This clinical trial aims to study the interest of the Pleth Variability Index (PVI) to evaluate perioperative fluid responsiveness in neurosurgery in adults.

The main question it aims to answer is:

• Does the Pleth variability index predict fluid responsiveness in neurosurgery? Researchers will compare the Pleth variability index to dela PP to see if it predicts fluid responsiveness in neurosurgery.

Once participants give their consent, they will be randomly assigned to one of two groups. In one group, fluid responsiveness will be monitored using the Pleth Variability Index, while in the other group, it will be monitored using delta PP.

Inclusion Criteria:

1. Patients proposed for intracranial surgery
2. Must be aged 18 and over
3. Must be classified as ASA I, ASA II, and ASA III according to the American Society of Anesthesiologists classification

Exclusion Criteria:

1. Non-consenting patients
2. Patients classified ASA IV or higher
3. Cardiac arrhythmia
4. Heart disease with left ventricular ejection fraction less than 45%
5. Obesity with a BMI greater than 40 Kg/m2.
6. Peripheral vascular disease
7. Severe lung disease
8. End-stage renal disease
9. Intraoperative cardiac arrhythmia
10. The occurrence of cardiac arrest
11. The occurrence of hemorrhagic shock
12. Intraoperative use of low tidal volumes or high respiratory rates.