Patients. The study was conducted in accordance with the ethical standard specifed by national health commission of China (Act 11, 2016) and approved by the ethics committee of Changhai Hospital (CHEC2023-060). Te requirement for written informed consent was waived by the ethics committee. This was a retrospective study analyzing the patients who received RAPN from October 2021 through October 2023 at our hospital.
The inclusion criteria were: 1) patients who underwent elective RAPN; 2) patients aged between 18 and 75 years; 3) patients classified as American Society of Anesthesiologists (ASA) I–III; 4) patients who received general anesthesia plus lateral or posterior QLB with identical analgesics. The exclusion criteria were: conversion to open surgery; discontinuation of patient-controlled analgesia (PCA) or additional use of other analgesic methods or medications within 48 hours after the operation.
Anesthetic procedure. Patient electrocardiogram, blood pressure, pulse oximetry, end-tidal carbon dioxide, and bispectral index (BIS) were monitored. General anesthesia was induced with propofol, remifentanil, and rocuronium. QLB block was performed by using a nerve stimulation needle (model: 001156-77, UniPlex Nanoline, PAJUNK GmbH Medizintechnologie, Germany) under ultrasound guidance using a high-frequency transducer (HFL38x/13 − 6 MHz, FUJIFILM Sonosite, USA) and an ultrasound diagnostic system (S Series, FUJIFILM Sonosite, USA).
For lateral QLB, with the patient positioned in a supine position, the transducer was placed horizontally between the rib margin and the iliac crest. The quadratus lumborum, obliquus internus abdominis, obliquus externus abdominis, and transverse abdominis were identified on the ultrasound image. Using the in-plane technique and a lateral approach, the nerve block needle tip was advanced into at the junction of the quadratus lumborum and transverse fascia. To confirm its accurate placement, a separation test was conducted by injecting 1 ml of normal saline. Subsequently, 30 ml of 0.5% ropivacaine was injected.
For posterior QLB, with the patient in the lateral position, the transducer was placed vertically against the axillary midline, between the ilium and rib margin. It was then moved posteriorly until the quadratus lumborum, psoas major, and erector spinae muscles were visualized. The "cloverleaf sign" was observed on the ultrasound, with the transverse process of the L4 vertebra as the stem, and the three muscles as the leaves. The needle tip was advanced from the anterior plane of the transducer to the triangular space between the quadratus lumborum and erector spinae, which was posterior to the quadratus lumborum. The needle tip position was confirmed by a separation test, followed by the injection of 30 ml of 0.5% ropivacaine.
During the surgical procedure, both groups received propofol and remifentanil via target-controlled infusion to maintain a BIS range of 45–60. When removing the excised specimens, intravenous sufentanil at a dose of 0.1 µg/kg was administered for analgesic treatment. Additionally, a PCA pump was initiated, delivering a continuous infusion of sufentanil at a rate of 1.5 µg/kg, with a total volume of 100 ml. There was no loading dose, and the infusion rate was set at 2 ml/h, with a self-administered dose of 0.5 ml per demand, and a lockout time of 15 minutes. During the perioperative period, if blood pressure exceeded 30% of the baseline value, ephedrine at a dose of 6 mg or nicardipine at a dose of 0.5 mg was administered for correction. Heart rate exceeding 100 beats or dropping below 50 beats per minute was corrected with esmolol or atropine, respectively.
Postoperative analgesia. Rescue analgesia was administered with PCA if the patient's Visual Analog Scale (VAS) score was greater than 3. Routine evaluation of pain by VAS was conducted at postoperative 24 and 48 hours. Meanwhile, the remaining medications in the PCA device was resupplied for the next 48 hours.
Data collection. Patient demographic and clinical data were collected from electronic clinical records. The primary outcome was the postoperative 24-hour cumulative sufentanil consumption. The secondary outcomes included postoperative scores of VAS and Bruggrmann comfort scale (BCS), postoperative 48-hour cumulative sufentanil consumption, sufentanil consumptions of different postoperative time intervals (0–2 h, 2–6 h, 6–12 h, 12–24 h, and 24–48 h), time to the first rescue analgesia, and intraoperative sufentanil consumption. Data of anesthesia-associated adverse effects were also collected.
Statistical analysis. Normally distributed continuous data were expressed as mean ± standard deviation, and between-group comparisons were analyzed using the Student’s t-test. Non-normally distributed continuous data were expressed as median and interquartile range, and between-group comparisons were analyzed using the Mann-Whitney U test. Categorical data were presented as percentages or frequencies, and between-group comparisons were analyzed using the chi-square test or the Cochran-Mantel-Haenszel test. All statistical analyses were performed using SPSS 26 software (IBM, Armonk, NY). A p-value of less than 0.05 was considered statistically significant.