Clinical effectiveness of ultrasound-guided dual transversus abdominis plane block for postoperative analgesia in open abdominal aortic surgery patients

Editor, Epidural analgesia is considered as the gold standard technique for pain relief after open aortic abdominal surgery (OAAS),1 but concerns regarding the risks of peri-operative haemodynamic instability or epidural haematoma limits its use in many centres.2 Bilateral ultrasound-guided dual transversus abdominis plane (TAP) block was reported to provide comparable analgesia with thoracic epidural analgesia after laparotomy.3 However, the effectiveness of bilateral dual TAP block for pain relief after OAAS is poorly described.4 The ETAP study was a single-centre, double-blinded, parallel-group randomised superiority trial designed to test the hypothesis that pre-incisional bilateral dual TAP block using ropivacaine could improve pain relief and lower postoperative opioid requirements in patients undergoing scheduled OAAS. The study protocol was approved by the Ethics Committee Est-II (no. 14/451, Chairperson: E Toussirot, 24 November 2014) and registered on ClinicalTrials.gov (NCT02292667). It was conducted in accordance with the French bioethics law. Written informed consent was obtained from all patients prior to inclusion. Patients scheduled for OAAS between January 2015 and November 2017 were eligible. Patients were excluded if they had an endovascular or combined peripheral vascular surgery, or an estimated creatinine clearance less than 30 ml min−1. Patients included were randomly assigned (1 : 1 ratio, computer-generated sequence) to either the dual TAP or control group. In the former, a dual TAP block was performed under general anaesthesia prior to skin incision on each side of the abdominal wall, according to the four-point approach described by Børglum et al.5 (10 ml of ropivacaine 3.75 mg ml−1 per injection, total dose = 150 mg). In the control group, no regional anaesthesia of the abdominal wall was performed. In both groups, the sites of TAP block needle insertion were covered to keep both the patient and the caregivers blinded to the treatment allocation. General anaesthesia was induced with intravenous propofol and maintained with inhaled sevoflurane and intravenous remifentanil. Muscle relaxation was obtained using cisatracurium. Postoperative pain management was standardised: intravenous morphine 0.05 mg kg−1 and paracetamol 15 mg kg−1 prior to skin closure; titration of intravenous morphine after emergence from anaesthesia; intravenous paracetamol 15 mg kg−1 every 6 h and patient-controlled analgesia (PCA) with morphine during the first 48 postoperative hours. The primary endpoint was the total dose of morphine administered during the first 24 h after emergence from general anaesthesia. The secondary endpoints were the total dose of morphine administered during the first 48 postoperative hours; and the pain intensity [visual analogic scale (VAS) value] at rest (every hour except when the patient was asleep) and at mobilisation (once a day) during the first 48 postoperative hours; and the incidence of side effects related to either morphine or dual TAP block. The expected mean value ± SD of the primary endpoint in the control group was 35.0 ± 15.0 mg. Considering a relative reduction of 35% (absolute reduction of 13 mg) in the dual TAP group, an α risk of 0.05, a β risk of 0.10, and a loss to follow-up rate of 10%, 30 patients were required in each group. Finally, 26 and 30 patients completed the 48-h study period and were analysed in the control and dual TAP groups, respectively (Table 1). The total dose of morphine administered within 24 h (primary outcome) and within 48 h after emergence from general anaesthesia did not differ significantly between the two groups (Table 2). Analysis of variance indicated that on days 1 and 2, there was no differences in the VAS scores for pain at rest (5 [3 to 7] versus 5 [3 to 6], P = 0.48) (Fig. 1) and at mobilisation (4 [2 to 5] versus 3 [1 to 4], P = 0.17) in the control and in the dual TAP groups. The secondary outcomes are reported in Table 2. Two (7%) patients presented a hematoma at the site of injection of the dual TAP block with complete spontaneous recovery.Table 1: Baseline characteristics of patients in the control and dual transversus abdominis plane groupsTable 2: Pain management in the control and in the dual transversus abdominis plane groupsFig. 1: Median [IQR] values for the visual analogue pain score at rest within 48 h after surgery in the control and dual transversus abdominis plane groups. P value for repeated measures ANOVA = 0.48.The current study showed that after OAAS, compared with morphine PCA a single-shot bilateral dual TAP block neither reduced morphine requirements nor improved pain relief at rest or mobilisation during the first 48 h postoperatively. Recent reports and meta-analysis reported a great heterogeneity among studies regarding TAP block efficacy for postoperative pain relief, depending on the technique used to perform the block, the postoperative co-analgesia, and the type of surgery.6,7 The lack of efficacy of dual TAP block in OAAS may be related in part to a prominent visceral, retroperitoneal component of postoperative pain, that is not covered by the parietal analgesia provided by the TAP block. Moreover, except for the initial first one or two postoperative hours, pain management appeared adequate in the control group and could explain that TAP block failed to improve pain relief after OAAS. The study has some limitations. We used a single-shot bilateral dual TAP block, and different results could be observed with a continuous infusion catheter TAP technique. Systemic analgesia in both groups was based on intravenous paracetamol and morphine PCA without any co-analgesic drugs. The sensory blockade of the TAP block was not tested to ensure that the patient and caregivers were blinded to the treatment allocation, and we cannot exclude TAP block failure in some patients. In conclusion, single-shot ultrasound-guided bilateral dual TAP block with ropivacaine did not improve pain relief after planned OAAS. Considering the underlying mechanisms of pain after OAAS, the clinical effectiveness of continuous dual TAP block via a subcostal approach deserves to be specifically addressed in further studies. Acknowledgements relating to this article Assistance with the letter: the authors would like to thank Fiona Ecarnot (PhD, Department of Cardiology, University Hospital of Besancon, and EA 3920, Bourgogne Franche-Comte University, 3 bvd Alexander Fleming, F-25000 Besancon, France) for her assistance in preparing the article. Financial support and sponsorship: the work was funded by a grant from the University Hospital of Besancon (APICHU 2014). Conflicts of interest: none.