Prediction of difficult laryngoscopy in patients undergoing endotracheal intubation: A comparative study of various airway assessment tests

Shoba Philip, Farah Fatima Nizar

Astrocyte 2016 3(2):90-95

Introduction: Predicting a difficult airway is one of the necessities in anesthetic practice. Multiple tests used singly and in combination have been used to predict it, with varied results. We conducted a study to compare the exactitude of various airway assessment tests individually and in combination with parameters suited to the Indian population for the prediction of difficult laryngoscopy. Aims: The aim of this study was to compare various airway assessment tests individually and to statistically analyze the three best tests from our analysis in combination with the Modified Mallampati Test (MMT) for their efficiency in predicting a difficult laryngoscopy in apparently normal individuals undergoing endotracheal intubation. Materials and Methods: This was a prospective, single-blinded, observational study, where 250 patients of American Society of Anesthesiologists Physical Status Grade I and II, without predictors for difficult airway undergoing elective surgeries, were assessed and graded for thyromental distance (TMD), ratio of height-to-TMD (RHTMD), inter-incisor gap, head and neck movement (HNM), MMT and upper lip bite test (ULBT), and correlated intraoperatively with Cormack and Lehane score, and combinations of the best three tests with MMT were then statistically analyzed using standard formulae and the IBM SPSS version 20 statistics software. Results: Analysis of tests for difficult laryngoscopy showed that RHTMD and TMD had the highest sensitivity (90.0% and 70%). ULBT and HNM had the highest specificity of 99.0% and 91.4%. ULBT and TMD were highest in positive predictive value (PPV) (90% and 58.3%) and RHTMD and TMD in negative predictive value (NPV) (97.8% and 94.1%). Of the combinations, MMT + RHTMD had the highest sensitivity (95.0%), NPV (98.4%), odds ratio (23.5), and relative risk, but MMT + ULBT had higher specificity (65.7%), PPV (32.1%), and likelihood ratio (2.5). The combination of MMT + ULBT + RHTMD had 100% sensitivity and  100% NPV and 57% specificity and 30.8% PPV. Conclusion: Ratio of height to TMD is the single best test for difficult laryngoscopy. A combination of MMT + RHTMD + ULBT would be the best option for the prediction of difficult laryngoscopy in apparently normal patients.

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