Thoracotomy is one of the most painful operation. Continuous thoracic epidural or paravertebral analgesia are gold standard for postoperative pain. But both techniques require skills. Spinal morphine is alternative simple method with less efficacy. Adding low dose ketamine during intraoperative may be helpful in postoperative pain relief.

Inclusion Criteria:

• ASA physical status 1-3
• elective thoracotomy
• can operate patient-controlled analgesia (PCA) machine

Exclusion Criteria:

patient with history of

• allergy to morphine or ketamine
• contraindicate to ketamine
• remain intubated in the postoperative period