DISCUSSION
In this systematic review and NMA, we aimed to evaluate the effects of single-shot ultrasound-guided RA techniques on 24-hr MME consumption in patients undergoing open cardiac surgery. Our NMA showed a statistically significant reduction in MMEs for the ESP, TTMP, and PIF blocks compared with placebo. No evidence was found for the PECS I block.
The efficacy of the ESP block in cardiac surgery has been extensively proven.21,31 There is evidence in the literature that this block has good analgesic effects in sternotomy cardiac surgery. In our NMA, we can infer that the ESP block has greater efficacy than placebo; compared with other blocks, it seems to be more effective than the PIF block. No differences were found between the ESP and TTMP blocks (Table 3). As in other fascial plane block studies, dermatomal analysis is not performed in studies evaluating the effectiveness of the ESP block, and the component of pain that is blocked has not been established. As mentioned before, pain in cardiac surgery may be caused by several factors, and the effectiveness of the ESP block may be due to blocking of the median sternotomy incision pain or acting in other ways. In future studies, questioning the exact location of pain and revealing the source by dermatome analysis will shed light on the blocks to be preferred and the combinations may provide postsurgical analgesia in cardiac sternotomy surgery.
The PIF and TTMP blocks are two new truncal fascial plane blocks that aim to anesthetize the anterior cutaneous branches of the thoracic intercostal nerves (Th2-6). Although these blocks have only recently been discovered, a 2021 ASRA-ESRA consensus renamed them superficial and deep parasternal intercostal plane blocks, respectively, to better define them anatomically.32 It was shown to be effective in postoperative pain management in the context of cardiac sternotomy surgery.26 The TTMP block in our NMA would seem to have a benefit in terms of 24-hr MME consumption compared with placebo, not so evident is the benefit when compared directly to PIF block and indirectly to ESP block (Table 3). The PIF block is the first among these blocks to be described as effective in the literature regarding the use of sternotomy cardiac surgery.33 In this NMA, its use seems to be the most questioned, as there does not appear to be a clear benefit in terms of reduction in MMEs when compared to placebo (Table 3).
When we evaluated the other outcomes, the PIF block seemed to be the only one to increase extubation time with a statistically significant result by increasing the time. This result is highly influenced by one study16 that showed a high difference among the groups. Therefore, further evidence for this outcome is warranted.
The impact of the ESP and TTMP blocks on ICU LOS is significant and favorable. Another NMA that evaluates the effects of fascial blocks in cardiac surgery can be found in the literature, but this one does not discriminate between sternotomy and non-sternotomy procedures, and this is a major limitation, as these are quite different procedures in terms of postoperative pain compared to each other.34In-hospital LOS is assessed only for PIF and TTMP blocks and is not statistically significant.
While there are no clear data to define the minimal clinically important difference (MCID) for 24-h opioid consumption in the literature referring to sternotomy cardiac surgery procedures, it is difficult to determine the magnitude of the analgesic effect of fascial blocks in this population. Hussain et al. evaluated breast cancer operations and considered reductions equivalent to 10 mg i.v. morphine reduction to be clinically important.35 Aware of the differences in the analgesic setting, considering the different structures involved in the surgical procedure, and comparing this to our results, we can assume that the ESP and TTMP blocks are effective.
This study has several limitations. First, the included studies are few, and most of them compared the blocks with placebo, making indirect comparison essential. In addition, publication bias assumed by Egger’s test makes indirect comparison possible for 24 hr MMEs, which is more difficult to estimate for other outcomes. Therefore, there is reduced consistency for untestable assumptions. Second, the heterogeneity in our analysis was very high. We attribute this to the fact that these blocks are relatively new, have been used in clinical settings in the last five years, and are being developed daily. Third, it should be specified that a placebo is often defined as an injection of saline instead of a local anesthetic, but sometimes studies represent placebo as no injection or medication. Fourth, the volume, type, and concentration of the local anesthetic administered varied. In some trials, adjuncts were added to the local anesthetic.