|Year : 2012 | Volume
| Issue : 2 | Page : 98-102
Ultrasound-guided transversus abdominis plane block does not improve analgesia after elective caesarean section when intrathecal diamorphine is used-A randomised double-blind controlled trial
Elizabeth Puddy, Sireesha Aluri, Ian Wrench, Ben Edwards, Fleur Roberts
Department of Anaesthetics, Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield, UK
|Date of Web Publication||17-Dec-2012|
Department of Anaesthetics, Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield
Source of Support: None, Conflict of Interest: None
Context: Previous studies comparing transversus abdominis plane (TAP) block and opioids for postoperative analgesia for caesarean section under spinal anaesthesia have been performed in the absence of a long-acting intrathecal opioid or with intrathecal morphine. In our unit, we use spinal diamorphine for caesarean sections under spinal anaesthesia. We wished to establish whether the performance of ultrasound-guided TAP blocks should be introduced into routine practice.
Materials and Methods: Following local ethics committee approval, 53 parturients presenting for elective caesarean section were recruited. All patients received a spinal anaesthetic with 0.5% heavy bupivacaine and 300 mcg diamorphine. The study was completed by 48 patients who were randomised to undergo postoperative TAP blocks with 20 mL to each side of either 0.25-0.5% bupivacaine (n = 23) or normal saline (n = 25). Standard postoperative analgesia comprised of regular diclofenac and paracetamol, and subcutaneous morphine on request via an indwelling subcutaneous cannula. A blinded investigator assessed each patient at 2, 6, and 24 h postoperatively.
Results: There were no statistically significant differences in postoperative morphine requirements or visual analogue pain scores between the two groups. The incidence of side effects was similar.
Conclusions: We conclude the ultrasound-guided TAP block does not improve analgesia following elective caesarean section under subarachnoid block with intrathecal diamorphine and its routine implementation during utilisation of a multimodal analgesic regimen may not be beneficial.
Keywords: Caesarean section, intrathecal diamorphine, spinal anaesthesia, transversus abdominus plane block
|How to cite this article:|
Puddy E, Aluri S, Wrench I, Edwards B, Roberts F. Ultrasound-guided transversus abdominis plane block does not improve analgesia after elective caesarean section when intrathecal diamorphine is used-A randomised double-blind controlled trial. J Obstet Anaesth Crit Care 2012;2:98-102
|How to cite this URL:|
Puddy E, Aluri S, Wrench I, Edwards B, Roberts F. Ultrasound-guided transversus abdominis plane block does not improve analgesia after elective caesarean section when intrathecal diamorphine is used-A randomised double-blind controlled trial. J Obstet Anaesth Crit Care [serial online] 2012 [cited 2021 May 16];2:98-102. Available from: https://www.joacc.com/text.asp?2012/2/2/98/104735
| Introduction|| |
Lower segment caesarean section (LSCS) is one of the most commonly performed abdominal operations where the uterus is typically accessed via a Pfannenstiel incision through the lower abdominal wall. Postoperative pain frequently requires the use of parental opiates as part of a multimodal analgesic regime. The additional demands of caring for a new infant, together with the need for early mobilisation, render some of the side effects of morphine (e.g., nausea, vomiting, pruritus, dysphoria, and urinary retention) undesirable.  Any addition to current anesthetic technique that leads to a reduction in postoperative morphine requirements is therefore a welcome development.
The TAP block is a relatively recently described peripheral nerve field block, with a number of applications for lower abdominal surgery.  The analgesic efficacy of the block has been established for several surgical procedures including laparotomy, total abdominal hysterectomy, appendicectomy, laparoscopic cholecystectomy, and retropubic prostatectomy. ,,,, In 2008, McDonnell et al. published a study that demonstrated that performing TAP blocks significantly reduced morphine requirements post caesarean section.  In this study, patients did not receive long-acting intrathecal opioids which have been shown to significantly reduce postoperative pain in this patient group. ,
Most of the studies to date compare intrathecal morphine use with or without TAP blocks to postoperative morphine requirements. We used intrathecal diamorphine, as studies have shown it to be beneficial over intrathecal morphine with regard to the side effect profile ,, and it is a standard practice in our unit to use 300 μg of diamorphine.  A service evaluation in our unit  suggested that the use of TAP blocks improved analgesia following caesarean section under spinal anaesthesia in combination with intrathecal diamorphine. We now report a study to formally test the hypothesis that TAP blocks are beneficial in this patient group.
| Materials and Methods|| |
After South Yorkshire ethics committee approval ASA class I-II patients, scheduled to undergo elective LSCS, were recruited into this randomised double blinded controlled trial. Written informed consent was obtained from patients before inclusion in the study. Patients were excluded if consent could not be obtained, if there was local sepsis at the site of local anaesthetic injection or if subarachnoid anaesthesia was converted to general anaesthesia. Any patients that had a relevant drug allergy, contraindication to standard analgesic regimen, bleeding disorder, ASA physical status III or higher, body mass index higher than 45 kg/m 2 or difficulty in visualising and performing TAP blocks were also excluded.
