Effective postoperative pain management following open nephrectomy remains a significant clinical challenge.

Inadequate pain control after this procedure may lead to impaired respiratory function, delayed mobilization, prolonged hospital stay, increased opioid consumption, and a higher incidence of postoperative complications. Therefore, optimizing postoperative analgesia while minimizing opioid-related adverse effects is a key objective in perioperative care for patients undergoing open nephrectomy Traditionally, postoperative pain following open nephrectomy has been managed using systemic opioids, epidural analgesia, or paravertebral blocks.

Ultrasound-guided fascial plane blocks have emerged as valuable alternatives in modern regional anesthesia due to their simplicity, safety profile, and effectiveness. Among these techniques, the erector spinae plane (ESP) block has gained widespread popularity.

This block has been shown to provide effective analgesia for thoracic, abdominal, and urologic surgeries, including nephrectomy The ultrasound-guided serratus intercostal plane block (SIPB) is a more recently described regional anesthetic technique targeting the lateral cutaneous branches of the intercostal nerves by injecting local anesthetic between the serratus anterior muscle and the intercostal muscles or ribs By blocking these nerves, SIPB provides analgesia to the lateral thoracic wall and upper abdominal regions, which are particularly relevant to flank incisions used in open nephrectomy.

Patients will be randomly allocated into two equal groups. Patients in group (S) will receive serratus intercostal plane block and those in group (E) will receive Erector spinae plane block . Both of these blocks will be performed after induction of general anaesthesia by an experienced anaesthesiologist The aim of this study is to to compare the analgesic efficacy of ultrasound-guided serratus intercostal plane block and erector spinae plane block in patients undergoing open nephrectomy.

This double-blinded, prospective, randomized comparative study will be conducted in Fayoum University hospital after the approval of local Institutional Ethics Committee and local institutional review board. Written informed consent will be obtained from all patients for these scientific contributions before recruitment and randomization.

Patients will be randomly allocated into two equal groups using a computer-generated randomization sequence with a 1:1 allocation ratio. Group assignments will be concealed in sealed opaque envelopes opened immediately before block performance. The patients (as block will be given after induction of general anesthesia) and outcome assessors will be blinded to group allocation. The anesthesiologist performing the block will not participate in data collection or postoperative assessment.

All patients will receive standardized general anesthesia. Following induction of anesthesia and before surgical incision, the assigned regional block will be performed under ultrasound guidance using strict aseptic precautions.

Preoperative assessment Complete history taking, physical examination and investigation will be done according to hospital protocol to evaluate the patients, Which includes complete blood count, serum urea and creatinine, liver function tests, coagulation profile, electrocardiogram (ECG) and ECHO when clinically indicated and based on patient medical condition and perioperative risk assessment.

Before surgery, details of the nerve block procedures and the VAS pain score (0-10 cm) will be illustrated to the patients (where 0=no pain and 10 = worst pain imaginable).

An informed consent will be obtained from participants. Patients will fast for about 6 hours for solid meals, 4 hours for non-clear liquids and 2 hours for clear liquids before surgery Anesthetic technique

• Intravenous access with a 18-gauge intravenous (IV) cannula will be inserted in the hand and standard monitoring (noninvasive blood pressure, electrocardiography, pulse oximetry and capnography ) will be applied.
• All patients will receive pre-oxygenation with O2 100% for 3 min. Anesthesia will be induced by using fentanyl 1μg/kg, propofol 1.5-2 mg/kg and atracurium 0.5 mg/kg will be used for muscle relaxation. Anesthesia will be maintained by controlled ventilation with oxygen and air (50:50) with target of EtCo2≈ 35-40 mmHg, isoflurane 1 minimum alveolar concentration (MAC), 0.5μg/kg fentanyl will be given intraoperative when either heart rate or NIBP report an increase by more than 20% of the basal record. The standardized rescue protocol will be applied by independent anesthesiologist unaware of study hypothesis
• At the end of the operation, Anesthesia will be discontinued and extubation will be done once patient fulfilled the extubation criteria.

Block techniques Patients in group (S) will receive serratus intercostal plane block and those in group (E) will receive Erector spinae plane block . Both of these blocks will be performed after induction of general anaesthesia by an experienced anaesthesiologist

Group (S) Serratus Intercostal Plane Block:

Block will be performed in the operating room, With the patient in the supine decubitus position, aseptic conditions were provided for the block, The high-frequency linear transducer of ultrasound (LOGIQ P7) will be placed in the mid-axillary line at the level of the eighths rib. The serratus anterior muscle and underlying intercostal muscles will be identified. A 22-gauge, 50 mm echogenic needle (Stimuplex D; B Braun, Germany) will be advanced in plane in the caudo-cranial direction. After negative aspiration, 25 mL of 0.25% bupivacaine HCl (plain)will be injected between the serratus anterior muscle and the intercostal muscles.

