The study was carried out in a tertiary care public hospital in Shenzhen, China. It was approved by the Hospital Institutional Review Board (szkcw201628) and registered with the Clinical Trial Registry of China (ChiCTR-INR-16010130). After patient informed consent was obtained, the parturients scheduled for elective caesarean delivery under spinal anaesthesia were enrolled in the study. Inclusion criteria were American Society of Anaesthesiologists physical status I or II. Exclusion criteria were inability to comprehend or use the verbal rating pain scoring system, or contraindication to the use of tramadol, cyclooxygenase-2 inhibitor or paracetamol. An independent statistician prepared a randomization list with block of group allocation was kept in a concealed opaque envelop. Attending anaesthetists would disclose group assignment at the start of surgery and prepare for the TAP block if necessary. In order to ensure the recruited parturients who had spinal anaesthesia were blind from group allocation and avoid sham block, the surgical drape which block parturients’ view of her surgical site was kept after surgery. A linear 13- to 6-MHz ultrasound probe (Sonosite TM, Bothell, Washington) scan of bilateral flank was performed. Only parturients who were allocated to have TAP block would have injection of local anaesthesia under aseptic techniques. A 22-gauge, 90-mm SonoPlex Stim needle (Pajunk Medizintechnik, Geisingen, Germany), attached with flexible tubing to a syringe filled with 0.9% normal saline, was introduced through the skin anteriorly in the plane of the ultrasound beam, and advanced into the fascial plane between the internal oblique muscle and transversus abdominis muscles. Ropivacaine(Naropin, Astrazeneca AB. Sweden)15 ml (0.25%) was injected on each side for the TAP block. Since the parturients who had effective spinal block would not feel the needle injection of TAP block, it was possible to blind the participants from group allocations as ultrasound scan would be performed even if TAP block was not administered.
All recruited patients had intravenous cyclooxygenase-2 inhibitor before the end of operation. They were also prescribed multimodal oral analgesia postoperatively, and this included slow release tramadol 100 mg twice a day for the first two days, celecoxib 200 mg twice a day for three days, and paracetamol 1000 mg four times a day for four days. Oxycodone 10 mg was prescribed and given as rescue analgesia.
Participants were given instruction to fill in a survey for postoperative pain control. The numeric rating scale (NRS) for pain and satisfactory scale was explained. NRS consist scores of 0 to 10, with 0 equals to no pain and 10 equals to the worst pain. A scale of 5 were used as a satisfactory score, with 1 equals to “very unsatisfactory” and 5 equals to “very satisfactory” with pain relief. The participants were asked to record the NRS at rest, with movement, and with uterine massage and the satisfactory score at 2 hours, 4 hours, 6 hours and 12 hours after completion of surgery. In addition, they were asked to record if there was an episode of nausea and vomiting. The parturients would also record if oxycodone or uterotonic was used in the first 24 hours. Moreover, they would also record if there was any instant pain when NRS was greater than 6 in the first 24 hours. The survey was collected one day after surgery and the NRS at rest and with movement were also enquired by pain nurse during follow up and this pain score on day 1 after operation.
Primary outcome is the percentage of parturient who required oxycodone rescue analgesia. Secondary outcomes include the NRS at rest, with movement and during uterine massage, patient satisfactory score, the percentage of parturients who experienced pain with NRS > 6 during the first 24 hours after surgery, and the percentage of parturients who required oxycodone for breakthrough pain and the incidence of nausea and vomiting. According to our record of routine postoperative visit, approximately 20% of our patients required oxycodone rescue. If TAP block would decrease the requirement of oxycodone from 20–5%, 73 parturients per group is required for 80% power with 5% type 1 error.
Parametric primary and secondary outcomes are presented as mean (SD) or number (percentage) and were compared by t-test or Chi-square test. Non-parametric data are presented as median (IQR [range]) and compared by Mann-Whitney U test. The area under the curve (AUC) for pain scores and satisfactory scores were derived using the trapezoidal rule. The mean AUC of pain scores and satisfactory scores were presented as mean (SD) and compared using t-test. A p value < 0.05 was considered significant. Data were analysed using SPSS (version 21.0; SPSS Inc., Chicago, IL, USA).
This manuscript adheres to the applicable CONSORT guidelines.