Postoperative cognitive dysfunction (POCD) is a decline in cognitive function (especially in memory and executive functions) that may last from 1–12 months after surgery, or longer. In some cases, this disorder may persist for several years after major surgery. POCD is distinct from emergence delirium. Its causes are under investigation and occurs commonly in older patients and those with pre-existing cognitive impairment. The causes of POCD are not understood. It does not appear to be caused by lack of oxygen or impaired blood flow to the brain and is equally likely under regional and general anesthesia"

Source : Wikipedia

It's estimated that about 40% of all persons over age 60 who are hospitalized for surgery have some degree of POCD on discharge, and about 10% still have POCD three months later.

As a rule, the shorter the duration of action of the anesthetic agent, the shorter the duration of cognitive impairment in the immediate postoperative period. No definitive evidence has been found to date for the hypothesis that anesthesia itself causes prolonged POCD.

Source : Dtsch Arztebl Int. 2014 Feb; 111(8): 119–125.

Also see : General Anaestheticsplugin-autotooltip__plain plugin-autotooltip_bigGeneral Anaesthetics

A general anaesthetic is a drug that brings about a reversible loss of consciousness.* [ see note below ]

In formal use since 1842 - the first public demonstration used Diethyl ether to carry out surgery. (Though it's likely that alcohol, another chemical classed as an anaesthetic, was previously used, extensively, for similar purposes). and Deliriumplugin-autotooltip__plain plugin-autotooltip_bigDelirium

"Over 2.6 million adults over the age of 65 develop delirium each year in the United States (US). Delirium is associated with a significant increase in mortality and the US health care costs associated with delirium are estimated at over $164 billion annually.