Perioperative Cognitive Function - Dexmedetomidine and Cognitive Reserve

Postoperative Delirium or PD and Postoperative Cognitive Dysfunction or POCD are syndromes of central nervous system dysfunction that significantly complicate the recovery of a proportion of elderly patients following surgery. Delirium is typically a transient syndrome characterized by a de-novo appearance of several pathognomonic behaviors, including disorientation, decreased attention span, sensory misperceptions, a waxing-and-waning type of confusion, and disorganized thinking. PD typically occurs on postoperative days 1 to 3 and is associated with prolonged hospital stays, increased risks for morbidity and mortality and significant health care expenditures. The neuroendocrine stress response to surgery, including the immediate postoperative period, remains an important potential etiologic factor. In particular, our data suggests that stress in the immediate postoperative period is poorly controlled by all anesthetic techniques and the normal diurnal variation in cortisol is suppressed in subjects who develop POCD. Dexmedetomidine is a highly selective alpha 2A agonist currently approved for sedation in the ICU. Dexmedetomidine produces analgesia, sympatholysis, and a light sedation characterized by easy arousal. Its action converges on the endogenous substrates for natural sleep to produce their sedative action, an effect that could prove beneficial to elderly postoperative patients. We hypothesize that treatment with dexmedetomidine will diminish both PD and POCD. The essential proposition is that modulation of perioperative stress can ameliorate perioperative delirium and cognitive dysfunction. Based on both the concept of cognitive reserve as well as clinical experience, there is concern that patients with preoperative cognitive impairment are particularly vulnerable to POCD. In general, such patients have been excluded from previous studies. This study is unique in that we will assess all participants for mild cognitive impairment prior to surgery. Assessment of the impact of preexisting cognitive impairment is a secondary aim. A broad goal of this interdisciplinary project is to evaluate POCD, which is primarily an anesthesia concept, in the more general context of dementing illness as explored by geriatric psychiatry.