Predictors of difficult intubation – a simple approach

Abstract

Background: A common cause of anaesthesia related morbidity and mortality is difficult or failed intubation. A lot of studies have attempted to create a score or mathematical model to predict difficult intubation accurately without much success. Many of them consider all predictive parameters as equal. This study attempts to rank the predictors of difficult intubation without creating complicated mathematical models.Methods: Modified mallampati class, degree of head extension, mento-hyoid distance, thyromental distance, interincisor gap, forward movement of the mandible and indirect laryngoscopy were assessed in 498 patients scheduled for elective surgery. Grading of glottis exposure on direct laryngoscopy was done based on CormackLehane classification. Logistic regression analysis was done to identify factors that were significantly associated with difficult glottis exposure (Grades 3 & 4). The predictors were ranked according to the ‘odds’ derived from regression analysis.Results: Direct laryngoscopy was difficult in 40 patients (8%). Indirect laryngoscopy was excluded from the analysis in view of poor patient cooperation in a large number of patients (13%). Degree of head extension, Mento-hyoid distance of < 4 cm and modified Mallampati class 3&4 were found to have significant association with difficult glottic exposure . These predictors could be ranked in the same order based on ‘odds’ ratio (11, 3.4, and 2.5 respectively) calculated from logistic regression analysis.Conclusion: Patients with restricted head movement have much higher ‘odds’ of having a difficult glottic exposure at direct laryngoscopy, followed by those with decreased mentohyoid distance and higher modified mallampati class.