Studies on postoperative neurological complications, particularly cognitive dysfunction

Abstract

Postoperative respiratory and circulatory complications are increasingly successfully managed by advanced medical technologies. However, prevention of central nervous system (CNS) complications is not as successful. This trend seems to be more apparent in developed countries, where most patients undergoing surgeries are elderly people with coexisting diseases. For example, neuropsychological dysfunction after cardiopulmonary bypass (CPB) has been reported in more than half of patients during the early postoperative period [1]. Many original reports and review articles regarding this topic have been published in this journal. In particular, cognitive dysfunctions following cardiac and orthopedic surgery are often discussed. Cerebral infarction can be fatal or can cause severe disabilities. Hence, this complication is the most serious central neurological complication after surgery. Fortunately, however, the incidence of severe cases is not very high, the overall stroke rate in an analysis of large cohorts reportedly being approximately 1–2 % [1, 2]. However, the incidence of minor neurological complications following major surgeries is quite high, with cognitive dysfunction being far more common than stroke [2]. Although these are categorized as ‘‘clinically minor complications,’’ they are capable of interfering with the life of patients postoperatively. There is wide variation among the reported rate of cognitive dysfunction after major surgery [1, 2]. In the immediate postoperative period, the incidence ranges as high as 80–90 %, which means that almost all patients experience cognitive abnormalities after major surgery. However, at several months after the surgery, the incidence decreases to less than half of the patients, further decreasing to around one-fourth of patients at 1 year after the surgery. Although it may be true that most of the early cognitive loss is transient, multiple longitudinal studies demonstrated that, in some cases, it persists for several years after surgery, especially after cardiac surgery [3]. The incidence of long-lasting neurological symptoms seems not to be negligible. Minor neurological injuries, such as cognitive dysfunctions, do not necessarily increase the number of bedridden patients as seen after stroke. However, the extremely high incidence compared to stroke makes these injuries extremely problematic, in terms of the social impact, such as quality of life of an aged population and economic burden on healthcare resources. Among the various postoperative cognitive dysfunctions, postoperative cognitive decline (POCD) represents trivial cognitive dysfunction [2]. After a surgical procedure, patients frequently complain of memory loss and lack of concentration. Symptoms of such subtle cognitive abnormalities experienced after an operation are described as POCD. Although minor symptoms are not noticeable to other people, the patients themselves can sense the apparent abnormalities. Minor cognitive dysfunction itself is not life threatening, and the subtle differences in cognitive performance are extremely difficult to measure. For this reason, the true prevalence of POCD is uncertain. S. Saito (&) Department of Anesthesiology, Gunma University Graduate School of Medicine, 3-39-22 Showa-machi, Maebashi 371-8511, Japan e-mail: shigerus@showa.gunma-u.ac.jp