Postoperative magnesium sulphate infusion reduces analgesic requirements in spinal anaesthesia

Magnesium sulphate infusion during general anaesthesia reduces anaesthetic consumption and analgesic requirements. The aim of this study was to assess the effects of postoperative magnesium infusion on duration of block, sedation and analgesic consumption after spinal anaesthesia.

Fifty ASA I-II patients were included in the randomized double blind study. Spinal anaesthesia was performed at L3-4 or L4-5 interspace with 12.5 mg 0.5% heavy bupivacaine, using a 25 G Quincke needle. Patients received a 5 mg kg(-1) bolus of magnesium sulphate followed by a 500 mg h(-1) infusion or saline in the same volumes for 24 h. Time to first pain, analgesic request, return of motor function, visual analogue pain and sedation scores were evaluated every 4 h during the 24 h postoperative period. The t- and U-tests were used for statistical analyses. Data were expressed as mean +/- SD, with P < 0.05 being considered significant.

Vital signs were stable during spinal anaesthesia and postoperative period. When compared to the control group, time to analgesic need was increased and total analgesic consumption was reduced in the magnesium group (meperidine consumption 60.0 +/- 73.1 mg control group, 31.8 +/- 30.7 mg magnesium group, P = 0.02).

Magnesium sulphate infusion may be used as an adjunct for reducing analgesic consumption after spinal anaesthesia.