The allocation sequence was achieved by a computer-generated table of random numbers and placed in a sealed envelope. Patients were randomly assigned to receive bilateral TAP blocks with two injections of either 20 mL 0.25-0.5% bupivacaine (up to 2 mg/kg) or 20 mL 0.9% normal saline. A member of the anaesthetic team not involved with the study prepared two 20 mL syringes of medication. They were not involved in the performing of the block or the postoperative assessment of pain. The patients, the anaesthetists, and nursing staff were blinded to group allocation.
Large bore intravenous access was secured in the nondominant arm, with monitoring of pulse, noninvasive blood pressure, and oxygen saturation. All patients received subarachnoid anaesthesia with 0.5% heavy bupivacaine and 300 mcg diamorphine, and as per the standard practice in our unit. Surgery was performed by standard Pfannenstiel incision.
Bilateral ultrasound-guided TAP blocks were performed at the completion of surgery. The same person performed all TAP blocks. Full aseptic precautions were observed and a Sonosite I-Look 180 portable ultrasound machine (Sonosite Inc. Bothell, WA, USA) with 5 cm high frequency linear array probe was utilied. The probe was positioned transverse to the abdomen in the midaxillary line between the lower border of the ribs and the iliac crest. The external oblique, internal oblique, transversus abdominis muscles and the transversus abdominis fascia were visualised. A 22 g 100 mm Stimuplex (B. Braun, Melsungen AG) needle was directed under continuous in-plane ultrasound visualisation between internal oblique and transversus abdominis into the posterior aspect of the fascial plane. After negative aspiration and distension of the fascial plane by hydro dissection, 20 mL of the study solution was injected under ultrasound guidance. This procedure was repeated on the contralateral side of the abdomen with the remaining 20 mL of study solution.
Information about intraoperative pain, nausea and vomiting and maximum height of spinal blockade were recorded. The occurrence of any complications and the patient's satisfaction score were recorded at the end of the surgery. The patients were then transferred to a recovery facility, where routine postoperative monitoring of pulse, blood pressure, and oxygen saturations were commenced.
Each group received a standardised postoperative analgesic regimen. This consisted of an intraoperative loading dose of 1 g of paracetamol and 100 mg of diclofenac per rectum, followed by regular postoperative analgesia in the form of
1 g of oral paracetamol every 6 h and 50 mg of oral diclofenac every 8 h. Patients were instructed to request additional analgesia for breakthrough pain. This was in the form of midwife administered boluses of 5-10 mg of subcutaneous morphine. A subcutaneous cannula was sited in all patients at the end of surgery. A prophylactic antiemetic was not administered. Postoperative nausea was treated with cyclizine 50 mg every 8 h in the first instance, and subsequently with ondansetron 4 mg every 8 h if nausea persisted.
The patients were visited by the researcher at 2, 6, and 24 h after TAP blockade. At each visit pain was assessed using a visual analogue pain scale (VAPS). This consisted of a 10 cm line where point 0 = no pain and point 10 = worst pain imaginable. The patients were asked to mark the line at the point which they felt represented their pain at the time. Nausea was assessed using a nil/mild/moderate/severe scoring system, the presence of vomiting (present/absent) and the use of anti-emetics were also recorded. Pruritus was assessed in a similar fashion (nil/mild/moderate/severe). The consumption of and time to demand of first dose of subcutaneous morphine was recorded at 24 and 48 h.
Power analysis was performed by the Sheffield Statistics Unit. The primary outcome measure of the study was the time to first postoperative dose of morphine. Secondary outcomes were the total morphine consumption in 24 h and visual analogue pain scores. A small service evaluation of 15 patients who had received TAP blocks and an historical control from our unit was used to calculate the sample size required. , The time in minutes to first dose of postoperative morphine for those receiving TAP blocks (mean (SD)) was 773 (387) and for the control group 372 (188). It was calculated that a sample size of 24 would have 90% power (significant level (α) = 0.05) to detect a difference in time to first dose of subcutaneous morphine, assuming a standard deviation of differences of 370, using a 2-sample t-test.
