Does the addition of magnesium to bupivacaine improve postoperative analgesia of ultrasound-guided thoracic paravertebral block in patients undergoing thoracic surgery?

Magnesium is a plentiful intracellular cation that has been reported to possess analgesic effect. The present study was aimed to see whether addition of magnesium to bupivacaine in thoracic paravertebral block (TPVB) improved the analgesic effect after thoracic surgery. Fifty adult patients undergoing elective open thoracic surgery were divided into two equal groups. Group I received 12 ml of 0.5 % bupivacaine plus 0.9 % saline (3 ml) whereas Group II received 12 ml of 0.5 % bupivacaine plus 150 mg magnesium sulphate (in 3 ml 0.9 % saline) for TPVB. The following parameters were assessed: onset, dermatomal levels and duration of sensory block, duration of analgesia, visual analogue scale (VAS) for pain, postoperative intravenous morphine consumption, pulmonary function tests (peak expiratory flow rate [PEFR], forced expiratory volume in 1 s [FEV1] and forced vital capacity [FVC]) before and 24 h after surgery, and complications from the drugs and technique. Group II patients showed a significantly longer sensory block duration (224.6 +/- A 59.3 vs 160.1 +/- A 55.2 min, P < 0.05), longer duration of analgesia (388.8 +/- A 70.6 vs 222.2 +/- A 61.6 min, P < 0.05), less VAS during the postoperative 48 h, less need for postoperative morphine (16.2 +/- A 7.4 vs 29.5 +/- A 11.1 mg, P < 0.05) and lower incidence of somnolence (0 [0 %] vs 5 [20 %], P < 0.05). Furthermore, postoperative pulmonary function tests (PEFR, FEV1 and FVC) were significantly better in Group II whereas there was no significant difference between both groups regarding the sensory block dermatomal level or hemodynamic data. Addition of magnesium to bupivacaine in TPVB improved the analgesic effect of bupivacaine in patients undergoing thoracic surgery.