In this preoperative observational study, the effect of preoperative ultrasonographic measurements on the success of videolaryngoscopy in predicting difficult airways was investigated; furthermore, the aim was to determine new cut-off values that can predict difficult intubation in videolaryngoscope use. In our study, it was tested that the use of videolaryngoscope significantly increased the success of intubation in patients who were assessed as having difficult airways with upper airway ultrasound measurements.

Upper airway ultrasonography has emerged as a promising tool for difficult airway assessment by enabling non-invasive, bedside, repeatable, and objective evaluation of airway anatomy. However, a substantial proportion of the existing literature has correlated ultrasonographic measurements with direct laryngoscopy findings. Whether these measurements retain their predictive value in the setting of videolaryngoscopy, and which ultrasonographic parameters best reflect technical intubation difficulty during videolaryngoscopic intubation, remain unclear. Furthermore, several studies have proposed specific cut-off values for upper airway ultrasonographic measurements to predict difficult laryngoscopy when direct laryngoscopy is used. However, these cut-off values may not be directly applicable to videolaryngoscopy because the improved glottic visualization provided by videolaryngoscopes fundamentally alters the relationship between airway anatomy and intubation difficulty.

Therefore, after obtaining a detailed medical history, including both general medical and difficult airway-related history, all patients underwent a comprehensive airway assessment. Conventional predictors of difficult airway were evaluated, including Mallampati classification, inter-incisor distance, thyromental distance, atlanto-occipital joint extension, neck circumference, and the upper lip bite test.

On the day of surgery, ultrasonographic measurements including the distance from the skin to the epiglottis (ESD), hyomental distance (HMD), tongue thickness (TT), and tongue cross-sectional area (CSA) will be obtained. Following these assessments, patients will be transferred to the operating room, where standard general anesthesia induction will be performed. Orotracheal intubation will subsequently be carried out using a videolaryngoscope. After intubation, the difficulty of mask ventilation, laryngoscopy, and orotracheal intubation will be evaluated by the anesthesiologist using established clinical assessment tools and scoring systems.

Inclusion Criteria:

• Patients aged 18 years and older
• Patients undergoing elective surgery under general anesthesia requiring endotracheal intubation (ASA I-III)

Exclusion Criteria:

• Patients undergoing surgery under sedation or regional anesthesia
• Patients not planned for endotracheal intubation
• Patients with a history of difficult airway
• Patients with an acute respiratory tract infection
• Patients with congenital or acquired upper airway anomalies
• Patients with facial or maxillofacial tumors or fractures
• Patients with cervical spine fracture
• Patients with a history of cervical or craniofacial radiotherapy
• Patients with a tracheostomy
• Pregnant patients
• Patients who do not meet the required fasting period or who refuse to -participate in the study

Patients undergoing elective surgery under general anesthesia requiring endotracheal intubation

Individual participant data will not be shared because the study contains personal health information and no regulatory or ethics approval has been obtained for external data sharing.