Dexmedetomidine and Hypoxic Pulmonary Vasoconstriction in Thoracic Surgical Procedures and One-Lung Ventilation

Inclusion Criteria: 1. Subject is \> 18 years of age. 2. Subject is American Society of Anesthesiologists (ASA) Physical Status I, II, III, or IV. 3. If female, subject is non-lactating and is either: * Not of childbearing potential, defined as post-menopausal for at least 1 year or surgically sterile due to bilateral tubal ligation, bilateral oophorectomy or hysterectomy. * Of childbearing potential but is not pregnant at time of baseline and is practicing one of the following methods of birth control: oral or parenteral contraceptives, double-barrier method, vasectomized partner, or abstinence from sexual intercourse. 4. Subject requires thoracic surgical procedure . 5. Subject (or subject's legally authorized representative) has voluntarily signed and dated the informed consent document approved by the Institutional Review Board. Exclusion Criteria: 1. Subject has received general anesthesia within 7 days prior to study entry, has received any experimental drug within 30 days prior to study drug administration, or has been previously enrolled in this study. 2. Subject has central nervous system (CNS) disease with an anticipated potential for increased intracranial pressure, an uncontrolled seizure disorder and/or known psychiatric illness that could confound a normal response to sedative treatment. 3. Subject has received treatment with an alpha-2 agonist or antagonist within 14 days of the scheduled surgery/procedure. 4. Subject for whom opiates, benzodiazepines, DEX or other alpha-2 agonists are contraindicated. 5. Subject has received an IV opioid within one hour, or PO/IM opioid within four hours, of the start of study drug administration. 6. Subject has acute unstable angina, acute myocardial infarction documented by laboratory findings in the past six weeks, heart rate \< 50 bpm, SBP \< 90 mmHg, or third-degree heart block unless patient has a pacemaker. 7. Subject has known elevated SGPT (ALT) and/or SGOT (AST) values of \> 2 times the upper limit of normal (ULN) within the two months prior to screening, and/or a history of liver failure. 8. Subject has any other condition or factor which, in the Investigator's opinion, might increase the risk to the subject. 9. On vasodilators, i.e.,nitroglycerin, nitroprusside, or ACE inhibitors 10. on vasopressors, i.e, norepinephrine,epinephrine, or vasopressin