Remifentanil Only vs. Midazolam and Meperidine During Elective Colonoscopy

Inclusion Criteria: * Aged 19-65 years * American Society of Anesthesiologists physical status (ASA PS) 1-2 * Patients scheduled for elective colonoscopy under Monitored Anesthesia Care in a University Hospital * Patients who signed on written informed consent. Exclusion Criteria: * The exclusion criteria are refusal or inability to provide written informed consent * Age \< 18 years * Pregnancy * Previous large bowel surgery * Psychiatric disorders * History of addiction to opiates and / or sedatives, and previous adverse reaction to any drug used in the study.