In the classical group, Double Lumen Tube selection was based on gender and height. For males, a 41 F tube was chosen if height >170 cm, and a 39 F tube if height ≤170 cm. For females, a 37 F tube was used if height >160 cm, and a 35 F tube if height ≤160 cm. The depth was determined using the formula: 12 + (patient height/10). The calculated depth was marked on the DLT, and after intubation, the mark was positioned at the level of the upper teeth.

In the Ultrasonography (USG) group, Double Lumen Tube selection was based on the transverse cricoid cartilage diameter measured preoperatively using ultrasound. A 41 F tube was selected if the cricoid diameter was ≥18 mm, 39 F for 16-17.9 mm, 37 F for 15-15.9 mm, 35 F for 13-14.9 mm, and 32 F for <13 mm (Table 5) (5). To determine placement depth, the distance between the vocal cords and the Louis angle was measured (the Louis angle was used as a guide as it anatomically aligns with the carina). The position of the vocal cords was identified using USG. The measured length was marked starting from the bronchial cuff line, and this mark was positioned at the level of the vocal cords during intubation.

In the Computed Tomography (CT) group, Double Lumen Tube selection was based on CT measurements. Radiologists measured the cricoid diameter and the distance between the carina and the vocal cords. A 41 F tube was selected if the cricoid diameter was ≥18 mm, 39 F for 16-17.9 mm, 37 F for 15-15.9 mm, 35 F for 13-14.9 mm, and 32 F for <13 mm (Table 5) (5). The calculated depth was marked starting from the bronchial cuff line, and this mark was positioned at the level of the vocal cords during intubation.

Double-Lumen Tube Intubation

After intubation in all three groups;

1. The upper teeth level was checked and the cm was recorded. It was checked whether both lungs were equally ventilated with the inspection and auscultation method. First, the tube lumens were clamped on the left side; it was checked whether the right lung was ventilated, then the same procedure was repeated for the right side and noted. Then, both lungs were ventilated with 6-8 ml/kg tidal volume and the airway pressure was recorded. With the help of the clamp, the left side was clamped first, the right lung was ventilated with 4-6 ml/kg tidal volume and the airway pressure was checked. The same procedure was repeated for the other side. It was determined whether there was sufficient isolation according to the difference between the airway pressures and recorded.

Isolation criteria:

Satisfactory isolation: If the respiratory sounds are clearly heard on the opposite side when one lung is isolated and the airway pressure on the other side increa

The selected tube was evaluated to see if it was of appropriate size.

Appropriate size: If the double-lumen tube tip entered the left main bronchus and no obvious resistance was encountered and there was no airway leakage and isolation was achieved when the bronchial cuff was inflated with 1-3 ml and the tracheal cuff with 2-6 ml of air, it was accepted that the double-lumen tube was selected in an appropriate size.

Large tube: If the double-lumen tube tip could not enter the left main bronchus or was placed in the left main bronchus, but when the bronchial cuff was inflated with less than 1 ml and the tracheal cuff with less than 2 ml of air, pulmonary isolation was achieved and there was no air leakage, it was accepted that it was a large-sized double-lumen tube.

Small tube: If the bronchial cuff was inflated with more than 3 ml and the tracheal cuff with more than 6 ml of air, pulmonary isolation was achieved and there was no air leakage, it was accepted that it was a small-size

While the patient was in the supine position, the location of the tube was checked with fiber optic bronchoscopy. It was noted whether the tube was in its optimum location. If not, how many cm it should be advanced or retracted for its optimum location.

Subglottic resistance was assessed and recorded as none, mild, moderate, or severe based on the level of resistance.

It was noted with FOB whether there were petechiae in the trachea, bronchi, or both.