All patients will be taught how to interpret the visual analogue scale (VAS) of 0 to 10 with 0 experiencing no pain and 10 being the worst pain imaginable. All patients will fast for 8 hours prior to surgery and will be allowed to consume clear fluids for up to 2 hours before surgery. On the day of surgery, a peripheral cannula will be inserted on the contralateral limb. Basic monitors will be attached to the patients (NIBP, ECG, pulse oxime try, ETCO2).

Then, either technique will be performed. Both RLB and SAPB procedures will be completed by experienced anesthesiologists specialized in regional anesthesia. In group SAPB under aseptic technique, a linear ultrasound transducer (10-12 MHz) will be attached to a Sonosite M Turbo (Sonosite Inc, Bothell, WA, USA) will be put in a sagittal plane over the second intercostal space in the midclavicular region, while the patient will lei supine. After that, the probe will be moved downward and laterally to count the ribs till the fifth rib will be detected in the midaxillary line. The following muscles will be delineated overlying the fifth rib: the latissimus dorsi (superficial and posterior), teres major (superior), and serratus muscle (deep and inferior). Targeting the plane between the latissimus dorsi and serratus anterior muscles, the needle (20 G Tuohy nee dle) will be inserted in plane with the ultrasound probe. A total of 20 ml of 0.25% bupivacaine will be administered under continuous ultrasound guidance [19]. For RLB, the ultrasound probe will be placed in a sagittal orientation on the lateral side of the posterior median line to identify the lamina, erector spine muscle, and transvers spinalis muscles at the target thoracic segment [12]. A 20G puncture needle will be inserted using an intra-plane technique in a cephalocaudal direction. Once the needle contact the lamina and aspiration reveals with no blood, gas, or cerebrospinal fluid, 20 mL of local anesthetic solution, comprising 20 mL of 0.25% bupivacaine will be administered between the transvers spinalis muscle and lamina.

Five minutes after nerve block, anesthesiologists will assess the block plane by acupuncture at the medial and lateral nipple lines from T2 to T6. The anesthesiologists performing the blocks also monitored block-related complications, including pneumothorax, hypotension, and vascular injury.

Induction of general anesthesia will be done by propofol until loss of verbal response, atracurium (0.5 mg/ kg), fentanyl (1mic/kg). Intubation of trachea will be done. Maintenance of anesthesia by using isoflurane (MAC1.2-1.5), mechanical ventilation (to keep ETCO2 35-40 mm. Hg), and atracurium top-up doses according to the train of four (TOF). All patients will be given fluids according to the standardized guidelines. An appropriate type of antibiotics and paracetamol (15 mg/kg) will be given at the start of surgery. Ondansetron IV (4-8 mg) and ketorolac IV (30 mg) will be given at the end of surgery.

Reversal of muscle relaxant will be done by using neostigmine (0.07 mg/kg) and atropine (0.01 mg/kg) and extubate the patient when having the criteria of extubation. Patients then will be transferred to the post- anesthesia care unit (PACU) for 2 hr for observation of any complications and early assessment of pain then will be transferred to the ward.

At the ward, patients will be given paracetamol (15 mg/kg) IV every 8 hr. Rescue analgesia in form of nalbuphine IV (6 mg/dose) when VAS score ≥4 at any time postoperatively during the first 24 hr.

Hemodynamics will be recorded (HR, MAP) throughout the first 24 hr at 30 min, 2 hr, 4 hr, 6 hr, 12 hr, 18 hr, and 24 hr together with pain assessment by using VAS score at rest and with the movement of the ipsilateral arm, time to first rescue analgesic (min), the total dose of rescue analgesia (mg) and frequency of consumption. Any technique-related complications will be detected and managed accordingly. Patients' satisfactions were taken by using the verbal rating scale (from 1 to 5). Patients then will be discharged home when they are eligible and ready.

The primary outcome will be the VAS scores during coughing at 6 hours after surgery. In addition, VAS scores at rest, during activity, and during coughing will be recorded at 1, 6, 12, 24 and 48 hours after the operation. If the postoperative resting VAS score exceeds 4, patients will receive 5 mg intravenous nalbuphine as rescue analgesia. Secondary outcomes will include the extent of sensory block (T2 to T6 at the medial and lateral nipple lines) assessed by pin-prick testing, intraoperative hemodynamic changes, and analgesia-related adverse reactions, such as postoperative nausea and vomiting (PONV), respiratory depression, and pulmonary atelectasis [20,21]. Follow-up will be completed after recording the VAS score and postoperative complications at 24 hours.

