• Truncal Blocks
• Anatomy
• Ultrasound in Pain Medicine

To the editor,

Erector spinae plane block (ESPB) has recently become a popular regional anesthesia technique. However, local anesthetic (LA) spread and anatomical studies regarding the mechanism of effect of ESPB have been both confusing and conflicting.1 2 Recently, Nielsen et al3 published a cadaveric study in which single injection thoracic ESPB was compared with paravertebral block and multiple injection costotransverse block (CTB). CTB is another recent addition to regional anesthesia literature, in which LA is injected immediately superficial to the superior costotransverse ligament; to the cephalic aspect of the lower transverse process (figure 1), CTB delivers LA closer to the paravertebral space when compared with ESPB with a single study demonstrating spread of LA to both the ventral rami and the sympathetic truncus in CTB.3

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Figure 1

Basic illustration of ESPB, costotransverse block and mid-transverse process block injection points. ESPB, erector spinae plane block; TP, transverse process.

For ESPB, cadaveric studies and clinical applications have demonstrated that the level of application, approach to block (in plane or out-of plane), type and concentration of LA, angle of needle insertion and, most importantly, the block performance technique of clinicians are the most important factors for block success and LA spread. ESPB is, however, not a completely standardized regional anesthesia technique. We would therefore like to open the following points for discussion:

1. In plane or out-of-plane? ESPB was initially described as being performed from cephalad to caudal using the in-plane technique. Thereafter, out-of-plane approaches were reported with a vast majority of clinicians preferring this approach.4 While some authors aim for interfascial plane deep to the erector spinae muscle in the in-plane technique, many applicants of both the in-plane and out-of-plane technique aim for the transverse process (TP). Could the change of success of ESPB be lower when performed using in-plane techniques between two TP as compared with ESPB that touches the TP? Could the difference between interfascial or sheath block be made through simple sonographic imaging?

2. Where does the CTB begin and end? CTB can be defined as LA application superficial to the superior of the costotransverse ligament. It therefore is very similar to the mid-point transverse process to pleura block.

3. If the osseous tissue is touched at corners above or below the dorsal aspect of TP, could this block still be named ESPB? (figure 1) As the LA would be placed deep to the intertransverse ligament, could this modification be the same as CTB? Could the intertransverse ligament of the musculus intertransversarii be determined by ultrasonography? Does the intertransverse ligament actually serve as an anatomic membrane?5 Or do the answers to our questions regarding ESPB lie in the anatomic structures? Does applying LA anterior to these structures guarantee spread to the paravertebral area?

4. When touching the TP, do repeated manipulations when injecting LA lead to opening of several leafs of fascia, effecting block performance? Would this lead to increased spread of LA to paravertebral space?

Success with ESPB and other peri-paravertebral blocks are commonly reported, yet their failures are not. While we are unable to give a ratio, we do observe block failure or lack of efficiency at our institutes after some ESPBs.4 Different modifications may be required in order to decrease block failure rates or to increase the spread of LA to the paravertebral space.6

We believe regional anesthetists should review both the thoracic and lumbar spinal anatomy. ESPB applications should be standardized and non-standard applications should be accepted as modifications or nomenclature revised.