The objective of the current study is to compare the efficacy of the analgesic effect of ultrasound-guided unilateral Rhomboid intercostal and sub serratus plane block (RISS) versus Serratus anterior plane block (SAPB) in Thoracotomy incision.

Open thoracotomy is commonly considered to be one of the most agonizing surgical operations. Pain following thoracotomy greatly impedes patient recovery and postoperative respiration. The pain experienced after a thoracotomy can originate from various factors, including the surgical incision, injury to the ribs and intercostal nerves, manipulation of the pleura and lung tissue, and the placement of a drainage tube.Recent advances in regional anesthesia techniques have aimed to provide more targeted and effective pain relief. Among these, ultrasound-guided fascial plane blocks, such as the rhomboid intercostal sub-serratus plane (RISS) block and the serratus anterior plane (SAP) block, have emerged as promising options. Both blocks target the thoracic nerves, but they differ in their anatomical approach and potential analgesic effects Postoperative pain was not only related to a comfortable recovery but also related to postoperative complications including pulmonary dysfunction, so the management of postoperative pain is an important part of the care of post operation.

Regional anesthesia techniques have been shown to have a good effect on postoperative analgesia and helps patients gain early recovery after operation.

Serratus anterior plane block (SAPB) is an easy, and safe method used for blockade of the sensory plane of the lateral cutaneous branch of the intercostal nerve (T2-T9).

The Serratus anterior plane block targets the lateral cutaneous branches of the thoracic intercostal nerves, which arise from the anterior rami of the thoracic spinal nerves and run in a neurovascular bundle immediately inferior to each rib. At the midaxillary line, the lateral cutaneous branches of the thoracic intercostal nerve traverse through the internal intercostal, external intercostal, and serratus anterior muscles innervating the musculature of the lateral thorax. These branches of the intercostal nerves travel through the two potential spaces described above.

The "Rhomboid intercostal and sub serratus plane block" (RISS) is a relatively newer block technique whose efficacy was documented in patients undergoing thoracic surgeries.

The RISS plane block involves the injection of local anesthetics into fascial planes, theoretically allowing for catheter placement to achieve continuous analgesia. Successful RISS plane blocks have been reported in various procedures, including lung transplantation, radical mastectomy, and nephrectomy, strongly suggesting favorable outcomes in postoperative pain relief.

In 2016, Elsharkawy et al. introduced a RA technique known as the rhomboid intercostal block (RIB). Rhomboid intercostal block involves injecting a local anesthetic into the upper intercostal muscle plane beneath the rhomboid muscles, providing analgesia to both the anterior and posterior thorax.Based on past studies, investigators found that RISS and SAPB are effectively decrease total opioid consumption, so investigators hypothesized one of them is the best.

Statistical analysis:

Statistical analysis will be conducted using IBM SPSS Statistics 22(IBM Corp., Armonk, NY, USA). The normal distribution of data will be assessed by the Kolmogorov-Smirnov and Shapiro-Wilk tests. Mean and standard deviation will be used as descriptive statistics for normally distributed numerical variables, while median and interquartile range (25th to 75th percentiles) will be used as descriptive statistics for non-normally distributed numerical variables. In addition, Chi-square test or fisher exact test will be employed to test the significance between categorical variables as appropriate. Independent t test will be employed for numerical data that exhibited normal distribution, whereas the Mann-Whitney test will be used for numerical data that did not adhere to normal distribution. A significance level of p < 0.05 will be deemed to be statistically significant.

Inclusion Criteria:

• Patients aged 18-70 years.
• Patients scheduled for unilateral Thoracotomy.
• American Society of Anesthesiologists (ASA) physical status I-III.
• Patients who are candidates for general anesthesia.
• No history of severe allergies to local anesthetics or other medications used during the procedure.

Exclusion Criteria:

• ASA PS class ≥ IV patients.
• obese (BMI ≥ 35) patients.
• Patients with uncontrolled cardiovascular.
• patients with neurological deficits, cardiopulmonary, hepatorenal , or metabolic diseases; anticoagulants; any drug allergies.
• Patients with emergency surgeries or re-do surgeries.
• Systemic infections or infections at the site of injection.
• Psychiatric illnesses (schizophrenia, bipolar, uncontrolled anxiety or depression).
• Narcotic dependency.

Triple (Participant, Care Provider, Outcomes Assessor) Apart from the anesthesiologists who performed the blocks, all patients, surgeons, and postoperative nurses remained blinded to randomization throughout the study period.