The Effects of TFPB on Opioid Consumption in Patients Undergoing HLDN

Study Objective and Hypothesis The primary objective of this prospective, randomized controlled clinical trial is to evaluate the analgesic efficacy of the transversalis fascia plane block (TFPB) in patients undergoing hand-assisted laparoscopic donor nephrectomy (HALDN). The study hypothesizes that the addition of ultrasound-guided TFPB using a local anesthetic will result in lower postoperative opioid consumption and reduced postoperative pain scores, as measured by the Numeric Rating Scale (NRS), during the first 24 hours after surgery.

Background and Rationale HALDN is widely used as a minimally invasive surgical technique for living kidney donation. Despite its minimally invasive nature, postoperative pain remains a significant clinical issue and may negatively affect patient recovery, mobilization, and overall satisfaction. Pain following HALDN is primarily attributed to trocar insertion sites and the lower abdominal incision required for kidney extraction.

Regional anesthesia techniques have increasingly been incorporated into multimodal analgesia strategies to improve postoperative pain control and reduce opioid requirements. However, an optimal regional anesthesia technique for HALDN has not yet been established.

The transversalis fascia plane block is an ultrasound-guided regional anesthesia technique in which local anesthetic is injected between the posterior surface of the transversus abdominis muscle and the transversalis fascia. This approach targets the thoracolumbar nerve branches at the T12-L1 level, including the ilioinguinal and iliohypogastric nerves, which are responsible for sensory innervation of the lower abdominal wall and groin. TFPB has been shown to provide effective analgesia following inguinal hernia repair, lower abdominal surgeries, and urologic procedures.

When performed under ultrasound guidance, TFPB is considered a safe and minimally invasive technique. Potential complications are rare and may include block failure, local anesthetic systemic toxicity, or inadvertent injury to surrounding structures.

Study Design This is a single-center, prospective, randomized controlled trial conducted at Koç University Hospital.

Study Population Eligible participants are adult patients aged 18 to 80 years who have been approved by the transplant committee as living kidney donors and are scheduled for HALDN. Written informed consent will be obtained from all participants prior to enrollment.

Exclusion Criteria Known allergy to any study medications Chronic opioid or opioid receptor agonist use Inability to communicate effectively Presence of chronic organ failure Refusal or inability to provide informed consent Foreign nationality American Society of Anesthesiologists (ASA) physical status classification ≥ III Randomization and Group Allocation

Patients will be randomized using the sealed envelope method into two groups:

Group A (Control Group): General anesthesia only, without any regional anesthesia technique Group B (TFPB Group): General anesthesia plus ultrasound-guided transversalis fascia plane block Anesthesia and Block Technique All patients will undergo standardized general anesthesia. Induction will be achieved with intravenous fentanyl (1-2 µg/kg), propofol (1-2 mg/kg), and rocuronium (0.9-1.2 mg/kg). Maintenance of anesthesia will be provided using oxygen (FiO₂ 35%), desflurane (1 MAC), and continuous intravenous remifentanil infusion (0.02-0.2 µg/kg/min).

In Group B, after induction of general anesthesia and prior to surgical incision, an ultrasound-guided TFPB will be performed using 30 mL of 0.25% bupivacaine. The local anesthetic will be prepared by the anesthesia technician responsible for intraoperative care.

Postoperative Analgesia At the end of surgery, all patients will receive intravenous paracetamol 1 g and morphine 0.05 mg/kg as part of a multimodal analgesia regimen. Neuromuscular blockade will be reversed with sugammadex (200 mg), and patients will be extubated in the operating room before transfer to the post-anesthesia care unit (PACU).

In the PACU, patients with an NRS pain score >4 will receive intravenous fentanyl 50 µg, which may be repeated every 15 minutes, and the total amount will be noted. After stabilization, patients will be transferred to the surgical ward.

Postoperative pain management during the first 24 hours will include routine intravenous paracetamol (1 g three times daily) and patient-controlled analgesia (PCA) with morphine (1 mg bolus, 8-minute lockout, no basal infusion). If pain remains ≥4 on the NRS despite PCA use, intravenous tramadol 50 mg will be administered as rescue analgesia.

Outcome Measures

Primary Outcome:

Total opioid consumption during the first 24 hours after surgery

Secondary Outcomes:

NRS pain scores recorded every 6 hours for 24 hours Incidence of opioid-related side effects (nausea, vomiting, pruritus, allergic reactions) Patient satisfaction with pain management Opioid-related adverse events will be recorded as binary variables (yes/no) every 6 hours.

Statistical Analysis Data will be analyzed using SPSS version 25.0. Continuous variables will be compared using independent t-tests or Mann-Whitney U tests, as appropriate. A p-value <0.05 will be considered statistically significant.

Sample Size Calculation Sample size was determined using power analysis based on institutional data from a previous study evaluating erector spinae plane block in kidney donors, in which 24-hour opioid consumption in the control group was 37.5 ± 18.5 mg. Assuming a 50% reduction in opioid consumption with TFPB, with α = 0.05, β = 0.2, and a completion rate of 90%, a total of 50 patients (25 per group) was calculated to be sufficient. The analysis was performed using G*Power version 3.1.9.7.