Dementia is a syndrome characterized by cognitive and behavioral impairment in older adults, which usually manifests as memory loss, communication difficulties or changes in mood. Dementias affect around 50 million people in the world, having an impact on their ability to carry out their daily activities, often requiring family and social support.

The main cause of dementia in Chile and in the world is Alzheimer's disease (AD), which is characterized by affecting large areas of the cerebral cortex and hippocampus, manifesting mainly in alterations in selective memory. The pathogenesis of AD involves the neuronal accumulation of β-amyloid (Aβ) proteins in the form of extracellular plaques, and tau, which gives rise to neurofibrillary tangles. AD diagnosis is usually made based on clinical criteria, however, the accurate diagnosis of AD is clinical-neuropathological. Several studies have supported the neuropathological study based on the presence of Aβ and tau proteins in cerebrospinal fluid (CSF), using them as biomarkers of the disease, which has allowed updating the definition of AD based on them. However, our country does not perform a study of dementia biomarkers in CSF, which is essential for the diagnosis of certainty of the pathology.

The objective of this project is to evaluate a set of biomarkers of EA (tau, ptau, Aβ) in CSF and blood of elderly patients who will undergo surgery in the Clinical Hospital of the University of Chile (HCUCH) and in whom it is performed lumbar puncture (LP) by anesthesia, to detect those patients who have these CSF biomarkers and who show lower performance in cognitive evaluations. For this, it is intended to mount a biobank of CSF samples with samples of 30 subjects by conducting a clinical pilot study. Patients will be evaluated prior to surgery with the Montreal Cognitive Assessment (MoCA) to determine the presence of cognitive impairment, and CSF samples, obtained by LP, will be analyzed by immunodetection of Aβ40, Aβ42, tau and ptau with multiplex technology. In addition, tau will be detected in platelets by Western Blot of blood samples from patients, and the relationship between plateau tau levels and biomarkers in CSF will be evaluated. Finally, the correlation between performance in cognitive assessment and levels of biomarkers in blood and CSF will be evaluated, in order to assess the usefulness of these markers in the detection of the presence of cognitive impairment.

Inclusion Criteria:

• Subjects older than 65 years who will undergo surgery in the HCUCH (for any reason) and who require lumbar puncture for anesthesia.
• Autovalent, with no history of dementia, with MoCA ≥ 20 points (score adapted to the Chilean population).
• The subjects will not be carriers of medical, neurological or psychiatric pathologies that could affect their participation in the study or its results. The presence of chronic pathologies will be admitted, as long as they are under stable treatment and without evidence of decompensation in the last 3 months.

Exclusion Criteria:

• Antecedents of being carriers of dementia or symptomatic neurodegenerative disease.
• Medical or surgical decompensated pathology.
• Contraindication of lumbar puncture.
• Physical or mental inability to consent to study entry.

Patients who will undergo surgery in the HCUCH, for any reason