The patients who will participate in the study will be determined and informed according to the inclusion and exclusion criteria, and the patients who signed the informed consent form will be included in the study.52 patients who will undergo elective thoracotomy surgery will be divided into double-blinded 2 sided as preemptive and postoperative erector spina plane block.

Intraoperative pain status of the patients will be determined by the "Nociception Level Index" device and analgesia will be provided with fentanyl. The primary aim of the study is to compare the intraoperative opioid consumption of two groups with plan block at different times.

In the postoperative period, patient-controlled analgesia device will be given to both groups for rescue analgesia. The opioid consumption of the patients will be controlled in this way in the postoperative period and their pain status will be determined. The secondary aim of the study is to examine the effect of plan block application time on the postoperative period.

Inclusion Criteria:

• Age between 18-65 years
• ASA classification <4
• No history of allergy or hypersensitivity to the drugs we use throughout the procedure
• BMI ≤ 35
• No history of neuropathy
• Surgeries other than emergency surgery
• Volunteer for the study
• No presence of infection at the injection site
• No any pyschiatric disease that would prevent the evaluation of the pain score

Exclusion Criteria:

• Under the age of 18 or over the age of 65
• ASA classification ≥ 4
• History of allergy or hypersensitivity to the drugs we use throughout the procedure
• BMI > 35
• History of neuropathy
• Undergoing emergency surgery
• Not be a volunteer for the study
• Presence of infection at the injection site
• Having a pyschiatric disease that would prevent the evaluation of the pain score
• Pregnancy
• Undergo surgery again during the postoperative follow-up period for any reason