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 (ChCTR-INR-16010130). After patient informed consent was obtained, the parturients scheduled for elective caesarean delivery under spinal anaesthesia were enrolled in the study. Spinal anesthesia was performed in a lateral position at the L2/3 or L3/4 interspace with 0.5% hyperbaric bupivacaine 10mg (2ml) combined with fentanyl 15µg (0.3ml) in both groups. Inclusion criteria were American Society of Anaesthesiologists physical status I or II parturients, scheduled for elective caesarean delivery under spinal anesthesia. Exclusion criteria included a body mass index of more than 35kg/m2, major systemic disease, chronic pain disorders, neurological disorders, abuse of drugs or alcohol, and allergies to any medication included in the study protocol and inability to comprehend or use the visual rating pain scoring system.
An independent statistician prepared a randomization list while block of group allocation was kept in concealed opaque envelops. Attending anaesthetists would disclose group assignments at the start of surgery, and prepare for the TAP blocks if necessary. In order to ensure the recruited parturients who had spinal anaesthesia were blind from group allocation and to avoid sham block, the surgical drape which blocks the parturient’s view of her surgical site was kept after surgery. After a wound was covered with dressing, an ultrasound-guided bilateral single-shot of TAP blocks was performed by the attending anaesthetists who are experienced with this technique before conducting the investigation. A linear 13- to 6-MHz ultrasound probe (Sonosite TM, Bothell, Washington) was placed transversely on the anterolateral abdominal wall between the iliac crest and costal margin. The three layers of muscles - the external oblique, the internal oblique, and the transversus abdominis - were identified. Only parturients who were allocated to have TAP blocks would receive an 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)15ml (0.25%) was injected on each side of the abdominal wall for the TAP blocks. A local anaesthetic solution was injected in 5 ml increments after aspiration. After each 5 ml bolus, patients were monitored for an increase in heart rate or signs of local anesthetic toxicity such as tinnitus, perioral numbness, metallic taste in mouth, slurring of speech, and mental status changes. Since the parturients who had effective spinal block would not feel the needle injection of TAP blocks, it was possible to blind the participants from group allocation as an ultrasound scan would be performed even if TAP blocks were not administered.
All recruited patients had intravenous parecoxib 40mg before the end of the operation. They were also prescribed multimodal oral analgesics postoperatively, and this included slow release tramadol 100mg twice a day for the first two days, celecoxib 200mg twice a day for three days, and paracetamol 1000mg four times a day for four days. Oxycodone 10mg for once as PRN was prescribed and used when necessary.
Participants were given instructions to fill in a survey for postoperative pain control. The numeric rating scale (NRS) for pain and satisfaction scale was explained. NRS consists of scores of 0 to 10, where 0 equal to no pain and 10 equal to the worst pain. A scale of 5 was used as a satisfaction score, with 1 equal to “very unsatisfactory” and 5 equal to “very satisfactory” with pain relief. The participants were asked to record the NRS at rest, with movement, and with uterine massage and the satisfaction 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 instance of pain when the NRS score was greater than 6 in the first 24 hours. The survey was collected by the pain nurse during follow up on day 1 after the operation.
The primary outcome is the percentage of parturients who required oxycodone as rescue analgesia. Secondary outcomes include the NRS at rest, NRS with movement and NRS during uterine massage, patient satisfaction score, the percentage of parturients who experienced pain with NRS > 6 during the first 24 hours after surgery, and the incidence of nausea and vomiting. According to our record of routine postoperative visits, approximately 20% of our patients required oxycodone as rescue pain relief. If TAP blocks were to decrease the requirement of oxycodone from 20% to 5%, 73 parturients per group would be required for 80% power with a 5% type 1 error.
Parametric primary and secondary outcomes are presented as the mean (SD) or number (percentage) and were compared by t-test or Chi-square test. Non-parametric data are presented as the median (IQR [range]) and compared by the Mann-Whitney U test. The area under the curve (AUC) for pain scores and satisfaction scores was derived using the trapezoidal rule. The mean AUC of pain scores and satisfaction scores were presented as the mean (SD) and compared using a t-test. A P value <0.05 was considered significant. Data were analysed using SPSS (version 21.0; SPSS Inc., Chicago, IL, USA).