It has been observed that some elderly people suffer temporary and sometimes permanent cognitive decline following a lengthy operation. Researchers at the University of South Florida and Vanderbilt University suspected that this might be due to excessive exposure to oxygen . Typically, during an operation, people are often administered high doses of oxygen, even as much as 100% oxygen. The researchers conducted an experiment on young adult mice, which had been engineered to be predisposed towards Alzheimer's but had not yet suffered cognitive decline. They did however already have amyloid-beta deposits in their brains. The re-engineered mice, as well as a control group that did not have the Alzheimer's susceptibility gene, were exposed to 100-percent oxygen for a period of three hours, three times over the course of several months, simulating repeated operations. They found that the Alzheimer's pre-disposed mice suffered significant cognitive decline following the oxygen exposure, by contrast with the control mice.
This is a strong indication that the excessive oxygen exposure during operations is causing oxidative damage in the Alzheimer's brain. Given the arguments I have presented above, this result makes good sense. The brain, by converting to anaerobic metabolism for generating energy (with help from amyloid-beta) is trying its best to avoid exposing the fatty acids and cholesterol to oxidative damage. But an extremely high concentration of oxygen in the blood makes it very difficult to protect the fats and cholesterol during transport through the blood, and also probably causes an unavoidable increase in oxygen uptake and therefore exposure within the brain itself.