The review included 46 studies (8,001 participants). The included studies were cohort studies (8 without controls, 886 participants; 12 with controls, 3,903 participants), comparisons with general anaesthetics (2 non-randomised studies, 132 participants; 15 randomised studies, 1,569 participants) and comparisons of anaesthesia techniques (9 studies, 1,511 participants).
7- to 21-day assessments.
Three of the 4 cohort studies without controls reported a decline in cognitive function, ranging from 41 to 71% of patients; the result of the fourth study was unclear. Six of the 7 cohort studies with a control group reported a decline in cognitive function, ranging from 6.8 to 31% of patients.
It appeared from the review that the elderly are more at risk of post-operative cognitive decline than younger patients. Three studies found that age over 70 years is associated with a higher risk of post-operative cognitive dysfunction in comparison with younger patients. Three other studies with similar methodology found greater rates of post-operative cognitive dysfunction in patients aged over 60 compared with those aged 40 to 59 years (25.8 to 32.7% versus 19.2%).
22-day up to 6-month assessments.
The results from these studies were mixed. Five out of 17 studies reported no decline. Two out of 9 controlled studies found a significant difference in cognitive decline between the surgical and control groups; the results from other studies were either not clear, or showed no difference or no statistically significant difference between the groups.
Over 6 months.
Nine of 14 studies reported no decline or an improvement in cognitive function; two stated than a decline could be shown. Eight studies that tested significance stated that there was no difference, or that it was not statistically significant, and some results were unclear.
There was little evidence to suggest a difference in post-operative cognitive dysfunction comparing general versus local anaesthesia at 7 to 21 days, or in follow-up to 6 months.