Ketamine added to intravenous patient-controlled analgesia may be effective on prevention of postoperative nausea and vomiting by reducing opioid requirement after surgery.

Inclusion Criteria:

• Non-smoking female patients undergoing elective lumbar spinal surgery
• Age 20-65
• American Society of Anesthesiologists physical status classification I or II

Exclusion Criteria:

• Antiemetic within 24 hrs, Taking Steroids, Opioids within 1 week
• Psychiatric disease, Active drug or alcohol abuse
• GI motility disorder, severe renal/ hepatic disease
• insulin-dependent DM
• admission to ICU after surgery