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

B. Steinlechner1,*, M. Dworschak1, B. Birkenberg1, G. Grubhofer1, M. Weigl2, A. Schiferer1, T. Lang1 and A. Rajek1
1Division of Cardiothoracic and Vascular Anaesthesia and Intensive Care, University Hospital Vienna Austria
2Division of General Anaesthesia and Intensive Care, University Hospital Vienna Austria

*Corresponding author: Division of Cardiothoracic and Vascular Anaesthesia and Intensive Care, University Hospital Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria. E-mail: barbara.steinlechner@meduniwien.ac.at

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 µg 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 µg 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.

Presented in part at the 79th Clinical and Scientific Meeting of the International Anaesthesia Research Society on March 11, 2005 in Honolulu, HI, USA.