Pain after thoracotomy is very severe and may cause pulmonary complications. Thoracic epidural analgesia has greatly decreased the pain experience and its consequences. However, new ways of decreasing post-operative opioid drugs consumption is an important issue of research. We aim to evaluate the effect of adding epidural magnesium sulfate to bupivacaine and morphine on pain control and the amount of opioid consumption after thoracotomy. Eighty patients undergoing thoracotomy at a tertiary cardiothoracic referral center will be enrolled in a randomized double blind trial. Patients randomly will be allocated in two groups. Bupivacaine (12.5 mg) plus morphine (2 mg) will be administered epidurally for all patients at the end of operation. Patients in group I will be received epidural magnesium sulfate (50 mg) and patients in Group II will be received normal saline as an adjuvant. Visual analog scale (VAS) score and the amount of morphine consumption will be measured during 24 hours post-operation.

Inclusion Criteria:

• American Society of Anesthesiologists physical statuses I-III
• Undergoing thoracotomy

Exclusion Criteria:

• Known hypersensitivity to magnesium sulfate
• Renal failure
• Hepatic dysfunction
• Severe obesity
• Psychotic or neurologic diseases
• Currently taking opioid or calcium channel blocker
• AV block degree II or III
• Refused to participate in trial