Standard ASA fasting guidelines will be followed. IV 20 gauge cannula will be inserted and dedicated to the infusion drugs. Standard ASA monitors will be attached, and baseline heart rate (HR), mean arterial blood pressure (MAP), and oxygen saturation (SpO2) will be recorded. The SedLine Brain Function Monitor's electrode (Masimo O3™, Masimo corporation, Irvine, California, USA) will be positioned on the patient's forehead.

Fifty Patients will be involved in this study and randomized into two groups: 25 patients as propofol/dexmedetomidine (PD) group and another 25 patients as propofol/saline (PS) group. The PD group will receive dexmedetomidine 0.5 µ/kg bolus over 10 min before induction of anesthesia followed by a continuous infusion of (0.5 µ/kg/h) throughout the procedure . PS group will receive normal saline infusion over 10 min before induction of anesthesia and then throughout the procedure with an infusion rate adjusted to match dexmedetomidine infusion in PD group.

Anesthesia protocol, Induction of anesthesia in all patients will be done with 1% IV propofol (2 mg/kg), and IV fentanyl (2 µ/kg), IV atracurium (0.5mg/kg). Ventilation will be achieved by face mask until introduction of RB. When RB is introduced, rapid manual jet ventilation by venturi technique, In case of hypoxemia (SPO2 < 90%), bronchoscope will be used as an endotracheal tube by occluding the main port of bronchoscope and patient will be ventilated by providing intermittent positive pressure ventilation. In case of persistent hypoxemia despite adequate jet ventilation, RB will be withdrawn followed by endotracheal intubation and mechanical ventilation. Anesthesia is maintained by propofol infusion started in both groups in 4 mg/kg/h. Rate of propofol infusion will be adjusted to maintain PSI between 25-50 in order to ensure adequate depth of anesthesia. After insertion of RB above the level of carina and before proceeding to the desired bronchus, 2% lidocaine 2-3 ml will be instilled in the targeted bronchus through suction port. Hydrocortisone 100 mg will be given to minimize laryngeal edema.

At the end of the procedure, RB will be removed and replaced with a regular endotracheal tube to secure the airway, infusions will be stopped and muscle relaxation will be reversed by using neostigmine and atropine when clinically observed that it is proper timing. After end of procedure, Modified Observer's Assessment of Alertness/Sedation scale (MOAAS) will be recorded every 10 min after bronchoscopy removal. The following descriptions of MOAAS scores will be used: 0 does not respond to pain; 1 does not respond to mild prodding or shaking; 2 responds after mild prodding or shaking; 3 responds after calling loudly or repeatedly; 4 responds slowly to voice with normal tone; 5 responds readily to voice with normal tone. Patients will be transferred to the post anesthesia care unit (PACU) when MOAAS scale in between 4 and 5. They will be observed for 2-3 h in PACU for complications and hemodynamic changes, The patient will be asked if he remember anything between going to sleep and waking by using modified Brice questionnaire: 1. What was the last thing you remembered before going to sleep? 2. What was the first thing you remembered on waking? 3. Do you remember anything between going to sleep and waking? 4. While you were sleeping during the operation, did you dream?.

Inclusion Criteria:

• Patients aged 18 - 60 years, scheduled for elective rigid bronchoscopy procedure.
• ASA physical status I-II
• Both genders.

Exclusion Criteria:

• Patient refusal.
• Known allergy to any of the used drugs.
• Bleeding disorders.
• Hemodynamically unstable patients ( mean arterial blood pressure [MAP] < 60 mmHg).
• Tracheostomy tube in situ.
• Patients with stridor and any upper airway emergency.