Mg Sulfate Versus Dexmedetomidine on Cerebral Oxygen Saturation

spine surgery in prone position

Patients will receive loading dose of 40 mg/kg of magnesium sulfate diluted in 50 ml of 0.9% saline IVI will be given in 10 min before anesthesia induction then continuous infusion of 10 mg/kg/hour during the surgery.

Patients will receive loading dose of 1 mcg/kg dexmedetomidine diluted in 50 ml of saline 0.9% IVI will be given in 10 min before anesthesia induction then continuous infusion of 0.5 mcg/kg/hour during the surgery.

Patients will receive the same volume of normal saline.