Both elderly and children appear to have a higher incidence of cognitive brain problems after even routine surgery. It has been considered that both have delicate blood flow to regions in between the large vessels. These are called watershed regions. It has been postulated that not being able to guarantee perfectly even oxygen during anesthesia to these regions might be causing these problems. But, this mechanism has not been proven. Recent studies with children after surgery show inconsistent findings—one implying a higher incidence of cognitive brain problems.
In the elderly there are no exact studies because of problems performing them, but the percentage of those with mental changes after surgery is great—some considered a reversible delirium and some small regions where a lack of oxygen causes very small microscopic strokes that cannot be seen on MRIs. There is no question that there is a greater amount in the elderly, but the reasons have not been clear. It may not be from loss of oxygen, but rather signals from parts of the body related to inflammation after a physical assault might be altering the brain.