Can we Get Conscious Sedation by Combining Dexmedetomidine With Alfentanil?

Inclusion Criteria: Adult over 18 years, of both sexes, for which a procedural sedation is needed in emergency room. The rules for sedation, in accordance with the international guidelines, are: * The insertion of a chest drain * Abscess incision and drainage * Closed reduction of a dislocated joint Exclusion Criteria: * Patients refusing to participate in the study (refusal to sign the consent form) * Patients refusing sedation * Patients unable to participate in the study (consent is impossible to obtain) * Pregnant women * The hypersensitivity to the active ingredient, dexmedetomidine hydrochloride. * Patients with poor respiratory status determined by: Respiratory rate \> 30 / min Oxygen saturation \<90% * Patients with unfavorable hemodynamic status determined by : A heart rate \> 120 / min A heart rate \< 50 / min Systolic blood pressure ≥ 180 mmHg or ≤100mmHg Diastolic blood pressure ≥ 110mmHg * Patients with contraindication to the use of dexmedetomidine : Advanced heart block (level 2 or 3) unless pacemaker Acute cerebrovascular disease