Cognitive Reserve and the Risk of Postoperative Cognitive Dysfunction

Abstract

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.

Figures

Figure

Forest plot of a) n = 8 studies on years of education and risk of POCD, b) n = 4 studies on high school education versus further/higher education and risk of POCD, c) n = 4 studies on high school education versus lower than high school education and risk of POCD and d) n = 4 studies on lower than high school education versus further/higher education and risk of POCD. Meta-analyses shown here are from fixed-effects models. SE, standard error; IV, inverse variance; POCD, postoperative cognitive dysfunction; CI, confidence interval

eFigure 1

Flow chart for search on cognitive reserve and postoperative cognitive reserve (POCD)

eFigure 2

Years of education and risk of POCD in subgroup analyses according to a) follow-up period, b) sample size, c) mean sample age, d) surgery type, e) proportion of males, and f) across all studies in fixed effects models. P-values are shown for meta-regression analyses to determine the contribution of study characteristics to overall pooled estimates. Of sample size, sample age, proportion of males, and follow-up period, none moderated the relationship of education with POCD. Pooled risks per year increment in education were smaller for 2 studies on non-cardiac surgery (RR 0.84; 95% CI 0.78, 0.90) compared with 1 study on mixed type of surgery (RR 0.98; 95% CI 0.91, 1.07) (meta-regression p = 0.036). POCD, postoperative cognitive dysfunction; RR, relative risk; CI, confidence interval

eFigure 3

Funnel plot for meta-analysis of years of education and POCD

eFigure 4

Funnel plot for meta-analysis of high school education versus further/higher education and POCD

eFigure 5

Funnel plot for meta-analysis of high school education versus lower than high school education and POCD

eFigure 6

Funnel plot for meta-analysis of lower than high school education versus further/higher education and POCD