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Abstract
During the time period 1984 to the turn of the millennium, interpleural nerve blockade was touted as a very useful regional anesthetic nerve blockade for most procedures or conditions that involved the trunk and was widely practiced despite the lack of proper evidence-based support. However, as an adequate evidence base developed, the interest for this type of nerve block dwindled and very few centers currently use it—thereby to us representing the rest in peace (RIP) I block. Unfortunately, we get a deja-vù sensation when we observe the current fascination with the erector spinae plane block (ESPB), which since 2019 has generated as many as 98 PubMed items. This daring discourse point out the lack of a proper evidence base of the ESPB compared with other established nerve blocking techniques as well as the lack of a proven mechanism of action that explains how this nerve block technique can be effective regarding surgical procedures performed on the front of the trunk. Emerging meta-analysis data also raise concern and give cause to healthy skepticism regarding the use of ESPB for major thoracic or abdominal surgery. Against this background, we foresee that ESPB (and variations on this theme) will end up in a similar fashion as interpleural nerve blockade, thereby soon to be renamed the RIP II block.
- analgesia
- anesthesia
- conduction
- pain
- postoperative
- acute pain
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Introduction
Aging is associated with certain problems but is also related to positive issues such as perspective and previous experience, something that younger people lack by default. Among anesthesiologists that frequently practiced regional anesthesia in the mid-1980s, the latest craze was the use of the interpleural (also called intrapleural) block technique, first described by Kvalheim and Reiestad in 1984.1 This was touted as the most versatile block that could successfully be used for any unilateral surgical procedure on the trunk, for example, posterolateral thoracotomy, open cholecystectomy, renal surgery or conditions such as multiple rib fractures and herpes zoster.2 The fact that it involved intentional pleural puncture and insertion of a pleural catheter to permit reinjection was not seen as a problem. This is in in sharp contrast to today, where the low risk of unintentional pleural puncture when performing a thoracic paravertebral block even without ultrasound guidance3 4 is often voiced as a counterargument against using this quite useful nerve blocking technique. However, when realizing that the patients needed to be supine with the blocked side slightly elevated (to allow the local anesthetic (LA) to pool on top of the paravertebral space (PVS; retrograde diffusion from the pleural cavity to the PVS being one of the plausible mechanisms of action)5 6 and if having a chest drain in place a substantial part of the LA would just be evacuated,7 reduced the enthusiasm. This was further compounded by the fact that with nursing patients in the proper, slightly head up position, not only did the block not work as expected but the LA would then pool on top of the diaphragm. Such pooling of LA could cause interference both with the phrenic nerve proper8 but also directly cause a negative effect on regular function of the diaphragm, both these components reducing effective ventilation. Not surprisingly paravertebral blockade (PVB) was found superior with regards to preserving lung function compared with interpleural analgesia.9 Some of us have in fact previously questioned the rationale for using this technique.10 The final challenge was when this block was subjected to comparisons against other alternatives in a structured review,11 where it was shown to be inferior to the alternatives.
Apart from certain reviews,12–14 a PubMed search on “Interpleural” or “Intrapleural” block revealed very few citations after 2000, and in most centers it is not used anymore. However, there remain pockets of interest (or resistance…) but unfortunately this is not evidence based but more based on opinion.15 Hence, the interest for this block has dwindled and will most likely not be resurrected. Thus, the interpleural block does, in our opinion, represent the rest in peace (RIP) I block.
Daring discourse
Unfortunately, we get a deja-vù sensation when we observe the current fascination with the erector spinae plane block (ESPB) and closely related variations on the same theme (eg, the retrolaminar block). A PubMed search on ESPB revealed more than a hundred items following the original description in 2016,16 with as many as 98 items just since 2019. Let us now dissect (!) some of these publications.
