Difficult Airway Assessment Score for Prediction of Difficult Intubation in Pre-Operative Assessment

Abstract

Background:Maintaining a patent airway in anesthetized patients undergoing any procedure or surgery is very important for an anaesthesiologist. The vast majority of the airway-related events, especially inability to maintain patent airway, involve brain damage or death. Several independent bedside tests have been designed to predict a difficult airway or intubation but many have not gained popularity due to practical difficulties. So a new scoring system of Difficult Airway Assessment score based on ratio of patient’s height to thyromental distance, upper lip bite test, head and neck movements, modified mallampati test and neck circumference was developed.Objectives:To determine the diagnostic validity of Difficult Airway Assessment score in predicting difficult intubation defined by Intubation difficulty scale.Methods:This prospective study was conducted among 300 patients aged between 18 and 65 years with ASA physical status I, II and III who underwent elective surgeries under general anaesthesia with endotracheal intubation at a tertiary care centre. Patients with history of burns, trauma or surgeries to airway, any obvious airway anomalies, inability to sit, edentulous or need awake intubation were excluded from the study. The Difficulty Airway Assessment Scoring system was devised with the airway parameters of Modified Mallampati test, Upper Lip Bite Test, Ratio of Height to Thyromental Distance, Neck Circumference and Head and Neck Movements. Each airway parameter was assessed pre-operatively and assigned a score of 0, 1, 2 depending on the severity and summated all the individual scores. Wilson score was also calculated for all the subjects. The difficulty in intubation was assessed with Intubation difficulty scale.Results:Out of 300 patients, the incidence of difficult intubation was 12%. Modified Mallampati test had the highest sensitivity (61.1%) and head and neck movements had the highest specificity (95.5%). Upper lip bite test and head and neck movements had highest Positive predictive value (42.9%) and likelihood ratio (5.5). Accuracy was highest for head and neck movements followed by Upper Lip Bite Test and RHTMD. Difficult airway assessment score with cut off >=3 had a sensitivity of 88.9%, specificity of 82.6%, PPV of 41%, NPV of 98%, likelihood ratio of 5.1 and the accuracy was 83.3%.Conclusion:Difficulty airway assessment score constructed using Modified Mallampati test, Upper Lip Bite Test, Ratio of Height to Thyromental Distance, Neck Circumference and Head and Neck Movements has a good predictive accuracy and was very much better compared to individual parameters.