Several case reports have shown that local anaesthetic injection around the quadratus lumborum is effective in providing pain relief after various abdominal operations and in patients with chronic pain.7–10 However, a literature search identified no randomised controlled trials that evaluated the effect of QLB after caesarean section. The purpose of this randomised, controlled, double-blinded study was to evaluate the analgesic efficacy of QLB after caesarean section.
Ethical approval for this study was provided by the Research Ethics Committee at Corniche Hospital, Abu Dhabi, United Arab Emirates (Chairperson Dr P. Bosio) on 20 March 2014, reference number CH27021403. The study was registered with a clinical trials registry (ClinicalTrials.gov identifier: NCT02328378).
After obtaining informed consent, 50 parturients who were scheduled for elective caesarean section under spinal anaesthesia were enrolled into the study. Inclusion criteria were American Society of Anesthesiologists physical status 1 or 2 and a normal singleton pregnancy with a gestation of at least 37 weeks. We excluded patients who had congenital coagulopathy, anatomical abnormalities, localised infection, who used anticoagulants or were unable to comprehend or use the verbal rating pain scoring system or patient-controlled analgesia (PCA) pump.
Patients were allocated randomly into one of two groups with an internet-based randomisation program (Urbaniak GC, Plous S. Research Randomizer version 4.0). The QLB group received a QLB at the end of surgery with 0.125% bupivacaine 0.2 ml kg−1 (n = 25) and the control group received a QLB with 0.9% normal saline 0.2 ml kg−1 (n = 25). A sealed opaque envelope containing the study number was opened by an anaesthetist who was not involved in the study. This anaesthetist prepared the study medication and labelled the syringe with a unique study number; this number was used to identify the study medication and was revealed only on completion of data collection at the end of the study. The anaesthetists who were involved in the study, parturients and other healthcare providers who were involved in postoperative care were blinded to the patient group assignment.
Perioperative anaesthesia management was according to departmental guidelines. The patients received oral ranitidine 150 mg on the evening before and again on the morning of surgery. In the operating room, all patients received oral 0.3 M sodium citrate 30 ml. A 16-gauge intravenous cannula was inserted in the nondominant hand or arm after 2% lidocaine had been infiltrated at the cannulation site. In all patients, spinal anaesthesia was performed with ultrasonograph guidance. With the patient in the sitting position the midline and level of the L3–4 and L4–5 intervertebral spaces were identified with ultrasonography (transverse and longitudinal approaches). At the level selected by the anaesthetist, the distance from the skin to the dura mater and the angle of the probe used to achieve the optimal view of the dura mater were noted. The predetermined point of entry for the introducer needle was marked on the patient's back using a skin marker. With the patient still in the sitting position, spinal anaesthesia was administered with a 26-gauge pencil point needle (Portex, Smiths Medical, Ashford, UK) using hyperbaric bupivacaine 15 mg and fentanyl 20 μg. Patients were immediately placed in the supine position with left uterine displacement. Spinal anaesthesia was considered successful when a bilateral block to T6, assessed by loss of cold (ice cube) and touch (blunt pin) discrimination, was established 5 min after the spinal injection.
Anaesthetic and surgical treatment was performed in the usual manner. At the end of surgery, all patients received rectal diclofenac 100 mg and intravenous paracetamol 1 g. While in the supine position, patients received bilateral QLBs performed by one of the authors (R.B.) who had more than 8 years’ experience of using this technique. All patients were monitored throughout the performance of the block. A broadband (5–8 MHz) convex probe (Sonosite EDGE Portable Ultrasound System, SonoSite, Bothell, Washington, USA) was used, and imaging depth was set between 1 and 9 cm. After cleaning the abdomen with surgical solution (iodine povacrylex and isopropyl alcohol solution 26 ml; 3 M DuraPrep, 3 M, St. Paul, Minnesota, USA), the probe was placed at the level of the anterosuperior iliac spine and moved cranially until the three abdominal wall muscles were clearly identified. The external oblique muscle was followed posterolaterally until its posterior border was visualised (hook sign) leaving underneath the internal oblique muscle, like a roof over the quadratus lumborum muscle. The probe was tilted down to identify a bright hyperechoic line that corresponded with the intermediate layer of the thoracolumbar fascia. The needle (Sonoplex Pajunk, 21 gauge × 100 mm, Pajunk, Norcross, Georgia, USA) was inserted in plane from medial (anterior) to lateral (posterior). The optimal point of injection was determined using hydrodissection. The spread of local anaesthetic was posteromedial rather than anterolateral (Fig. 3).
