Plethysmographic Variability Index in Post Spinal Anesthesia Hypotension in Cesarean Section

* Full term pregnant female patients presented for elective C.S for single viable fetus will be included in this study. * Before anesthesia, the patient will be attached to a monitor of: ECG , heart rate, non invasive blood pressure, pulse taximeter applied on the index finger of the limb not attached to the blood pressure cuff, pulse oximetry and plethysmographic variability index (PVI) and perfusion index (PI) will be taken by (Massimo radical 7, Massimo corp. USA). Measures will be recorded every 5 minutes preoperative. * Patients with PVI \ 15 are started on intravenous infusion of warm ringer lactate solution via suitable pore intravenous cannula to reach target of PVI \<15 or a total 1 liter of ringer lactate. * The patients in which the PVI is corrected by fluid to level below 15 will be Group (C) or corrected group. Patients in which intravenous fluid administration did not result any change in PVI or changed but still higher than 15 will be Group (NC) or non corrected group. After preoperative preparation patient is shifted to operating theater, with all monitors applied. She will receive spinal block at lumbar 3-4 space with hyperbaric bupivacaine 8 mg plus 25 mic fentanyl. After giving anesthesia and positioning for surgery with a left lateral tilt of 15 degrees,