This randomized prospective double-blind clinical trial was approved by the Affiliated LiHuiLi Hospital of Ningbo University Ethics Committee (identifier: KY2022PJ214). The study was registered on www.chictr.org.cn (ChiCTR2300070731). Written informed consent was provided by all subjects before participation in the study.

Patients undergoing arthroscopic shoulder surgery under general anesthesia were recruited between May 2023 and December 2023 in the Affiliated LiHuiLi Hospital of Ningbo University. Inclusion criteria: aged between 18 and 70 years; body mass index (BMI) between 18 and 32 kg/m2, American Society of Anesthesiologists Classification (ASA) Grade I to II; and scheduled to undergo arthroscopic shoulder surgery. Exclusion criteria: severe cardiopulmonary disease, allergy to LA, infection at the puncture site, bleeding diathesis, language communication disorder, cognitive impairment, and refusal to participate.

All subjects were randomly assigned into two groups using a computer-generated random number table 1 day before surgery: the ESPB group and the control group. A nerve block specialist with extensive experience performed the ESPB. The specialist was not involved in anesthesia management. Patients, surgeons, anesthesiologists, nurses, postoperative evaluators and statistical analysts were all blinded to the study.

All patients underwent standard monitoring procedure which included an electrocardiogram (ECG), pulse oxygen saturation(SPO2), non-invasive arterial blood pressure (NIBP), and bispectral index (BIS) were performed in the operating room. A peripheral intravenous cannula pathway was established. Patients in the ESPB group underwent an ultrasound scan in the lateral decubitus position with the surgical side up, 30 min before general anesthesia induction. A linear ultrasound transducer (6–13 MHz, Edge, Sonosite, Seattle, USA) was positioned in a longitudinal sagittal plane at the level of C7-T1, 3–4 cm lateral to the posterior midline, to identify the 1st rib and the T1 transverse process. Then the transducer was moved to the cephalic side to identify the erector spinae muscle and the C7 transverse process. After disinfection and subcutaneous infiltration with 2% lidocaine (1 mL), a 21G×100 mm nerve block needle (Pajunk, Geisingen, Germany) was inserted in a caudal-to-cranial direction until its tip reached the interfascial plane between the erector spinae muscle and C7 transverse process using the in-plane technique (Fig. 1). After confirming the location of the needle tip with hydrodissection, a total of 30 mL of 0.25% ropivacaine (Naropin, AstraZeneca AB Company, Södertälje, Sweden) was slowly administered. In contrast, patients in the control group only received an ultrasound scan of the erector spinae muscles at the C7 level, as well as subcutaneous infiltration with normal saline (1 mL) but no nerve block needle was inserted. All patients had a motor block test and dermatomal evaluation of sensory block with a cold test 20 min after ESPB. Motor and sensory block tests were performed by a nurse anesthetist who was not involved in the study.

Image of ultrasound-guided C7 ESPB. (A) pre block. (B) post block. LA spreads between the C7 spinous process and the erector spinae muscle. ES, erector spinae muscle, LA, local anesthetic, C7 TP, C7 transverse process, and the arrow indicates the path of the needle

Both groups underwent standardized general anesthesia. To induce general anesthesia, intravenous 0.04 mg/kg midazolam, 2 mg/kg propofol, 0.3–0.4 µg/kg sufentanil, and 0.6 mg/kg rocuronium was administered. Endotracheal intubation was performed after achieving adequate muscle relaxation, followed by mechanical ventilation. To maintain general anesthesia, a continuous intravenous infusion of propofol 0.1–0.15 mg/kg/min and remifentanil 0.1–0.2 µg/kg/min was used to keep the BIS at 40–60. Remifentanil dosage was adjusted to maintain hemodynamic parameters [heart rate (HR) and mean blood pressure (MAP)] within 20% of the baseline.

Both groups were treated with the same postoperative multimodal pain management protocol. 0.15ug/kg sufentanil was administered intravenously 10 min before the end of the surgery. Following surgery, patients were given 40 mg of parecoxib sodium intravenously every 12 h, and treated with acupoint application and needle embedding. If the static visual analogue scale (VAS) score was greater than 4, tramadol 100 mg was given intramuscularly for remedial analgesia.

The primary outcome measure was the static VAS pain score (0–10: 0, painless,10, excruciating pain) at 4, 12, and 24 h after surgery.

Secondary outcomes included HR and MAP before anesthesia (t1), 5 min after anesthesia (t2), 10 min after skin incision (t3), and 10 min after extubation (t4); intraoperative remifentanil consumption; the Bruggrmann comfort scale (BCS) score, quality of recovery-15 (QoR-15) scale score, number of patients requiring rescue analgesia and adverse events 24 h after surgery [LA systemic toxicity (LAST), respiratory depression, postoperative nausea and vomiting (PONV), dizzy and pruritus].

The BCS (0–4; 0, persistent pain; 1, severe pain when breathing deeply or coughing; 2, mild pain when breathing deeply or coughing; 3, painless when breathing deeply; and 4 painless when coughing) was used to assess patients’ comfort level.

The QoR-15 scale was used to evaluated the overall quality of postoperative recovery. It includes 15 items to measure five dimensions: physical comfort, emotional state, physical independence, psychological support and pain. The scores range from 0 to 150, with higher scores indicating better recovery [13].

A preliminary study of 10 patients in each group found that the mean and standard deviation (SD) of VAS score was 2.1 (1.6) in the ESPB group and 2.9 (1.1) in the control group at 12 h after surgery. According to the findings, a sample of 28 participants was required in each group to achieve a statistical power of 0.8 and a two-sided (two-tailed) type I error of 0.05. Therefore, we planned to recruit 35 subjects in each group to account for possible dropouts. The sample size was estimated with IBM SPSS Sample Power version 3.0 (IBM Corp., Armonk, New York, USA).

Normality was evaluated with the Kolmogorov-Smirnov test. Normally distributed continuous variables were analyzed with the two-sample t-test and reported as mean ± SD (VAS scores, HR, MAP, the consumption of remifentanil, BCS scores, and QoR-15 scale score). A repeated-measures analysis of variance was used to compare groups at different time points (VAS scores, HR and MAP). Categorical variables were analyzed with the chi-square (χ2) test or Fisher’s exact test and reported as frequency (percentage) (rescue analgesia requirement, the incidence of PONV, dizzy and pruritus). We calculated a 95% confidence interval (CI) for differences in means (for continuous variables) or relative risk (RR) (for categorical variables). A P-value of < 0.05 was considered statistically significant. SPSS V.25.0 (IBM Corp., Armonk, New York, USA) was used to perform statistical analyses.