The ethics committee of the First Affiliated Hospital of Nanchang University approved our trial. Our study was registered at the Chinese clinical trial registry (ChiCTR2000038506), and written informed consent was obtained from the parents. The trial was conducted in accordance with the Declaration of Helsinki.

This randomized, double-blind study was performed on patients with a diagnosis of pectus excavatum, and all participants underwent Nuss procedures from 1 February 2021 to 30 January 2023. Patients aged between 8 and 18 years with American Society of Anesthesiologists Physical Status I to II were included in our trail.

Exclusion criteria included previous thoracic surgery, history of neuropathic pain, allergies to study drugs, infection at the puncture site, inability to consent to the study, and long-term opioid use. Our study randomly divided all participants undergoing the Nuss procedure into two groups: the NB group, receiving bilateral TTMP block combined with SAPB, and CON group, receiving the same block with saline.

Our study used a computer program to perform a random allocation sequence for each patient. All participants in our trial were randomly divided into the NB group and the CON group, and we used a sealed envelope for concealed allocation. The ropivacaine and saline, which look identical, were prepared by a nurse who was blinded to the grouping. Another experienced anesthesiologist injected the identical-looking fluid into the SAP and TTMP. Postoperative data collection was recorded by another researcher who was also blinded to group allocation. The enrolled participants and all researchers were unaware of the patients’ grouping.

Before anesthesia, all patients established appropriate venous access and were monitored with five-lead electrocardiography, noninvasive blood pressure, and peripheral oxygen saturation. The induction of general anesthesia was achieved with 0.03 mg/kg of midazolam, 0.3 µg/kg of sufentanil, 2–3 mg/kg of propofol, and 0.4 mg/kg of rocuronium. After tracheal intubation, we used remifentanil combined with propofol for the maintenance of anesthesia and the bispectral index (BIS) was maintained between 45 and 55 during surgery. We adjusted the remifentanil infusion according to the BIS, heart rate, and blood pressure of patients. The children in the NS group received ultrasound-guided TTMP block and SAPB with ropivacaine, and patients in the CON group got the same block with saline after the induction of general anesthesia. After the surgery, all patients were sent to the post-anesthesia care unit (PACU) as scheduled.

All Nuss procedures were performed by the same group of experienced surgeons in our study. Patient-controlled analgesia with intravenous sufentanil but no other opioids was used to perform postoperative analgesia, and patients received acetaminophen 16 mg/kg 3 times a day at most as a supplementary analgesic according to the demands of the children at 48 h after surgery. After discharge, all patients were taking codeine tablets according to their own needs.

We performed TTMP block and SAPB with the high-frequency linear ultrasound probe (Mindray, Shenzhen, China) with the patients in the supine position after endotracheal intubation. After appropriate sterile preparation, the ultrasound probe was situated parallel to the T4–T5 rib interspace. Then the pectoralis major internal muscle, intercostal muscle, and transversus thoracis muscle were found. The needle (Tuoren, Henan, China) was inserted through the pectoralis major internal muscle and intercostal muscle and advanced to the interfascial plane between the intercostal muscle and transversus thoracis muscle [18] with 10 ml of 0.2% ropivacaine. SAPB was performed through the midclavicular line at the level of the T4–5 intercostal space, and the same needle was advanced into the interfascial plane between the serratus anterior and latissimus dorsi muscles [19] with an injection of 10–20 mL of ropivacaine (for a patient height < 150 cm, 10 mL of ropivacaine were given; for a patient height between 150 and 160 cm, 15 mL of ropivacaine was given; for patient height > 160 cm, 20 mL of ropivacaine were given). The same nerve block methods were repeated on the other side. The total dose of ropivacaine in all participants did not exceed 3 mg/kg.

The primary endpoint of our study was postoperative pain at 2, 4, 8, 16, 24, 36, and 48 h, which was measured using the Numerical Rating Scale (NRS) score, from 0 (no pain) to 10 (worst severe pain), at rest and movement (during coughing). The secondary outcomes included the intraoperative dosage of remifentanil, the time to extubation, and the length of stay in the PACU, the total acetaminophen and codeine tablet consumption, time to first bowel movement, time to first flatus, and opioid-related adverse events and the length of hospital stay.

The sample size of the study was calculated on the basis of our preliminary research (n = 6 in each group), and we compared postoperative pain, which was measured using the Numerical Rating Scale (NRS) score, from 0 (no pain) to 10 (worst severe pain), at 8 h in two groups (1.1 ± 0.3 in the CN group versus 2.9 ± 0.7 in the CON group).

According to these data, an estimated sample size of 60 patients were needed with a type I error of α = 0.05, a type II error of β = 0.1, and a power of 90%. Considering a dropout rate of 20%, we included 20% additional patients for the final sample size (n = 36 in each group).

Statistical analysis was performed using SAS statistical software (version 9.1.3, North Carolina, USA). Continuous data with the two groups were statistically analyzed using the Student t test/Mann–Whitney U test. The qualitative data were analyzed using Chi-square or Fisher’s exact test. Pain intensity at rest and movement was compared with repeated-measures (two-way) analysis of variance. P-values less than 0.05 were considered statistically significant.