**4.3 Neurocognitive dysfunction**

Adversely affected central nervous system is a well-defined problem following cardiac surgeries especially requiring hypothermic circulatory arrest. However, it is not clear that these neurological problems are related to procedure itself or to the underlying cardiovascular disease. In that point of view Wahrborg et al. found no difference between percutaneous coronary interventions and CABG (Wahrborg et al,2004). The most frequently reported form of brain injury is postoperative neurocognitive decline (POCD), of which recovery is variable, mostly transient, also which may prolong for several years and has no known treatment, leading the search for finding various interventions to reduce this decline (Lombard et al,2010;Grigore et al,2009). The other forms of brain injury such as stroke and encephalopathy have incidences of 1-5.2% and 10% respectively; when compared to POCD the difference is striking; 10-60% at 6 months (Funder et al,2009;Newman et al,2006). Early decline rate is 50-70% within the first week, 30-50% after 6 weeks and 20-40% at 6 months and first year. As mentioned before, multiple factors influence cognitive functions including surgical recovery and analgesic and sedative requirements, that it is difficult to accuse procedures only for the adverse neurocognitive decline. It is well-known that most patients with advanced coronary artery disease already have neurocognitive decline before surgery and have more potential to develop further decline independent of surgery (Lombard et al,2010). Selnes et al (2008) reported that there is a significant late decline in neurocognitive functions after CABG sugeries, however no significant difference compared to non-surgical patients with coronary artery disease. The degree of preexisting vascular disease may influence adverse neurocognitive outcomes after CABG more than expected, as the results of many trials suggest the natural progression of cerebrovascular disease is the main determinant of cognitive decline rather than CABG (Lombard et al,2010;Grogan et al,2008).

*The clinical forms of brain injury and their frequencies (Grogan et al, 2008)* 


In the preoperative period, brain imaging can detect the prior brain infarction, white matter lesions and/or lacunar infarcts that are clinically asymptomatic and also abnormal brain perfusion areas can be detected by SPECT prior to the operation; demonstrating the highrisk patients for the development of POCD.

There are several factors that have been associated with neurological problems such as patient risk factors including aortic atherosclerosis and surgical risk factors including type of surgery, temperature control, glucose control and intraoperative hemodynamics.
