Deterioration of posoperative cognitive function (DCPO) is an intermediate state between normal cognitive aging and dementia, defined as a cognitive alteration greater than expected for the patient's age and educational level, but which doesn't interfere with the activities of daily life, in its evolution it can lead to dementia or it can present reversal of the deterioration with return to a normal cognitive state, or a stabilization with permanence in a state of moderate alteration. In general, higher cognitive function can be affected by organic or functional problems, anesthetic-surgical, diseases associated with the elderly and / or chronic-degenerative comorbidities. Older patients who undergo regional anesthesia have special interest, the adverse cardiovascular effects, or prolonged sedation due to a pharmacokinetics that is altered by age, call special attention to reduce complications in the postoperative period. In 2010 at the Siglo XXI Hospital in Mexico City, the 68-year-old population attended was 30% of those with postoperative cognitive dysfunction 26% a week, and 10% persistence at 3 months. The DSM V recommends a neuropsychiatric, psychological and cognitive evaluation of the patient in the postoperative period, through tests such as the Mini Mental State Examination. sub-anesthetic doses of ketamine have been recently proposed to reduce the postoperative markers of inflammation, pain and opioids, in addition to having an antidepressant effect. There is a pharmacological rationale for using ketamine as a preventative measure against postoperative delirium based on its N-methyl-D-aspartate (NMDA) antagonism, It has the potential to protect against such neurological injury.

Randomized double blind clinical trial. Male and female patients 60-90 years of age scheduled in elective surgery under regional anesthesia and sedation.

The researchers will be double blind and the data analyzer will ignore the drug used ( it it should be midazolam or ketamine in an intravenous infusion). The principal investigator will limit himself to collecting the questionnaires and following up to 3 months. Simple finite randomization in two groups, will be done through envelopes.

The pre-surgical, post-surgical Mini Mental questionnaire will be applied on the first day, 1 month and 3 months. During the trans-anesthetic, hemodynamic variables and anesthetic depth index measurements will be taken, surgical time, estimated bleeding, use of other adjuvant medications, type of surgery and comorbidities will be taken as intervening variables.

Inclusion Criteria:

• age 60-90 years,
• complete primary,
• ASA I-II,
• scheduled for non-urgent surgery,
• to whom regional anesthesia and sedation are applied
• sign the informed consent
• Able to answer the brief examination of the mental state (MMSE ) preliminary with more than 24 points

Exclusion Criteria:

• not able to respond to MMSE, deaf-mute, blindness,
• history of surgery the last 6 months,
• use of pacemakers,
• allergy to anesthetics,
• use of psychiatric medication, or drugs,
• diagnosed neurological disease (cerebrovascular disease, dementia, seizures) ,
• surgery scheduled for prostate resection, or reduction of hip fractures

the participant, the researcher and the outcomes assesor don't know the drug used for sedation.