Prediction of difficult intubation in patients with postburn sternomental contractures: modified onah class

Postburn sternomental contractures cause various changes in mouth, oral cavity, pharynx, larynx and related structures. Although there are many methods to predict difficult intubation, the modified Mallampati test (mMT) and the El-Ganzouri multivariate risk index (EGRI) are popular tests. The authors wanted to compare modified Onah class with these 2 tests and also explored the possibility that Onah class could be an adequate independent predictor for difficult intubation.

One hundred and nine patients, aged 18 to 60 years of age, scheduled for elective surgery for reconstruction of postburn sternomental contractures were divided according to the modified Onah class. We made assessments prior to general anesthesia with respect to mouth opening, thyromental distance, mMT, neck movement, ability to prognath, body weight, and history of difficult tracheal intubation. The accuracy, specificity, positive and negative predictive values were calculated from the data of the 3 tests, and as the 3 tests were compared with patient's laryngoscopic view grade according to Cormack and Lehane criteria by using the Chi-square test.

The incidence of Cormack and Lehane grade III, IV was 39.4%. Onah class showed significantly higher accuracy, specificity, and positive predictive value than mMT and EGRI. There were significant correlations between modified Onah class 2b, 3 and the Cormack and Lehane grade III, IV.

Application of modified Onah class for preoperative prediction of the degree of difficulty with laryngeal visualization can reduce the frequency of both an unanticipated failure to visualize laryngeal structures as well as potential unnecessary interventions related to over-prediction of airway difficulty in patients with postburn sternomental contractures.