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*.

Coronary artery bypass surgery, performed with or without cardiopulmonary bypass, is frequently followed by postoperative cognitive decline. Near-infrared spectroscopy is commonly used to assess cerebral tissue oxygenation, especially during cardiac surgery. Recent studies have suggested an association between cerebral desaturation and postoperative cognitive dysfunction. We therefore studied cerebral oxygen desaturation, defined as area under the cerebral oxygenation curve < 40% of > 10 min.%, with respect to cognitive performance at 4 days (early) and 3 months (late) postoperatively, compared with baseline, using a computerised cognitive test battery. We included 60 patients, of mean (SD) age 62.8 (9.4) years, scheduled for elective coronary artery bypass grafting, who were randomly allocated to surgery with or without cardiopulmonary bypass. Cerebral desaturation occurred in only three patients and there was no difference in cerebral oxygenation between the two groups at any time. Among patients who received cardiopulmonary bypass, 18 (62%) had early cognitive decline, compared with 16 (53%) in the group without cardiopulmonary bypass (p = 0.50). Three months after surgery, 11 patients (39%) in the cardiopulmonary bypass group displayed cognitive dysfunction, compared with four (14%) in the non-cardiopulmonary bypass group (p = 0.03). The use of cardiopulmonary bypass was identified as an independent risk factor for the development of late cognitive dysfunction (OR 6.4 (95% CI 1.2-33.0) p = 0.027. In conclusion, although cerebral oxygen desaturation was rare in our population, postoperative cognitive decline was common in both groups, suggesting that factors other than hypoxic neuronal injury are responsible.

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

Postoperative 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.