MgSO4 was found to reduce the perioperative anesthetic and analgesic requirements when used as an adjuvant to general anesthesia. Fentanyl is a potent opioid and used as adjuvant to other sedatives in awake craniotomy procedure. No study, to the best of our knowledge had evaluated fentanyl continuous infusion, nor MgSo4 infusion as adjuvant sedative agents to propofol during Burr-hole surgery. The aim of this study is to evaluate and compare MgSO4 versus fentanyl continuous infusions for conscious sedation in patients undergoing burr hole surgery for evacuation of subdural hematoma with local infiltration.

All participants or their proxy will be informed about the anesthetic techniques and the operative procedure and will provide written informed consent before enrollment in the study.

The eligible patients will be randomly divided by computer designed lists and then will be concealed in closed envelopes into the two study groups. A research assistant who will not be involved in patient management will be responsible for opening the envelope, group assignment and drugs preparation.

Anesthetic management Pre-induction No premedication will be administered. Upon arrival to the operating theater, an intravenous (IV) cannula will be placed, and standard monitors, including 5-lead electrocardiogram, noninvasive arterial blood pressure monitor, and pulse oximetry, will be applied. Oxygen supplementation at fraction of inspired oxygen (FiO2) of 0.35 will be achieved through a suitable air entrainment mask. Bispectral index (BIS: apparatus info) will be applied before starting the drug infusions and will be used for maintenance of sedation during operation.

Induction of anesthesia Group M (n=17): will receive a loading of 50 mg/kg in 15 minutes of Magnesium sulphate, and will be followed by continuous infusion at 1 ml/kg/h of 15 mg/ml solution Group F (n=17): will receive a loading of 1 mcg/kg in over 15 minutes of fentanyl then will receive continuous infusion starting at 1 ml /kg/h. of 0.5 mcg/ml solution Both groups will be given 0.5-1.5 mg/kg bolus of propofol over 10 minutes to achieve target Ramsay sedation scale (RSS) of 3 (respond to command), if RSS afterwards does not reach 3 a supplementary bolus dose of 0.2 mg/kg propofol will be given to the patients, and will be followed by 1-2.5 mg/kg/hr infusion to maintain Intraoperative BIS readings between 60 - 80.

Intraoperative management After achieving the target sedation level (RSS of 3), surgeons will infiltrate the surgical site with 20 mL of a local anesthetic solution containing 10 mL of 0.5% bupivacaine and 10 mL of 2% lidocaine with adrenaline at least 5 minutes before surgical incision. After performing burr-hole craniotomy soaked pledgets with lidocaine will be applied to anaesthetize the dura, the dura will be then opened, and the hematoma will be evacuated. The Infusion of sedatives will be ceased after skin closure.

Intraoperative patient's movements (defined as those which may interfere with the surgical conduct such as twisting of hand and/or leg and head mobility) will be managed by reassurance and support for 30 seconds. However, when movements continue, a bolus dose of propofol of 0.5 mg/kg will be given then infusion dose will be increased till the maximum dose (2.5mg/kg/hr) to regain BIS sedation score between 60-80. If the patient starts to move again the same sequence will be repeated. Minute movements of other body parts as well as movements of fingers or toes that unlikely to hinder the operative intervention, will be deemed insignificant to be documented.

Induction of general anesthesia will be only indicated if satisfactory surgical conditions will not be attained by the rescue propofol.

Intraoperative bradycardia and tachycardia (defined as heart rate (HR) < 45 bpm or > 120 bpm respectively) will be treated with intravenous atropine 0.2 mg, or propranolol 0.5-1 mg respectively. Hypertension and hypotension (defined as a more than 25% increase or decrease from baseline respectively) will be treated with nitroglycerine (0.1-10 mcg/min) or ephedrine (5 mg) respectively.

Postoperative management All patients will be transferred to the post-anesthesia care unit (PACU) after surgery where they will be closely monitored with the aid of five-lead electrocardiography and non-invasive arterial blood pressure, peripheral oxygen saturation (SpO2), and respiratory rate readings using an automated system for 24 h after surgery. Postoperative pain intensity will be assessed using VAS score at 1, 2, 3 and 6 hours after PACU admission. If VAS score exceeds 3, 30 mg of ketorolac will be administered.

Inclusion Criteria:

• patients with unilateral, chronic subdural hematoma,
• aged above 50 years,
• american society of anesthesiologist-physical status (ASA-PS) grade I-II,
• Glasgow coma scale of 14-15.

Exclusion Criteria:

• Patients with hypertension (Systolic blood pressure > 160 mmHg),
• bradycardia (<50 bpm),
• ischemic heart disease,
• second- or third-degree heart block,
• long-term abuse of or addiction to opioids, and sedative-hypnotic drugs (>6 months),
• allergy to study drugs
• neuropsychiatric diseases
• patients with predicted difficult airway
• patients with history of obstructive sleep apnea
• patients with deviation in the surgical technique
• inadequacy of local anesthesia