The Association Between Minor Brain Injuries and Level of Anesthesia Detected by a New EEG Based Tool, to Delirium and Post-operative Cognitive Dysfunction After Cardiac and Non-cardiac Surgery - a Proof of Concept Study

As the population ages and medical progress is made, many elderly patients that previously would not have been candidates for surgery are now undergoing operations. In this group of older patients, brain dysfunction after anesthesia and surgery is well recognized and categorized into two distinct clinical entities; Post-operative cognitive delirium (POD) and post-operative cognitive dysfunction (POCD).

Delirium is an acute and fluctuating deterioration in attention accompanied by either a change in cognition or arousal and is often diagnosed by criteria established in the Confusion Assessment Method (CAM). Delirium can present as hypoactive (decreased alertness, motor activity and anhedonia), as hyperactive (agitated and combative) or as mixed forms. Age and the type of operation are the major risk factors.

Post-operative cognitive dysfunction (POCD) is a term used to describe subtle changes in cognition, such as memory and executive function. The most commonly seen problems are memory impairment and impaired performance on intellectual tasks. In severe cases, it can lead to inability to perform daily living functions. The reported incidence figures for postoperative cognitive dysfunction vary depending on the group of patients studied, the definition of POCD used, the tests used to establish the diagnosis and their statistical evaluation, the timing of testing, and the choice of control group. The diagnosis of POCD relies on the use of neuropsychological tests, including; visual verbal learning test, based on Rey's auditive recall of words, the concept shifting test, based on the trail- making test from Halstead and Reitan's neuropsychological test battery, the Stroop color word interference test , the letter-digit coding, based on the symbol-digit substitution task from the Wechsler adult intelligence scale and the four boxes test. In a large prospective multicenter cohort study, it was found that the presence of cognitive dysfunction 3 months after noncardiac surgery was associated with an increased mortality. Furthermore, patients with cognitive decline at 1 week had an increased risk of leaving the labor market prematurely and a higher prevalence of time receiving social transfer payments. The mechanisms leading to cognitive impairment after anesthesia and surgery are not yet fully clear. The risk factors for developing POCD are related to patient characteristics, type of operation and anesthetic management.

Cardiovascular, respiratory, hepatic, and renal insufficiency are all associated with impaired brain performance. It is theoretically obvious that an adequate intraoperative oxygen supply for all vital organs is essential if postoperative cerebral dysfunction is to be avoided. Casai et al found that brain desaturation (rSO2 decrease <75% of baseline) occurred in 40% of elderly patients after noncardiac surgery, and the cerebral desaturation was linked with a high incidence of POCD. A recent systematic review shows that reductions in cerebral oxygen saturation (rSO2) during cardiac surgery may indicate CPB cannula malposition, particularly during aortic surgery. However, only weak evidence links low rSO2 during cardiac surgery to POCD.

POCD is a well-recognized clinical phenomenon of multifactorial origin; emboli, hypoperfusion, inflammation, and patient's preoperative cerebral dysfunction Meticulous surgical and anesthesiological techniques are important for preventing complications and keeping the risk of POCD to a minimum.