Postoperative cognitive dysfunction

(Parts of the presentation have been previously published as Deiner, S and Silverstein J Postoperative Delirium and Cognitive Dysfunction Br. Postoperative cognitive dysfunction (POCD) is diffi cult to defi ne. Broadly, POCD refers to deterioration in cognition temporally associated with surgery. While the diagnosis of delirium requires a detection of symptoms, the diagnosis of POCD requires preoperative neuropsychological testing (baseline) and a determination that defi nes how much of a decline is called cognitive dysfunction. The spectrum of abilities referred to as cognition is diverse, including learning and memory, verbal abilities, perception, attention, executive functions and abstract thinking. It is possible to have a decre-ment in one area without a defi cit in another. Self reporting of cognitive symptoms have been shown to correlate poorly with objective testing, so valid pre and postoperative testing is essential to the diagnosis of POCD (1). Many elderly patients may have preexisting mild cognitive impairment that has gone undiagnosed. Unfortunately, there has not been a standard methodology used in the multiple studies within the POCD literature (2). Selection of neuropsychological test instruments and the amount of change considered to be signifi cant, timing of testing, inclusion and exclusion criterion have all varied (3). Furthermore, the batteries used, while relevant, have had fl oor effects and have not incorporated batteries than are somewhat different than those employed by dementia researchers. Hence it is diffi cult to defi ne the presence and therefore incidence of POCD or to clearly understand the relationship between POCD and other dementing illnesses. Some commonly used testing instruments include the Logical Memory Test, the CERAD word list memory, the Boston Naming test, Category Fluency test, Digit Span Test, Trail making test, Digit symbol substitution test. Interestingly, POCD test batteries tend to be a compilation of tests which have shown differences among subjects in previous studies of POCD. The domains that were most sensitive include: verbal learning and working memory, episodic memory, processing speed, and set shifting. The method of scoring the testing batteries and determining how much dysfunction is clinically signifi cant remains an open subject. One method is the percentage change method i.e. postoperative score-preoperative score/preoperative score. Averaging across groups is discouraged, because while some patients will decline, others may improve over time and this difference may be masked. Another method defi nes a number of standard deviations outside of which a score will be called a decline. However, this …