The main finding of this meta-analysis is that performing ESPB constitutes an effective postoperative analgesic for reducing opioid consumption 24 hours after surgery, pain scores at 1 h and 6 h following surgery. Furthermore, it has been shown there is a significant reduction on patients who need rescue analgesia and prolongation in the time to first request of rescue analgesia. However, PONV was not significantly lower in patients treated with ESPB.
The significant decrease postoperative opioid is of great value for patients to enhance comfortable feelings and recovery following surgery. PONV is one of opioid dose-related side effects, which is not conducive to the rapid recovery after surgery, one study reported the use of postoperative opioids is related to PONV with a high rate of 79% among 4 risk factors
Therefore, we hypothesized that a decrease in opioid use could lessen PONV, however, on the contrary, the PONV difference was not statistically significant while opioid consumption and rescue analgesia reduced in our meta-analysis. The most likely Interpretation for this result was the PONV prophylaxis intraoperatively by applying antiemetic drugs such as iv. tropisetron or dexamethasone.
Despite ESPB has been successfully applied in postoperative analgesia with few adverse reactions, the mechanism of ESPB is still controversial. Altinpulluk EY, Forero M and Chin KJobservated an extensive spread to ventral rami and dorsal rami in the paravertebral space when ESPB is utilized, at the same time, Aponte A found posterior rami of spinal nerves was diffused, while no spread to the paravertebral space and anterior rami. Elsharkawy H described the paravertebral space infiltrated was not observed too. The optimum concentration and volume of LA in ESPB have not been described in the clinical guideline. Only one RCT make a comparison between different concentration of bupivacaine. Therefore, future research should focus on investigating the pattern of LA spread and impact of LA concentration and volume in ESPB.
Several factors may account for the extensive heterogeneity of the analysis. First, various severity of illness and surgery types (open and endoscopic surgeries) are undoubtedly play an important role in heterogeneity, Second, opioid (fentanyl, tramadol, morphine and so on) doses were not converted to morphine-equivalent doses which could make a wide dissimilarity between the data. Besides, utilizing supplementary analgesics such as paracetamol[25, 26]added an extra heterogeneity, Last, a short of clinical studies to use this technique make a difference among those studies.
Several notable limitations should be considered when interpreting the results. Firstly, the trials included have a modest sample size which could magnify the treatment effect. Secondly, the substantial heterogeneous make our results less convincing. Furthermore, owing to all patients were under GA surgeries, sensory blocking could not be evaluated adequately to detect potential block failures in all trails included.