Accuracy of Preoperative Ultrasonographic Airway Assessment in Predicting Difficult Laryngoscopies in Adult Patients

Background and objectives Presently, neck ultrasonography is used as a tool to predict a difficult airway. There are no standardized ultrasonographic criteria that help to predict a difficult airway. This study aims to ultrasonographically assess the anterior neck soft tissue thickness preoperatively based on two parameters-the minimal distance from the hyoid bone to skin (DSHB) and the distance from the skin to the epiglottis midway between the hyoid bone and thyroid cartilage (DSEM)-and find out whether these parameters can predict a difficult airway in adults by correlating with the Cormack-Lehane (CL) grading. Background and objectives After obtaining ethical committee clearance and patient consent, we conducted this study on 96 patients aged between 18 and 60 years, belonging to American Society of Anesthesiologists (ASA) classes one and two, who were admitted for elective surgery under general anesthesia with endotracheal intubation to RL Jalappa Hospital and Research Centre, Tamaka, Kolar, from January 2020 to May 2021. The exclusion criteria were patients with anticipated difficult airway cases, such as obesity, pregnancy, head and neck anatomical pathologies, maxillofacial anomalies, and edentulous patients. The sonography of the airway was first performed preoperatively by an anesthesiologist along with standard clinical tests such as Mallampati (MP) grading. The sonography included two parameters: DSHB and DSEM. The patients were later classified as having easy or difficult laryngoscopy based on USG criteria from the available literature. A DSHB value of greater than 0.66 cm was predicted to be a difficult airway, and less than 0.66 cm was predicted to be easy. A DSEM value greater than 2.03 cm was predicted to be a difficult airway, and less than 2.03 cm was predicted to be easy. After induction of anesthesia, another experienced anesthesiologist performed direct laryngoscopy in the sniffing position with an appropriate-sized Macintosh blade and CL grades. CL grades I and II were considered to be easy laryngoscopies. The quantitative data were presented by mean SD and confidence interval (CI). The qualitative data were presented in percentages, and p-values less than 0.05 were considered statistically significant. To determine the discriminative power of individual tests, the receiver operating characteristic curve and the area under the curve with a 95% confidence interval was noted. Results The two USG parameters DSHB and DSEM may be used to predict difficult laryngoscopy in adult patients, as both have very strong statistical significance. Of the two parameters, DSHB seems to have a better diagnostic value for predicting a difficult airway in our study, as supported by the area under the curve (AUC) of 97.4% compared to DSEM with an AUC of 88.8%. DSHB has better sensitivity (100%), and DSEM has better specificity (89.77%). Conclusion Our study showed that DSHB and DSEM may aid in predicting difficult laryngoscopies, as a strong statistical significance was present between sonographic measurements and CL grading. DSHB also appeared to have a better diagnostic value for predicting a difficult airway.