RISS Versus Lower Thoracic ESP Block for Analgesia After Laparoscopic Abdominal Surgery: A Randomized Trial

The aim of this study is to investigate the analgesic efficacy of ultrasound-guided Romboid Intercostal and Subserratus (RISS) block versus lower thoracic Erector Spinae Plane (ESP) block after laparoscopic abdominal surgery.

Hypothesis

This study hypothesize that both RISS and ESP blocks relieve somatic pain equally, but ESP block relieves visceral pain better than RISS block, thereby reducing opioid consumption and improving patient satisfaction.

Methodology using:

I. Study design

Double-blinded randomized clinical trial study.

II. Study setting and location The study will be conducted at the operative theater of Souad Kafafi University Hospital (SKUH), Misr University for Science and Technology (MUST).

III. Study population:

Patients aged from 18 to 60 years old scheduled for laparoscopic abdominal surgery will be randomized in a 1:1 ratio after induction of general anesthesia, either:

Group A: Receiving ultrasound-guided RISS block. A solution composed of 20 ml mixed xylocaine 1% + 0.25% bupivacaine + 4 mg dexamethasone on each side.

Group B: Receiving ultrasound-guided lower thoracic ESP block (T8-T9) A solution composed of 20 ml mixed xylocaine 1% + 0.25 % bupivacaine + 4 mg dexamethasone on each side.

The infiltrative local anesthesia will be administered via a 22-gauge, 80-mm Echogenic block needle.

Postoperative analgesia:

The participants in both groups will receive analgesia in accordance with the following protocol:

• Pain will be assessed using a Numerical Rating Scale (NRS) 0-10.

• Mild pain (NRS 1-3) will be treated with 1 g paracetamol IV every six hours (maximum 4 g/day).
• Moderate pain (NRS 4-6) will receive the same paracetamol regimen plus ketorolac 30 mg IV every eight hours (maximum 120 mg/day).
• Severe pain (NRS 7-10) will receive the above plus 0.1 mg/kg IV morphine when indicated.

Study outcomes:

Primary Outcome Measure:

• Efficacy of postoperative analgesia for first 24 hours.

Secondary Outcome Measures:

• Total morphine equivalent consumption (mg) in 24 h.
• Surgeon satisfaction (ability to perform active movements, 1-5 scale).
• Patient satisfaction (1-5 scale).
• Onset time of analgesia (min).
• Duration of postoperative analgesia (time to first rescue).
• Pain intensity via NRS at 2, 6, 12, 18, and 24 h.
• Intraoperative vital signs (HR, NIBP).
• Possible complications (pneumothorax, LAST, and vascular puncture) intra- and post-operatively.

Sample size calculation The sample size calculation was performed using G. power 3.1.9.2 (Universität Kiel, Germany). The sample size was calculated according to the total morphine dose in 24hr (4.21 in RISS vs. 4.65 in ESP) according to previous studies (9, 10). Based on the following considerations: 0.05 α error and 80% power of the study. Four cases were added to overcome dropout. Therefore, 70 patients will be allocated.

Statistical Analysis Statistical analysis will be done by SPSS v26 (IBM Inc., Chicago, IL, USA). Shapiro-Wilks test and histograms will be used to evaluate the normality of the distribution of data. Quantitative parametric variables will be presented as mean and standard deviation (SD) and compared between the two groups utilizing unpaired Student's t- test. Quantitative non-parametric data will be presented as median and interquartile range (IQR) and will be analyzed by Mann Whitney-test. Qualitative variables will be presented as frequency and percentage (%) and will be analyzed utilizing the Chi-square test or Fisher's exact test when appropriate. A two tailed P value < 0.05 will be considered statistically significant.

Inclusion criteria

• Patients scheduled for laparoscopic abdominal surgery (e.g., cholecystectomy, colectomy, sleeve gastrectomy, hernia repair, appendectomy).
• Age from 18 - 60 years old.
• Both sexes.
• American Society of Anesthesiology (ASA) classification I, II. (i.e., ASA I: a normal healthy patient; ASA II: patients with mild controlled systemic disease.

Exclusion criteria

• Patients who refuse the research consent.
• Allergy to local anesthetic drugs.
• Cardiac arrhythmia.
• Bleeding tendency (including pre-existing blood disease and patients on full anticoagulant therapy).
• Morbid obese patients (BMI>35 kg/m2)
• Vascular compromise of lower extremity (e.g., Burger disease, Raynaud's disease).
• Connective tissue disease (e.g., Scleroderma).
• Suspected malignancy or intra-abdominal infection.