The effect of adding intrathecal magnesium sulphate to morphine-fentanyl spinal analgesia after thoracic surgery. A prospective, double-blind, placebo-controlled research study.

BACKGROUND

We investigated whether intrathecally magnesium sulphate added to morphine and fentanyl reduces patients' postoperative analgesia requirements and prolongs spinal opioid analgesia after thoracotomy.

METHODS

In a single-center, prospective, placebo-controlled, double-blind trial, we enrolled 58 adult patients undergoing elective posterolateral thoracotomy. Patients were randomized to receive either 25 μg of fentanyl citrate (0.5 mL)+300 μg of morphine+1.0 mL of preservative-free 0.9% sodium chloride (Group S) or 25 μg of fentanyl citrate (0.5 mL)+300 μg of morphine+50mg of magnesium sulphate 5% (1.0 mL) (Group MgSO(4)) for intrathecal analgesia. Opioid consumption and postoperative pain were assessed for 36 hours.

RESULTS

VAS pain scores at rest and on coughing were similar in all groups. The total 36-h intravenous morphine requirements were significantly lower in group MgSO(4) (14 [9.50-26.50] mg vs. 33 [30-41] mg, p<0.001); i.e. 57% less for the group MgSO(4). The total dose of intravenous morphine administered during titration was significantly lower in this group (4 [2-8] mg vs. 8 [6-10] mg, p=0.001). Morphine consumption was significantly lower in the group MgSO(4) at intervals 0-12, 12-24 and 24-36 h. The number of patients requiring titration was significantly lower in group MgSO(4) (68% vs. 96%, p=0.001). There is no difference in opioid side effects. No patient experienced side effects resulting from lumbar puncture, or neurological deficit or signs of systemic magnesium toxicity.

CONCLUSION

We found that in patients undergoing pulmonary resection with elective posterolateral thoracotomy, magnesium sulphate (50mg), when added to spinal morphine analgesia reduces postoperative morphine requirements, the number of patients requiring morphine titration without increasing opioid side effects.

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