A Comparison of Sedative Drugs for Conscious Sedation During Ultrasound Guided Transbronchial Needle Aspiration

1. Appropriate sedation is needed for medical diagnosis, treatment, and the safety for patients. In non-surgical approaches, benzodiazepines are broadly used for ideal sedated status for patients. * However, especially in bronchoscope procedure, continuous monitoring of oxygen saturation is needed to prevent hypoxia due to respiratory distress induced by benzodiazepine. * A alpha-2 agonist, dexmedetomidine, which has similar sedative effect, but has less adverse effect of respiratory distress compared to previous agents, was introduced. 2. It is necessary to compare the efficacy and safety of dexmedetomidine with that of midazolam in ultrasound guided transbronchial needle aspiration (EBUS-TBNA). * Double blind randomized trial * Primary outcome: The number and duration of desaturation, volume of sedative, any use of rescue midazolam, and Ramsay Sedation Scale (RSS) score (for efficacy), and hypertension, tachycardia, any need for mandible support or manual ventilation, and any need for intubation (for safety).