Cognitive reserve and the risk of postoperative cognitive dysfunction: a systematic review and meta-analysis

Background: Post-operative cognitive dysfunction (POCD) occurs in 10 to 54% of older patients during the first few weeks after surgery, but little is known about risk factors predisposing to POCD. Methods: Systematic literature review and meta-analysis of cognitive reserve indicators and POCD risk. Results: Fifteen studies on 5104 patients were included. Follow-up periods spanned 1 day to 6 months. Educational level was the most commonly assessed cognitive reserve indicator, and a longer time spent in education was associated with a reduced risk of POCD (relative risk [RR] per year increment 0.90; 95% confidence interval: [0.87; 0.94]), i.e. each year increase in education was associated with a 10% reduced risk. Similar findings were made for some analyses on education as a categorical predictor (high school versus further/higher education, RR 1.71, [1.30; 2.25]; lower than high school versus further/higher education, RR 1.69, [1.17; 2.44]) though risk was equivalent for patients with high school education and those with lower than high school education (RR 1.02; [0.78; 1.32]). Conclusion: Patients with a relatively higher level of education are at reduced risk of POCD. Risk stratification of surgical patients according to educational level may prove useful.