After the patient was brought to the recovery room, a morphine PCA pump (Graseby 3300 Pump, Smith Medical International, Ashford, Kent, UK) was connected to the patient. The pump was programmed to deliver a 1-mg intravenous bolus on demand, with a lockout interval of 5 min and no background infusion.
The primary outcome measure of the study was the total number of PCA morphine demands and the actual doses delivered at predetermined time intervals (1, 2, 4, 6, 12, 24 and 48 h) after surgery. The following variables were measured and documented: heart rate, respiratory rate, oxygen saturation and noninvasive blood pressure. Pain was assessed with a visual analogue score (VAS) at rest (VASR) and with movement (dynamic) (0, no pain; 10, worst pain imaginable). Supplemental and regular analgesics, residual nerve block, sedation scores (Ramsay scale), itching (0, none; 1, mild; 2, moderate; 3, severe), nausea (0–3 scale: 0, none; 1, mild; 2, moderate; 3, severe or vomiting) and other complications were documented.
All patients received regular oral paracetamol 1 g 6 hourly, and diclofenac 50 mg at 8-hourly intervals. Intravenous ondansetron 4 mg was used to treat nausea and vomiting. Patients with a score of 10 in the modified Aldrete scoring system were considered eligible for discharge to the surgical ward. Data collection was continued on the ward for 48 h.
A sample size calculation (PS: Power and Sample Size Calculation, version 3.1.2, Vanderbilt University, Nashville, Tennessee, USA) showed that 25 patients were required in each group, based on 15% difference in morphine consumption between the two groups. Probability (power) was set at 0.8 and type I error associated with this test for null hypothesis was 0.01. All data analyses were performed according to a preestablished statistical plan. Correction of P for multiple testing was set to 0.01 to detect significance (Bonferroni adjustment for multiple comparisons). Data were collected and entered into the computer as numerical or categorical data (IBM SPSS Statistics for Windows, Version 20.0, IBM Corp., Armonk, New York, USA). Complete descriptive statistics were recorded for each variable including minimum, maximum, range, mean, standard deviation, 95% confidence interval of the mean, median and interquartile range. Comparisons were performed between the two groups using independent t tests or Mann–Whitney tests, as appropriate. Analysis of variance was performed within groups for normally distributed variables. The Friedman test was used for repeated measures for nonnormally distributed variables. Box plots, whisker plots and error-bar graphs were plotted. The χ2 test and Fisher exact test were used to evaluate the association between qualitative variables.
A total of 50 patients were recruited to the study (Fig. 4). Two were excluded because they delivered their baby on the night before the planned caesarean section. Of the remaining 48 patients, 25 had been allocated to the QLB group and 23 to the control group. There were no deviations from protocol. Patient demographics for the both the groups were comparable. There were no significant differences between the groups in operative time, blood loss, or time to perform the block. Oxygen saturation, heart rate, respiratory rate and blood pressure were similar in both the groups. There were no statistically significant differences in sedation, itching or nausea scores (Table 1).
Patients in the QLB group used significantly less morphine than the control group (P < 0.001) at 6 and 12 h but not at 24 and 48 hours after caesarean section. The QLB group had significantly fewer morphine demands than the control group (P < 0.001) at 6, 12, 24 and 48 h after caesarean section (Table 2).
The VAS was significantly lower in the QLB group than in the control group: VAS at rest at all times except 24 h after caesarean section; VAS with movement (dynamic) at all times (Table 3).
To the best of our knowledge, this is the first double-blind, randomised, prospective study of QLB for caesarean section. We studied the effects of QLB versus placebo on PCA morphine doses and demands. We found that the patients who received QLB had significantly less morphine consumption than the control group 6 and 12 h after the operation. They also had significantly fewer morphine demands at all time points after caesarean section. The VAS scores were significantly better at every observation time in the QLB group than in control patients.
QLB is a superficial fascial block between the posterior abdominal wall muscles and is not technically difficult to perform. We base this observation on our experience in the training and competency assessment of anaesthetists at our institution who perform this block. Every anaesthetist is evaluated by the main operator and designer of the technique (R.B.), and learning curves are currently being investigated.
QLB may be safer than TAP block because it is performed in close proximity to the surface and uses a fascial compartment path to extend the distribution of local anaesthetic into the posterior abdominal wall and paravertebral space. This requires a broader knowledge of ultrasonographic anatomy beyond the TAP plane. The anterior and posterior abdominal wall muscles must be identified.
