If the individual patient's pain is assessed and the amount of analgesic needed after surgery is predicted, appropriate injection of pain control and excessive injection of narcotic analgesic can be prevented. Therefore, investigators try to evaluate the degree of pain during surgery and the amount of analgesic use for management of postoperative pain.

Post-operative pain not only alleviates patient discomfort, but also delays recovery and thus prolongs the hospital stay. There are many ways to control postoperative pain, but analgesic infusion through venous route, patient controlled analgesia (PCA), especially narcotic analgesics, is often used to control the infusion when needed. However, because PCA is based on only age, weight, and underlying diseases, there are limitations in effective analgesia, and excessive sedation due to excessive infusion. Therefore, if the individual patient's pain is assessed and the amount of analgesic needed after surgery is predicted, appropriate injection of pain control and excessive injection of narcotic analgesic can be prevented. The noxious stimuli during surgery may have a negative effect on the healing process and surgical outcome of the wound due to stress reaction and catabolism, secretion of pituitary hormone, activation of the sympathetic nervous system, and immunological changes. Therefore, proper analgesia is needed during general anesthesia. A non-invasive, non-invasive analgesic device is currently available for Surgical pleth index (SPI) to assess the status of intraoperative analgesia. SPI = 100- (0.3 * heart beat interval + 0.7 * photoplethysmographic pulse wave amplitude) is automatically and continuously calculated from the waveform of peripheral oxygen saturation.

In the postoperative pain prediction study with SPI, the SPI value at the end of the operation was found to be proportional to the pain in the recovery room. However, only the pain score immediately after the operation was confirmed in these studies. Therefore, investigators try to evaluate the degree of pain during surgery and the amount of analgesic use for management of postoperative pain.

Inclusion Criteria:

undergoing liver resection (laparoscopic or laparotomy)

Exclusion Criteria:

patients who refused to participate patients who have cardiac arrythmia patients who have allergic history for remifentanil