Sedation During Bronchoscopy:Dexmedetomidine vs Alfentanil

The purpose of this study is to find the best sedation necessary for patients undergoing bronchoscopy. Patients are randomized to three different regimes of sedation during bronchoscopy were studied: 1. \- Group standard/control: local anesthesia only(C) 2. \- Group alfentanil + local anesthesia(A) 3. \- Group dexmedetomidine + local anesthesia(D) The primary endpoint is the bronchoscopy score. Secondary endpoints are: Level of sedation and tolerance bronchoscopy examination. Measured parameters on the safety of examination are: the lowest saturation, needs to supplemental oxygen, amnesia , choking sensation or chest pain and if the patient is ready or not to undertake bronchoscopy second time in his life if necessary. Endtidal CO2, Respiratory rate, Blood pressure, Heart rate, level of oxygen are collected every 5 minutes before, during and after the bronchoscopy.