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.