Study of Cognitive Functioning after Surgery Has Reassuring Findings Interview with:

Unni Dokkedal, M.P.H. Unit of Epidemiology, Biostatistics, and Biodemography University of Southern Denmark

Unni Dokkedal

Unni Dokkedal, M.P.H.
Unit of Epidemiology, Biostatistics, and Biodemography
University of Southern Denmark

MedicalResearch: What is the background for this study? 

Response: Early (seven days) postoperative cognitive impairment is common in adult surgical patients of all ages, but elderly patients are at higher risk for this complication. Previous studies have shown that these impairments are detectable up to three months after surgery in patients older than 60 years. Furthermore, the condition may persist for longer than six months in some patients with potential long-term implications of the surgery leading to impaired quality of life and increased mortality risk. We wanted to investigate the contribution of surgery, anesthesia, preexisting conditions and other factors on the postoperative cognitive functioning of elderly patients.

MedicalResearch:  What are the main findings?

Response: For a sample of 4,299 middle-aged twins younger than 70 years and 4,204 elderly twins over 70 years, all of whom were residents of Denmark, medical records were reviewed from 1977 and until the accomplishment of cognitive tests in the period from 1995 to 2001. Results from five cognitive tests were compared in twins exposed to surgery, classified as major, minor, hip and knee replacement, or other, with those of a reference group without surgery. A statistically significant lower composite cognitive score was found in twins with at least one major surgery compared with the reference group (mean difference, −0.27; 95% CI, −0.48 to −0.06), which is a negligible effect size. None of the other groups differed from the reference group except the knee and hip replacement group that tended to have higher cognitive scores (mean difference, 0.35; 95% CI, −0.18 to 0.87).To consider genetic and shared environmental confounding and to take preoperative cognition into account, intrapair analyses were performed in same-sexed pairs in whom one had a history of major surgery and the other no surgery. No difference was found in the intra-pair analysis. The results suggest that preoperative cognitive functioning and underlying diseases were more important for cognitive functioning in mid- and late life than surgery and anesthesia.

MedicalResearch: What should clinicians and patients take away from your report?

Response: Our results are reassuring in relation to long-term adverse cognitive effects of surgery and anesthesia. The report adds an important piece to the very complex research puzzle of potential adverse effects of surgery and anesthesia and could be used in clinicians’ preoperative counseling of patients. Cognitive impairment is one of the most dreaded aspects of aging and thus, without proper counseling, some elderly people may opt out of surgeries that could have improved their quality of life, for fear of becoming cognitively impaired due to surgery and anesthesia.

MedicalResearch: What recommendations do you have for future research as a result of this study?

Response: The cross-sectional design of our study did not allow us to thoroughly address selection bias due to mortality and non-attendance. This bias might have occurred as a result of patients with the largest cognitive decline not participating in the study either because they had died before study intake or because of severe cognitive impairment. In this case, the association between surgery and cognition may have been underestimated. Thus, a follow-up study, which is currently under preparation, including thorough drop-out analyses and supplementary analyses using multiple imputation techniques will complement the present study and make our results even more robust.


Unni Dokkedal, Tom G. Hansen, Lars S. Rasmussen, Jonas Mengel-From, Kaare Christensen. Cognitive Functioning after Surgery in Middle-aged and Elderly Danish Twins. Anesthesiology, 2016; 124 (2): 312 DOI:10.1097/ALN.0000000000000957

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Last Updated on March 9, 2016 by Marie Benz MD FAAD