Post Operative Delirium is a common and serious risk of surgery. Delirium, when it occurs is associated with an increased risk of mortality, increase length of stay, and more adverse outcomes in general, including increased risk of higher level of care required at discharge.

Namenda, which is currently approved for moderate or severe Alzheimer's disease has a unique mechanism of action than other drugs for this condition. It may have the ability to protect the brain from more severe consequences of hypoxia, or hypoglycemia. Hence it is being looked at in this study to see if it can reduce the incidence and/or severity of delirium post-operatively.

Objectives of this double blind placebo-controlled study are to determine the efficacy, safety and tolerability of Namenda in the prevention of post-operative delirium as defined by DSM-IV-TR categories 293.0 Delirium due to medical condition or medications, and 780.09 Delirium NOS. The incidence of post-operative delirium is 10-50% of general surgical cases, depending on the population studied. Delirium is known to affect mortality and morbidity, and increase the length of stay of patients. Hospital mortality estimates in patients with delirium range from 10-65%, estimated to be 2-20 times that of control patients without delirium. Delirium is an independent prognostic determinant of hospital outcomes, including death, new nursing home placements and functional decline. Delirium is an independent marker for increased mortality among older medical inpatients in the 12 months post hospitalization, particularly in those patients without dementia.

Delirium may be better understood by a Multifactorial Model of Delirium, which involves a complex inter-relationship between predisposing Factors/Vulnerability and Precipitating Factors/Insults.

If higher risk factors can be identified, then preventive interventions targeted to these groups may be able to significantly reduce morbitity, possibly mortality, but at minimum improve the quality of life of those patients who otherwise would have gone through such an enormously traumatic and disturbing experience as the psychosis and disorientation of a delirium.

The Academy of Psyhosomatic Medicine Task Force on Mental Disorders in General Medical Practice, found that co-morbid delirium increased hospital length of stay: 100% in general medical inpatients, 114% in elderly patients, 67% in stroke patients, 300% in critical care patients, 27% in cardiac surgery patients, and 200-250% in hip surgery patients.

Overall Design and Plan of Study: 30 Surgical patients (type of elective surgery: total hip and total knee replacements) will be randomized into two arms of the study attempting to get a similar mean age for each group: Group 1: 15 patients receive placebo Day --8,--7,--6,--5,--4,--3,--2,--1,Day 0 (surgery), Post-op day 1,2,3, and 4. Group 2: 15 patients receive (10 mg) of Namenda (memantine) Day --8,--7,--6,--5,--4,--3,--2, then 20 mg per day on Day --1, day 0 (surgery), Post-op day 1,2,3 then 10 mg per day Post-op day 4, then stop Namenda.

Both groups will receive a MMSE, CLOX, Confusion Assessment Method (CAM) and the Delirium Rating Scale-Revised-98 Scale on day --8 (or before drug/placebo), day --1, then post-op day 1-6. Actigraphy will be performed day --8 through post-op day 6, and sleep diaries will be collected (subjected diaries pre-hospital day --8 through day --1, then objective diaries, day --1 through post-op day 6 in hospital).

Baseline screening blood tests will be drawn on all patients and include SMA-8 including BUN and creatinine, serum albumin, TSH, NH3 and baseline BP, Pulse and Temperature. Pre-op hematocrit has been shown to be a predictor as well, and may be worthwhile to follow up in these patients.

If delirium should develop in any patients, treatment will be as per usual standard of care, with likely psychiatric consultation and medications used will be tracked.

Pharmaco-economic arm (PEA) of syudy: We are working with hospital administration and will be able to obtain costs of care such as the following: room charges, locations (whether ICU, step-down unit or regular floor etc), pharmacy costs, cost of consultations needed, number of days in the hospital needed for each group. Discharge outcome (disposition, need for SNF vs. home, visiting nurse service needs) will be compared at discharge, and fo;;ow-up 30 days later.

Inclusion Criteria:

• Medically stable
• 50 years of age or older
• having elective joint replacement surgery or other orthopedic procedures that are major surgery and require general anesthesia.

Exclusion Criteria:

• Alcohol or sedative hypnotic abuse or dependence
• Pregnancy
• Dementia or MR/DD patients if they do not have sufficient capacity to understand the consent
• renal impairment or a creatinine of 1.4 or higher
• currently taking cholinesterase inhibitors.