Another research group assessed pairs
Another research group assessed 8503 pairs of middle-aged (<70 years) and advanced age Danish twins (≥70 years). There were two groups: 1) those who had undergone at least one surgery (18–24 years before the cognitive evaluation); 2) those who had not undergone any surgical intervention. In addition, subjects who underwent surgery were allocated into four groups: 1) major surgeries; 2) knee and hip arthroplasty; 3) minor surgeries; 4) others. Results from five cognitive studies were compared between twins. Confounding of genetic and environmental factors were assessed in intra-pair analysis of 87 monozygotic and 124 dizygotic same-sex twin pairs with and without history of surgery, respectively. Twins who underwent major surgeries scored slightly worse on cognition tests compared with those who had not undergone any intervention; however, the authors consider the difference as an effect of negligible size. Intra-pair analysis showed that Prednisolone the twin exposed to surgery had lower scores on cognitive tests in 49% of the pairs. Twins aged 70 and older who underwent hip and knee arthroplasty scored higher on cognitive tests, even higher than those who had not undergone any intervention. The study suggests that underlying diseases may be an important risk factor for slight variations in cognitive function between surgical and non-surgical groups and preoperative cognitive function may be a more important determinant of cognitive functioning at later ages than surgery and anesthesia. Another prospective cohort study evaluating the association between anesthesia and dementia or Alzheimer disease included patients aged 65 years or older without dementia (n=3988) who were followed up to the onset of dementia, death, or abandonment. At the beginning of the study, information was collected on previous surgical procedures under general or neuraxial anesthesia and new interventions were reported every two years. A comparison was made between patients undergoing high-risk surgeries under general anesthesia, other surgeries under general anesthesia, other surgeries under neuraxial anesthesia and patients not undergoing surgical intervention and anesthesia. During the follow-up period, 946 (24%) subjects were diagnosed with dementia, 752 (19%) had Alzheimer's disease, and 42% of those involved reached the end of the study without any diagnosis of dementia. Adjusted risk of dementia was not higher in the group of subjects with high-risk surgeries under general anesthesia compared to the group without history of anesthesia (HR=0.86, 95% CI 0.58–1.28); the same was true for Alzheimer disease (HR=0.95, 95% CI 0.61–1.49). The authors concluded that there was no association between exposure to anesthesia and development of dementia/Alzheimer disease in older adults. In 2016, the Mayo Clinic researchers published a new population-based prospective cohort study assessing the association between general anesthesia exposure after 40 years of age and incidence of mild cognitive impairment in the elderly. Subjects aged between 70 and 89 years (n=19,731) undergoing various neuropsychological assessments at baseline and at 15 months were selected, and data on exposure to anesthesia after the age of 40 were also collected. Of the 1731 participants, 536 (31%) developed mild cognitive impairment. Exposure to anesthesia, number of exposures, and total time of cumulative exposure were not associated with mild cognitive impairment. However, on a secondary sensory analysis, rods found an association between anesthesia after the age of 60 and incidence of mild cognitive impairment (adjusted HR=1.25, 95% CI 1.02–1.55, p=0.04). The authors do not exclude the possibility that exposure to anesthetic agents at an advanced stage of life may be associated with increased incidence of mild cognitive impairment. However, they concluded that there was no significant association between cumulative exposure to anesthesia after the age of 40 and this cognitive change.