Patil Surekha1, Khatavkar Sonal2, Doshi Chaula3, Vaswani Jayashree4, Sharma Nitinkumar5, Vyas Varsha6, Nagpal Amit7, Maruvad Ravitej8

Simple bedside tests for airway assessment were performed in 500 randomly selected Indian adult patients posted for surgery. The parameters studied were Thyromental distance (TMD), Inter incisor distance (IID) Sternomental distance (STMD), Ratio of height to thyromental distance (RHTMD), Laryngeal mobility (LM) and Mallampati classification. The TMD, STMD, IID, RHTMD and LM measurements were consolidated into three groups namely normal, moderate and low scores. The airway parameters were finally co-related with the Mallampati classification. The normal range of values observed in Indian patients were TMD - 6-7cms, IID - 4. 5-5.5 cms, STMD-14-15cms, RHTMD-18-22 and LM was good in 90% of patients assessed. The airway parameters of TMD, STMD, RHTMD, IID and LM in conjunction with Mallampati classification may be a useful routine preoperative screening test for predicting intubation difficulties in Indian population.

BACKGROUND AND AIMS: Difficult airway assessment is based on various anatomic parameters of upper airway, much of it being concentrated on oral cavity and the pharyngeal structures. The diagnostic value of tests based on neck anatomy in predicting difficult laryngoscopy was assessed in this prospective, open cohort study.

METHODS: We studied 500 adult patients scheduled to receive general anaesthesia. Thyromental distance (TMD), Sternomental Distance (STMD), Interincisior Distance (IID), Ratio of Height to Thyromental Distance (RHTMD), Mallampatti Classification (MPC), Laryngeal Mobility (LM) was calculated. The laryngoscopic view was classified according to the Cormack-Lehane Grade (1-4). Difficult laryngoscopy was defined as Cormack-Lehane Grade 3 or 4. The optimal cut-off points for each variable were identified by using receiver operating characteristic analysis. Sensitivity, specificity and positive predictive value and negative predictive value (NPV) were calculated for each test. Multivariate analysis with logistic regression, including all variables, was used to create a predictive model.

RESULTS: Laryngoscopy was difficult in 11% of the patients. The cut-off values were: TMD ≤6.5 cm, STMD ≤15 cm, IID≤3.5cm, MPC grade 3 & 4, and laryngeal motility judged as good, restricted and nil. The laryngeal motility had highest specificity (90%), while TMD had highest specificity (85.4%). The area under curve (AUC) for the TMD, STMD, IID, LM, MPC was 0.64, 0.63, 0.61 and 0.54, respectively. The predictive model exhibited a higher and statistically significant diagnostic accuracy (AUC: 0.68, P <0.001).

CONCLUSIONS: The TMD, STMD, RHTMD and IID were found to be poor single predictors of difficult laryngoscopy, while a model including all four variables had a significant predictive accuracy.