Patients randomly assigned into Macintosh group, GlideScope (Verathon Medical, Bothwell, UT, USA) group, or CMAC(D) (Karl Storz GmbHand Co.KG, Tuttlingen, Germany) group. This will be done using a closed envelope technique using a computer-generated block randomization method. Before the study, the computerized randomization will be performed and the allocation results will be placed in individual numbered and sealed envelopes. Patients remained blinded about their intubation technique until post-operative assessment was completed. The researcher responsible for recruitment will be blinded to the allocation result. After a patient will be consented for the study, allocation will be revealed. All endotracheal intubations will be performed by fthe same anesthesiologist with 10 years' working experience skilled in videolaryngoscopy. Left-side or right-side 32Fr/35Fr Mallinckrodt™ DLTs (Mallinckrodt Medical, Athlone, Ireland) will be selected for female patients and 35Fr/37Fr DLTs for male patients depending on whether their heights were below or above 155 cm for females and 165 cm for males. If the operation side will be the left, right-side DLT will be used; otherwise, the left-side DLT will be used. To facilitate intubation, the distal 10-12 cm concavity of the DLT (with the stylet in situ) will be molded along the blade convexity in each group. The tracheal and the bronchial cuffs of the DLT tubes will be lubricated with sterile Surgilube. No premedication will be given before induction. Standard monitoring prior to induction included ECG, invasive arterial blood pressure, SpO2, and end-tidal carbon dioxide. After pre-oxygenation with 100% oxygen, anesthesia will be induced with intravenous midazolam 0.05 mg. kg- 1 , propofol 1.5 mg. kg- 1 , fentanyl 5 μg. kg- 1 , and rocuronium 0.6 mg. kg- 1 . Two minutes after rocuronium administration, DLT intubation will be performed using the allocated laryngoscope. The DLT will be inserted with the distal concavity facing anteriorly until the bronchial lumen cuff passed the vocal cords. The stylet will be then removed, and rotation will be performed while tube will be advanced. The left DLT rotated 90° counter-clockwise, and the right DLT will be rotated 90° clockwise to enter the respective mainstem bronchus. The number of intubation attempts, ease of laryngoscopy insertion, Quality of view, Assist maneuvers, Intubation difficulty will be recorded. Hemodynamic changes will be monitored during induction. If systolic blood pressure fell below 80 mmHg, ephedrine 5 mg will be administrated intravenously. Atropine 0.5 mg will be given for heart rate below 50 beats per minute. After the tip of the DLT was located in the targeted bronchus, the tracheal cuff will be inflated and ventilation of the lungs started. Fiberoptic bronchoscopic assessment of adequate bronchial cuff placement will be followed by DLT placement. DLT insertion time will be defined as from the time the laryngoscope passed the patient's lips until three complete end-tidal carbon dioxide cycles were displayed on the monitor. Intubation success rate at the first attempt will be recorded by the same observer. The difficulty of DLT insertion and delivery will be assessed by the operator, using NRS ranging from 0 to 10. The NRS results will be grouped as 0 = none, 1-3 = mild, 4-6 = moderate, and 7-10 = severe. C/L degrees were classified as four degrees (I, IIA, IIB, and III) and will be assessed by the same operator. If the degree will be not class I, external laryngeal pressure will be provided by an assistant. Time required to successful intubation. Intubation time is defined as the time taken for insertion of the blade between the teeth till the tracheal tube cuffٴ passed through the vocal cords. Failure of intubation was defined as any intubation attempt of \>120 s or inability to intubate. Number of intubation attempts, Ease of laryngoscope insertion, Quality of view by Cormack and Lehane grade . Assist maneuvers. Intubation difficult score indicates the degree of difficulty of intubation using 7 parameters (0=easy intubation, 0 ˂IDS≤5 =slight difficulty, 5 \< IDS =moderate to major diffculty, IDS= ∞ impossible intubation) . The time taken for fiberoptic bronchoscopy was defined as the time from endobronchial intubation to placement confirmation using fiberoptic bronchoscopy. The operators examined blade surfaces for blood after removal. Hemodynamic parameters (mean arterial blood pressure and heart rate) will be recorded 10 min before induction and 1, 3, and 5 min after intubation. After the assessment by fiberoptic bronchoscopy, the oral cavity, pharynx, larynx and teeth will be examined for signs of laceration or bleeding by an independent investigator who will be unaware of the type of laryngoscope used. One day after surgery, an independent investigator will interview patients to assess the presence of sore throat and hoarseness of voice.
