The meta-analysis of 8RCTs showed that the pain scores at 2, 4, 6, 12 and 24 postoperative hours were significantly lower in the QL group than in the TAP group. The amount of postoperative morphine consumption was lower in the QL group than in the TAP group. The duration of postoperative analgesia was longer in the QL group than in the TAP group. In addition, there were no differences in PONV.
In the UK, approximately 700,000 people undergo abdominal surgery every year[21]. Patients experience severe pain, which leads to a series of complications. Due to pain and discomfort, patients do not cough and cannot carry out their normal activities, resulting in respiratory complications that may lead to pulmonary infections[4, 22]. If the symptoms are severe, patients may have postoperative delirium, myocardial ischemia and other serious complications. If the pain cannot be controlled in a timely fashion, acute pain can transform into chronic pain, which distresses the patient, affects wound healing, reduces the quality of life of the patient, and prolongs his or her length of hospital stay[23, 24]. Therefore, adequate postoperative analgesia has important clinical significance. In recent years, regional blocks, as a key link in multimodal analgesia, have been increasingly widely used for postoperative analgesia after abdominal surgery. TAP blocks and QL blocks belong to this treatment category[5, 25]. Thus, the potential for effective analgesia after abdominal surgery is becoming increasingly promising.
TAP blocks were first described by Rafi in 2001[26]. TAP blocks involve the Petit triangle (that is, the lower lumbar triangle: the outer boundary is the posterior edge of the abdominal external oblique muscle, the inner boundary is the leading edge of the latissimus dorsi muscle, and the lower boundary is the iliac crest). The TAP is a nanatomical space between the transverse abdominal muscle and the medial oblique muscle[27]. The thoracolumbar nerve originates from the T6 to L1 segment of the spinal nerve root and innervates the abdominal wall, providing anterolateral sensation. The injection of local anesthetics into this space can block nerve afferents and provide adequate analgesia for the anterolateral abdominal wall[28]. However, due to the narrow range of abdominal transverse muscle plane blocks, they are often limited to use as postoperative analgesia for lower abdominal surgery, and the application of these blocks as postoperative analgesia for upper abdominal surgery is limited. As a new technique for abdominal trunk block, QL blocks were first proposed by Blanco in 2007; anesthetic is injected adjacent to the anterolateral aspect of the QL muscle and its fascia, blocking the posterior abdominal wall[16]. The block level is high (T7-L1), which can provide postoperative analgesia for both upper and lower abdominal surgery. The key to the analgesic effect of a QL block is the thoracolumbar fascia (TLF). The TLF is a complex tubular structure formed by connective tissue. Local anesthetics can spread through the TLF to the paravertebral space to generate an indirect paraspinal block[29, 30]. Therefore, it has an effect on visceral pain and abdominal incision pain. Additional studies[7, 12, 31] have shown that two different trunk blocks have adequate analgesic effects for the management of pain after abdominal surgery. FuscoP[32] et al confirmed the analgesic effect of TAP blocks after cesarean section. Blanco[16] et al conducted a RCT of 76 patients after cesarean section to compare the effects of pain management via QL block and TAP block. The results showed that TAP blocks were better able to reduce postoperative morphine requirements. However, there was no significant difference in postoperative pain scores between the two groups. In addition to clinical trials, other meta-analyses have confirmed the feasibility of the use of TAP blocks and QL blocks as analgesia after abdominal surgery.
Previous studies have reported the effectiveness and safety of QL blocks and TAP blocks for postoperative pain management after abdominal surgery. However, it is not yet clear which option is better. Zhu[17] et al found no significant difference in VAS scores between patients receiving QL blocks and those receiving TAP blocks 4 hours and 8 hours after surgery, while the resting and motor scores 12 hours and 24 hours after surgery were lower in the QL block group than in the TAP block group. However, Oksuz[14] et al reported that QL blocks provided superior analgesic relief. They compared the numbers of patients who needed analgesia in the first 24 hours and the pain scores at 30 minutes and 1, 2, 4, 6, 12, and 24 hour(s), and they found that the QL block was significantly superior to the TAP block. At the same time, Kumar’s study [18]demonstrated that the pain scores of the patients in the QL block group were lower than those of the patients in the TAP block group 2, 4, 8, 12 and 24 hours after lower abdominal surgeries.
In contrast to the above studies, we systematically evaluated the analgesic effects and adverse reactions of QL blocks and TAP blocks to determine which is the better regional blocking technique for pain management after abdominal surgery. The results of our meta-analysis, which included 8 RCTs, indicated that the QL block is superior to the TAP block with respect to the analgesic effect at 2, 4, 6, 12 and 24 hours after surgery. Overall, the present study suggests that the effect of the QL block is better than that of the TAP block for the early management of pain after abdominal surgery. We found that the QL block is superior to the TAP block with regard to reducing postoperative opioid requirements and that pain control lasts longer after the QL block, which is consistent with the findings of Blanco et al. The reason may be that the TLF is formed by the arrangement of the anterior, middle and posterior layers. After the posterior layer and the middle layer meet at the lateral edge of the vertical spinal muscle, they converge with the anterior layer at the lateral edge of the lumbar quadratus muscle to form the aponeuros is starting point of the transverse abdomen muscle. When QL block is performed, the local anesthetics can spread not only within the TLF but also to the abdominal transverse muscle plane and paraspinal space, creating an effect similar to the effect of a paravertebral nerve block[33]. The TLF has receptors that can regulate autonomic nerve function and pain mechanisms. Local anesthetics applied to the QL block some sympathetic nerves and thereby achieve a better effect. There was no significant difference in the incidence of PONV between the two groups. The reasons may be related to the different methods of anesthesia but may also stem from the sample size; therefore, a large number of consistent clinical trials are still needed.
Regarding the sensitivity analysis, there was still significant heterogeneity when performing the analysis by omitting one study in turn and when performing subgroup analyses. The main reasons for heterogeneity include the following: (1) Five RCTs originated in Asia, and the patient sample of one of the RCTs was limited to children. There may be relevant differences in the analytical results of the integrated data.(2) The types of surgery varied, including cesarean sections, total abdominal hysterectomies and appendectomies. The degree of postoperative pain varies among patients undergoing different abdominal surgeries. (3) The anesthetic drugs and concentrations used in the RCTs were different. Bupivacaine was used in 4 RCTs at concentrations of 0.125%, 0.2% and 0.25%. The concentrations of ropivacaine used in the other 4 RCTs were 0.25% and 0.375%. (4)Three RCTs used subarachnoid anesthesia, and five RCTs employed general anesthesia.
The limitations of this meta-analysis are as follows: in the data extraction, some observation indexes in the literature were only reported as the mean and median or in the form of graphics and text; thus, these results could not be included in the analysis, which may have excluded some high-quality studies. Furthermore, there was no explicit mention of the optimal drug type and concentration for the two trunk plane blocks, which need to be further studied to arrive at a satisfactory approach. During the data collection process, the original data from requested from the author by e-mail, but no response was received. Finally, although our meta-analysis has shown that there is a statistically significant difference in postoperative pain scores between patients receiving QL blocks and TAP blocks, a difference in pain scores that is less than 2 points has limited clinical relevance. Further studies are needed to clarify the more subtle clinical differences in pain after receiving a QL block compared with a TAP block after abdominal surgery.