Thoracic wall (PECS) blocks

Thoracic (PECS)

Rafael Blanco

****Important: The blocks described on this page are at an early developmental stage and described largely based on anatomical assumptions. Clinical data is limited so we urge caution before readers offer these blocks to patients.

Paravertebral block, either single injection or continuous, has been the most commonly used regional anesthetic/analgesic technique for breast surgery. However, many practitioners are not comfortable performing paravertebral block due to the risk of pneumothorax, and inadvertent entry of the block needle into the vertebral canal with consequent spinal cord trauma. Furthermore, paravertebral block does not provide complete sensory block to the anterior chest wall, as neural innervation is not only from the thoracic spinal nerves, but also the brachial plexus via the medial and lateral pectoral nerves.

Thoracic wall blocks (PECS I, PECS II and Serratus plane block) are peripheral nerve block alternatives to paravertebral block for providing both surgical anesthesia and postoperative analgesia for breast surgery. All rely on LA placement between the thoracic wall muscles. Thoracic wall blocks are to the chest what the TAP (transversus abdominis plane) block is to the abdomen. Like the TAP block, their introduction has been facilitated by the widespread availability of portable ultrasound.

Anatomy

Muscles relevant for thoracic wall blocks include the pectoralis major muscle, pectoralis minor, serratus anterior, the intercostal muscles and latissimus dorsi (Fig. 1).

 

                          

 Fig. 1. Anterior thoracic wall muscles relevant to thoracic wall blocks: pectoralis major, pectoralis minor (not labelled but visible on the left cut away and passing down from the coracoid process to the ribs), serratus anterior, intercostal muscles and on the right, latissimus dorsi.

 Neural innervation of the anterior chest wall and breast involves the following nerves:

1. Pectoral nerves - from the brachial plexus cords (Fig. 2):

        a. Lateral pectoral nerve - from C5-7, runs between pectoralis major and minor to supply                 pectoralis major.

        b. Medial pectoral nerve - from C8-T1, runs deep to pectoralis minor to supply pectoralis                 major and minor.

2. T2-6 spinal nerves - run in a plane between the intercostal muscles and give off lateral and         anterior branches (Fig. 3):

        a. Lateral – pierces the intercostal muscles/serratus anterior in the mid axillary line to give               off anterior and posterior cutaneous branches*

        b. Anterior – pierces the intercostal muscles and serratus anterior anteriorly to supply the                 medial breast.

3. Long thoracic nerve and thoracodorsal nerve:

        a. Long thoracic nerve – from C5-7, runs on outer surface of serratus anterior to the axilla               where it supplies serratus anterior (Fig. 2).

        b. Thoracodorsal nerve – from C6-8 via the posterior cord, runs deep in the posterior                       axillary wall to supply latissimus dorsi.

* except T2, which doesn’t divide but becomes the intercostobrachial nerve.

Fig. 2. Axillary anatomy.

NB. The terminology of the spinal nerve terminations is potentially confusing (Fig. 3). Each spinal nerve divides into a ventral and dorsal ramus. The ventral ramus enters a plane between the intercostal muscles and divides into lateral and anterior branches. In turn, the lateral branch divides into “anterior” and “posterior” cutaneous terminations. The anterior branch terminates in an “anterior” cutaneous termination (Fig. 3)

                                                     Fig. 3. Branches of the spinal nerves innervating the chest wall.

 

Depending on the extent of surgery, anesthesia/analgesia for breast surgery requires blockade of several nerves innervating the chest wall. For example, for the insertion of breast expanders and submuscular prostheses, tissue trauma is generally limited to the pectoralis major muscle, and therefore only blockade of the lateral and medial pectoral nerves is required. For more extensive procedures such as tumour resections, mastectomy and sentinel node dissection, surgical dissection is typically deeper and requires blockade of the thoracic spinal nerves. For even more extensive reconstructions particularly those involving the axilla, blockade of the long thoracic nerve is needed. Blockade of the thoracodorsal nerve is required for lattissimis dorsi flap reconstruction.

Based on this neural innervation, 3 block types are described depending on the target nerves to be blocked (Fig. 4).

1. PECS 1 block (“Original” PECS block) – 10mL LA injection between pectoralis major and minor at the 3^rd rib level to block the lateral and medial pectoral nerves. Appropriate for surgery limited to pectoralis major.

