I don't have the article, but the department head where I am, quoted some research on this very topic. As a result, we use the BIS on all patients > 65 years, and try and keep it above 40, as there has been a correlation between memory loss and low BIS readings. If I remember right, there was mention of multiple anesthetics causing memory and function loss as well. I have also had patients and families complain about this, and have done hips and such under spinal anesthesia to prevent it.
Here is an article I found with a quicky search of sciencedirect.
Cognitive function after anaesthesia in the elderly
Alex Y. Bekker md, PhD, Chief of Neuroanesthesia, Associate Professor of Anesthesiology,
Edwin J. Weeks md, Assistant Professor of Anesthesiology
Department of Anesthesiology, New York University Medical Center, 560 First Avenue, IRM 605, New York, NY 10016, USA
New York University Medical Center, New York, NY, USA
Despite advances in peri operative care, a significant percentage of elderly patients experience transient post operative delirium and/or long-term post-operative cognitive dysfunction (POCD). This chapter reviews the aetiology, clinical features, preventive strategies and treatment of these syndromes. Pre-operative, intra-operative, and post-operative risk factors for delirium and POCD following cardiac and non-cardiac surgery are discussed. It is most likely that the aetiology of delirium and POCD is multifactorial and may include factors such as age, decreased pre-operative cognitive function, general health status and, possibly, intra-operative events. Currently there is no single therapy that can be recommended for treating post-operative cognitive deterioration. Primary prevention of delirium and POCD is probably the most effective treatment strategy. Several large clinical trials show the effectiveness of multicomponent intervention protocols that are designed to target well-documented risk factors in order to reduce the incidence of post-operative delirium and, possibly, POCD in the elderly.