Dexmedetomidine Versus Magnesium Sulphate in Patients Undergoing Craniotomy for Deeply Settled Intracranial Tumours

Anesthetic management: Peripheral i.v line will be inserted and 2-3 mg midazolam is given. A pre-induction radial arterial line is inserted with the aid of infiltration of 2 ml lidocaine 2%. Invasive arterial blood pressure monitoring is started and pulse oximetry, 5-leads ECG, and NIBP are attached to the patient and mindray ipm-12 monitor is used. Anesthetic induction started with propofol 1-2 mg/kg, lidocaine 1 mg/kg, cis-atracurium 0.2 mg/kg and fentanyl 1-2 microgram/kg. Intubation is done with cuffed endotracheal tube and tidal volume and respiratory rate are set to achieve end-tidal Co2 of 30-28 mmHg. Esophageal temperature probe and urinary catheter are put in place. Patients then will receive maintenance of anesthesia with isoflurane \< 1 MAC, propofol 10-60 microgram/kg/min, and cis-atracurium 2-3 microgram/kg/minute. Patients are then grouped into two groups: Group A: will receive dexmedetomidine loading 1 microgram/kg bolus in 10 minutes followed by 0.2-1 microgram/kg/hour till the end of surgery. Group B: will receive 2 gm magnesium infusion for 30 minutes. All Patients will receive mannitol 20% 0.5-1 gm/kg and dexamethasone 8mg and paracetamol 1gm near the end of surgery. Patients will receive their fasting requirements of normal saline in the first 3 hours of surgery. Maintenance fluid used will be ringer acetate and will be given according to pulse pressure variation index (PPVI) that is derived from pulse contour analysis of invasive arterial blood pressure waveform. Patients will be given ringer acetate when PPVI is \> 12%. If hypotension occurred without change in PPVI targets, it will be treated with 10 mg ephedrine. On dural opening, brain relaxation score will be assessed which is a four points score 1. relaxed, 2. satisfactory, 3. firm, 4. Bulging. Arterial blood gas samples will be collected at induction and at the end of surgery. After removal of cranial fixation pins, anesthesia is discontinued and reversal of muscle relaxant is done with atropine 0.5 mg and neostigmine 0.05 mg/kg then extubation is done and patient is transferred to the ICU.