Breast cancer is the most common cancer affecting women worldwide. Modified radical mastectomy is one of the main surgical treatments for breast cancer. However, this surgery is often associated with significant postoperative pain, which may delay recovery and increase the need for opioid medications such as morphine.

Regional anesthesia techniques are increasingly used to improve pain control after breast surgery and reduce opioid consumption. The erector spinae plane block (ESPB) is a well-established ultrasound-guided technique that provides effective chest wall analgesia. The serratus posterior superior intercostal plane (SPSIP) block is a newer ultrasound-guided technique that targets intercostal nerves and may provide effective postoperative pain relief.

The purpose of this randomized clinical trial is to compare the effectiveness of SPSIP block versus ESPB block in controlling pain after modified radical mastectomy. The primary outcome will be total morphine consumption during the first 24 hours after surgery. Secondary outcomes include pain scores, time to first request for rescue analgesia, hemodynamic stability, recovery profile, patient satisfaction, and postoperative side effects such as nausea and vomiting.

This study aims to determine whether the newer SPSIP block provides comparable or superior pain control to ESPB, with the goal of improving postoperative recovery and reducing opioid requirements in breast cancer patients.

Breast cancer represents a major global health burden and remains one of the leading causes of cancer-related mortality among women. Modified radical mastectomy (MRM) is frequently performed as part of surgical management. Despite advances in perioperative care, postoperative pain following MRM remains significant due to extensive tissue dissection involving skin, muscles, and intercostal nerves.

Inadequate postoperative analgesia may result in delayed mobilization, increased opioid consumption, higher incidence of opioid-related adverse effects, prolonged hospital stay, and potential development of chronic post-mastectomy pain syndrome.

Ultrasound-guided fascial plane blocks have gained popularity as part of multimodal analgesia strategies in breast surgery. The erector spinae plane block (ESPB) involves injection of local anesthetic deep to the erector spinae muscle at the thoracic level, allowing spread to dorsal and ventral rami of spinal nerves. ESPB has demonstrated effectiveness in reducing postoperative pain scores and opioid consumption after breast surgery.

The serratus posterior superior intercostal plane (SPSIP) block is a recently described regional anesthesia technique. It involves ultrasound-guided injection of local anesthetic into the fascial plane between the serratus posterior superior muscle and the intercostal muscles, targeting the intercostal nerves. Preliminary reports suggest that SPSIP may provide effective thoracic analgesia with a favorable safety profile.

This prospective randomized clinical trial will include 50 female breast cancer patients undergoing modified radical mastectomy at the National Cancer Institute, Cairo University. Patients will be randomly assigned into two equal groups:

Group SPSIP: Ultrasound-guided serratus posterior superior intercostal plane block.

Group ESPB: Ultrasound-guided erector spinae plane block.

Both blocks will be performed preoperatively under ultrasound guidance using 20 mL of 0.25% bupivacaine. All patients will receive standardized general anesthesia and multimodal analgesia.

The primary outcome measure is total morphine consumption during the first 24 hours postoperatively.

Secondary outcomes include:

Visual Analog Scale (VAS) pain scores at rest and during movement at predefined time intervals (1, 3, 6, 12, 18, and 24 hours)

Time to first request for rescue analgesia

Hemodynamic parameters intraoperatively and postoperatively

Recovery time

Patient satisfaction

Incidence of adverse effects such as nausea and vomiting

The study hypothesis is that SPSIP block provides postoperative analgesia comparable or superior to ESPB in patients undergoing modified radical mastectomy.

The results of this study may contribute to optimizing regional anesthesia strategies for breast cancer surgery and support evidence-based, opioid-sparing perioperative pain management.

Inclusion Criteria:

Female patients diagnosed with breast cancer

Scheduled for modified radical mastectomy (MRM)

American Society of Anesthesiologists (ASA) physical status II or III

Age 18-65 years

Body mass index (BMI) > 20 kg/m² and < 35 kg/m²

Ability to understand the study protocol and provide written informed consent

Exclusion Criteria:

Patient refusal to participate

ASA physical status IV or higher

BMI ≤ 20 kg/m² or ≥ 35 kg/m²

Known hypersensitivity or contraindication to local anesthetics, opioids, or study medications

History of chronic pain or regular opioid use

Significant psychiatric disorders affecting pain assessment

Contraindications to regional anesthesia (e.g., infection at injection site, coagulopathy, pre-existing peripheral neuropathy)

Severe respiratory, cardiac, hepatic, or renal disease

Individual participant data (IPD) will not be shared due to institutional policies and ethical considerations regarding patient confidentiality. Although all data will be anonymized, sharing individual-level data outside the research team is not permitted under the current Institutional Review Board (IRB) approval. Aggregated results will be available through publication and may be provided upon reasonable request to the corresponding author, in accordance with institutional regulations.

Participants will be blinded to group allocation. Postoperative pain assessment and data collection will be performed by investigators who are unaware of group assignment. The anesthesiologist performing the block cannot be blinded due to the nature of the intervention.