Dexmedetomidine Versus Propofol in Vitreoretinal Surgery

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: Adequate sedation Hemodynamic and respiratory stability intraoperatively Secondary: surgeon satisfaction Time to achieved " street fitness " status subject satisfaction Hemodynamic stability in PACU

Subject will receive a bolus of0.5ug/kg intravenously over a period of 10-15 minutes, followed by an infusion of 0.2-0.7ug/kg/hr of drug.

bolus of 0.5ug/kg intravenously over a period of 10-15 minutes, followed by an infusion of 0.2-0.7ug/kg/hr of drug

Bispectral Index Score measurement uses processed electroencephalogram signals to measure sedation depth of a scale from 0-100 (0=coma; 40-60=general anesthesia;60-90 sedated;100=awake) University of Michigan Sedation Scale (1-4) is an observational scale that quantifies sedation.1=normal response to verbal stimuli, 2=conscious sedation, responsive to tactile stimuli, 3= deeply sedated responsive to repeated or painful stimuli, 4=general anesthesia: not arousable.

systolic and diastolic blood pressure was recorded at 5 minute intervals up to 120 min and were averaged per study arm

respiratory rate data were recorded at 5 minutes intervals throughout the surgical procedure up to 120 mins for both groups and averaged per study arm

Subjects will be kept in the Post Anesthesia Care Unit (PACU) for a period of 2 hours. However it will be documented as to when, in the opinion of the PACU staff, the subject has met the criteria for discharge.

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