Ratio of Neck Length to Thyromental Distance as a Predictor of Difficult Airway: Prospective Observational Study

Abstract Background: It is very important to predict and manage difficult intubation because difficult or failed intubation is con-sidered one of the major causes of morbidity and mortality in anaesthesia. Several preoperative airway assessment tests can be used for that purpose. Aim of Study: This study aimed to assess the predictive ac-curacy of the ratio of Neck Length to Thyromental Distance (RNTMD) in identifying difficult laryngoscopy and intubation. Patients and Methods: This observational study was done prospectively and involved adult patients undergoing elective operations under general anesthesia. The airway indices, name-ly the RNTMD, thyromental distance, modified Mallampati test, ratio of height to thyromental distance, and interincisor gap, were assessed preoperatively. Difficult laryngoscopy was considered when the Cromack-Lehane grade was >2, and dif-ficult intubation was considered when the intubation difficulty scale was >5. Our primary outcome was the ability of RNT-MD to predict difficult laryngoscopy using area under receiver operating characteristic curve (AUC) analysis. The ability of previously mentioned airway indices to expect difficult laryn-goscopy and intubation were the secondary outcomes. Results: We analyzed data from 129 patients, and the in-cidence of difficult laryngoscopy and intubation was 18/129 (14%) and 11/129 (9%), respectively. The RNTMD’s AUC (95% confidence interval) for prediction of difficult laryngos-copy and intubation was 0.69 (0.60-0.76) and 0.69 (0.61-0.78). The ability of RNTMD to predict difficult laryngoscopy and intubation was not significantly different from that of other air-way indices. At a cut-off value of 1.2, RNTMD a NPV of 94 and 97% for difficult laryngoscopy and intubation, respectively. Conclusion: In adult patients, RNTMD can predict dif-ficult airway with moderate accuracy. An RNTMD <1.2 can exclude difficult laryngoscopy and intubation with 94 and 97% accuracy.