Cadaver studies
In line with what can be expected when dye is injected into the erector spinae plane (ESP) in cadaver studies, the dorsal thoracic ramus of the spinal nerve is always properly stained over several adjacent spinal levels. If directly transferable to the clinical situation, this will most likely provide anesthesia or at least analgesia from the midline of the back to approximately the mid-axillary line. Thus, it may possess interesting qualities, for example, for various types of back surgery. However, most cadaver studies fail to demonstrate reliable staining of the PVS proper, with the thoracic part of the sympathetic trunk, or of the anterior ramus of the spinal nerve (=intercostal nerve) that supplies the anterior part of the trunk.17–22
Some anatomical reports only deal with very few subjects, but others do show occasional staining of the nerve components of the PVS17 19—so how should we interpret that? First, it is quite difficult to judge the quality of dissection work since there is no international consensus as to the standards of anatomical studies. Second, only few authors exactly report the time between injection and dissection.15 17 This is of special importance when using various mixtures of methylene blue (as most investigators have done). As a rule, the longer the time, the less accurate the true extension of spread. Moreover, only one contribution evaluated the possible spread of dye into the epidural space by opening the vertebral canal.22 Third, anatomical proof of the colored area is unfortunately often done by non-specialists.19 Thus, staining could also be due to less than perfect dissection skills.
Furthermore, even if just one drop of methylene blue stains a nerve structure, providing a quite striking visual result, does not infer that one drop (drop size for intravenous infusions with regular drop chamber: 0.05–0.07 mL per drop) of LA would provide a relevant conduction block. Marhofer et al have determined the minimal volume/dose of LA that is required to block either the ulnar or the sciatic nerves (approximately 0.10–0.5 mL per mm2 cross-sectional area)23 24 and that is clearly more than just one or two drops.
At this point, we would also briefly address the comment by Cornish regarding the cadaver study by Ivanusic et al.17 Cornish claim that LA will flow from the ESP alongside the dorsal ramus of the spinal nerve and accompanying vessels to reach the PVS, but that this route is blocked by the embalming procedure in cadavers.25 For an adequate amount of LA to travel through this still not verified route builds on the fact that the ESP injection results in a substantial pressure buildup in the ESP space, thereby forcing LA through the foramen/canal that is quite small and is to a major part taken up by the nerve and the vessels. However, since an injection will spread along the way of least resistance, the finding by Ivanusic et al 17 that the injected dye spreads over the entire back of the patient, contradicts any relevant pressure developing in the ESP that could even theoretically push LA into the PVS. Additionally, the complex arrangement of tissues between thoracic transverse processes22 26 makes this mode of spread unlikely.
Although not a cadaver study, Zhang et al 27 recently published a seminal work with regards to the loss of cutaneous sensation following ESP blocks in healthy volunteers. They found that ESPB results in widespread cutaneous sensory block of the posterior part of the thorax. However, no cutaneous sensory block could be observed concerning the lateral part of the chest or the anterior part of the thorax or abdominal wall. Their conclusion was that an ESPB does only block the dorsal ramus of the spinal nerve. This is further supported by the findings reported by Bryne and Smith, who failed to produce any relevant sensory changes anterior to the mid-axillary line if the injection was not in fact done in the PVS.28
In conclusion, even a conservative interpretation of the dissection reports is that the ESPB by no means produce reliable and widespread staining of the PVS proper or the anterior ramus of the spinal nerve. Thus, the mechanism responsible for how ESPB will provide analgesia to the anterior part of the trunk remains to be anatomically proven in a conclusive way by its advocates.
Comparative studies
Following a multitude of case reports and small case series, we are finally seeing prospective randomized trials being published where ESPB is compared with other established nerve blocking techniques.
Recent meta-analyzes concluded that ESPB provides better postoperative analgesia compared with either placebo or regular systemic analgesia regimen.29 30 This is really to be expected since this is like “stacking the odds” or “hedging your bets”. Thus, you are in fact comparing two possible analgesic option with nothing, that is, possible effect of blocking nerves plus the very likely analgesic effect of the high, but usually non-toxic, plasma LA levels that fascial plane blocks are associated with.31 This does not prove that ESPB is effective but again show that systemic plasma levels of LA provide clinically relevant postoperative analgesia.32 33 A further meta-analysis and one narrative review find the technique interesting but point out the lack of randomized controlled trials (RCTs) showing that the block is superior to other more well-established RA alternatives and that the mechanism of action needs to be properly elucidated.34 35
First, not surprisingly the use of ESPB has been shown to be of value in the context of back surgery.36 Since ESPB readily blocks the posterior ramus of the spinal nerve over several adjacent spinal levels, this is in line with anatomical innervation of the back and, thus, back and spine surgery may prove to be a useful indication for ESPB.
