Interest of the Pleth Variability Index in Neurosurgery

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.