Modified radical mastectomy (MRM) is one of the most common surgeries performed, and one that may be associated with significant acute postoperative pain in breast surgery. Acute postoperative pain is an independent risk factor in the development of chronic post-mastectomy pain .

Various regional anesthetic procedures have been tried to provide better acute pain control and, consequently, less chronic pain. They can reduce perioperative opiates requirement and thereby decreasing their possible side effects. These regional procedures include local wound infiltration, lumbar intrathecal fentanyl injection, thoracic epidural, thoracic paravertebral block (PVB), and ultrasound (US)-guided interfascial plane blocks. Currently, Ultrasound (US)-guided interfascial plane blocks have been recommended as safe, easy, and reliable alternatives to the use of thoracic epidural and paravertebral blocks in providing analgesia for patients about to undergo breast surgery.

Serratus anterior plane block (SAPB) is one of the Ultrasound (US)-guided interfascial plane blocks, it blocks the intercostal nerves II-VI by injection above or below the serratus muscle in the mid-axillary line and spares the pectoral nerves.

We assumed that SAPB could safely provide a better analgesic profile with an opioid-sparing effect than Intrathecal fentanyl. We will perform this study to evaluate this assumption.

Inclusion Criteria:

• 50 patients with American Society of Anesthesiologists (ASA) grade I to II, 18 to 60 years of age scheduled for Modified Radical Mastectomy surgery

Exclusion Criteria:

• Patient refusal.
• Patient with significant neurological , psychiatric or neuromuscular disease
• Alcoholism .
• Drug abuse .
• Pregnancy or lactating women .
• Suspected Coagulopathy .
• Morbid obesity .
• Known allergy to study medications .
• Septicaemia and local infection at the block site.