When comparing ESPB, intercostal nerve blocks and PVB in thoracoscopic surgery, Chen et al found PVBs much more effective than the other two analgesic options.37 In two other RCTs, also investigating ESPB for minimally invasive thoracoscopic procedures, ESPB has been found non-inferior to PVB.38 39 However, a very interesting finding by Takeda et al was that significantly more dermatomes in the parasternal regions were anesthetized in the PVB group (see below).38 In this context, it is also interesting to note that adding a PECS to bilateral ESPB in minithoracotomy for mitral/tricuspid valve replacement resulted in significantly reduced VAS scores, lower oxycodone consumption and greater patient satisfaction compared with ESPB alone.40
RCTs studying laparoscopic cholecystectomies have found ESPB to be of value when compared with either multimodal analgesia alone41 or an oblique subcostal transversus abdominis plane block.42 However, an RCT comparing ESPB to epidural analgesia in the context of open cholecystectomy showed a clear advantage for using epidural analgesia.43
This raises the issue of the analgesic effect of the ESPB and the degree of surgical trauma. If the surgical trauma is minimal, then the systemic LA analgesia of ESPB (authors opinion) may well be enough to enhance postoperative analgesia. Thus, an ESPB may add benefit in the setting of minimally invasive surgery but not in more traditional settings, for example, sternotomy and open posterolateral thoracotomies or open cholecystectomies.
There is to date no proof presented that convincingly show that the anterior part of the intercostal nerve is reliably affected by the ESPB. Since this apparently cannot be anatomically proven, it is not reasonable to expect that ESPB should be able to offer any analgesia (other than that of systemically absorbed LA) with regards to the anterior part of the trunk. As shown by Taketa et al, ESPB did not produce anesthesia of the parasternal area.38 Thus, it is hardly surprizing that bilateral ESPB has not yet been studied in cardiac surgery involving sternotomy (major anterior chest surgery) against any other adequate alternative (eg, epidural block or PVB).
It is also interesting to note that PEC blocks (that in fact do cover the front of the chest) have repeatedly been found more effective in the context of breast surgery than ESPB44 45 and the role of ESPB in breast surgery has recently been questioned.46 The fact that ESPB does not possess any major effects in the territory of the anterior chest was recently published in this esteemed medical journal.47 This study conclusively showed that PVB provided significantly better analgesia (both clinically and statistically) compared with ESPB. We hope that this well-conducted study by Swisher et al ends any further attempts at showing any relevant analgesic effect by ESPB in the setting of surgical procedures performed on the anterior part of the chest or abdomen.
Finally, it is truly astonishing that a PubMed search using the term “ESP block” results in so many items as mentioned above. Remember that this is a block that still has no proven mechanism of action or produces anesthesia, except from the back to the mid-axillary line. To us, the only reason for this is the simplicity in performing the block using ultrasound guidance and the apparent safety associated with the procedure. What you harvest, except for back surgery, is most likely the analgesic effect of systemically absorbed LA and nothing more
Recommendations for further research regarding ESPB and other fascial plane blocks
We have previously raised the issue regarding the necessity of an additional control group when investigating any facial plane block31; a randomized group that get an intervention resulting in comparable systemic plasma levels of the LA used for the fascial plane block (eg, an intravenous infusion or subcutaneous injection producing relevant plasma levels of the same amount of LA). Without such a control group, we will never know what the effect of the fascial plane block is per se and what is due to systemically absorbed LA. We urge the editors of anesthesia and analgesia medical journals to take this into account when receiving manuscripts on ESPB or other fascial plane blocks and from now on only accept ESPB contributions that either conclusively can explain an effect on the anterior part of the trunk or RCTs that include the important control group mentioned above.
In conclusion, that ESPB should be of value for procedures involving the front of the torso is merely wishful thinking. Thus, we predict the “rise and fall” of the ESP block, making it the RIP II block when it comes to surgical procedures on the anterior part of the trunk. Interestingly, also other authors have shown skepticism about ESPB being the “Holy grail” of regional anesthesia and analgesia.48
References
Footnotes
Contributors PAL: underlying idea and manuscript writing. MKK: manuscript writing and manuscript reviewing. JR: manuscript reviewing, language revision, expertise in interpleural blockade. BM: manuscript writing, manuscript reviewing, expertise in relevant anatomy and cadaver dissection. All authors have read and approved the final manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.