Intertransverse Process Block Versus Erector Spinae Plane Block for Postoperative Analgesia After Percutaneous Nephrolithotomy

BACKGROUND AND RATIONALE. Percutaneous nephrolithotomy (PCNL) generates moderate-to-severe mixed somatic and visceral pain that peaks within the first 24 to 48 postoperative hours. Fascial plane blocks are central to opioid-sparing ERAS pathways in urology. The erector spinae plane block (ESPB) has supportive evidence in PCNL. The intertransverse process block (ITPB) targets the retro-superior costotransverse ligament (retro-SCTL) space, which lies closer to the paravertebral space than the ESPB target and may therefore provide better visceral analgesia. No randomised trial has directly compared ITPB with ESPB in PCNL or in any urological procedure. OBJECTIVES AND HYPOTHESIS. Primary objective: to determine whether a single preoperative ITPB is superior to ESPB in reducing cumulative 48-hour opioid consumption. H0: mu_ITPB minus mu_ESPB is greater than or equal to 0. H1: mu_ITPB minus mu_ESPB is less than 0. DESIGN. Single-centre, prospective, parallel-group, stratified block-randomised, triple-blind, superiority trial. Stratification by ASA physical status (I-II versus III) and stone complexity (complex, that is staghorn, cast or multiple calculi, versus non-complex, that is single calculus under 2 cm). Within each stratum, permuted blocks of 4 or 6 allocate participants 1:1. The sequence is generated by an independent statistician using a fixed-seed computer algorithm and concealed in sequentially numbered opaque envelopes held by a designated investigator (Zhifeng Gao) who is not involved in block performance, outcome assessment, data entry or follow-up. Envelopes are opened in numerical order after enrolment and baseline assessment; allocation is communicated only to the block operator. BLINDING. Participants, outcome assessors (postoperative pain assessors) and the data analyst are blinded to allocation. The principal investigator and the block operator cannot be blinded because the two techniques require different needle trajectories, but they take no part in postoperative assessment, follow-up or data analysis. To reduce indirect unblinding, all blocks are performed in a separate preparation room with the patient behind a screen, a standard transparent dressing covers the puncture site, the site is fully covered during assessment, assessors do not ask about the procedure, and patients are instructed not to disclose procedural details. INTERVENTIONS. Both blocks are performed before induction of general anaesthesia with the patient prone, using a high-frequency linear probe (6 to 13 MHz) in a transverse orientation at T10-T11 on the operative side, with 20 mL of 0.375 percent ropivacaine (75 mg). The ITPB is performed in-plane through the intertransverse space, with the needle tip advanced through the superior costotransverse ligament into the retro-SCTL space and injectate given in aliquots with re-aspiration every 5 mL. The ESPB is performed in-plane from the lateral end of the probe with the needle tip placed in the fascial plane between the transverse process tip and the erector spinae muscle. Both groups then receive identical general anaesthesia and identical intravenous patient-controlled analgesia with sufentanil 200 ug in 100 mL (2 ug/mL; 1 mL bolus, 15-minute lockout, no background infusion) for 48 hours, with intravenous flurbiprofen axetil 50 mg as rescue (not counted as OME). OUTCOMES AND FOLLOW-UP. Assessments are performed at 2, 6, 12, 24, 48 and 72 hours after surgery by blinded assessors; visceral pain is assessed at 6, 12, 24 and 48 hours; dermatomal sensory extent is tested by cold sensation at 24 hours; satisfaction is recorded before discharge. SAMPLE SIZE. n = 2(Z_alpha/2 + Z_beta)^2 sigma^2 / delta^2 with a two-sided alpha of 0.05, 90 percent power, sigma of 20 mg OME and delta of minus 12 mg OME, giving 58.4 per group; allowing for 15 percent dropout gives 68.7, rounded up to 70 per group (140 total). Because the assumed sigma derives from 24-hour rather than 48-hour data, a blinded re-estimation of sigma is planned once approximately 35 participants per group have been recruited. STATISTICAL ANALYSIS. Primary analysis by ANCOVA with 48-hour OME as the dependent variable and stratification factors, operative duration and BMI as covariates; superiority is declared if the upper limit of the two-sided 95 percent confidence interval for the between-group difference is below 0 and P is below 0.05, with Wilcoxon rank-sum testing as a sensitivity analysis. Repeated NRS measures are analysed with GEE or mixed-effects models. The primary analysis set is per-protocol with intention-to-treat as sensitivity analysis; multiple imputation (M equals 5) is used when missingness reaches 5 percent or more. Analyses are performed in SPSS 26.0.