Several studies have examined the role of TAP block as part of a multimodal approach in postoperative analgesia after caesarean section, with variable results.11,12 This block has also been used for other abdominal operations in which the supraumbilical areas must be covered. The contribution of TAP block to the treatment of visceral pain is nonexistent because it comprises infiltration only into the anterior abdominal wall. Baaj et al.13 found an advantage in reducing morphine consumption when using TAP blocks after caesarean section but other clinical trials have suggested no benefit. TAP block after caesarean section may be less effective and more costly than intrathecal morphine, with no evidence of either improvement in analgesia, or decreased supplemental morphine requirements or lower pain scores.14–17 A meta-analysis confirmed that there was better analgesia with intrathecal morphine than TAP block alone, but morphine was associated with a higher incidence of adverse events.18 In a systematic review and meta-analysis by Abdallah et al.,19 it was concluded that TAP block constitutes an effective analgesic option for postoperative analgesia after caesarean section. This applies when spinal morphine is not used, but if intrathecal morphine is administered then there is no evidence that TAP block is of benefit. In another meta-analysis a year later, the same lead author concluded that more prolonged analgesia was produced with a posterior rather than a lateral TAP block during the first 48 h after lower abdominal surgery through a transverse incision.20
Pruritus is the most common side-effect after the use of intrathecal morphine and has a variable incidence that can be up to 87% of patients. Urinary retention is another major factor (up to 70%) in these patients, with a mean interval until the first urination of 693 min. Nausea and vomiting can also be important and the possibility of ventilatory depression cannot be excluded in patients receiving intrathecal morphine. We used 20 μg of fentanyl intrathecally instead of morphine to try to minimise the side-effects of longer acting opioids.21
We performed QLB after the end of surgery with the patient supine and still under the effects of spinal anaesthesia. We opted against performing the block before surgery because the ultrasonographic anatomy may be less clear with the gravid uterus. In our experience, the optimal point of needle insertion is posterior to the quadratus lumborum because this approach is safer and quicker to perform. Our previous MRI studies showed consistent dispersion of the local anaesthetic into the posterior abdominal wall and paravertebral space. While performing the block, it is common to visualise the lower pole of the kidneys and lower lobes of the liver and spleen. In this situation, the probe should be moved more posterior and inferior.
The possible effect of local anaesthetic dispersion through the paravertebral space must be investigated further. From the MRI images obtained, it appeared that a small volume of contrast was reaching the paravertebral space, but this may be because of the parameters used for the three-dimensional reconstructions. We know from our clinical experience that when QLB is performed as a rescue block after abdominal surgery, the block can produce relief of dull visceral pain within several minutes. This could be explained by a hypothetical role of the sympathetic nervous system in acute pain; autonomic C fibres are much smaller and may be blocked faster than myelinated fibres.
In our study, we showed that QLB produced prolonged postoperative analgesia, up to 48 h. Therefore, the use of catheters for additional boluses or for infusions of analgesics, is not likely to be beneficial in QLB for caesarean section.
In the present study, we did not assess the postoperative dermatomal levels of block as part of our measurements. We had concerns that the finding of a prolonged area of numbness would have unblinded both the anaesthetists who collected data and nurses who cared for these patients. Another possible limitation was that the patients may have been using morphine PCA to treat nonoperative pain; we educated our patients before the study not to use morphine for these purposes.
In a busy unit such as our hospital, with more than 8000 deliveries per year, the introduction of an additional procedure at the end of surgery has the potential to slow turnover time between cases. However, we have shown that in experienced hands the average time to perform QLB is less than 2 min. The advantages of introducing QLB as part of routine perioperative care for caesarean section may offset the drawback of adding a few minutes to the anaesthetic time.
In summary, the present results showed that QLB has an important contributory role in the treatment of postoperative pain after caesarean section. The optimal point of injection was posterior to the quadratus lumborum muscle. This was a more superficial approach than our previous version of the block at the anterolateral side of the muscle. Safety of the block is improved, and complications may be avoided, because of better image resolution, longer distance to the intra-abdominal viscera and the presence of adjacent muscles. Proper implementation of the technique can significantly decrease opioid use after caesarean sections.
Acknowledgements relating to this article
Assistance with the study: none.
Financial support and sponsorship: none.
Conflicts of interest: none.
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