This study aims to evaluate and compare the analgesic efficacy of two ultrasound-guided regional anesthesia techniques, the serratus anterior plane (SAP) block and the serratus posterior superior intercostal plane (SPSIP) block, in patients undergoing elective mastectomy surgery. Postoperative pain following mastectomy is a common and significant clinical problem that negatively affects patient comfort, delays mobilization, and may prolong hospital stay. Although systemic analgesics are commonly used, they are associated with adverse effects such as sedation, constipation, and potential dependency.

In this randomized clinical study, female patients aged 18-75 years with ASA physical status I-III scheduled for elective mastectomy will be included after obtaining informed consent. Patients will be allocated into two groups to receive either SAP block or SPSIP block under ultrasound guidance prior to surgery. Standardized general anesthesia and perioperative analgesia protocols will be applied to all patients.

The primary objective is to compare postoperative pain scores between the two groups using the Numeric Rating Scale (NRS). Secondary outcomes include time to first analgesic requirement, total analgesic consumption, intraoperative opioid use, and hemodynamic parameters. By comparing these two interfascial plane blocks, this study aims to identify a more effective analgesic technique that improves postoperative pain control, enhances patient comfort, and facilitates early mobilization following mastectomy.

Postoperative pain following mastectomy surgery remains a significant clinical concern, as it negatively impacts patient comfort, delays recovery, and may prolong hospital stay. Effective pain management is essential not only to improve patient satisfaction but also to reduce complications associated with delayed mobilization. Although systemic opioids and other analgesics are frequently used, they are associated with adverse effects such as sedation, nausea, constipation, and risk of dependency. Therefore, regional anesthesia techniques have gained increasing importance as part of multimodal analgesia strategies.

Ultrasound-guided interfascial plane blocks, such as the serratus anterior plane (SAP) block and the serratus posterior superior intercostal plane (SPSIP) block, have been shown to provide effective analgesia for thoracic and breast surgeries by targeting similar dermatomal distributions. However, comparative data regarding their relative efficacy in mastectomy patients are limited. This study aims to compare these two techniques in terms of postoperative analgesia and recovery outcomes.

Female patients aged between 18 and 75 years, classified as ASA physical status I, II, or III, and scheduled for elective mastectomy will be included in the study after obtaining written informed consent. Patients will be randomly assigned into two groups.

In Group 1, patients will receive an ultrasound-guided SAP block using a linear probe under aseptic conditions. The block will be performed in the lateral decubitus position by advancing the needle between the second and seventh ribs to the plane beneath the serratus anterior muscle, and 30 mL of 0.25% bupivacaine will be administered.

In Group 2, patients will receive an ultrasound-guided SPSIP block under aseptic conditions in the sitting position. The needle will be inserted medially to the scapula between the second and seventh ribs, targeting the plane between the serratus posterior superior muscle and intercostal muscles, and 30 mL of 0.25% bupivacaine (maximum dose 2 mg/kg/day) will be administered.

All patients will undergo standardized general anesthesia, including induction with midazolam, lidocaine, propofol, fentanyl, and rocuronium, followed by maintenance with desflurane at 1 MAC. Standard intraoperative monitoring (heart rate, blood pressure, oxygen saturation, end-tidal CO₂, and ECG) will be applied. Intraoperative administration of paracetamol, tenoxicam, and granisetron will be performed routinely.

Hemodynamic parameters will be recorded at 30-minute intervals during surgery. Total intraoperative opioid consumption, duration of surgery, and anesthesia time will also be documented. At the end of surgery, neuromuscular blockade will be reversed with sugammadex.

Postoperative pain will be assessed by a blinded investigator using the Numeric Rating Scale (NRS) at 0, 30 minutes, and at 1, 2, 4, 8, 12, 24, 36, and 48 hours. Time to first analgesic requirement, additional analgesic use, and total consumption will be recorded.

Patients with NRS ≥4 will receive intravenous paracetamol as first-line rescue analgesia. If pain persists, intravenous opioid (1 mg/kg) will be administered as second-line rescue analgesia.

Secondary outcomes include postoperative complications, pain during first mobilization, and patient and surgeon satisfaction assessed using a 5-point Likert scale.

Statistical analysis will be performed using SPSS version 25. Normality of data will be assessed using Kolmogorov-Smirnov and Shapiro-Wilk tests. Parametric or non-parametric tests will be used accordingly. Independent samples t-test or Mann-Whitney U test will be used for comparisons between groups, while paired t-test or Wilcoxon test will be used for within-group comparisons. ANOVA or Kruskal-Wallis tests will be used for comparisons involving more than two groups. A p-value <0.05 will be considered statistically significant.

This study is expected to determine the comparative effectiveness of SAP and SPSIP blocks in reducing postoperative pain, minimizing analgesic consumption, and improving recovery outcomes in patients undergoing mastectomy.

Inclusion Criteria:

• Female patients aged between 18 and 75 years
• Patients scheduled for elective mastectomy surgery
• American Society of Anesthesiologists (ASA) physical status I-III
• Patients who provide written informed consent

Exclusion Criteria:

• Patients who refuse to participate in the study
• Patients with American Society of Anesthesiologists (ASA) physical status IV or V
• Patients receiving anticoagulant therapy or with suspected coagulopathy
• Patients with known allergy to local anesthetic agents
• Infection at the site of block application
• Pregnant patients or those with suspected pregnancy
• Patients with severe neurological or psychiatric disorders
• Patients with severe cardiovascular disease
• Patients with chronic opioid use
• Patients with hepatic failure or renal failure (glomerular filtration rate <15 mL/min/1.73 m²)

This study includes only female patients, as it is conducted in individuals undergoing mastectomy surgery.

The individual participant data (IPD) will not be shared to protect patient privacy and confidentiality. The data collected for this study will only be used for the purposes of this specific research and will not be made available to other researchers to comply with institutional ethical guidelines.