesthesia for difficult pediatric patients

43. 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.

44. 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

45. 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.

47. 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.

48. Difficult airway: neurosurgical perspective • Diseases of the cervical spine • Trauma • Pituitary disease, e.g. acromegaly Ref. Dr. Umamaheswara Rao, Indian J. Anaesth. 2005

49. Diseases of the Cervical Spine • Limited neck mobility • Congenital  Klippel-Feil syndrome • Acquired • Rheumatoid arthritis • Ankylosing spondylitis • Cervical spine instability • Congenital • Down’s syndrome • CVJ anomalies • Mucopolysaccharidosis • Acquired • Trauma • Rheumatoid arthritis

50. 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 • Arnold-chiari malformation Ref. Airway Management by Jonathan Benumof