Thoracotomy is among the most painful surgical procedures and can cause severe pain with a high incidence. Inadequate treatment of acute postoperative pain may lead to undesired complications. Paravertebral block (PVB) is an effective technique that provides adequate analgesia in thoracic surgeries. However, it is an advanced technique with potential complication risks. Erector spinae plane block (ESPB) is a relatively new and considered as a safer technique that provides comparable analgesia. However, the results are controversial and there are few studies that compares the effect of these blocks in thoracic surgeries. As well as the undesired effects of inadequate pain management, high doses of perioperative opioid usage may contribute to the development of dose-dependent long-term adverse events. Hemodynamic parameters are generally used to determine the intraoperative need for opioids in patients; however, hemodynamic parameters are not standardized and they do not provide a clear assessment. The Nociception Level (NoL) index is generated from five different parameters (heart rate, heart Rrate variability, photo-plethysmographic waveform amplitude, skin conductance level, number of skin conductance fluctuations, and their time derivatives) using a finger probe and is a promising monitoring technique. Selecting an effective analgesia method and determining the appropriate dose of opioids using NoL monitoring can reduce perioperative and postoperative complications and shorten hospital stays, allowing patients to return to daily life sooner. Additionally, preventing chronic pain syndromes that may develop in patients with inadequate analgesia, personalizing each patient's analgesia level, reducing healthcare costs, and improving quality of life can be achieved. The data from this study can demonstrate the analgesic efficacy of simpler regional anesthesia techniques, contributing to the widespread adoption of regional anesthesia applications, which is a crucial step in multimodal analgesia, thereby ensuring more effective pain management for surgical patients.

Inclusion Criteria:

• Patients undergo elective thoracotomy surgery
• ASA physical status I-III

Exclusion Criteria:

• Spinal deformities
• BMI>35
• Patiens <50 kg
• Allergies to study medications