Forty patients were enrolled, and all patients used total intravenous anesthesia (remifentanil-propofol based total intravenous analgesia) as anesthesia induction and maintenance. According to the preliminary data of this department, patients who underwent intracranial surgery for skull pin fixation used remifentanil 5.0-6.0 ng/ml, while the hemodynamics is relatively stable. Therefore, when this plan is implemented, the patient needs to be under the same depth of anesthesia (monitored by electroencephalography, maintaining a value of 40-60), first start with remifentanil 5.0 ng/ml, and use the up and down method as adjust 0.5 ng/ml of concentration of remifentanil each time. Inadequate antinociception (Surgical Pleth Index(SPI) > 80 and hyperdynamics (the increased heart rate (HR) and mean blood pressure (MBP) above 20% of baseline or HR>100bpm and arterial blood pressure(ABP)>180/100mmHg)) is defined as failure, therefore we increase remifentanil by 0.5 ng/ml; otherwise, the setting is considered successful without abovementioned situations.

Data collection: heart rate, mean blood pressure, Surgical Pleth Index, bispectral Index, pulse pressure variance, systolic pressure variance, concentrations of propofol and remifentanil before 2 mins, during, 5, and 15 mins of skull pin fixation were recorded and analyzed.

Inclusion Criteria:

1. Must be at least 20 years old and less than 80 years old
2. With anesthesia risk grade below grade three (including grade three) (ASA I~III).
3. Patients who are expected to undergo intracranial surgery for skull pin fixation

Exclusion Criteria:

1. Those with anesthesia risk classification ASA class IV or higher
2. Those who are allergic to opioid analgesics or propofol drugs
3. Emergency patients