Magnesium Sulphate Versus Fentanyl for Conscious Sedation in CSDH

Magnesium sulphate will be given to the experimental group in a dose of 50mg/kg IV over 15 minutes followed by continuous infusion at 15 mg/kg/h

Fentanyl will be given to the active comparator group in a dose of 1 μg /kg IV bolus over 15 minutes followed by continuous infusion starting at 0.5 μg /kg/h

In both groups Fentanyl and magnesium sulphate will be accompanied by IV propofol at a dose of 50- 150 μg /kg) bolus over 15 minutes to achieve target sedation level, that is Ramsay sedation scale (RSS) 3,if RSS afterwards does not reach 3, a supplementary bolus dose of 0.2 mg/kg propofol will be given to the patients, followed by ( 20-40 μg /kg/ min) to maintain Intraoperative level of sedation by bispectral index (BIS ) reading by 60-80%