Use of airway ultrasonography in preoperative detection of difficult airway:Prospective study

ABSTRACT Objective: The aim of this study is to evaluate the effectiveness of clinical and ultrasonographic tests in predicting difficult intubation in adult patients undergoing elective surgery under general anesthesia. The study compares clinical and ultrasonographic methods in predicting difficult laryngoscopy and intubation, with the goal of identifying the most sensitive parameters. Materials and Methods: The airway evaluation of 150 adult patients aged 18-80 years, with a body mass index (BMI) <35 kg/m², and American Society of Anesthesiologists (ASA) classification I-III, scheduled for elective surgery under general anesthesia, was conducted using both clinical and ultrasonographic methods. Data collected included gender, age, height, body weight, BMI, thyromental distance (TMD), sternomental distance (SMD), neck circumference, interincisor distance (IID), upper lip bite test (ULBT), and modified Mallampati score (MMS). During the ultrasonographic assessment, while the patients were in sniffing position, measurements of the skin-epiglottis distance, skin-hyoid bone distance, and skin anterior commissure distance of the vocal cords were taken by the same anesthesiologist. Following standard anesthetic induction, the difficulty of endotracheal intubation was assessed using the modified Cormack-Lehane Classification (CLC). Results: Thirty-five patients (23.3%) were classified as having difficult laryngoscopy (CLC class 2b or higher), and 42 patients (28.0%) were considered to have difficult intubation (CLC class ≥2b or requiring two or more intubation attempts). All patients were successfully intubated. In the analysis predicting difficult intubation, the upper lip bite test (ULBT), interincisor distance (IID), neck circumference, neck circumference/TMD ratio, and the ultrasonographically measured skin-epiglottis distance were found to be statistically significant predictors. However, no significant relationship was found between difficult intubation and MMS, BMI, TMD, SMD, the ultrasonographically measured skin hyoid bone distance, or skin-anterior commissure distance. In predicting difficult intubation, the cut-off values for the clinical parameters IID, neck circumference, and neck circumference/TMD ratio were 4.3 cm, 39.3 cm, and 4.9, respectively, with area under the curve (AUC) values of 0.744, 0.713, and 0.690. The skin-epiglottis distance was identified as the ultrasonographic measurement with the highest predictive power for difficult intubation, with a cut-off value of ≥19.6 mm yielding a sensitivity of 76.2%, specificity of 76.9%, and an AUC of 0.818 (p<0.001). Combining clinical tests with ultrasonographic measurements provided higher sensitivity and significantly improved predictive accuracy for difficult intubation. The highest predictive performance was achieved with the combination of interincisor distance and skin-epiglottis distance, with an AUC of 0.841, sensitivity of 80.7%, and specificity of 85.7%. Conclusion: In this study, the skin-epiglottis distance was identified as the ultrasonographic parameter with the highest predictive power for difficult intubation. Additionally, combining ultrasonographic measurements with routine clinical tests, such as using the interincisor distance and skin-epiglottis distance together, may lead to better outcomes in predicting difficult airways. Therefore, ultrasonographic measurements, as a non-invasive and reliable method, can be used by clinicians in preoperative evaluation. However, it should be noted that difficult intubation cases cannot be fully predicted, and practitioners must always be prepared for the possibility of difficult intubation. Keywords: Airway Management, Airway Ultrasonography, Ultrasonography, Difficult Intubation, Difficult Laryngoscopy, Skin-Epiglottis Distance