Background and Goal of study:
Although magnesium demonstrated promising analgesic and anti-nociceptive properties, a relevant clinical role in postoperative pain control remains unclear.
This prospective randomized, double-blind placebo-controlled trial was designed to assess the effect of a single intravenous dose of magnesium sulphate administered 1h before the end of the procedure, on acute postoperative pain relief during first 24h post-procedure in major abdominal surgery patients.
Material and Method:
After local Ethics Committee approval and obtaining informed written consent, 73 patients (ASA I-III) undergoing elective major abdominal surgery under general anesthesia, were randomly allocated to two groups: group M (n=37 patients) that received 40 mg/kg magnesium sulphate, intravenously infused in 250 ml normal saline and group C (n=36) treated with the same volume of placebo, just 1h before the end of surgery.
Postoperative analgesia during first 24h postoperatively was achieved with iv morphine via PCA and paracetamol (1g/8h) in both groups.
Pain scores (VAS) at rest and while coughing assessed at 1h, 6h, 12h, 24h and total morphine requirement during study period were recorded as primary end-points. The secondary end-points included the incidence of shivering, nausea/vomiting, the hemodynamic profile and patient satisfaction (4 stage scale).
Data were analyzed using t-test and Mann Whitney U-test, p<0.05 being considered significant.
Results:
Pain scores evaluated at rest and while coughing were significantly lower in group M compared to group C, throughout the study period (p<0.05). Magnesium-treated patients consumed less morphine via PCA during first 24h post-procedure (p<0.05).
The incidence of shivering, as well as nausea/vomiting were statistically decreased in group M compared to group C (p<0.05). No difference was reported between groups with respect to hemodynamic parameters. High satisfaction with pain management was experienced by less patients in group C, compared to group M (p<0.05).
Conclusion:
Magnesium sulphate administered 1h before the end of surgery, as a single intravenous dose could be considered as an effective and safe adjuvant for  postoperative analgesia strategy, reducing opioid consumption without increase of adverse events, during first 24h after major abdominal procedures. 


03 / Effectiveness of intraoperative magnesium sulphate on acute pain management after major abdominal surgery