Dexmedetomidine administration for minor procedure, such as extracorporeal shock wave lithotripsy, provides good quality of sedation and analgesia. Dexmedetomidine is a highly selective α2-adrenergic receptor agonist which causes sedative effects and reduces opioid requirements in the perioperative period. Extracorporeal shock wave lithotripsy may cause pain and result in tachycardia and vasoconstriction-related hypertension. Surgical or procedural stress may induce inflammation and it may cause further microthrombosis. Both vasoconstriction and microthrombosis will alter the microcirculatory status. Dysfunction of microcirculation may impair tissue perfusion and result in organ dysfunction. Dexmedetomidine may induce vasodilation by slow intravenous infusion for sedation. Dexmedetomidine may also reduce inflammation. After reviewing the literature, the investigators found that the effect of dexmedetomidine on microcirculation was not well investigated. By application of the non-invasive technique of sidestream dark field imaging, the investigators can investigate the vessel density, percentage of perfused vessels, and microvascular flow index on sublingual vessels.