Magnesium moderately decreases remifentanil dosage required for pain management after cardiac surgery

Background. Magnesium is a calcium and an NMDA-receptor antagonist and can modify important mechanisms of nociception. We evaluated the co-analgesic effect of magnesium in the postoperative setting after on-pump cardiac surgery. Methods. Forty patients randomly received either magnesium gluconate as an i.v. bolus of 0.21 mmol kg(-1) (86.5 mg kg(-1)) followed by a continuous infusion of 0.03 mmol(-1) kg(-1) h(-1) (13.8 mg kg(-1) h(-1)) or placebo for 12 h after tracheal extubation. After surgery, remifentanil was decreased to 0.05 mu g kg(-1) min(-1) and titrated according to a pain intensity score (PIS, range 1-6) in the intubated, awake patient and a VAS scale (range 1-100) after extubation. If PIS was >= 3 or VAS >= 30, the infusion was increased by 0.01 mu g kg(-1) min(-1); if ventilatory frequency was <= 10 min(-1) it was decreased by the same magnitude. Results. Magnesium lowered the cumulative remifentanil requirement after surgery (P < 0.05). PIS >= 3 was more frequent in the placebo group (P < 0.05). Despite increased remifentanil demand, VAS scores were also higher in the placebo group at 8 (2 vs 8) and 9 h after extubation (2 vs 7) (P < 0.05). Dose reductions attributable to a ventilatory frequency <= 10 min(-1) occurred more often in the magnesium group (17 vs 6; P < 0.05). However, time to tracheal extubation was not prolonged. Conclusions. Magnesium gluconate moderately reduced the remifentanil consumption without serious side-effects. The opioid-sparing effect of magnesium may be greater at higher pain intensities and with increased dosages.