Patients and study design
A total of 128 patients undergoing elective SILC were enrolled in this study from February 2019 to April 2019 at the Affiliated Hospital of Nantong University. The inclusion criteria were as follows: male and female patients between 18 and 59 years of age with an American Society of Anesthesiology (ASA) score of I or II and a body mass index(BMI) of 18-30 kg/㎡. Patients with preexisting neuropathy, coagulopathy, local skin infection, hepatic, renal or cardiorespiratory failure, local anaesthetic allergy, pregnancy, complications of gallstones with gallbladder perforation, diffuse peritonitis or acute pyogenic cholangitis were excluded.
The study was registered prospectively with the Chinese Clinical Trial Registry（reg no.ChiCTR1900020738) and approved by the ethics committee of Affiliated Hospital of Nantong University (approval number: 2018-K067), and written informed consent was obtained.
Randomization and blinding
All 116 patients (64 males, 52 females) scheduled for elective, SILC were randomly divided into four groups using a computer-generated random sequence concealed in consecutively numbered, opaque, sealed envelopes, which were opened on the morning of surgery.
In a total of 116 patients, anaesthesia was induced with intravenous midazolam 0.1 mg/kg, propofol 2 mg/kg, sufentanil 0.5 µg/kg and cisatracurium 0.15 mg/kg. Anaesthesia was maintained with an infusion of 10 mg/ml propofol at 4 mg/kg/h and 50 µg/ml remifentanil at 0.2 µg/kg/min. To ensure an adequate depth of anaesthesia, response entropy indexes were kept between 40 and 60 during the entire anaesthesia period by adjusting the rate of infusion of sufentanil and propofol.
After systemic anaesthesia was induced, in groups III and IV, the probe was transversely placed at the lateral level of the umbilicus. Using the in-plane technique, the needle was advanced until the posterior aspect of the rectus muscle was penetrated. No blood and no gas were drawn back; furthermore, a small volume of saline (＜2 ml) was initially injected to ensure that the needle tip was correctly positioned. When the needle was located between the posterior rectus muscle and posterior sheath, 20 ml of 0.5% ropivacaine was injected bilaterally (Figure 1).
Patients in groups II and IV received an intravenous infusion of 1 mg of butorphanol 30 min before the end of surgery. Those in groups I and III received an intravenous infusion of 10 µg of sufentanil 30 min before the end of surgery.
Vital signs, such as blood pressure, heart rate, oxygen saturation, and electrocardiogram pattern, were recorded during the operation. The operative duration, haemorrhage volume and consumption of remifentanil and propofol were also recorded.
PCIA with a bolus dose of 2 µg of sufentanil, a lock-out interval of 15 min and a maximum dose of 2 µg/h was used for routine analgesia in groups I and III. In groups II and IV, all patients received butorphanol PCIA at a background rate of 170 µg/h and a demand dose of 170 µg every 15 min as rescue analgesia for postoperative pain management. During a preoperative visit, patients were adequately informed about the concept of the VAS and trained how to use PCIA.
All patients were treated by the same experienced anaesthesiologist, who specialized in ultrasound-guided regional anaesthesia and did not participate in the postoperative data collection.
Primary outcome: In both groups, a blinded investigator who was not involved in patient recruitment or the anaesthesia procedure recorded the incisional pain at rest using a 10-cm visual analogue scale (VAS; 0 cm=no pain; 10 cm=worst pain) at 6 h after the operation.
Secondary outcomes: Incisional and visceral pain at rest and during cough at 2, 12 and 24 h after the operation, incisional and visceral pain during cough at 6 h after the operation, PONV, somnolence, constipation, uroschesis, pruritus, and respiratory depression were separately assessed by a blinded observer. Butorphanol 1 mg was administered intravenously as rescue analgesia in patients with a VAS score＞3 in all groups. The blinded observer recorded the doses of butorphanol and sufentanil and the number of PCIA presses.
Statistical analysis was performed using IBM SPSS 21. Normality testing was performed using the Levene method. The patients’ data are presented as the mean and standard deviation (SD) if they are normally distributed; otherwise, they are presented as the mean and interquartile range. Count data were analysed by the chi-squared (χ2) test. The χ2 test and Fisher’s exact test were used to compare proportional data, and the Nemenyi test was used to determine differences between two groups. P＜0.05 was considered statistically significant. Power Analysis and Sample Size (PASS) software (NCSS, LLC, Kaysville, UT, USA) was used for the sample size calculation. An ɑ=0.05, a power of 90%, and an expected difference in efficacy of 20% in the ultrasound-guided RSB combined with the butorphanol group were used to calculate the sample size. If the attrition rate was set at 20%, a total of 72 patients (18 in each group) would be required. Thus, 116 patients (29 in each group) met our experimental needs.