This study was approved by the medical ethics committee of the local hospital and written informed consent was obtained from all subjects participating. All methods were performed in accordance with the relevant guidelines and regulations.
All the patients undergoing elective left sided thoracic surgery and without contraindication to the use of RDLT were included in this study. Exclusion criteria were as follows: age ≤ 18 years or age ≥ 70 years; America Society of Anesthesiologist (ASA) classification > III; distorted anatomy of the tracheobronchial on a chest CT; an intraluminal lesion of the right bronchus; thoracic aortic aneurysm; previous thoracotomy; severe cardiopulmonary disease. The length of RMSB of these eligible patients was measured by an independent anesthesiologist trained by a senior radiologist using Picture Archiving and Communication System (PACS) on a computer according to preoperative chest CT (No CT scan was done specifically for this study). The measurements were made on the coronal plane in the axis of the RMSB, on the frame that a clear carina was showed and the RMSB was on the largest diameter. The enrolled sequence was as follows: First, measured the length of RMSB in eligible patients with Carina-proximal method (measured the distance between the tracheal carina and the proximal margin of the right upper lobe orifice), until there was a patient’s carina-proximal distance ≥14 mm and assigned the patient to Carina-Proximal group (C-P group) (Fig. 1A, D); Second measured the length of RMSB in eligible patients with carina-distal method (measured the distance between the tracheal carina and the distal margin of the right upper lobe orifice), until there was a patient’s carina-distal distance ≥20 mm and assigned the patient to Carina-Distal group (C-D group) (Fig. 1B, E); Third, measured the length of RMSB in eligible patients with carina-carina method (measured the distance between the tracheal carina and the first right interlobar carina of the right upper lobe orifice), until there was a patient’s carina-carina distance ≥24 mm and assigned the patient to Carina-Carina group (C-C group) (Fig. 1C, F). Repeated the above process until the numbers of patients in each group was 56 (Fig. 2).
All the patients were placed in supine position and monitored with Noninvasive blood pressure (NIBP), Heart rate (HR), saturation of pulse oxygen (SpO2) and Electrocardiogram (ECG) in the operating room. All the patients were administered with midazolam 0.03mgkg− 1, etomidate 0.3mgkg− 1, fentanyl 3μgkg− 1 and cisatracurium 0.2mgkg− 1 for anesthesia induction. All the patients were intubated with a RDLT (Tuoren Medical Technology Company, Xinxiang, China, the size selection was based on the transverse diameter of the narrowest part of the trachea and the right main bronchus measured by chest CT) exactly 3 minutes after intravenous cisatracurium by the same experienced anesthesiologist using a video laryngoscope.
The intubation steps were as follows. First, after the tip of RDLT had passed the vocal cords, removed the stylet then advanced the RDLT slightly and rotated 90° toward the RMSB, until a slight resistance was encountered; Second, a Fiberoptic bronchoscope (FOB: external diameter 2.8 mm; MDHAO Medical Technology, Zhuhai, China) was inserted into the right sided lumen of the RDLT to seek for the right upper lobe orifice. If the right upper lobe orifice was not found, retreated the RDLT as sought for the right upper lobe orifice via FOB. If the right upper lobe orifice was not found at the first time, retreated the RDLT into the trachea then inserted the RDLT into the right main bronchus and look for the right upper lobe orifice again during insertion, until the right upper lobe orifice was found and made sure the distal margin of right upper lobe ventilation slot aligned with the distal margin of the right upper lobe orifice (Fig. 3) [7] then inflated the endobronchial cuff (pressure less than 25cmH2O). If the right upper lobe orifice was not found after three times, we defined this as intubation failure and a bronchial-blocker tube was used. Third, the FOB was inserted into the left sided tracheal lumen of the RDLT to assess the position of endobronchial cuff at the level of the carina and the scores was recorded (the scores of endobronchial cuff position: 1 = invisible, 2 = visible, not herniated, 3 = slight herniation, ventilation maintained, 4 = herniation, inadequate ventilation) (Fig. 4) [6] then inflated the tracheal cuff (pressure less than 25cmH2O).
After deflation of the endobronchial cuff, the patients were turned to the lateral decubitus position. In this process, the RDLT was securely held at the level of the incisors and the patients’ heads were kept in the neutral position. After turning, inflated the endobronchial cuff then checked the positions of the right upper lobe orifice and the positions of endobronchial cuff via FOB again. If there was a sudden increase of peak airway pressure or poor lung isolation intraoperative, the FOB was inserted into the RDLT to detect the positions of the endobronchial cuff and reposition manoeuvre was performed if the endobronchial cuff herniated and affected the ventilation of left lung.
The primary endpoints were the scores of endobronchial cuff position of the RDLT after initial placement and after turning the patients to the lateral decubitus position. The failure of intubations, the number of total malposition of the RDLT intraoperative, the attempts to check the position of RDLT on supine position and on lateral decubitus position were also recorded. The data was collected and analyzed by an independent anesthesiologist.
In this study, the sample size was determined according to a pilot study, with significance set at 0.05 and power set at 80%, the sample size required to detect the differences of the accuracy of RDLT position was 50 patients in each group. Taking into account that the potential risk of patients excluded from the study for unforeseen reasons we recruited 56 patients each group.
