In thoracic surgery, one-lung ventilation using a double-lumen tube (DLT) is often performed to protect dependent lung and provide comfortable surgical conditions. However, serious complications and adverse events can be encountered during DLT placement. One of the most important steps to avoid these drawbacks is to choose the appropriate size of DLT. The width of the trachea can be measured by using different imaging methods such as computed tomography (CT) and ultrasonography (US) to predict the appropriate DLT size. CT can also contribute to the proper placement of DLT by giving us the length of the trachea and main bronchi. In this study, we hypothesized that the size of the DLT can be determined more accurately by measuring the trachea diameter by using US and CT before DLT intubation. At the same time, we aimed to determine whether the evaluation of tracheobronchial anatomy with CT would contribute to the placement of DLT at a more appropriate level.

Inclusion Criteria:

• Patients who will undergo elective thoracotomy or video-assisted thoracic surgery with general anesthesia with DLT intubation
• BMI 18 - 35 kg/m2
• Age 18 - 80 years old

Exclusion Criteria:

• Mallampati score 3 and 4
• History of tracheostomy, tracheal deviation, or distortion
• Emergency surgery

A total of 100 patients with a body mass index between18-35 kg/m2 in the ASA I-II-III risk group, aged 18-80, who will undergo elective thoracic surgery, require intubation with a double-lumen tube will be included in the study.