The Effect of Balanced Anesthesia Regimen on Intraoperative Trans-cranial Motor Evoked Potential During Spine Surgeries:

in a rate of 75-100 μg/kg/min in P group, and 25μg/kg/min in BA group

in BA group will be 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.

using NIM-SPINE™ SYSTEM (2005 Medtronic Sofamor Danek USA, Inc.). The stimulation used is a train-of-five square wave stimulation, 2ms inter-stimulus interval, 500 μs width and 40-220 mA intensity which can be increased with 10 mA steps till muscle answer potential is recorded.