Airway Assessment

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NECK CIRCUMFERENCE On its own, neck circumference has not been shown to be predictive of difficult intubation. However, greater neck circumference may be associated with increased body mass and several studies have shown the significance of obesity on difficult bag-mask ventilation and intubation 26, 58-60 . HYOMENTAL DISTANCE A short (less than 4cm) hyomental distance (HMD) has been reported to be a significant finding in patients who were unexpectedly found to be difficult to intubate 54 . However, this may be difficult to assess in obese patients. COMBINED TESTS Individual tests perform poorly. Unfortunately, combination scores also prove unsuccessful in low prevalence populations. Combined tests may represent sensible practice in high prevalence populations. In a review by Shiga and colleagues 4 reporting on 35 studies including 50,760 patients, the overall incidence of difficult intubation was reported to be 5.8 per cent (CI, 4.5-7.5 per cent). Screening tests were reported with poor to moderate sensitivity (20-62 per cent) and moderate to fair specificity (82-97 per cent). In an attempt to improve upon the predictive power of singular tests and measurements, combined tests and scoring systems have been investigated. The combination of the Mallampati and Thyromental distance are more predictive than either test alone 61 . Shiga and colleagues identified the combination of Mallampati and Thyromental distance as the most useful bedside test for prediction of difficult laryngoscopy (positive likelihood ratio 9.9; 95 per cent confidence interval 3.1-31.9). The Wilson and Arne rating systems have a sensitivity of about 75-94 per cent, but low positive predictive value. The Naguib model was reported to have a sensitivity of 81.4 per cent but a positive predictive value of just 15.3 per cent 62 . WILSON RISK SUM SCORE The Wilson risk sum score is based upon five risk factors: weight, head movement, neck and jaw movement, mandibular recession, and buck teeth with three possible scores for each (0,1,2) yielding a total score between zero and 10 (Table 12 Wilson Risk sum) 26 . A score greater than two predicts 75 per cent of difficulties but includes a high number of false positives. Shiga and colleagues reported a low true-positive rate and a low false positive rate indicating that the Wilson score correctly identified patients in whom intubation was easy 4 . A score greater than four reduces the number of false positives but at the cost of missing some of the difficult intubations. The importance of the Wilson risk sum score is highlighted in a study of 372 obstetric patients undergoing caesarean section where a score greater than two produced a likelihood ratio of more than 20 63 . The score has been shown to be highly reproducible 4 . Predictive powers of both the Mallampati and the Wilson risk score are similarly poor, however there may be less inter-observer variation with the Wilson risk score 26 . 24 <strong>Airway</strong> <strong>Assessment</strong>
Table 18. Wilson risk sum score. Wilson risk sum Score Weight 110kg 2 Head & neck movement >90 0 ±90 1 5cm, SLux >0 0 Inter-incisor gap 5cm, SLux = 0 1 Inter-incisor gap
Page 1 and 2: Airway Assessment Authors: Dr Pierr
Page 3 and 4: Part 1. Introduction This airway as
Page 5 and 6: REFERENCES 1. Yentis SM. Predicting
Page 7 and 8: SUMMARY Preoperative airway assessm
Page 9 and 10: Table 3. Difficult airway screening
Page 11 and 12: PREDICTORS OF DIFFICULT BAG-MASK VE
Page 13 and 14: INCIDENCE OF IMPOSSIBLE MASK VENTIL
Page 15 and 16: DIFFICULT ENDOTRACHEAL INTUBATION D
Page 17 and 18: Figure 1. A 100 per cent POGO score
Page 19 and 20: When the patient has risk factors,
Page 21 and 22: TONGUE ABNORMALITIES Direct laryngo
Page 23: Class A B C Position of the lower t
Page 27 and 28: Table 20. Arne risk index. Risk fac
Page 29 and 30: fibreoptic intubation has a finite
Page 31 and 32: 8. Practice guidelines for manageme
Page 33 and 34: 46. Samsoon GL, and Young JR. Diffi
Page 35 and 36: 86. Komatsu R, et al. Ultrasound qu
Page 37 and 38: RE-EXAMINING THE FOUNDATIONS OF AIR
Page 39 and 40: Figure 3. Stylised orientatation of
Page 41 and 42: Figure 5. Retrognathic patient (lef
Page 43 and 44: POSTERIOR COLUMN The original descr
Page 45 and 46: It is postulated that any reduction
Page 47 and 48: 7. Chou HC, Wu TL. A reconsideratio
Page 49 and 50: CHANGING THE PARADIGM: THE NEXT STE
Page 51 and 52: Compression of submandibular struct
Page 53 and 54: Figure 5. Passage of a bevel-tipped
Page 55 and 56: Figure 7. Predicted alteration in p
Page 57 and 58: Figure 9. Accentuation of primary a
Page 59 and 60: LARYNGEAL MASK-FACILITATED INTUBATI
Page 61 and 62: 17. Sanuki T, Sugioka S, Hirokane M
Page 63: 54. Law-Koune JD, Liu N, Szekely B,

Airway Assessment

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