Cerebral Oxygenation in Total Hip Arthroplasty Patients

Inclusion Criteria: * Patients 18-80 years old undergoing unilateral total hip arthroplasty * Hypotensive epidural anesthesia Exclusion Criteria: * Contraindication to controlled hypotension and/or neuraxial anesthesia. * Severe pulmonary hypertension or pre-op systolic blood pressure reading \>150 mm Hg * Moderate to severe valvular stenosis. * History of stroke, dementia, or post-op delirium * Prior OSA diagnosis * History of benzodiazepine use (regular use for longer than 3 months) * Chronic renal or hepatic disease (renal failure, history of liver failure, cirrhosis) * History of alcoholism or heavy alcohol intake (defined as averaging more than 3 drinks per night; recovery is OK) * Parkinson's disease * Severe chronic pulmonary disease * Total anterior hip approach being used * Hip resurfacing procedure * Non-English Speaking\* * Questionnaires being used to assess mental status are only validated in English.