This study aims to compare time of first request of analgesia among patients undergoing rhomboid intercostal sub-serratus plane block versus external oblique intercostal block for perioperative pain management in open nephrectomy.

Open nephrectomy is a common surgery usually performed for malignant and non-malignant renal pathologies. Open nephrectomy incision is associated with a high incidence of intense immediate postoperative pain and chronic pain the months following surgery.

The rhomboid intercostal block has previously been used for pain management in thoracic wall surgery.

Subserratus plane block in the treatment of post-abdominal surgical pain and the combination of the two blocks was subsequently renamed the "RISS block". The nerves targeted by the RISS block include the lateral cutaneous branches of the ventral branches of the thoracic intercostal nerves, located between the rhomboid muscle and the intercostal muscles, and deep into the scapula serratus anterior muscle. RISS block provides analgesia from T4 to T9 thoracic dermatomes and has been used in postoperative pain management for thoracic surgeries and upper abdominal surgeries.

Inclusion Criteria:

• Both sexes.
• American Society of Anesthesiologists (ASA) physical status II, III.
• Body mass index (BMI): > 20 kg/ m2 and < 35 kg/ m2.
• Patients undergoing open nephrectomy.

Exclusion Criteria:

• Patient refusal.
• BMI <20 kg/m2 and >35 kg/m2
• Known sensitivity or contraindication to drug used in the study (local anesthetics, opioids).
• History of psychiatric and cognitive disorders or chronic pain.
• Contraindication to regional anesthesia e.g pre- existing peripheral neuropathies.
• Severe respiratory or cardiac disorders.
• Advanced liver or kidney disease.
• Pregnancy.
• Physical status ASA IV.
• Coagulopathy with INR ≥ 1.6: hereditary (e.g. hemophilia, fibrinogen abnormalities & deficiency of factor II) - acquired (e.g. impaired liver functions with prothrombin concentration less than 60 %, vitamin K deficiency & therapeutic anticoagulants drugs).

The data will be available upon a reasonable request from the corresponding author after the end of study for one year.

After the end of study for one year.

The data will be available upon a reasonable request from the corresponding author.