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SUMMARY
The use of a modified Cormack-Lehane scoring system (MCLS) of laryngoscopic views, as previously introduced in the Western population, was investigated during direct laryngoscopy in the Asian population. We studied the distribution of the different grades of MCLS, the predictive factors and rate of difficult laryngoscopy, and the association with difficult intubation. Six hundred and five patients requiring tracheal intubation during general anaesthesia were prospectively studied. The optimal views during direct laryngoscopy were scored using the 5-grade MCLS system. The distribution of the laryngoscopy scores was 73.9% Grade 1 (full view of the vocal cords), 21.0% Grade 24 (partial view of the vocal cords), 3.3% Grade 2B (only the arytenoids and epiglottis seen), 1.6% Grade 3 (only epiglottis visible) and 0.2% Grade 4 (neither the epiglottis nor glottis seen). External laryngeal pressure was necessary in 45.3% of cases to optimize laryngoscopic views. Grade 2B was associated with significantly higher incidence of difficult intubation compared with Grade 24 (65% vs 13.4%). The rates of difficult laryngoscopy and intubation were 5.1 % and 6.9% respectively. The Mallampati classification and thyromental distance were associated with low predictive value for difficult laryngoscopy. The MCLS better delineates the difficulty experienced during laryngoscopy than the original Cormack-Lehane grading.
Key Words: ANAESTHESIA, LARYNGOSCOPY: intubation, tracheal
Cephalometric studies have shown that distinct differences exist between Asian and Western populations1-3. Butler reported that the Asian population has a higher incidence of retrognathia compared with the British population4. This may result in differences in the rates of difficult laryngoscopy and intubation in the different populations. In addition, comparing the incidences of ease of laryngoscopy and tracheal intubation is difficult because there is neither a standardized classification of glottic views nor an accepted definition of difficult laryngoscopy and intubation.
Level of difficulty in intubation has been shown to correspond to the proportion of the laryngeal inlet visualized. The widely accepted Cormack and Lehane scoring systems used to describe the view at direct laryngoscopy, has been criticized for its lack of sensitivity in providing information as to the difficulty of direct laryngoscopy. A modified Cormack-Lehane scoring system by Yentis and Lee has been presented6.
The aims of this prospective study were to ascertain the distribution of laryngoscopic grades using the modified Cormack-Lehane score...