Cognition, anesthesia, and surgery.

General anesthesia is a state of unconsciousness with the absence of pain sensation over the entire body, achieved through the administration of anesthetic drugs. It is used during certain medical and surgical procedures. The induction of unconsciousness raises the interesting question of whether this state is completely reversible, e.g. when the patient regains consciousness will all faculties return to their pre-existing state. As early as 1887 (the first demonstration of general anesthesia occurred in the 1840’s), Savage wrote “I only point out that I have met with a series of cases of insanity in which the use of anaesthetics, in predisposed subjects, has been followed by insanity.”1 In his article he goes on to describe delirium and suggests that any cause that will give rise to delirium could result in progressive “weak mindedness” and subsequent dementia. To a large extent, that level of understanding has not evolved substantially; there is still a lack of clarity as to whether delirium results in persistent cognitive change. However, modern studies have provided significantly more information on cognitive aspects of anesthesia particularly as it relates to elderly patients. If, as described in this review, cognitive alterations following anesthesia and surgery do occur, the questions are whether these problems are the direct result of drug action, a result of specific physiology such as aging, a reaction to the surgery or some combination of these effects. These questions are important in that they could impact decisions regarding surgical care and choice of anesthetic regimens, and might direct clinicians toward means of prevention and/or treatment. In this review, we survey the current knowledge of cognitive function and aging as a background for a discussion of the primary concerns arising when providing anesthetic care for elderly patients. Some definitions are important. Delirium, or acute confusional state, is a syndrome that presents as confusion and disorientation. Cognitive dysfunction, frequently called postoperative cognitive dysfunction (POCD) or long term cognitive impairment (LTCI or LCI), is most typically defined as deterioration on specific tests that are administered at two or more times. The times at which the tests are administered vary tremendously but the first test is typically administered before surgery. The content of the tests, from a neurocognitive perspective, and the means by which they are evaluated are highly variable, as will be described below. Dementia is a general term that describes a group of symptoms including judgment, language and motor skills that result from neuronal injury. From a practical perspective, cognitive dysfunction is one component of dementia. Amongst the types of dementia are Alzheimer’s disease, Lewy body disease, and vascular dementia.2 In an attempt to define states and symptoms of individuals who are developing dementia, a number of pre-dementia constructs have been defined. The most common versions are called mild cognitive impairment (MCI).3 These states are intermediate between those cognitive changes expected with normal aging and those associated with dementia.