This prospective randomized study will compare the effects of Erector Spinae Plane Block (ESPB) and Serratus Anterior Plane Block combined with Pectoral Nerve Block Type II (SAPB + PECS II) on intraoperative analgesia and postoperative opioid consumption in patients undergoing breast cancer surgery. Seventy patients (ASA I-III, aged 18-75 years) will be randomized into two groups using the sealed envelope method. Ultrasound-guided blocks will be performed preoperatively by the same anesthesiologist, with Group 1 receiving ESPB and Group 2 receiving a combined SAPB + PECS II technique performed through a single skin puncture (single needle entry site) with sequential injections into the two target fascial planes. All patients will undergo surgery under general anesthesia and receive postoperative analgesia via morphine patient-controlled analgesia. Pain scores and total opioid consumption will be statistically analyzed, with p < 0.05 considered significant.

Study Design and Methods The study planned to compare the effects of Erector Spinae Plane Block (ESPB) and Serratus Anterior Plane Block combined with Pectoral Nerve Block Type II (SAPB + PECS II) on intraoperative analgesia and postoperative opioid requirement in patients undergoing breast cancer surgery will be conducted at Kayseri City Hospital with voluntary participants.

________________________________________ Anesthesia and Block Procedures All patients will undergo surgery under general anesthesia. To provide intraoperative and postoperative analgesia, block procedures will be performed in the preoperative period before induction of general anesthesia by the same experienced anesthesiologist. The effectiveness of the blocks will be evaluated using the pinprick test following the procedure.

Group 1: ESPB Technique Standard preoperative monitoring, including ECG, SpO₂, and non-invasive blood pressure (NIBP), will be applied under operating room conditions. Patients will be positioned in the lateral decubitus position with the operative side facing upward. A PHILIPS ClearVue 550 ultrasound device with a high-resolution linear probe (12-5 MHz) will be used. The probe and cable will be covered with a sterile sheath, sterile ultrasound gel will be applied, and skin antisepsis will be achieved using povidone-iodine.

The transverse process beneath the erector spinae muscle will be targeted. A 22G atraumatic, nerve stimulator-equipped block needle (B. Braun Stimuplex® Ultra 360, 0.7 × 80 mm) will be advanced in-plane from lateral to medial. After confirmation of correct placement by saline hydrodissection, 35 mL of 0.25% bupivacaine will be injected slowly, and longitudinal spread will be observed. Block success will be assessed using the pinprick test.

________________________________________ Group 2: SAPB + PECS II Technique Standard monitoring will be applied. Patients will be placed in the supine position with the ipsilateral arm abducted. Using the same ultrasound equipment, the PECS II block will be performed first. The needle will be advanced in-plane into the fascial plane between the pectoralis minor and serratus anterior muscles, and 15 mL of 0.25% bupivacaine will be injected after hydrodissection. Both blocks will be performed through a single skin puncture (single needle entry site); after the first injection, the needle will be redirected under ultrasound guidance to the serratus anterior plane for the subsequent injection. Subsequently, the SAPB will be performed at the level of the 5th or 6th rib, with the needle tip positioned beneath the serratus anterior muscle. After confirming the correct fascial plane, 20 mL of 0.25% bupivacaine will be injected. Block efficacy will be assessed using the pinprick test.

________________________________________ Intraoperative and Postoperative Management After induction with propofol (2-3 mg/kg), fentanyl (1-2 µg/kg), and rocuronium (0.6 mg/kg), anesthesia will be maintained with sevoflurane at 1 MAC and remifentanil infusion (0.05-0.25 µg/kg/min), adjusted according to hemodynamic parameters.

All patients will receive 1 g paracetamol and ondansetron 0.15 mg/kg IV intraoperatively.

Postoperatively, patients will be followed in the PACU for 30 minutes and connected to a morphine patient-controlled analgesia (PCA) device. Rescue analgesia and antiemetic protocols will be applied according to NRS and nausea-vomiting scale scores.

________________________________________ PCA Preparation The PCA solution will be prepared with 100 mg morphine diluted in 100 mL saline (1 mg/mL), without basal infusion. The lockout interval will be 15 minutes, and the maximum dose will be 4 mg per hour.

________________________________________ Data Analysis After completion of patient enrollment, collected data will be statistically analyzed and recorded.

Inclusion Criteria:

• Age between 18 and 75 years
• ASA physical status I-III
• No history of bleeding or coagulation disorders
• Absence of neuropathy
• Preoperative breast region NRS score < 4

Exclusion Criteria:

• systemic or regional infection
• known allergy to local anesthetics
• Unwillingness to participate in the study

only biological females

The person who creates the block and the person who looks at the patients' pain scores are different.