Forest plot in predefined subgroups. Forest plot assessing the effect of combined epidural–general anesthesia versus general anesthesia alone in predefined subgroups. Logistic models were applied for assessment of treatment-by-covariate interactions. Treatment-by-covariate interactions were assessed separately for each subgroup factor, including study center, age, sex, education level, body mass index, preoperative mini-mental status evaluation, duration of surgery, location of surgery, and type of surgery. ICU, intensive care unit.