Interest of the Pleth Variability Index in Neurosurgery

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.