The investigators would like to determine if using Dexmedetomidine alone or in a reduced dose can prevent or reduce the incidence of adverse effects, while providing adequate sedation, and respiratory stability as compared to propofol.

Alpha2 adrenergic receptor agonist have been used increasingly as a new armamentarium to provide sedative/hypnotic, analgesic, anxiolytic and sympatholytic effects in the perioperative settings. Dexmedetomidine, a selective and specific alpha2- adrenoceptor agonist has unique properties that makes it an almost ideal sedative drug for monitored anesthesia care in procedures under local or regional block. Unlike other drugs use for sedation, dexmedetomidine induces sedation that is similar to natural sleep (readily arousable) without causing respiratory depression. It attenuates the stress-induced sympathoadrenal response seen with laryngoscopy and intubation. It has anesthetic and opioid sparing effects, hence it may be a useful adjunct to general anesthesia and monitored anesthesia care in patients susceptible to narcotic induced respiratory depression. Another unique property of dexmedetomidine is that its sedative effect is reversible with Atipamezole. A previous study wherein dexmedetomidine has been used in procedures under local and regional block had shown that it provides effective sedation and better operating condition without significant respiratory depression. As a supplement to general anesthesia, it has been shown to provide stable hemodynamics. However, it is associated with some adverse events such as hypertension, hypotension and bradycardia, these commonly occur during bolus administration of the recommended dose of 1ug/kg. Post-operatively it can cause nausea and vomiting. Vitreoretinal surgery requires either an injection of local anesthetic within the muscle cone (retrobulbar block),or into the periorbital space (peribulbar block). This can be done individually or in combination. This surgery can also be done under a safer technique of retrobulbar block that is given using a sub-tenon's approach through a snip peritomy; a blunt cannula can be used with this technique mitigating the complications of retrobulbar hemorrhage or inadvertent injection into the optic nerve sheath or perforation of the globe using a sharp needle. The anesthetic goal is to provide an immobile and uncongested operative field. Hemodynamic stability of the patient is also important since some patients that require this procedure are elderly with co-morbid conditions such as hypertension, diabetes mellitus and Coronary Artery Disease (CAD). In our study we would like to investigate if Dexmedetomidine alone and in a reduced dose can prevent or reduce the incidence of adverse effects, provide hemodynamic and respiratory stability, provide adequate sedation with patient and surgeon satisfaction and compare it with Propofol.

Objectives:

Primary:

1. Adequate sedation
2. Hemodynamic and respiratory stability intraoperatively

Secondary:

1. surgeon satisfaction
2. Time to achieved " street fitness " status
3. subject satisfaction
4. Hemodynamic stability in PACU

Inclusion Criteria:

• American Society of Anesthesiologists rating of I-III
• good renal and liver function

Exclusion Criteria:

• renal and hepatic insufficiency
• uncontrolled diabetes
• uncontrolled hypertension
• severe cardiac disease Class III or IV
• heart blocks
• chronic use of sedatives, narcotics, alcohol or illicit drugs
• allergy to either propofol or dexmedetomidine
• pregnancy or inability to tolerate technique of the study drugs

Heart rate, blood pressure, pulse oximetry are collected for all patients undergoing sedation or anesthesia for the entire time they are in the operating room which was between 1-2 hrs. Additionally heart rate, blood pressure, pulse oximetry were monitored for 2 hours in the Post Anesthesia Care Unit where patients are placed immediately following the procedure.

Change in ECG, T wave inversion was noted on the cardiac monitor in the operating room, no intervention was required and the surgery continued without incident. A cardiology consult was called and the subject was admitted for observation. A myocardial perfusion test demonstrated a fixed deficit in the left ventricle, the Ejection fraction was 55% and serial Troponin levels were<0.2, well below threshold for evidence of myocardial injury

Termination of study due to difficulty recruiting subjects who fit the study criteria.