Magnesium sulfate reduces postoperative morphine requirement after remifentanil-based anesthesia

The aim was to investigate the effect of magnesium sulfate on postoperative pain and analgesic consumption after remifentanil-based anesthesia.

Forty women 18 to 65 years old were enrolled in this prospective, randomized, double-blinded clinical study. The study solutions were randomly preoperatively prepared for groups M (magnesium) and R (normal saline). A bolus of 0.2 ml/kg of study solution (30 mg/kg magnesium or saline) was given before induction of anesthesia and infusion was started at a rate of 3.3 ml/h (500 mg/h magnesium or saline). A 1 microg/kg loading dose of remifentanil following infusion was started at a rate of 0.25 micro g/kg/min, subsequently increasing stepwise by 0.05 micro g/kg/min increments if insufficient anesthesia was suspected. All postoperative outcome data were collected by an anesthesiologist who was blinded to the anesthetic regimen. Pain intensity using a visual analogue scale (VAS) was recorded for 24 hours postoperatively.

Hemodynamic and respiratory variables such as diastolic and systolic blood pressure, heart rate, and oxygen saturation were similar in both groups. The mean intraoperative remifentanil consumption in groups M and R was similar. The VAS score was significantly lower in the magnesium group at 15 and 30 minutes postoperatively. Total morphine consumption was significantly lower in the magnesium group than in the remifentanil-alone group.

It was concluded that magnesium sulfate decreased the postoperative morphine requirement when remifentanil was used for intraoperative analgesia.