This randomized, controlled, single-center study received ethical approval from the Ethics Committee of North Sichuan Medical College Affiliated Hospital on January 12, 2024 (approval no. 2024ER12-1) and was registered on https://www.chictr.org.cn on February 24 (registration no. ChiCTR2400081157). Informed consent was obtained from all participants after they were fully informed of the study’s risks. The first participant was enrolled on February 27, 2024. The study adheres to the Consolidated Standards of Reporting Trials (CONSORT) guidelines for reporting clinical trials (Sk et al. 2010).

We enrolled patients aged 18–65 years, classified as ASA grades I–III, who were undergoing laparoscopic radical surgery for rectal cancer under general anesthesia. Exclusion criteria were comprehensive: site infection at the puncture site, history of blood disorders or coagulation dysfunction, chronic pain management, mental disorders or central nervous system diseases, recent opioid usage, and sensory impairments preventing cooperation with scale assessments.

A total of 60 eligible patients were included and randomly assigned in a 1:1 ratio to either the TAPB group or the ESPB group. Randomization was facilitated through a computer-generated randomization sequence and managed by an anesthesiologist uninvolved with the study’s execution. Group assignments were recorded on separate pages and concealed in sequentially numbered, opaque, sealed envelopes. On surgery day, a different anesthesiologist, also not involved in the trial, opened the envelope and administered the regional blockade in the anesthesia preparation room. Consequently, the patients, attending anesthesiologists, surgeons, postanesthesia care unit (PACU) staff, data collectors, and the individual responsible for conducting the statistical analysis were blinded to group assignment throughout the observation period, including all postoperative follow-up periods.

Patients were not premedicated prior to surgery. Anesthesia was induced using standardized techniques, which included administration of sufentanil (0.4 μg/kg), etomidate (0.3 mg/kg), cisatracurium (0.2 mg/kg), and propofol (1 mg/kg). During the surgery, anesthesia was maintained with a balanced mixture of 2% sevoflurane in an oxygen/air blend (1:1 ratio) and a continuous infusion of remifentanil, dosed at 0.05–0.2 μg/kg/min. Muscle relaxation was achieved by administering intermittent injections of rocuronium as needed. The bispectral index (BIS) was monitored and maintained within a range of 40–60 to ensure adequate depth of anesthesia, while hemodynamic parameters were closely monitored and kept within 20% of baseline values. Upon completion of the surgery, tracheal extubation was performed once adequate muscle strength returned, and patients were subsequently transferred to the PACU. For postoperative analgesia, each patient was equipped with a patient-controlled intravenous analgesia (PCIA) device. The PCIA contained sufentanil at a concentration of 1 μg/ml, with a background infusion rate set at 2.5 ml/h, delivering a dose of 2.5 μg of sufentanil. Should the patient’s VAS score exceed 5 during activity or 3 at rest, pressing the analgesic pump delivered a rescue dose of 1 μg of sufentanil. The device was programmed with a lockout interval of 15 min to prevent overdose.

All blocks were administered by an experienced attending anesthesiologist. Patients allocated to the ESPB group underwent an ESPB block as follows: The patient was positioned in the lateral decubitus posture, and the skin puncture site was sterilized. A linear ultrasound probe (UMT-400 Plus, Mindray, China) was longitudinally placed 2–3 cm lateral to the T9 spinous process to delineate the transverse process and erector spinae muscles. Employing an in-plane approach, an 80-mm-long, 22-gauge nerve block needle (Stimuplex D, Braun, Germany) was advanced through the muscles to the T9 transverse process. Subsequently, 2 ml of normal saline was administered to separate the erector spinae from the transverse process. After confirming the accurate placement of the needle tip, 20 ml of a 0.25% ropivacaine solution diluted with normal saline was injected. Ultrasound imaging confirmed a linear spread between the transverse process and the erector spinae muscle group, indicating a successful injection. The procedure was then repeated on the opposite side.

Patients in the TAPB group received a similar procedure in the following manner: The patient was placed in a supine position, and the skin was sterilized. A linear ultrasound probe (UMT-400 Plus, Mindray, China) was placed on the abdominal wall below the costal edge to visualize the three muscular layers—external oblique, internal oblique, and transversus abdominis. Using the in-plane method, an 80-mm-long, 22-gauge nerve block needle (Stimuplex D, Braun, Germany) was inserted between the internal oblique and transversus abdominis muscles. After injecting 2 ml of normal saline to separate these muscles, the correct needle tip placement was verified, and 20 ml of a 0.25% ropivacaine solution mixed with normal saline was injected. Ultrasound confirmed the separation of the internal oblique and transversus abdominis muscles, validating the successful injection. This procedure was similarly replicated on the contralateral side.

This study primarily outcome the quality of recovery 24 h after surgery using the Chinese version of the QoR-15 questionnaire. The QoR-15, a validated multidimensional patient-reported outcome tool for the perioperative period (Erica et al. 2022), consists of 15 questions spanning 5 health domains: emotional state, physical comfort, psychological support, physical independence, and pain, allowing for a comprehensive assessment of the patient’s overall recovery experience. The QoR-15 questionnaire has a scoring range from 0 to 150, where a higher score indicates a better quality of postoperative recovery. The secondary outcomes encompassed QoR-15 scores at 48 h, postoperative pain scores at rest and during movement, requirements for rescue analgesia, time to first flatus and ambulation, cumulative opioid consumption, incidence of postoperative nausea and vomiting (PONV), PACU duration, length of hospital stay, adverse events related to nerve blocks, patient satisfaction, and the Comprehensive Complication Index (CCI) score. The CCI score was determined using an online calculator to evaluate complications within 30 days post-surgery graded. Hospital stay was delineated as the duration from the day of surgery until discharge. Pain intensity at rest and during coughing was assessed using the VAS at 2, 6, 12, 24, and 48 h postoperatively. The CCI score was determined through an online calculator accessible at https://cci-calculator.com/cciCalculator. We continuously monitored the patients’ conditions throughout their entire hospital stay. For patients discharged before the 30-day mark, we followed their progress remotely through our electronic medical record system to track outpatient appointments and readmissions. Patient satisfaction was assessed at postoperative day 2 by using an 11-point Likert scale (0 = entirely unsatisfied; 10 = fully satisfied).

The sample size for our study was determined based on the QoR-15 score, 24 h postoperatively. The minimum clinically important difference for the QoR-15 score was identified as 8 points, based on previous literature (Myles et al. 2016). Preliminary studies indicated a mean QoR-15 score of 105 ± 10.2 at this time point. We posited that an 8-point difference between groups would be clinically meaningful, setting significance levels at α = 0.05 and a power of 80% (β = 0.2). This calculation yielded a necessary sample size of 27 patients per group. To accommodate a potential 10% dropout rate, we enrolled 30 participants per group in this study.

Statistical analyses were conducted using SPSS 27.0 (IBM Corporation, NY, USA). The Shapiro–Wilk test and Q-Q plots assessed the normality of quantitative variables. Normally distributed data were reported as mean ± standard deviation (SD) and analyzed using the independent samples t-test. Non-normally distributed variables were reported as median and interquartile range (IQR) and analyzed with the Mann–Whitney U-test. Categorical variables were presented as frequencies (percentages) and analyzed using Fisher’s exact test or the chi-square test, as appropriate. Multiple repeated measurements between groups were evaluated using repeated measures analysis of variance, with Bonferroni corrections applied for multiple comparisons. A two-tailed p-value of less than 0.05 was considered statistically significant.