A review of postoperative cognitive dysfunction and neuroinflammation associated with cardiac surgery and anaesthesia

Abstract

SummaryPostoperative cognitive dysfunction is receiving increasing attention, particularly as it mainly affects the (growing) elderly population. Until recently, cognitive deficits after cardiac surgery were thought to be caused by physiological disturbances associated with the cardiopulmonary bypass technique. Although the technique of 'off-pump' coronary revascularisation may potentially be associated with improved outcome, long-term follow-up studies have failed to demonstrate a significant reduction in the incidence of postoperative cognitive dysfunction. The focus of research is thus shifting from cardiopulmonary bypass to other factors common to both techniques, such as surgery, anaesthesia and patient-related predisposing factors. Priming of the immune system by ageing and atherosclerosis may result in an exaggerated systemic and cerebral inflammatory response to cardiac surgery and anaesthesia, causing neuronal loss or dysfunction resulting in cognitive dysfunction. We briefly discuss the evidence for cardiopulmonary bypass-related neuronal injuries in adult cardiac surgery patients, and review the evidence that immune priming is a key factor in the pathogenesis of cognitive dysfunction after cardiac surgery.

A pilot study of cerebral tissue oxygenation and postoperative cognitive dysfunction among patients undergoing coronary artery bypass grafting randomised to surgery with or without cardiopulmonary bypass*

“…There were no significant differences in any of these parameters between the two groups of patients. Median (IQR [range]) length of stay in ICU and in hospital was 1 (1-1 [1][2][3][4][5][6][7][8][9][10][11][12]) and 9 (6-12 ) days, respectively, in the CPB group, and 1 (1-1 [1][2][3][4][5][6][7][8]) and 8 (6-11 [4][5][6][7][8][9][10][11][12][13][14][15]) days for patients in the no-CPB group (p = 0.840 and p = 0.552, respectively).…”

“…If, however, one accepts that postoperative cognitive dysfunction exists and is the result of diffuse neuronal injury, then there are two possible conclusions. The first is that CPB is not harmful, and that neuronal injury arises with both techniques (with and without CPB) as a result of common responses to surgery and anaesthesia (such as a priming-induced exaggerated inflammatory response) [2]. A second possibility is that both techniques have adverse effects on the brain with similar cognitive consequences, but via different mechanisms.…”

“…Coronary artery bypass graft surgery (CABG) is frequently associated with a systemic inflammatory response [1] and injury and dysfunction of several organs, including the brain [2][3][4]. Diffuse cerebral injury after CABG may result in delirium and/or cognitive decline.…”

“…AUC 40 = ∑ [∫(40 À rSO 2 ) dt] for all periods where 40 À rSO 2 > 0). Secondary outcomes were the incidence of postoperative cognitive dysfunction at 4 days and 3 months postoperatively, the incidence of major complications, and the duration of ICU and hospital admission.…”

Understanding terminology of delirium and long-term cognitive impairment in critically ill patients

“…Several approaches have been taken to define POCD. 74,75 Commonly used criteria include a 20% percentage change from a baseline evaluation in a pre-defined number of tests (usually two or more tests) or an absolute decline (>1 S.D.) from baseline scores in two or more neuropsychological tests, though numerous other definitions have been employed as well.…”