Cross section of the paraspinal muscle at T5. (Reprinted with permission from Dr. Vicente Roques from imedar.com)
The target of the ESP block is between the most anterior and deepest layer of the erector spinae muscle and the tip of the transverse process (Fig. 11.1). The erector spinae muscle is surrounded by fasciae that contain multiple layers (Fig. 11.2). The architecture of the erector spinae muscle is complex, with three muscle layers distributing in the lumbar, thoracic, and cervical area (brief explanation below).
Target of erector spinae plane block. (Reprinted with permission from Dr. Vicente Roques from imedar.com)
The aim of the ESP block is to penetrate the most anterior layer of the erector spinae muscle and deposit the injectate between this layer and the tip of the transverse process. The plane allows cranial-caudal spread in multiple spinal segments (Fig. 11.3). The injectable is placed in close relation to the inter-transverse connective soft tissue, which allows the infiltration of the local anesthetic to the paravertebral space, through its porous surfaces or through the foramen where the dorsal ramus of the spinal nerve leaves the intervertebral foramen to innervate back structures.
Ligaments and muscles around the erector spinae plane. (Reprinted with permission from Dr. Vicente Roques from imedar.com)
The erector spinae plane is surrounded by soft tissues: ligaments (inter-transverse ligament, costotransverse ligament), muscles (levatores costarum, rotatores costarum, and external intercostal muscles), and fat (Fig. 11.4).
Magnetic resonance imaging with gadolinium contrast added to bupivacaine erector spinae plane block (30 mL total volume) injected at the left T10 level. (a) Sagittal view at the level of the intervertebral foraminae showing transforaminal spread of the gadolinium from T5 to T12 of the left side (yellow arrows). (b) Sagittal view of the spinal canal depicting epidural spread (red arrows) of the contrast from T5 to T12. (c) Axial view at the T12 level demonstrating the spread of gadolinium from the erector spinae plane through paravertebral space (dashed white arrow) transiting the intervertebral foramina (yellow arrow) to spread circumferentially (red arrows) within the epidural space. Some venous uptake of gadolinium is also noted. (Modified, with permission, from the original unpublished image in the Philip Peng Educational Series collection (Toronto, ON, Canada))
Schematic diagram showing the spread of injectate following an ESP block. (Reprinted with permission from Dr. Vicente Roques from imedar.com)
The mechanism of action has been examined through clinical (contrast spread) and cadaveric (imaging and dissection) studies. Following a single injection (usually 20 mL), the injectate spreads in paravertebral space in multiple segments over an average of 6 spinal segments, reaching the ventral and dorsal ramus of the spinal nerve along with the sympathetic ramus communicans at the intervertebral foramen level (Figs. 11.5 and 11.6). Epidural spread has been noticed as well. Spread to the intervertebral spinal foramen typically results in analgesic effect only even when anesthetic concentration of local anesthetic is used, although two reports had been published on the use of ESP block for mastectomy and ventral hernia repair with minimum sedation.
The ESP block has characteristics of differential blockade. The small amount of local anesthetic reaching the paravertebral space through the foramen provides sufficient local anesthetic mass to block small A delta and non-myelinated C fibers (pain and sympathetic fibers) but is not able to block large myelinated sensory and motor fibers. Analgesia without motor block along discernable cutaneous sensory block is consistent with the findings in most ESP literature.
Patient Selection and the Choice of Level
The ESP block has been published extensively in the upper thoracic level (thoracic indications) and the lower thoracic level (abdominal-pelvic indications). At these levels, the erector spinae muscle is located over the paraspinal gutter which consists of three muscular layers from medial to lateral: (1) spinalis, (2) longissimus, (3) iliocostalis (Figs. 11.1 and 11.2). When performing an ESP block at the thoracic level, the thoracic longissimus is the muscle in the needle path before the needle in contact with the tip of the transverse process, which is the target of ESP block. Usually, the level chosen for thoracic indications is between T2 and T5, and for abdominal pelvic indications between T7 and T10.
The cervical portion of erector spinae muscle is formed by semispinalis cervicis, longissimus cervicis, and iliocostalis cervicis, which inserts onto the transverse processes of C2–C6, extending the ESP plane from the upper thoracic region to the neck to reach cervical foraminae. This anatomic arrangement is the rationale for performing the ESP block at the upper thoracic area to provide analgesic effect to cervical nerve roots (shoulder analgesia).
The thickness of erector spinae muscle in the lumbar level is thicker than in the thoracic area, making lumbar ESP block under ultrasound technically more challenging. However, same rationale applied to the cervical region can be applied here to the lumbar levels. Lower thoracic ESP block to reach lumbar nerve roots is recommended either by a single injection or by placing a catheter for interfascial infusion.
Area of blockade for erector spinae plane block in different surgeries
Spine region | Indications | Catheter after single shot | Single shot volume |
|---|---|---|---|
High thoracic T2 or T3 | Chronic shoulder pain syndrome | Unilateral | 20 cc |
Post-surgical shoulder pain | Unilateral | ||
Mid thoracic T4 to T6 | Rib fracture (midpoint of level of ribs fracture) | Unilateral or bilateral | 20 cc |
Open thoracotomy and Vats lobectomy(T5) | Unilateral | ||
Rescue after TE failure for thoracic surgery(T5) | Unilateral | ||
Cardiac surgery – sternotomy (T5) | Bilateral | ||
Breast surgery with axillary lymph node dissections (T3) | Unilateral | ||
Chronic post-herpetic neuralgia (level of segments involved) | Unilateral | ||
Chronic post-thoracotomy pain (level of segments involved) | Unilateral | ||
Metastatic ribs cancer (level of segments involved) | Unilateral | ||
Low thoracic T7 to T12 | Nephrectomies (T8) | Unilateral | 20 cc |
Hysterectomies (T10) | Bilateral | ||
Laparoscopic ventral hernia repair with mesh (T7) | Bilateral | ||
Laparotomies (T7) | Bilateral | ||
Chronic post-herpetic neuralgia (level of segments involved) | Unilateral | ||
Chronic abdominal pain syndrome (T7 to T10) | Bilateral or unilateral | ||
Chronic pelvic pain syndrome (T10) | Bilateral or unilateral | ||
Lumbar (L4) | Vertebral surgery (mid-point of levels involved) | Bilateral | 20 cc |
Post-surgical hip replacement pain management (L4) | Unilateral |
Ultrasound Scanning
Position: Sitting/lateral decubitus/prone; depending on the operator’s and patient’s comfort (Fig. 11.7).
Probe: Usually a linear probe (7–12 MHz) is sufficient. For high BMI a curvilinear (2–6 MHz) is advised.
Various positions for the performance of ESP block. (Reprinted with permission from Dr. Vicente Roques from imedar.com)
Scan 1
Find the tip of transverse process using transverse view
Place the probe in transverse orientation over the spinous process in the midline and transverse process laterally (Fig. 11.8). Just lateral to the spinous process is the lamina, a flat hyperechoic structure covered by ESM. Lateral to the lamina is the tip of transverse process which is a well-defined hyperechoic flat structure more superficial to the lamina. Mark the target on the skin (tip of transverse process) and then rotate the probe in cranio-caudal orientation, keeping the tip of transverse process on the middle of the ultrasound scream.
Scan 2
Find the tip of transverse process using cranio-caudal probe orientation, moving from RIBS to TRANSVERSE PROCESS.
Cranio-caudal probe orientation over the rib. (Reprinted with permission from Dr. Vicente Roques from imedar.com)
Scan 2a
Cranio-caudal probe orientation over the rib in the selected spinal level (for instance the diagram depicts T5 level).
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