Statistical analysis of the final results was performed using the Minitab version 13 statistical programme. For the majority of data, Kruskal-Wallis and Mann-Whitney U-tests were used for nonparametric data and t-test for parametric data. Where other tests have been used, this is indicated in the text. P < 0.05 was taken to be significant.
| Results|| |
We gave information about the study to 107 parturients at their preoperative assessment for elective caesarean section. From this group, 53 patients were recruited into the study, of which five were withdrawn. Three patients required general anaesthesia; one patient had an oophorectomy and in another case diclofenac was omitted in error. Of the remaining 48 patients, 23 were randomised to receive TAP block with bupivacaine and 25 with 0.9% saline. There is a flow diagram illustrating patient allocation [Figure 1]. Demographic data were comparable between the two groups [Table 1]. There was no significant difference in the time to the first dose of postoperative morphine [Table 2], or the total morphine consumption up to 48 h between the bupivacaine and placebo group. Postoperative VAPS values at 2, 6, and 24 h, both on movement and rest were also not significantly different [Table 3].
|Table 3: Postoperative visual analogue pain scores— median (interquartile range [range])|
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No significant difference was found between the study and control group in the incidence of nausea, vomiting or requirement for postoperative antiemetic therapy. The number of patients complaining of itching did not differ significantly between groups [Table 4]. No adverse incidents or complications of performing the block were encountered in either group.
| Discussion|| |
Our study is the first randomised double-blinded control trial that compares intrathecal diamorphine with or without bupivacaine in TAP blocks for postcaesarean analgesia. In this, we were unable to demonstrate that TAP blocks improve postoperative analgesia following caesarean section under spinal anaesthesia with intrathecal diamorphine and regular postoperative multimodal analgesia. Our findings are consistent with recent studies comparing TAP blocks with intrathecal morphine in this patient group. ,,, The studies which demonstrated a beneficial effect of this regional block in caesarean section patients did not utilise a long acting intrathecal opiate. ,
One of the key aims of this study was to assess what the impact of the introduction of ultrasound-guided TAP blocks would be on postoperative analgesia for our patients. For this reason, we elected to incorporate the standard means of postoperative pain relief that we use in our unit (subcutaneous administration of morphine) into the research protocol. We had previously used this method, although with subcutaneous diamorphine, in a dose finding study of intrathecal diamorphine for postcesarean section analgesia.  Our findings were very similar to other studies which had used morphine consumption from patient-controlled analgesia as a means to assess postoperative pain. Thus, we felt that this was a legitimate method of assessing postoperative analgesia.
Unfortunately, the postoperative subcutaneous morphine requirement of patients in our study was much lower than we had anticipated. It would appear that locally postoperative parenteral opioid usage has declined significantly from the time when the original study used for the placebo estimate was performed.  It is not clear why this has happened, although our unit is significantly busier now (7200 deliveries per year) than it was then (5600 deliveries per year). Even so the pain scores that were recorded in this study are very similar to those that we reported previously. 
All of the TAP blocks in this study were performed by an experienced operator using continuous in-plane ultrasound guidance. We believe that the use of ultrasound-guided regional nerve blockade represents best practice. In support of this, there have been recent case reports of hepatic injury during TAP block placement where the operators either did not use ultrasound or used ultrasound intended for vascular access only. ,, Previous studies have also shown that blocks performed with ultrasound guidance are safe, more likely to be successful, take less time to perform, and have a faster onset time and a longer duration of action. ,,,
There has been controversy in the literature regarding the spread and level of block achieved with a single TAP injection. While an early study showed a T7 to L1 spread with a single posterior injection making the block suitable for midline abdominal incisions,  a subsequent investigation failed to demonstrate a spread cephalad to T10 making it more suited for lower abdominal surgery.  In this small cadaveric study, T11-L1 were consistently included in the tranversus abdominis plane but higher thoracic nerves were frequently absent. Subcostal augmentation of the block has been described to supplement the analgesia to T7. The ultrasound-guided approach to the posterior aspect of the TAP fascia that we utilised should have been sufficient to augment a lower midline Pfannenstiel incision.
The question remains as to whether we have failed to identify a clinically important improvement in postoperative analgesia produced by using TAP blocks. Our findings are similar to other studies by Costello et al.,  McMorrow et al.,  Loane et al.,  Kanazi et al.  that could not demonstrate an advantage of TAP block over intrathecal long-acting opiate such as morphine. Although intrathecal diamorphine used in our study is shorter acting and has lesser side-effect profile than intrathecal morphine, we still could not demonstrate a significant advantage of TAP block over spinal diamorphine. The role of TAP block for postcaesarean section analgesia has been neatly summarised in a recent editorial by McDonnell and Paech. 
In conclusion, we could not demonstrate that TAP blocks improve analgesia following elective caesarean section under subarachnoid block with intrathecal diamorphine. Ultrasound-guided TAP blocks are unlikely to be beneficial when long-acting intrathecal opioids and a multimodal analgesic regimen are used for this patient group.
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[Table 1], [Table 2], [Table 3], [Table 4]