Transdermal fentanyl patch (TFP)(50 mcg/hr) can release fentanyl into blood circulation at rate 50 mcg/hr for three days. It has slow onset of about 12-14 hours, so it's used to treat chronic pain, not popular for a cure of pain. If the investigators apply TFP at appropriate times, i.e. 12-14 hours before surgery, it may be used to treat acute postoperative pain.