Postoperative delirium and postoperative cognitive dysfunction in the elderly - what are the differences?

Postoperative cognitive impairment is an increasingly common problem as more elderly patients undergo major surgery. Cognitive deficits in the postoperative period cause severe problems and are associated with a marked increase in morbidity and mortality. There are two main entities of postoperative cognitive decline, delirium and postoperative cognitive dysfunction, which are often reported as being part of the same continuum. Although there are similarities in the predisposing factors, it seems unlikely that they share the same pathophysiology. Both have multifactorial pathogenesis but differ in numerous other ways, with delirium being well-defined and acute in onset and postoperative cognitive dysfunction (POCD) being subtler and with longer duration. This review aims to provide an overview of the differences in the diagnosis of the two entities and to illustrate the methodological problems that can be encountered when evaluating cognitive deficits postoperatively.