EEG is a powerful tool that refers to the recording of the brain's spontaneous electrical activity along the scalp and it can be used to measure voltage fluctuations which result from ionic current flows within neurons found in the brain.The electroencephalogram is increasingly used to measure anesthetic drug effect on the central nervous system.The use of electroencephalographic monitors has been proven to decrease drug consumption during anesthesia and to lead to a faster recovery from anesthesia. Recently, the use of the Bispectral Index® (BIS®) monitor (Aspect Medical Systems, Newton, MA) has been shown to decrease the incidence of intraoperative awareness. Depth of anesthesia is frequently assessed using electroencephalogram processing systems, such as BIS and M-Entropy® (Datex-Ohmeda, Helsinki, Finland). The use of these monitors has been claimed to allow more accurate drug administration which has the theoretical benefit of avoiding phases of too light or too profound anesthesia and the associated risks of hemodynamic instability. Inadequate general anesthesia caused by under dosage causes intraoperative awareness whereas prolonged anesthesia increases the risk of postoperative complications because of over dosage. The most important factor that contributes to the inadequate general anesthesia is the current limited ability to determine the level of awareness. In this study, the investigators want to analyze the raw EEG waves under general anesthesia using sevoflurane of MAC 1.0 for different age groups from 0 to 80 years old. The relation between concentration of 1.0 MAC sevoflurane and raw EEG states in different age groups is relatively unstudied. In this prospective randomized study the investigators want to know if there is any correlation of brain waves under general anesthesia in different age groups. Given that the brain rapidly develops and undergoes significant changes from childbirth into adulthood, anesthesia induced EEG oscillations in children might differ from those of adults, and could vary significantly with age. Characterizing the structure of the EEG in relation to age would help establish the foundations for age-appropriate monitoring of brain states during general anesthesia and sedation in children. The investigators aimed to examine the effects of age on the EEG during general anesthesia, with sevoflurane as the sole hypnotic agent.

After arrival in the operating room, an intravenous line will be inserted into a large forearm vein, and standard monitors will be applied. Each patient will be continuously monitored by a 3-lead electrocardiogram, noninvasive arterial pressure, pulse oximetry, and end-tidal carbon dioxide concentration.

The induction of anesthesia will be the same in all age groups and will consist of sufentanil 0.2-0.3mcg/kg or fentanyl 1-2 mcg/kg before intubation and 0.2 mg/kg cisatracurium to facilitate intubation. Sevoflurane inhalation will be adjusted in all age groups to maintain 1.0 MAC concentration. After tracheal intubation, patients will be ventilated with a tidal volume of 6-8 ml/kg and the respiratory rate will be adapted to obtain an end-tidal carbon dioxide concentration of 30-35 mmHg.