This meta-analysis of 4 RCTs included 216 patients to evaluate the analgesic efficacy and safety of RIB in thoracoscopic surgery and breast surgery. RIB was more effective in controlling acute pain after breast surgery and thoracoscopic surgery than intravenous analgesia. Preoperative RIB significantly reduced pain scores at early time points and reduced 24-hour opioid consumption. The reduced difference in pain scores between the two groups at the later time point (24h postoperatively) may be result of an increase in opioid intake.
RIB is a new interfascial plane block which can provide analgesia between the T2 and T9 dermatomes7. Earlier cadaveric studies suggested that the spread of the dye in a cadaver which revealed extensive craniocaudal and anteroposterior spread, potentially accounting for the effectiveness of the block7, 19. As previously reported, RIB has been shown to be effective in both thoracoscopic and breast surgery20–25.
The results of our review are limited by considerable heterogeneity. Our sensitivity analysis found that significant heterogeneity remained between trials after alternating omissions of a study. Then we performed the subgroup analysis, but they still existed the heterogeneity. And Our subgroup analysis showed that early RIB had a favorable effect in both types of surgery. Data of the time to first postoperative analgesic request was given in only one trial15: the time to first postoperative analgesic request in the RIB group was significantly longer than that in control group (p < 0.001).
In terms of NRS, the RIB group showed significant lower scores than the no block group in 0–1 and 6–8 hour, which mean lower pain level in RIB group. Although there was no significant difference between groups in NRS at resting time of first 24 h, RIB showed excellent postoperative analgesic effect, which may be beneficial to early postoperative rehabilitation of patients.
In terms of postoperative complications, several studies have shown that the RIB group has fewer postoperative complications. The most common complication was PONV, and there was a significant difference between the RIB and no block groups. The incidence of PONV was 10.30% in the RIB group and 34.60% in the no block group, respectively. This may be due to low fentanyl consumption in the RIB group. Nausea and vomiting is mainly result of vagus nerve excitation, hypotension, distension of the stomach and the use of opioids. RIB does not affect the vagus nerve, has little effect on hemodynamics, and the use of opioids after surgery is relatively rare, so the incidence of vomiting is relatively low.
Postoperative respiratory depression is also caused by pain. In addition to discouraging the sufferer from inhaling deeply, reducing tidal volume and increasing respiratory rate, it may also suppress the cough reflex. Postoperative analgesia is an effective measure to prevent respiratory depression, atelectasis and pulmonary infection26, 27. One of the studies reported the occurrence of respiratory depression in the RIB group and the no block group. The rate of respiratory depression was 10% in the RIB group and 30% in the no block group, which showed a significant difference. Other complications were not reported in the included studies. Block-related complications did not occur in any of the studies. Therefore, we have to conclude that RIB is a relatively safe blocking technique.
The erector spinae plane block (ESP) is a relatively new technique that was first described by Forero et al. in 201628. And it's proven to be effective in breast surgery and thoracoscopic surgery29, 30. The injection site of RIB is more peripheral than that used with ESP, and the spread of local anaesthetic runs mostly towards the lateral branches of the intercostal nerves rather than to the paravertebral and epidural space. Because the sympathetic chain blockade is not as deep with RIB as compared with ESP, the incidence of hypotension could reduce. Since there is no study about comparing ESP and RIB, we suggest future studies to determine if RIB is non-inferior to ESP.
Future studies should also incorporate better double- blinding techniques and sham controls which were lacking in the current studies. There is also no study comparing paravertebral block and RIB. Given the higher risk profile of paravertebral blocks31, we also suggest future studies to determine if RIB is non-inferior to paravertebral block.
There are several limitations to this study. First, although sensitivity analysis and subgroup analysis were used to reduce heterogeneity, there was still significant heterogeneity in some subgroups. Second, many of the included studies only provided data on PONV, but not on other common complications (bleeding, arrhythmias, postoperative respiratory system, etc.). Only one study compared respiratory depression between RIB and the no block group. Therefore, we were unable to make a comprehensive assessment of postoperative safety between them. Finally, compared with other meta-analyses, the sample size of the studies we included was small, which may weaken our conclusions. Large sample and multicenter RCTs should be performed for further discussion.