Open inguinal hernia repair is commonly associated with early postoperative pain, which may delay mobilization, reduce patient satisfaction, and increase opioid consumption. Low-dose intrathecal morphine may provide prolonged postoperative analgesia after spinal anesthesia; however, it may also be associated with opioid-related adverse effects such as nausea, vomiting, pruritus, urinary retention, sedation, and respiratory depression.

The transversalis fascia plane block is an ultrasound-guided fascial plane block that targets the sensory innervation of the lower abdominal wall, particularly the T12-L1 dermatomal region and the ilioinguinal and iliohypogastric nerve distribution. Although TFP block has been evaluated in lower abdominal procedures, direct comparison with low-dose intrathecal morphine in open inguinal hernia repair is limited.

This prospective, randomized, controlled, assessor-blinded trial aims to compare ultrasound-guided TFP block with low-dose intrathecal morphine in adult patients undergoing elective unilateral open inguinal hernia repair under spinal anesthesia. The primary outcome is total rescue opioid consumption during the first 24 postoperative hours. Secondary outcomes include pain scores at rest and with movement, time to first rescue analgesia, opioid-related adverse effects, quality of recovery, patient satisfaction, mobilization time, readiness for discharge, block success, sensory block distribution, and block-related complications.

Adult patients scheduled for elective unilateral open inguinal hernia repair under spinal anesthesia will be enrolled. After written informed consent, eligible patients will be randomly assigned in a 1:1 ratio to one of two groups.

In the intrathecal morphine group, patients will receive spinal anesthesia with 15 mg of 0.5% hyperbaric bupivacaine plus 100 mcg intrathecal morphine. No TFP block will be performed in this group.

In the TFP block group, patients will receive spinal anesthesia with 15 mg of 0.5% hyperbaric bupivacaine without intrathecal morphine. In addition, an ultrasound-guided unilateral TFP block will be performed on the surgical side before surgery using 30 mL of 0.25% bupivacaine, within the maximum safe dose limits.

All patients will receive a standardized multimodal postoperative analgesia protocol. Pain scores, rescue analgesic consumption, opioid-related adverse effects, quality of recovery, and safety outcomes will be recorded during the first 24 postoperative hours. Persistent or chronic postoperative inguinal pain may be evaluated exploratorily during follow-up if sufficient data are available.

Inclusion Criteria:

• Adult patients aged 18-80 years
• Patients scheduled for elective unilateral open inguinal hernia repair
• ASA physical status I-III
• Patients planned to undergo spinal anesthesia
• Patients able to understand and report postoperative pain scores
• Patients who provide written informed consent

Exclusion Criteria:

• Refusal to participate
• Bilateral inguinal hernia repair
• Recurrent inguinal hernia repair
• Emergency, incarcerated, or strangulated hernia
• Need for general anesthesia
• Contraindication to spinal anesthesia
• Coagulopathy or anticoagulant use contraindicating neuraxial or peripheral block
• Infection at the injection site
• Known allergy to local anesthetics, morphine, or study medications
• Chronic opioid use
• Preoperative chronic groin pain or neuropathic pain history
• Severe hepatic or renal failure
• Neurological or psychiatric condition preventing communication or pain assessment
• Expected inability to complete postoperative follow-up

The outcomes assessor who records postoperative pain scores, rescue analgesic consumption, opioid-related adverse effects, quality of recovery, and follow-up outcomes will be blinded to group allocation. The anesthesiologist performing spinal anesthesia or the TFP block cannot be blinded because of the nature of the interventions