Given the burden of chronic postmastectomy pain and the need for effective, opioid-sparing analgesia, the propose of the randomized controlled trial is to evaluate the safety and efficacy of adding magnesium sulphate to the combination of PIP block and ESPB in patients undergoing modified radical mastectomy for reducing acute and chronic post mastectomy pain

Breast cancer remains one of the most common malignancies worldwide, and modified radical mastectomy (MRM) continues to be a mainstay surgical treatment in many cases. However, postoperative pain after MRM can be significant, both in the acute period and long-term, contributing to persistent pain syndromes, impaired recovery, and reduced quality of life. Regional anesthesia techniques such as the pectointercostal plane (PIPB) block and erector spinae plane block (ESPB) have gained wide acceptance as effective approaches to reduce perioperative analgesic requirements, improve pain control, and potentially mitigate chronic post-surgical pain. Magnesium sulphate (MgSO4 ) is increasingly studied as an adjuvant in regional anesthesia, owing to its NMDA-receptor antagonism, calcium channel modulation, and possible anti-inflammatory effects. Meta-analyses in peripheral nerve blocks, such as supraclavicular brachial plexus block, have demonstrated that adding MgSO4 prolongs sensory and motor blockade, delays the need for rescue analgesia, and is generally well tolerated. Moreover, in abdominal surgery, MgSO4 added to bupivacaine in a transversus abdominis plane (TAP) block significantly reduced postoperative pain scores and extended analgesia duration. Erector spinae plane block is particularly attractive in mastectomy because it provides extensive dorsal and lateral thoracic analgesia. Beyond ESPB and Pectointercostal Plane Block, other interfascial plane blocks in breast surgery have also shown benefit with magnesium. Such consistent results across different block techniques support the hypothesis that magnesium enhances regional anesthesia outcomes in breast surgery.

Despite this promising data, there remain gap. No study has yet, concurrently evaluated magnesium as an adjuvant to both PIP block and ESPB in the same patient population, nor assessed its effects on both acute postoperative pain and the development of chronic postoperative pain.

So, the aim of this randomized controlled trial is to evaluate the safety and efficacy of adding magnesium sulphate to the combination of PIP block and ESPB for reducing acute and chronic post mastectomy pain in patients undergoing modified radical mastectomy.

A randomized controlled double-blinded study will be conducted in South Egypt Cancer Institute, Assiut University, after approval from the Institutional Ethics Committee.

Primary outcome:

Time to first rescue analgesia.

Secondary outcomes:

Total opioid consumption (morphine equivalent) in the first 24 hours postoperatively.

Postoperative pain scores (VAS) at rest and movement. Incidence of postoperative nausea and vomiting. Block-related complications. Incidence and severity of chronic post mastectomy pain.

Inclusion Criteria:

• Female patients aged ≥18 years.
• American Society of Anesthesiologists (ASA) class I-III.
• Scheduled for unilateral modified radical mastectomy.

Exclusion Criteria:

• Known allergy to local anesthetics or magnesium.
• Coagulopathy or anticoagulant therapy.
• Local infection at injection site.
• Body mass index (BMI) ≥ 40 kg/m2.
• Chronic opioid use or chronic pain disorders.
• Neurological or psychiatric disorders affect pain perception.
• Severe hepatic or renal impairment.
• Pregnancy.
• Lactation.

An online randomization program (http://www.randomizer.org) will be used to generate a random list and each patient's code will be kept in an opaque sealed envelope. Patients will be randomly allocated with 1:1 allocation ratio into two equal groups in a parallel manner:Patients and outcome assessors will be blinded to the study groups.