The aim of this study is to compare the sedative, analgesic effect and hemodynamic changes due to dexmedetomidine and nalbuphine during elective colonoscopy.

Colonoscopy can be performed for the screening of cancer, adenomas, and polyps, for the assessment of known or possible bleeding, and for the evaluation of possible causes of abdominal pain, gastrointestinal symptoms, and/or changes in bowel habits. colonoscopy is associated with discomfort and sometimes pain. At present, the commonly used methods are the intravenous injection of propofol, etomidate, ketamine, and other drugs to make the patient's unconscious. The disadvantage is that the patient cannot cooperate during the examination (e.g., for changing position), and medical staff is needed to assist in turning over the patient, if necessary. This may compress the patient's stomach and abdomen, which may cause gastric reflux and aspiration, which may cause pneumonia, with morbidity and even mortality. Nalbuphine hydrochloride is a mixed agonist-antagonist opioid with a duration of action of approximately 3-6 hours. It is chemically related to both the agonist analgesic oxymorphone and the antagonist naloxone, and acts as an antagonist at the μ receptor and as an agonist at the κ receptor, resulting in analgesia and sedation with minimal effects in the cardiovascular system. Any slight RD that occurs would be restricted by a ceiling effect. Dexmedetomidine, a new drug, is highly selective α2-adrenergic receptor agonist. It possesses hypnotic, sedative, anxiolytic, sympatholytic, and analgesic properties without producing significant respiratory depression. It also reduces both anesthetic and opioid analgesic requirements during the perioperative period. It has an impressive safety margin,and it may be suitable for conscious sedation during painful procedures.

Inclusion Criteria:

1. The subject is scheduled for elective colonoscopy.
2. The subject is ≥ 18 years and ≤ 80 years.
3. Both sexes.
4. No obvious abnormalities in preoperative ECG, blood routine ,electrolytes, and other tests .
5. ASA class 1-3.

Exclusion Criteria:

1. Subject is known or believed to be pregnant or lactating women.
2. Patients allergic to α2-adrenergic agonist or sulfa drugs
3. Chronic Opioid Use (daily or almost daily use of opioids for > 3 months).
4. Patients that are immunologically compromised, or receiving chronic steroids (>30 days), excluding inhalers.
5. Sleep apnea syndrome or difficult airway.
6. Patient known to be asthmatic or recent chest infection.
7. Patients that are prisoners.
8. Patient refusal.