Investigators conduct this retrospective analysis to test this hypothesis that the EEG spectrogram guided general anesthesia with dexmedetomidine co-administration with propofol may significantly reduce the propofol consumption during craniotomy and to investigate potential benefits on postoperative outcomes.

The bispectral index (BIS), is widely applied to maintain anesthetic depth. However, this processed EEG index may be ambiguous when dexmedetomidine is administrated. Because each anesthetic produces distinct brain states that are readily visible in the EEG spectrogram which can be easily interpreted by anesthesiologists, the EEG spectrogram-guided anesthesia is theoretically beneficial to avoid unnecessary anesthetic exposure when dexmedetomidine is co-administrated but this remains not yet clarified. Recently, the investigators reported a randomized controlled trial which revealed that co-administration of dexmedetomidine with propofol by using the BIS score guidance, is associated with profound propofol sparing effects and more favorable postoperative neurological outcomes (Eur J Anaesthesiol . 2021 Dec 1;38(12):1262-1271.). Based on the advance of knowledge of EEG spectrogram, the investigators have transited our practice based on the EEG spectrogram guidance. In this study, the investigators analyze the influence of EEG spectrogram guidance on the propofol sparing effect and the postoperative profile in comparison to patients of our previous BIS-guided protocol.

Inclusion Criteria:

• Patients undergoing elective craniotomy for brain tumor resection, aneurysm clipping, an intracranial bypass procedure, or microvascular decompression
• age between 20 to 80 yr

Exclusion Criteria:

• Fever, elevated white blood cell or C-reactive protein
• Impaired liver function, eg. AST or ALT >100; liver cirrhosis > Child B class
• Impaired renal function, cGFR< 60 ml/min/1.73 m2
• Cardiac dysfunction, such as heart failure > NYHA class II

Patients undergoing elective craniotomy for brain tumor resection, aneurysm clipping, an intracranial bypass procedure, or microvascular decompression.