Breast cancer is one of the most diagnosed cancer worldwide. This resulted in improvements in screening techniques for early detection and management. Surgery, chemotherapy, radiation, and hormonal therapy are used to treat it. Modified radical mastectomy (MRM), either with or without axillary lymph node clearance, is one of the surgical options for treating breast cancer. This procedure results in a significant surgical scar and intense pain after surgery. It is imperative that this pain be effectively handled so that no negative out comes result.

Adverse effects of postoperative pain affect almost all of the body systems. It is associated with anxiety, depression, and psychological disturbance. It causes hemodynamic changes and affects the lungs with atelectasis and respiratory depression as a result of the excessive use of narcotic painkillers. Along with possible occurrence of limb edema, it results in delayed upper limb mobility as well leading to an increase in hospital costs and a delay of the hospital discharge. This acute pain can develop into the chronic illness known as post-mastectomy pain syndrome , a kind of nociceptive pain characterized by burning, itching, paresthesia, or numbness sensations.

Managing acute postmastectomy pain includes pharmacological methods (opioids, paracetamol, NSAIDS, lidocaine, dexmedetomidine, clonidine, gabapentin, corticosteroid, NMDA receptor antagonists) . The non-pharmacological methods include thoracic epidural anesthesia (TEA), paravertebral block (PVB), peripheral nerve blocks like erector spinae plan block (ESPB), pectoral nerve block (PECS I, PECS II), and serratus anterior plane block (SAPB), and lastly, wound infiltration or local anaesthetic instillation via the surgical drain

RLB is a modified form of paravertebral block (PVB) . While PVB is increasingly used for chest and abdominal surgeries due to its precise analgesic effects, it carries a risk of serious complications, including pneumothorax, hypotension, or nerve damage . Even with ultrasound guidance, performing a traditional PVB remains technically challenging, with its success heavily reliant on the operator's expertise. RLB, as an improved alternative to PVB, has received growing attention in recent years. It involves the ultrasound-guided injection of local anesthetic between the lamina of the thoracic vertebra and the erector spinal muscle . Compared to PVB, RLB is easier to perform, associated with fewer complications such as pneumothorax, intrathecal injection, or vascular damage. However, the spread of anesthetic in RLB appears highly variable and is dose-dependent

The serratus anterior plane block (SAPB) targets the fascial plane between the lateral border of the pectoralis major and the serratus anterior muscle. Due to its myofascial space, SAPB typically requires only a single injection. It has been widely utilized for anesthesia in operations such as mastectomy, thoracotomy, thoracoscopic surgery, and rib fracture repair . Additionally, injecting the local anesthetic deep into the serratus anterior muscle has been found to simplify the procedure while maintaining comparable analgesic efficacy However, SAPB has certain limitations. Local anesthetic may diffuse extensively within the myofascial plane, potentially infiltrating the surgical field, which could interfere with the procedure and theoretically increase the risk of cancer cell dissemination.

Previous clinical studies have demonstrated that both RLB and SAPB can provide effective postoperative analgesia following breast surgery offering multiple options for regional anesthesia in thoracic procedures.

Although the precise mechanism of RLB remains unclear, cadaveric studies suggest that local anesthetic may diffuse into the paravertebral space via anatomical apertures, thereby blocking spinal nerves, while SAPB is thought to act by blocking the lateral cutaneous branches of the intercostal nerves

2. AIM/ OBJECTIVES The newly introduced retrolaminar block (RLB) offers anesthesiologists an alternative regional anesthetic technique for radical mastectomy. However, few clinical studies have compared the efficacy of RLB with that of serratus anterior plane block (SAPB). This study aimed to investigate the postoperative analgesia efficacy between ultrasound-guided RLB and SAPB in patients undergoing radical mastectomy

Inclusion Criteria:

• aged 25-65 years; (2) American Society of Anesthesiologists (ASA) physical status I or II; (3) Body mass index (BMI) between 18 and 28 kg/m2; (4) No known allergy to medications used in the study; and (5) Scheduled for modified radical mastectomy or radical mastectomy for breast cancer.

Exclusion Criteria:

• (1) Patients with hepatic or renal dysfunction, severe hypertension, diabetes, coagulation disorders, cardiovascular diseases, or other critical illnesses; (2) Contraindications to regional nerve block, such as anatomical abnormalities of spine or thorax, or puncture site infection; (3) Allergy to narcotic drugs; (4) Pregnancy; (5) Chronic pain; (6) Chronic opioid use, substance abuse, or alcoholism; (7) Motion sickness; or (8) Communication disorder or inability to comprehend the visual analogue scale (VAS) scoring system.