Group (E) Erector Spinae Plane Block:

Block will be performed in the operating room, With the patient in the lateral decubitus position, Aseptic conditions were provided for the block, The high-frequency linear transducer of ultrasound (LOGIQ P7) will be placed parasagittally at the level of the T8-T10 transverse process. The erector spinae muscle and transverse process will be identified. A 22-gauge, 50 mm echogenic needle (Stimuplex D; B Braun, Germany) will be advanced in plane in the cranio-caudal direction and after negative aspiration, 25 mL of 0.25% bupivacaine HCl (plain) will be injected deep to the erector spinae muscle.

Local Anesthetic Dose, Safety, and Emergency Preparedness

1. Dose: 25 mL of 0.25% bupivacaine HCl (plain), equivalent to 62.5 mg. The maximum safe dose of plain bupivacaine will be strictly adhered to, defined as 2 mg/kg, not exceeding an absolute maximum of 150 mg.

2. Slow Incremental Injection: The standard practice is to inject the local anesthetic under ultrasound guidance in small boluses, commonly 5-10 mL at a time, followed by aspiration to rule out intravascular placement and systemic toxicity.

3. Emergency preparedness measures included:

   • Lipid rescue protocol availability: 20% Intralipid solution will be readily available for immediate intravenous administration in the event of local anesthetic systemic toxicity (LAST), according to ASRA guidelines.
   • Allergic/anaphylaxis management: Emergency medications (adrenaline, antihistamines, corticosteroids) and resuscitation equipment will be available, with a predefined protocol for prompt management of any hypersensitivity reactions.
   • Stop rule will be applied if unexpected adverse events (e.g., severe hypotension, arrhythmia, LA toxicity).

Block Success Assessment

After recovery from anesthesia (PACU):

Cold sensation test using alcohol swab at T7-T12 dermatomes. Block considered successful if ≥3 dermatomes sensory loss within 30 min. Failed blocks will be recorded and analyzed

Postoperative Analgesia

• Routine Analgesia: Paracetamol (1 g every 6 hours) will be administered intravenously as a baseline routine analgesic.
• Rescue analgesia will be administered via intravenous morphine using a PCA pump programmed to deliver 1 mg per demand with a 10-minute lockout interval and no basal infusion. Cumulative 24-hour morphine consumption will be recorded.

Sample size calculation The sample size was calculated using G*Power software (version 3.1.9.7) based on the primary outcome measure: VAS pain score at rest and during deep inspiration at 12 hours postoperatively. Based on data from Fernandez Martin et al. (2025), who compared SIPB with posterior quadratus lumborum block in laparoscopic nephrectomy and reported a mean NRS score of 2.35 (±1.92) in the SIPB group at 12 hours, and from Wadood et al. (2024), who reported a median NRS score of 3.0 in the ESPB group at 12 hours in open nephrectomy. the investigators estimated the mean and standard deviation in the ESPB group to be 3.24 (±1.47) based on Luo et al. (2018) and Wan et al. (2014).

Using a two-sided independent samples t-test with a type I error (α) of 0.05 and a statistical power (1-β) of 80%, a minimum of 59 patients per group was calculated to be required. Accounting for an anticipated dropout rate of approximately 10%, the total sample size was increased to 66 patients per group, yielding a final target enrollment of 132 patients in total. The calculation was based on the following parameters: effect size d = 0.524, α = 0.05 (two-tailed), power = 0.80, and equal allocation ratio (1:1).

Statistical Analysis Data will be collected and analyzed using IBM SPSS Statistics for Windows, Version 26.0 (IBM Corp., Armonk, NY, USA). Continuous variables will be expressed as mean ± standard deviation (SD) or median with interquartile range (IQR), depending on the normality of data distribution. Categorical variables will be presented as frequencies and percentages. Normality of distribution will be assessed using the Shapiro-Wilk test.

For normally distributed continuous data, comparisons between the two groups will be performed using the independent samples Student's t-test. For non-normally distributed continuous data, the Mann-Whitney U test will be used. Categorical variables will be compared using the Chi-square test or Fisher's exact test, as appropriate. Repeated measurements over time (e.g., VAS scores at multiple postoperative time points) will be analyzed using a repeated-measures analysis of variance (ANOVA) or the Friedman test for non-parametric data, with appropriate post-hoc corrections (Bonferroni) for multiple comparisons.

The primary outcome (VAS score at rest at 12 hours postoperatively) will be the main variable for inferential testing. Time to first rescue analgesia will be analyzed using Kaplan-Meier survival analysis and compared between groups using the log-rank test. All tests will be two-tailed.

Effect size with 95% CI reported A p-value of less than 0.05 will be considered statistically significant.

Inclusion Criteria:

1. Patients scheduled for elective open nephrectomy under general anesthesia via flank incision .
2. Adult patients aged 18-65 years.
3. Patients with an American Society of Anesthesiologists (ASA) physical status I to III.

Exclusion Criteria:

1. Patient refusal.
2. Allergy to local anesthetics and patient with infection at the injection site of block.
3. Coagulation disorders or ongoing anticoagulant therapy.
4. Patients receiving opioids for chronic analgesic therapy (cancer, addiction).
5. Cognitive impairment preventing pain scoring.
6. Neurological or psychiatric disorders affecting pain assessment.

douple blinded (The patients and outcome assessors will be blinded to group allocation).