Effect of magnesium infusion on thoracic epidural analgesia

Patients of lung volume reduction surgery (LVRS) having an ASA status III or more are likely to be further downgraded by surgery to critical levels of pulmonary function.

To compare the efficacy of thoracic epidural block with (0.125%) bupivacaine, fentanyl combination and (0.125%) bupivacaine, fentanyl combination with adjunctive intravenous magnesium infusion for the relief of postoperative pain in patients undergoing LVRS.

Patients were operated under general anesthesia. Thirty minutes before the anticipated completion of skin closure in both groups, (Group A and Group B) 7 ml of (0.125%) bupivacaine calculated as 1.5 ml/thoracic segment space for achieving analgesia in dermatomes of T4, T5, T6, T7, and T8 segments, along with fentanyl 50 μg (0.5 ml), was administered through the catheter, activating the epidural block, and the time was noted. Thereafter, in patients of Group A, magnesium sulfate injection 30 mg/kg i.v. bolus was followed by infusion of magnesium sulfate at 10 mg/kg/hr and continued up to 24 hours. Group B was treated as control.

A significant increase in the mean and maximum duration of analgesia in Group A in comparison with Group B (P<0.05) was observed. Total epidural dose of fentanyl and bupivacaine required in Group A was significantly lower in comparison with Group B in 24 hours.

Requirement of total doses of local anesthetics along with opioids could be minimized by magnesium infusion; therefore, the further downgradation of patients of LVRS may be prevented.

Intravenous magnesium can prolong opioid-induced analgesia while minimizing nausea, pruritus, and somnolence.