title: Cognitive Functioning after Surgery in Middle-aged and Elderly Danish Twins.
abstract: BACKGROUND
  Postoperative cognitive dysfunction is common, but it remains unclear whether there are long-term adverse cognitive effects of surgery combined with anesthesia. The authors examined the association between exposure to surgery and level of cognitive functioning in a sample of 8,503 middle-aged and elderly twins.
  
  
  METHODS
  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 using linear regression adjusted for sex and age. Genetic and shared environmental confounding was addressed in intrapair analyses of 87 monozygotic and 124 dizygotic same-sexed twin pairs in whom one had a history of major surgery and the other did not.
  
  
  RESULTS
  Statistically significantly 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), corresponding to one tenth of an SD, that is, a negligible effect size. In the intrapair analysis, the surgery-exposed co-twin had the lower cognitive score in 49% (95% CI, 42 to 56%) of the pairs. 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).
  
  
  CONCLUSIONS
  A history of major surgery was associated with a negligibly lower level of cognitive functioning. The supplementary analyses suggest that preoperative cognitive functioning and underlying diseases were more important for cognitive functioning in mid- and late life than surgery and anesthesia.
authors.affiliation: From the Unit of Epidemiology, Biostatistics, and Biodemography, and the Danish Twin Registry, and the Danish Aging Research Center, Department of Public Health, University of Southern Denmark, Odense, Denmark (U.D., J.M.-F., K.C.); Departments of Anaesthesiology and Intensive Care Medicine (T.G.H.), Clinical Biochemistry and Pharmacology (K.C.), and Clinical Genetics (J.M.-F., K.C.), Odense University Hospital, Odense, Denmark; and Department of Anaesthesia, Centre of Head and Orthopaedics, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark (L.S.R.).
authors.forename: Unni
authors.initials: U
authors.lastname: Dokkedal
authors.forename: Tom G
authors.initials: TG
authors.lastname: Hansen
authors.forename: Lars S
authors.initials: LS
authors.lastname: Rasmussen
authors.forename: Jonas
authors.initials: J
authors.lastname: Mengel-From
authors.forename: Kaare
authors.initials: K
authors.lastname: Christensen
mesh_terms: D000368:Aged; D003072:Cognition Disorders / Q000453:epidemiology*; D003718:Denmark / Q000453:epidemiology; D005260:Female; D015577:Geriatric Assessment / Q000706:statistics & numerical data*; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D011183:Postoperative Complications / Q000453:epidemiology*