Introduction
ADVERSE EVENTS, CORTEX
The level of anesthesia can be tracked by a complete 16-lead, 8-channel electroencephalogram (EEG), which records the electrical activity and potentials in the cerebral cortex. EEG activity can be generically classified into four wave patterns: alpha, beta, theta, and delta. It primarily occurs at frequencies between 1 and 30 Hz. When a patient is resting with eyes closed, they produce alpha waves, which have a frequency of 8–14 Hz. Highly alert and focused patients will have beta waves, which have a frequency between 14 and 30 Hz. Theta waves, which have a frequency of 4–8 Hz, are present during “light” anesthesia or the early stages of sleep. At a frequency of 0.5 4 Hz, delta waves are present during “deep” anesthesia or deep sleep [During general anesthesia, monitors obtained from electroencephalograms (EEG) allow the titration and maintaining a sufficient level of anesthesia, benefit from shortening the recovery period after awakening, and advantages from lowering the risk of anesthetic adverse events [The bispectral index (BIS) monitor is one of the EEG-derived monitoring techniques and well-established devices used to measure the depth of anesthesia. It is a tool for quantitative EEG that is frequently utilized to evaluate the hypnotic effect of anesthesia. An acceptable level of the hypnotic state is recommended to be between 40 and 60 [However, in prone and lateral positions as in renal surgeries, problems in BIS monitoring may occur. Other areas of BIS electrode placement besides those recommended by the manufacturer should be considered, such as the mastoid and post-auricular region. But the validity and reliability of their BIS values have been questioned [However, given how close the forehead sensor is to the surgical site, using BIS during some surgeries can be difficult. Due to blood or an antiseptic cleaning solution contaminating the forehead sensor, there is a strong likelihood that BIS recording may be interrupted. The size and shape of a BIS forehead sensor in the shape of a long strip can significantly affect where the surgical incision will be made [Numerous alternative BIS sensor positions have been investigated where the frontal configuration is impractical [Moreover, growing research observed a shift in alpha oscillations (7.5–12.5 Hz activity) from occipital brain regions toward anterior brain during wakefulness to GA (“alpha anteriorization”) [This study’s primary goal was to determine the degree to which BIS values varied depending on the placements of either post-auricular or frontal sensors in patients undergoing renal surgeries while in lateral positions at different stages of anesthesia. Post-auricular and frontal BIS values were our primary outcome.