Comparison of airway ultrasound indices and clinical assessment for the prediction of difficult laryngoscopy in elective surgical patients: A prospective observational study

Abstract

Background: Ultrasound is evolving as a probable tool in airway assessment. The upper airway is a superficial structure and has sonographically identifiable structures which makes it ideal for evaluation with the ultrasound. Aims: The aim of this study was to evaluate the role of skin to hyoid and skin to thyrohyoid membrane distance in prediction of difficult laryngoscopy. Settings and Design: This is a prospective observational study included 150 patients aged 18–60 years of American Society of Anesthesiologists Physical Status I and II scheduled to undergo surgery under general anesthesia requiring laryngoscopy and endotracheal intubation. Materials and Methods: The modified Mallampati score, mouth opening, mentohyoid distance, thyromental distance were noted. Skin to hyoid bone distance and skin to thyrohyoid membrane distance were measured by ultrasound. Patients were clubbed retrospectively into easy and difficult laryngoscopy groups on the basis of Cormack Lehane grading, and the characteristics of both groups were compared. Statistical Analysis: Statistical Package for the Social Sciences, Version 23 was used for statistical analysis. Independent samples t -test was used to compare the means between difficult and easy laryngoscopy patients. Diagnostic accuracy of the significant ( P < 0.05) variables between difficult and easy laryngoscopy patients was calculated using receiver operating characteristics curve in terms of their area under curve. Appropriate cutoff values (with corresponding sensitivity, specificity, and overall accuracy) were also identified. Results: Out of 150 patients, 13 (8.7%) were identified as difficult laryngoscopy whereas 137 patients (91.3%) were identified as easy laryngoscopy. The demographics of both groups were comparable. Mentohyoid distance, skin to hyoid bone distance, and skin to thyrohyoid distance were statistically different between easy and difficult laryngoscopy patients, with lower mentohyoid distance and higher skin to hyoid bone distance and skin to thyrohyoid distance in difficult laryngoscopy patients. Diagnostic accuracy of the mentohyoid distance (70.3%) was slightly superior to skin to hyoid bone distance (67.1%) and skin to thyrohyoid distance (68.1%). Conclusion: Ultrasound measurements of skin to hyoid bone and skin to thyrohyoid membrane distance fail to eclipse clinical parameters in accurately predicting a difficult laryngoscopy.