The world health organization has estimated that the population over 60 years of age will increase exponentially between 2015 and 2050. This change will be more pronounced in developing countries, including Chile. Each year, the number of older people (≥ 65 years) undergoing surgical interventions raises. This is due to a sustained increase in life expectancy, demographic changes, and progress in surgical/anesthetic techniques that allow this population to undergo less invasive procedures. In addition, older patients have a higher risk of postoperative morbidity and mortality compared to younger people.

Frailty is one of the risk factors that increase adverse postoperative outcomes in the elderly population. It is defined as a state of vulnerability or lack of physiological reserve that is characterized by an inadequate resolution of homeostasis after a stressful event. Frailty determines that an event can generate changes in the postoperative state of dependence of these patients; causing a person who was independent prior to surgery to end up requiring assistance with their activities of daily living after it. Frailty has been associated with worse outcomes in different surgical settings, including increased mortality, readmission, referral to specialized care units, increased costs and hospital stay. In addition, preoperative frailty has also been associated with postoperative delirium.

Currently, there are several instruments for the diagnosis and screening of frailty that present good sensitivity and specificity. All of them require time for their execution, an experienced evaluator and adequate validation in the population in which they are intended to be used. Furthermore, with some instruments, specific elements may be required, for example the Handgrip dynamometer for the Fried phenotype. These conditions are not always easy to obtain in the local preoperative setting and the tools are not always adequately validated for non-English speaking populations. Moreover, there is uncertainty regarding which frailty instrument to choose among the dozens described in the literature, and there are time pressures that prevent the addition of more tests or evaluations in the preoperative clinic.

The use of frontal electroencephalography (EEG) during the intraoperative period has become increasingly popular. It is used to obtain a real-time record of brain electrical activity during administration of anesthetics. Interpreting the EEG in the time domain in real time in the operation room is challenging. Therefore, various processed EEG monitors (BIS®, SedLine®) currently clinically used, have incorporated the spectral analysis to their records. The spectrum presents the advantage to show the frequency decomposition of the EEG segment for all frequencies in a given range (usually \<30 Hz) by plotting the frequency on the X axis and power on the Y axis. The accumulation of spectra over time is called spectrogram and can be presented graphically on the monitor, where the X-axis represents time, Y axis the decomposition of frequencies, and the Z bar represents the amplitude or power of the different waves. With increasing age there is a decrease in spectral power and alpha wave coherence (8-12 Hz). In addition, decreased alpha spectral power during anesthetic administration has been correlated with preoperative cognitive dysfunction. Recently, preoperative physical activity, the spectral power of the alpha wave and the entire spectral band have been associated with postoperative delirium in the cardio-surgical population. In addition, the spectral power of the alpha wave and broadband power (baseline noise) has been correlated with changes in age and patient comorbidities.

The objective of this study will be to determine an intraoperative frontal electroencephalographic marker of preoperative frailty in a population older than 65 years undergoing general anesthesia with sevoflurane for elective non-cardiac surgery. Our hypothesis is that frail patients (determined by the FRAIL, Clinical Frailty Scale and Fried scales) undergoing general anesthesia with sevofluorane for non-cardiac surgery have a lower alpha spectral power and lower entire spectral band power of the EEG compared to patients of similar age, who are robust, undergoing the same type of surgeries.