The Effect of Propofol-based Anaesthesia Versus Low Dose Propofol With Less Than Half MAC Sevoflurane on Intraoperative Trans-cranial Motor Evoked Potential During Spine Surgeries: Ratios Rather Than Values.

This is a prospective double- blind randomized controlled study. After approval by the ethics committee at the National Cancer Institute (Cairo University) and El-Sahel Teaching Hospital (GOHTI, Cairo) and after written informed consents,46 ASA I-II patients who are scheduled for various spinal surgeries (such as: intra-spinal tumor resection, spondylolisthesis correction, traumatic spinal fractures' fixation,...) will be included in this study. Surgeons and neurophysiologists will be the same and will be blind to the anesthetic techniques in all patients.

Randomization list will be generated then patients will be randomized into two groups: control and study group.

Preoperatively, all patients will be checked for any exclusion criteria and the routine preoperative evaluation will be done. On arriving operative theater, all patients will receive 0.1 mg/kg midazolam IV. After connecting all the basic monitors' cables (NIBP, pulse oximetry and ECG) and canulating the radial artery to monitor IBP, induction of anesthesia will be done to all patients with 4μg/kg fentanyl, 2-3mg/kg propofol IV and 0.5mg/kg atracurium to facilitate endotracheal intubation. After intubation, central venous catheter( CVP), temperature probe through nasopharynx and urinary catheter will be inserted. Fentanyl infusion will be maintained in a rate of 2μg/kg/hour and will be discontinued 60 minutes before recovery.

From this time on, patients will be randomly allocated into control and study groups, each group is 30 patients; control group is the propofol (P) group and the study group is the balanced anesthesia (BA) group.

Control Group: propofol will be infused continuously in a rate of 75-100 μg/kg/min Study Group: propofol infusion in a rate of 25μg/kg/min will be given with sevoflurane. Sevoflurane concentration will be individually calculated by age-adjusted end - tidal MAC as follows: for age of 18-25 years, 26-40 years and ≥40 years MAC will be 2.6%, 2.2% and 1.8% respectively then final concentration to be delivered will be 0.2% lower than calculated half MAC.