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 microg 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 > or =3 or VAS > or =30, the infusion was increased by 0.01 microg kg(-1) min(-1); if ventilatory frequency was < or =10 min(-1) it was decreased by the same magnitude.


RESULTS
Magnesium lowered the cumulative remifentanil requirement after surgery (P<0.05). PIS > or =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 < or =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.
Division of Cardiothoracic and Vascular Anaesthesia and Intensive Care, University Hospital, Waehringer Guertel 18-20, A-1090 Vienna, Austria. barbara.steinlechner@meduniwien.ac.at
B
B
Steinlechner
M
M
Dworschak
B
B
Birkenberg
G
G
Grubhofer
M
M
Weigl
A
A
Schiferer
T
T
Lang
A
A
Rajek
D000328:Adult; D000368:Aged; D000701:Analgesics, Opioid / Q000008:administration & dosage*; D006348:Cardiac Surgical Procedures; D004311:Double-Blind Method; D004334:Drug Administration Schedule; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D005260:Female; D005942:Gluconates / Q000627:therapeutic use; D006801:Humans; D008274:Magnesium / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement / Q000379:methods; D010149:Postoperative Pain / Q000188:drug therapy*; D010880:Piperidines / Q000008:administration & dosage*; D000077208:Remifentanil
D000701:Analgesics, Opioid; D005942:Gluconates; D010880:Piperidines; D008274:Magnesium; D000077208:Remifentanil; C030691:gluconic acid