Adequate pain management following modified radical mastectomy (MRM) is crucial for early ambulation and patient satisfaction. Breast cancer is the most common malignancy in females, with an increasing incidence in recent years. Surgery is one of the mainstays of therapy for breast cancer, and modified radical mastectomy (MRM) is the most effective and common type of invasive surgical treatment. Post-mastectomy pain syndrome (PMPS) is a surgical complication of breast surgery characterized by chronic neuropathic pain. The aim of this study is to investigate the efficacy and safety of single injection CTB versus SAPB on post-operative acute pain as a part of a multimodal analgesia plan in patients undergoing MRM.

Patients will be divided randomly by the computer into three groups, group (A): will receive serratus anterior plane block, group (B): will receive costotransverse block and group(C): patient controlled analgesia group (PCA).

Group (A) (SAPB):

SAPB will be performed using an ultrasound machine with a high-frequency linear probe . All patients will be in lateral position to perform the block. At the level of the fourth rib with 45-degree angle, targeting the plane between the latissimus dorsi and serratus muscles, SAPB block will be performed unilaterally on the ipsilateral side of surgery.

Group (B) (CTB):

CTB will be performed using an ultrasound machine with a high-frequency linear probe. All patients will be in lateral position to perform the block. CTB block will be performed unilaterally on the ipsilateral side of surgery at the level of fourth rib.

Group (C) (patient controlled analgesia):

After successful extubation, patients will be transferred to PACU. Patients will receive a bolus dose of 5 mg nalbuphine then PCA pump in the form of 20 mg nalbuphine HCL in 100 ml 0.9% normal saline with basal rate of infusion 5ml/hr with self-administration bolus of 0.5ml with 15 min lock-out time.

Inclusion Criteria:

1. American Society of Anaesthesiologists (ASA) Physical Status Class I, II.
2. Scheduled for modified radical mastectomy (MRM).
3. Body weight ranging from 60 to 100 kilograms.

Exclusion Criteria:

1. Declining to give a written informed consent.
2. History of allergy to the medications used in the study.
3. Contraindications to regional anesthesia (including patient: refusal, coagulopathy, and local infection).
4. Psychiatric disorders.
5. Significant cognitive dysfunction.
6. American Society of Anesthesiologists (ASA) Physical Status Class III and IV.
7. Daily use of opioids.
8. Obesity (BMI > 35 kg/m2).