The effect of preemptive intravenous low dose magnesium sulphate on early postoperative pain after laparoscopic cholecystectomy

INTERVENTION: Patients that satisfy inclusion criteria will be randomly allocated in three groups. In two groups patients will receive magnesium sulphate intravenously in two different dosages once, after anaesthesia induction, prior to surgical incision. One group will receive intravenous bolus 5 mg/kg body weight magnesium sulphate and second group intravenous bolus 7.5 mg/kg body weight magnesium sulphate prior to surgical incision. Magnesium sulphate will be given slowly intravenously, bolus dose in 60 seconds, in both groups. The anaesthetic management of patients will be standardized. All patients will be premedicated with peroral midazolam (7.5 mg) 45 minutes before surgery. Anaesthesia will be induced with midazolam 0.2 mg/kg and propofol 1.5 mg/kg followed by vecuronium 0.1 mg/kg to facilitate tracheal intubation. Fentanyl in dose of 3 µg/kg will be given before surgical incision and nasogastric tube will be inserted for the duration of procedure. The lungs will be mechanically ventilated with oxygen/nitrous oxide, keeping the end‐tidal carbon dioxide between 35 – 40 mmHg. Throughout the procedure, intravenous infusion of 500 ‐ 1.000 ml of Ringer solution will be administered and in case of inadequate muscle relaxation, intermittent bolus of vecuronium 0.04 mg/kg will be added. During laparoscopy, intraabdominal pressure will be maintained at 12 mmHg. Troacar insertion sites would not be infiltrated with local anaesthetic, neither intraperitoneal local anaesthetic will be administered. Postoperative pain would be assesed at rest using visual analog scale (VAS) starting from 0 = no pain at all to 10 = worst pain imaginable. The intensity of postoperative pain would be assessed by an investigator blinded to the patient group. Assessment will be made at 1st,2nd, 3rd, 6th, 9th and 24th postoperative hour. According to score on VAS scale, a bolus dose of intravenous analgesic will be administered. If VAS scores will be 3 or 4, methamizol 2.5g intravenously would be given, if VAS scores will be 5 – 7, diclofenac 75 mg intravenously and if VAS scores will be 8‐10, tramadol 1mg/kg body weight intravenously would be given, respectively. CONDITION: early postoperative pain after laparoscopic cholecystectomy PRIMARY OUTCOME: severity of early postoperative pain assessed on visual analog scale ( VAS ) SECONDARY OUTCOME: analgesic consumption in 24 postoperative hours,according to pain score on VAS (visual analog scale) patients will be given analgesic intravenously and the whole consumption in 24 hours would be summed by an investigator INCLUSION CRITERIA: patients ASA ( American Society of Anesthesiologists ) I‐II undergoing elective laparoscopic cholecystectomy