Effects of Injection Volume and Site on Sensory Distribution After Rectus Sheath Block

This randomized controlled study aims to evaluate the effects of local anesthetic injection volume and injection site on cutaneous sensory distribution following ultrasound-guided rectus sheath block (RSB). Participants undergoing laparoscopic abdominal surgery will be randomized to receive RSB using different injection sites and volumes (20 mL or 30 mL per side). Injection sites will be selected according to the surgical location, including upper, middle, or lower rectus sheath approaches. Cutaneous sensory distribution will be assessed to determine the extent and pattern of sensory blockade associated with each technique. The findings may help optimize injection techniques and local anesthetic volumes to achieve adequate sensory coverage for abdominal surgery.

Inclusion Criteria: * Patients scheduled for laparoscopic upper abdominal surgery and laparoscopic lower abdominal surgery, including urological procedures * American Society of Anesthesia (ASA) physical status I-III * Have ability to communicate and understand the study and accept to participate in the study Exclusion Criteria: * Aged \< 20 years * Patients who have following underlying disease: severe hepatic impairment \[diagnosed of cirrhosis (Child-Pugh C)\], coagulopathy (diagnosed of disease associated with abnormal coagulation), pre-existing neurological deficits, end-stage renal disease (ESRD), chronic pain (diagnosed of chronic pain disease or current use regular analgesic drugs), or any drug addiction. * Known allergy to bupivacaine or weighing less than 50 kg * Patient with previous abdominal surgery * Patient with Morbid obesity (BMI \> 40 kg/m2)