Evaluation of ropivacaine in external oblique intercostal block for analgesia in major upper abdominal surgery: a randomized controlled clinical trial

2.1 Study design and ethics

This prospective, randomized controlled trial was approved by the Ethics Committee of Jiaxing First Hospital (approval number: 2024-LY-673) and conducted at the Department of Anesthesiology between 12 September and 25 October 2024. Written informed consent was obtained from all participants, and the study did not include minors. The trial was registered in the Chinese Clinical Trial Registry (www.chictr.org.cn; trial number: ChiCTR2400089685). All procedures adhered to the principles of the Declaration of Helsinki and followed the reporting standards outlined in the Consolidated Standards of Reporting Trials (CONSORT) guidelines.

2.2 Participants

A total of 78 patients aged 18–75 years scheduled for elective laparoscopic upper abdominal surgery were selected for this study. Patients were considered eligible if they had an American Society of Anesthesiologists (ASA) physical status classification of II–III and were to be admitted to the SICU postoperatively. They were stratified based on the type of upper abdominal surgery, including gastrectomy, hepatectomy and pancreatectomy. Exclusion criteria included known allergies to local anesthesia, severe coagulopathy, infection at the puncture site, significant cardiopulmonary disease or kidney dysfunction, a history of chronic pain or long-term analgesic use, and inability to comply with postoperative follow-up. All patients provided written and verbal consent before participation.

2.3 Randomization and blinding

The participants were randomly assigned to the control or EOI group using a computer-generated randomization table. Group assignments were concealed in sealed envelopes, which were opened by the anesthesiologist responsible for anesthesia induction upon the patient’s arrival in the operating room. Based on the assigned group, the anesthesiologist determined whether to perform an EOI block before surgery or not. To ensure blinding, an investigator who was unaware of group assignments did not enter the operating room until after surgery. While the anesthesiologist was aware of the patient’s allocation, the patients, outcome assessors, and data analysts remained blinded to group assignments.

2.4 Procedures

Upon entering the operating room, patients were monitored using standard anesthesia equipment to continuously record heart rate (HR), pulse oxygen saturation (SpO₂), and respiratory rate (RR). Mean arterial pressure (MAP) was measured via radial artery puncture. Preoxygenation was administered before anesthesia induction, which included intravenous atropine (0.01 mg/kg), propofol (2 mg/kg), rocuronium (0.6 mg/kg), and sufentanil (0.3 μg/kg). Following induction, tracheal intubation was performed after three minutes of mask ventilation.

During surgery, anesthesia was maintained with remifentanil, administered at a rate of 0.01–0.2 μg/kg/min, and sevoflurane, adjusted to a minimum alveolar concentration of 0.8–1. MAP was maintained within 20% of baseline, and electroencephalographic (EEG) dual monitoring was used to ensure a frequency range of 40–60. Mechanical ventilation was delivered in volume-controlled mode with a tidal volume of 6–8 mL/kg, ensuring an end-tidal carbon dioxide concentration of 35–45 mmHg. Muscle relaxation was sustained with intermittent boluses of cisatracurium (0.03 mg/kg).

The number of surgical incisions and drainage tubes was recorded at the end of surgery. Extubation was performed once the patient met the extubation criteria. Before emergence from anesthesia, 4 mg of ondansetron and 0.1 mg/kg of nalbuphine were administered. Postoperatively, all patients received intravenous patient-controlled analgesia (IV-PCA), prepared with sufentanil (1.5 μg/kg) and ondansetron (8 mg) in 0.9% normal saline, totaling 100 mL. The IV-PCA device (REHN(M01), Rehn Med Tech Ltd., Taizhou, Jiangsu, China) was connected at the end of surgery and programmed with a demand dose of 2 mL, a 20-minute lockout interval, and a continuous background infusion of 2 mL/h. Then, the patients were transferred to the SICU for postoperative management.

For the study group, the EOI block was performed by the same anesthesiologist before anesthesia induction. Ultrasound guidance (SC6-1U/Resona7, Mindray, Shenzhen, Guangdong, China) was used to visualize the intercostal muscles, external oblique muscle, and subcutaneous tissue in a sagittal plane at the level of the sixth rib, between the anterior axillary and midclavicular lines (Fig. 1). The injection site was identified as the fascial plane between the external oblique and intercostal muscles. Using an in-plane technique, a 22 G, 80 mm block needle (Stimuplex B-Braun Medical, Melsungen, HE, Germany) was inserted, and 20 mL of 0.375% ropivacaine was administered bilaterally.

Fig. 1.Ultrasound-guided visualization of the external oblique intercostal block.

In the SICU, patients were assessed while awake at 1, 4, 8 and 24 hours after extubation, and relevant clinical data were recorded. Pain intensity was evaluated using the visual analog scale (VAS), where 0 represented no pain and 10 indicated the worst possible pain. If a patient reported a VAS score of ≥4 at rest, intravenous tramadol (50 mg) was administered. Pain was reassessed after 30 minutes, and if the VAS score remained ≥4, an additional 50 mg dose of tramadol was given. If the patient continued to experience pain, further reassessment was conducted. Patients with persistent VAS scores of ≥4 despite tramadol administration were given 25 mg of intravenous pethidine as a rescue analgesic.

