The Role of Ultrasonographic Tracheal Measurements in Predicting Hypoxemia During Endobronchial Ultrasound-Guided Transbronchial Needle Aspiration

Bronchoscopic procedures performed under endobronchial ultrasound (EBUS) guidance are widely used minimally invasive diagnostic methods for the evaluation of mediastinal lymph nodes. Endobronchial Ultrasound-Guided Transbronchial Needle Aspiration (EBUS-TBNA) is an indicated procedure for the diagnosis, staging, and histopathological characterization of primary or metastatic tumors. The procedure is generally performed under moderate or deep sedation to enhance patient comfort and optimize procedural success. Deep sedation has been shown to be a safe and effective approach in terms of respiratory complications in both younger and elderly patients. However, hypoxemia may develop during EBUS procedures due to mechanisms such as mechanical airway obstruction, sedation-related ventilatory depression, and ventilation-perfusion mismatch. A decrease in oxygen saturation is frequently observed during bronchoscopic procedures, with reported rates of up to 94%. Studies have also reported a hypoxemia rate of approximately 25% during EBUS, even with the use of a nasopharyngeal oxygen cannula. Therefore, maintaining adequate oxygenation throughout the procedure is of critical importance. In patients receiving sedation under spontaneous respiration, oxygen support is typically provided via low-flow systems such as nasal cannulae, which can generally deliver flows of up to 15 L/min. It has been reported that a fiberoptic bronchoscope occupies approximately 10% of the tracheal cross-sectional area and about 15% at the level of the cricoid ring, leading to partial obstruction. EBUS endoscopes have a larger outer diameter and, in addition, may exert more pronounced negative effects on respiratory mechanics due to the balloon mechanism used. The outer diameter of EBUS bronchoscopes typically ranges between 6.2 and 6.7 mm, mechanically occupying a significant portion of the tracheal lumen. This may restrict tracheal airflow, leading to partial obstruction and consequently predisposin