Pediatric patients are exposed to increased risk during general anesthesia. A myriad of problems can be encountered in the pediatric population by misplaced endotracheal tubes. Especially, during one-lung ventilation (OLV) a right-sided or left-sided tube is inserted to facilitate the surgery. However, inadvertent tube use, caused by misinterpretation of the distances of the trachea and the main bronchi, may cause unintended hypoxemia, postoperative atelectasis and even mortality.

In this study, investigators will measure the distance between distal margin of right lung upper lobe orifice-carina and carina-lip with the help of fiberoptic bronchoscopy (FOB).

In ASA-PS I-II-III children between 1-18 years of age who are orotracheally intubated for any reason, the fiber optic bronchoscope will be advanced in the tube and first the carina distance and then the carina to right upper bronchus distance will be measured.

Age, weight, height, body mass index (BMI), weight percentile, height percentile, comorbidities, ASA score, tube size, lip margin distance, right upper bronchus to carina distance and right upper lobe to carina distance/ Carina to-lip margin ratio will be recorded.

Inclusion Criteria:

• All patients undergoing general anesthesia via an endotracheal tube
• ASA I-III

Exclusion Criteria:

• Patients that do not meet age criteria
• Uncontrolled asthma or hyper reactive airway
• hypoxemia, previous thoracic surgery
• ASA > III
• Unstable hemodynamics
• Patients with tracheal or oral malignancies
• Patients with face trauma
• Informed consent not given
• using a tube with a number too small for the fiberoptic bronchoscope to pass through

All patients undergoing general anesthesia via an endotracheal tube will be eligible for recruitment.

Data available on reasonable request