Although remifentanil provides profound analgesia during operation, postoperative occurrence of hyperalgesia and tolerance after remifentanil administration could be a challenge to the postoperative pain control. Evaluation of analgesia and anti-nociception during anesthesia is still a challenging issue. Surgical Pleth Index (SPI) is a non-invasive and simple access tool used to monitor autonomous nervous system during anesthesia. This technique is based on photoplethysmographic wave and heart beat analysis. SPI values range between 0 (no stress) and 100 (high stress level). The purpose of this study was to determine the appropriate use of Remifentanil for pain control in patients with SPI.

Patients were randomized into either SPI-guided analgesia or standard practice (Control). In both groups, anesthesia was maintained with total intravenous anaesthesia(TIVA) to keep bispectral index values between 40 and 60.

In the Remifentanil gradual reduction group (test group), 20 minutes before the end of the operation, remifentanil was gradually decreased by 25% every 5 minutes. The control group stopped remifentanil 10 minutes before the end of the operation.

SPI was recorded before the intubation, after the intubation, directly before the end of surgery. The number of unwanted somatic events, hemodynamics, Patient-controlled analgesia(PCA) consumption, narcotic analgesics consumption, and recovery times were recorded.

Inclusion Criteria:

• Patients who received the breast conserving surgery

Exclusion Criteria:

• Patients with arrhythmia who have poor SPI measurement
• When the patient refused
• Patients with decreased renal function of Cr> 2
• Surgery for more than 3 hours, surgery expected to bleed more than 500 ml