Prevalence of undiagnosed mild cognitive impairment in elderly patients undergoing thoracic surgery and its relationship with postoperative outcome: a prospective cohort study

Abstract Background The prevalence of undiagnosed mild cognitive impairment (MCI) in elderly patients scheduled for thoracic surgery and its association with adverse clinical outcomes is still unproven. Methods We enrolled 170 patients 65 year of age or older who were scheduled for thoracic surgery. 82 males and 88 females with ASA grade II-III. All the elderly patients were tested with Chinese modified version of MoCA preoperatively. According to the test results, they were divided into two groups: group N (MoCA score>25) and group AN (MoCA score≤25). Outcomes included the hospital length of stay (primary outcome), the length of stay in patients with PPCs (LOS-PPCs), the pulmonary complications (atelectasis, pulmonary infection, respiratory failure) and other complications (blood transfusion, chylothorax, new arrhythmia, myocardial infarction and acute cerebral infarction) (secondary outcomes). Data were analyzed using univariate and multivariate analyses. Results Seventy-four of 154 (49%) patients screened positive for probable mild cognitive impairment (MoCA ≤ 25) in the final analyses. The hospital length of stay and LOS-PPCs in elderly patients with mild cognitive impairment preoperatively were significantly longer than those with group N (P<0.05). Multivariate stepwise regression showed that preoperative MCI was an independent risk factor for prolonging the hospital length of stay and LOS-PPCs. Patients with a MoCA score less than or equal to 25 were more likely to have a longer hospital length of stay (OR = 2.355, 95% CI =1.137 to 4.877, P=0.021) and LOS-PPCs (OR = 6.867, 95% CI =1.116 to 42.257, P=0.038), but not related to increase the incidence of postoperative pulmonary complications (OR = 0.955, 95% CI =0.280 to 3.254, P=0.941) and other complications (OR = 1.687, 95% CI =0.502 to 5.665, P=0.398) compared to those with a MoCA score greater than 25. Conclusions The prevalence of undiagnosed probably mild cognitive impairment among elderly patients scheduled for thoracic surgery is high (49%). Such impairment is associated with a longer hospital stay and LOS-PPCs, while it is not possible to conclude that it is related to the incidence of pulmonary complications and other complications after surgery.