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

The concept of preemptive analgesia was introduced by C. J. Woolf et al. Magnesium Sulphate, an antagonist of N-methyl-D-aspartate (NMDA) receptors and its associated channels causes modulation of acute pain reducing postsurgical pain intensity and dosage of analgesics. Our study was done to evaluate the postoperative analgesic efficacy of single low dose magnesium sulphate (10 mg/kg) as preemptive analgesic in patients undergoing laparoscopic cholecystectomy.

After obtaining Institutional Ethical committee clearance and written informed consent from the patients, a prospective observational cohort study was conducted at Lakeshore Hospital and Research Centre, Kochi from August 1st 2015 to July 31st 2016. 100 ASA Grade I and Grade II patients of both sexes undergoing laparoscopic cholecystectomy were included in the study. Of the 100 patients who were part of the study, the first 50 consecutive participants who fulfilled our inclusion criteria received low dose (10mg/kg) magnesium sulphate as a pre-emptive analgesic (Group A). The next 50 consecutive patients served as a control arm who did not receive magnesium sulphate (Group B) . Intravenous magnesium sulphate (10mg/kg) was given immediately after induction of anaesthesia. Intraoperatively patients were observed for any hemodynamic changes ( hypotension, arrhythmia) and any prolongation of neuromuscular blockade. Postoperatively pain was assessed using VAS score and WBF pain rating score. In addition the total analgesic consumption in 24 hours following surgery and time for first rescue analgesia, postoperative haemodynamic parameters(heart rate , blood pressure, respiratory rate, SPO2 and sedation) and side effects if any were evaluated. Chi square test and Fisher‟s exact test was used for the comparison of qualitative variables. Independent sample t-test and Mann Whitney test were used for the comparison of quantitative variables. A p value <0.05 was considered significant.

Statistical analysis of the data showed significant reduction of both VAS scores and WBF pain rating scores at 1 and 3 hours postoperatively in patients who received (Group A) pre-emptive intravenous magnesium sulphate(10mg/kg). when compared to patient group (Group B) who did not receive magnesium sulphate. Significant reduction of 24 hour postoperative analgesic requirement on the first postoperative day was noted in Group A patients. Time to rescue analgesia was higher in patients who received magnesium sulphate when compared to non magnesium group. Intraoperatively after induction, patients who received magnesium of 10mg/kg were found to have mild hypotension 30 minutes after induction, which got corrected with fluid boluses. In the early postoperative period, patients who received magnesium sulphate were found to have transient hypotension and bradycardia, which was clinically not significant. Patients who received magnesium had higher sedation scores in early postoperative period (30 mts, 1 hour). Respiratory rate and oxygen saturation were comparable in both the groups postoperatively.

The present study evaluating the analgesic efficacy of preemptive magnesium sulphate in the early postoperative period (24 hours) in patients who underwent laparoscopic cholecystectomy, concluded that magnesium sulphate at a dose of 10 mg/kg as a preemptive analgesic is effective and safe. It has good postoperative synergistic effect with analgesics and reduces the postoperative analgesic consumption on the first day following surgery. Low dose magnesium sulphate favourably influenced the postoperative hemodynamic profile.


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