2. PECS 2 block (“Modified” PECS block) – a PECS 1 block, in addition to a further 20 mL LA injection between pectoralis minor and serratus anterior at the 3^rd rib level. By The latter injection blocks the lateral branch of the T2-4 spinal nerves, and possibly the anterior branch if sufficient LA penetrates the external intercostal muscles. By entering the axilla, the long thoracic nerve may also be blocked (Fig 2). Suitable for more extensive excisions e.g. tumour resections, mastectomy, axillary clearance.

3. Serratus plane block ^† – A single 40 mL LA injection between latissimus dorsi and serratus anterior at the 5^th rib level in the mid axillary line. This injection blocks the thoracodorsal nerve. Suitable for latissimus dorsi flap reconstruction.

 ^†Anaesthesia 2013 (in-press)

Fig. 4. Thoracic wall blocks: Left=PECS 1 block, Middle=PECS 2 block, Right=Serratus plane block.

All thoracic wall blocks are performed with the patient supine, the arm abducted, a high frequency linear probe and an in-plane medial to lateral (or posterior) needle direction (Fig. 4).

PECS 1 block (“Original” PECS block)

Nerves blocked – lateral and medial pectoral nerves.

Indications (surgery involving the pectoralis major muscle)

1. Breast expander insertion/subpectoral prostheses.

           2. Other – shoulder surgery with deltopectoral groove involvement, traumatic chest                          injuries, portacath, pacemaker or intercostal drain insertion.

LA deposition – 10 mL LA between pectoralis major and minor at the 3rd rib level.

Technique – with the probe at the mid clavicular level and angled inferolaterally, first locate the axillary artery and vein. Next move the probe laterally until pectoralis minor and serratus anterior are identified (Fig. 1, 5). Locate the 2^nd rib immediately under the axillary artery (Fig. 5, 6b), then count the 3^rd rib, and with further lateral probe movement, the 4^th rib.With the image centered at the level of the 3rd rib, advance the needle in-plane from medial to lateral in an oblique manner until the tip lies between pectoralis major and minor. Inject 10 mL LA between pectoralis major and minor (Fig. 6a-c, 7, 8a,b).

Fig. 5a,b. Axillary artery, vein, 2nd rib, pectoralis major (5a) and minor (5b)

.

Fig 6a. PECS block: structures first identified with the probe in the mid clavicular line.

Fig. 6b. PECS block. With probe movement laterally, pectoralis minor, serratus anterior and the 2^{nd and 3rd} ribs are visualised.

Fig. 6c. PECS block. Further laterally are the 4th and 5^th ribs.

Fig. 7. PECS block. LA injection between pectoralis major and minor (PECS 1 block) and then between pectoralis minor and serratus anterior (PECS 2 block). Purple indicates LA spread (also shown is a supplemental injection deep to seratus anterior).

  

Fig. 8a-b. Sonographic sequence to locate the LA injection point for the PECS block. aa=axillary artery, av=axillary vein, pM=pectoralis major, pm=pectoralis minor, pl=pleura, r3/r4/r5=ribs 3/4/5, sm=serratus (anterior) muscle. NB. Bottom left: am=anteromedial, sm=superomedial.

PECS 2 block (“Modified” PECS block)

Nerves blocked– T2-4 spinal nerves (including intercostobrachial nerve) and long thoracic nerve.

Indications (more extensive breast surgery involving serratus anterior and the axilla)

1. Breast expander insertion/subpectoral prostheses (will achieve better analgesia than         the PECS 1 block).

          2. Tumour resections/mastectomy

          3. Sentinel node dissection and axillary clearance. 

LA deposition – 20 mL LA injection between pectoralis minor (laterally) and serratus anterior at the 3^rd rib level (Fig. 9) (this injection aims to enter the axilla to reach the target nerves, but LA will only enter the axilla if the fascia on the pectoralis minor lateral border is breached by surgery)

Technique – Perform sonography as for PECS 1 (Fig. 5-7, 8a-b), but also identify the potential space between the lateral extent of pectoralis minor and serratus anterior. First perform a PECS 1 injection between pectoralis major and minor, then a second 20 mL injection between pectoralis minor and serratus anterior (Fig. 7, 9).

Fig. 9. PECS 2 block sonography: 2nd LA injection between pectoralis minor and serratus anterior at the level of the 4th rib.

Fig. 10. Typical sensory block produced by the PECS 2 block.

References 

1. Blanco R. The 'pecs block': a novel technique for providing analgesia after breast surgery. Anaesthesia. 2011 Sep;66(9):847-8.

2. Blanco R, Fajardo M, Parras Maldonado T. Ultrasound description of Pecs II (modified Pecs I): a novel approach to breast surgery. Rev Esp Anestesiol Reanim. 2012 Nov;59(9):470-5.

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