Introduction A lot of recent trials emphasized that perioperative magnesium sulfate (MgSO4) infusion has general anesthetic properties that could reduce anesthetic drug consumption and postoperative analgesia requirements in several types of surgery. Optimal post-operative pain control is necessary for early mobilization, improved respiratory function, and deep venous thrombosis. Administration of multimodal analgesics could limit the excessive use of systemic opioid analgesia especially (morphine), which has a high rate of postoperative side effects as sedation, respiratory depression, ileus, nausea, vomiting, constipation, urine retention, and itching. Therefore, medications and adjuvant drugs reducing the need for opioids have become widely used as parts of multimodal analgesia. Post-operative pain management begins with pre-operative planning and formulating a pain management plan that is tailored to an individual patient's liver function, respiratory and coagulation status, comorbidities and extent of resection.
Anesthetic technique:
Patients will be premedicated with tablet of alprazolam 0.25 mg the night before and 2 hours before surgery. Upon arrival in operating room usual monitoring will be established including heart rate, blood pressure, electrocardiogram (ECG),and temperature. After induction of anesthesia, an arterial line will be inserted for continuous monitoring of blood pressure and frequent blood gas analysis. End-tidal carbon dioxide (capnography) will be attached. General anesthesia will be administered using propofol 2 mg/kg, morphine 0.1 mg/kg and atracurium besylate 0.5 mg/kg followed by oral endotracheal intubation. Maintenance of general anesthesia with a mixture of isoflurane and 50% oxygen in air, morphine 2 mg/ h, mechanical ventilation will be adjusted to keep arterial oxygen saturation \< 95 % and end-tidal carbon dioxide between 35 and 40 mmHg. Atracurium (0.15 mg/kg) will be administered every 30 min.
Baseline intravenous infusion rate of lactated ringers solution will be set at (6ml/ kg/h) in both groups, additional solution will be infused if required. Magnesium sulfate infusion and anesthetic agents will be discontinued at the end of operation. The postoperative residual neuromuscular blockade will be reversed by using neostigmine 0.04 mg/kg and atropine 0.02 mg/kg. Then the patient will be extubated and transferred to the post-anesthesia care unit (PACU) for 1-hour observation.
Statistical analysis:
Statistical analysis will be done using Statistical Package for Social Sciences (SPSS) version 19 for Windows software. Data will be collected from all patients during and after anesthesia. Descriptive statistics (mean, standard deviation, or median and ranges) will be calculated. Comparative statistics between the two groups will be applied. Unpaired t-test will be used to compare the mean values between the two groups. The Kolmogorov-Smirnov test will be implemented to check the normality of continuous data distribution (P ≤ 0.05) Mann-Whitney-U test will be used to compare difference between the two groups for non-parametric variables (e.g.VAS). While the Chi-square test will be used to compare the categorical variables between both groups. The significant result will be considered when P value was less than (0.05).
Sample size calculations of this trial will be done upon the following assumption, α = 0.05 β = 0.2, effect size will be =0.7.The effect size is calculated by using G\*Power software version 3.1.9.2 (Institute of Experimental Psychology, Heinrich Heine University, Dusseldorf, German) and the authors found that 25 patients in each group have a power of 80% and plan to recruit 30 patients per group to account for possible dropout.
