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 6.0 ng/ml, and use the up and down method as adjust 0.5 ng/ml of concentration of remifentanil each time. An Analgesia Nociception Index(ANI) lower than 30 and hyperdynamics (the increased heart rate(HR) and mean blood pressure(MBP) up 20% of baseline or HR>100bpm and arterial blood pressure(ABP)>180/100mmHg) indicates insufficient analgesia, therefore increase it by 0.5 ng/ml; an ANI higher than 30 and stable hemodynamics (the changes of HR and MBP within 20% of baseline or HR<50bpm and ABP<90/50mmHg) indicates that analgesia is acceptable, and the next patient will decrease it by 0.5 ng/ml during skull pin fixation.

Data collection: Heart Rate, Measure blood pressure, Analgesia Nociception Index, Bispectral index, 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