The quality of postoperative recovery was assessed using the 15-item Quality of Recovery (QoR-15) scale, cognitive function was evaluated with the Mini-Mental State Examination (MMSE), and anxiety levels were measured using the Self-Rating Anxiety Scale (SAS) [14, 15, 16]. Complications related to the nerve block were systematically recorded. Puncture site hemorrhage was noted if present during the procedure. Postoperative inflammatory signs, including local redness, swelling, heat, pain or exudation at the block site, were classified as local infections. Local swelling, pain and skin discoloration were indicative of hematoma formation. Persistent skin numbness or tingling was categorized as nerve injury, while rash or respiratory distress was considered an allergic reaction.

2.5 Outcomes

The primary outcome of this study was sufentanil consumption via the analgesic pump at 24 hours post-extubation. Secondary outcomes included blood pressure, HR, SpO₂, VAS scores, rescue analgesic consumption, the QoR-15 score, the SAS score, the Mini-Mental State Examination (MMSE) score, and the incidence of complications.

2.6 Statistical analysis

A pilot study involving eight patients per group was conducted to determine the required sample size. The mean sufentanil consumption 24 hours postoperatively was 53.5 ± 1.91 μg in the control group and 52 ± 1.63 μg in the EOI group. Based on a statistical power of 80% and an α level of 0.05, a minimum sample size of 62 patients (31 per group) was calculated using PASS 2021 software (NCSS Inc, Kaysville, UT, USA). To account for a 20% dropout rate, the final sample size was set at 39 patients per group.

Statistical analyses were performed using SPSS software (version 25; IBM Corporation, Armonk, NY, USA). Continuous variables were expressed as mean ± standard deviation (SD) or median (interquartile range (IQR)), and categorical variables were presented as n (%). The normality of continuous variable distributions was assessed using the Shapiro-Wilk W test, and variance equality was evaluated with Levene’s test. Parametric data were analyzed using the Student’s t-test, while nonparametric data were assessed using the Mann-Whitney U-test, with the Hodges-Lehmann estimator used to determine the 95% confidence interval. Categorical variables were compared using either the chi-square test or Fisher’s exact test. A p-value of < 0.05 was considered statistically significant for all analyses.

3.1 Study population

A total of 78 patients were screened for eligibility and randomly assigned to one of two groups. During the study, four patients were excluded from the final analysis due to open surgery (n = 1), failure to be transferred to the SICU (n = 2), or loss to follow-up (n = 1). Consequently, 74 patients met the inclusion criteria and were included in the final analysis (Fig. 2). The demographic and baseline characteristics of the two groups were comparable, with no statistically significant differences (p > 0.05) (Table 1).

Fig. 2.The CONSORT flow diagram of the study design. EOI: external oblique intercostal; SICU: surgical intensive care unit.

3.2 Vital signs

The patients’ vital signs were monitored and recorded at each time point for both groups (Table 2). Data analysis showed no significant differences between the EOI and control groups at any recorded time point (p > 0.05).

3.3 Analgesic effect

Sufentanil consumption via the analgesic pump at 24 hours postoperatively was significantly lower in the EOI group compared to the control group (median: 52 μg (50–54) vs. 54 μg (52–54); difference in medians with 95% CI: 0.000 to 2.000, p = 0.027, calculated using the Mann-Whitney U test and Hodges-Lehmann estimate) (Table 3). The VAS pain scores demonstrated significantly higher incision pain in the control group compared to the EOI group at 1 hour postoperatively (median: 2 (1–4) vs. 1 (0–2); difference in medians with 95% CI: 0.000 to 2.000, p = 0.005, calculated using the Mann-Whitney U test and Hodges-Lehmann estimate). However, there were no significant differences between the two groups in VAS scores for visceral or shoulder pain. When comparing VAS scores for incisional and visceral pain at 1 hour, the control group exhibited significantly higher scores for incisional pain (p < 0.05) (Fig. 3). Regarding rescue analgesic consumption, tramadol use at 1 hour postoperatively was significantly higher in the control group than in the EOI group (median: 0 (0–50) vs. 0 (0–0); difference in medians with 95% CI: 0.000 to 0.000, p = 0.038, calculated using the Mann-Whitney U test and Hodges-Lehmann estimate). No significant differences in incision pain scores were observed among different surgical types (Table 4).

Fig. 3.Comparison of incision pain and visceral pain between the two groups at different time points. Note: *p < 0.05, **p < 0.01 and ***p < 0.001 indicate statistically significant differences between the two groups at the same time point. VAS: visual analog scale; EOI: external oblique intercostal.

3.4 Patient assessment indicators and nerve block complications

No significant differences were observed between the two groups in postoperative recovery quality, as measured by the QoR-15 score, or in assessments of anxiety (SAS score) and cognitive function (MMSE score). Additionally, the incidence of nerve block-related complications did not differ significantly between the two groups (p > 0.05) (Table 5).