Blanco and colleagues 1–3 have recently described novel ultrasound-guided thoracic interfascial nerve blocks, the pectoral nerve block (PECS) 1,2 and serratus plane block (SPB), 3 for anesthesia and/or analgesia of the anterior/anterolateral chest wall. 1–4 The SPB may also anesthetize the axilla via blockade of the intercostobrachial nerve. 3 These blocks were originally developed for breast surgery in an attempt to avoid some of the rare but serious complications of thoracic paravertebral and neuraxial blocks. During a PECS-I block, the local anesthetic (0.4 mL/kg or approximately 20–30 ml) 1 is injected as a single injection into the myofascial plane between the pectoralis major and minor muscle, aiming to block the medial and lateral pectoral nerves. 1 PECS-II block is a modification of the PECS-I block (modified PECS-I block) and involves two injections. 2 The first injection is the same as that for a PECS-I block (but with 10 mL of local anesthetic), 2 but the second injection is performed deep to the pectoralis minor muscle, at the level of the third and fourth rib, into the interfascial plane between the pectoralis minor and serratus anterior muscle (with 20 mL of local anesthetic). 2 The aim of the PECS-II block is to anesthetize the pectoral nerves, intercostobrachial nerve, third to sixth intercostal nerves, and the long thoracic nerve. 2,4 The PECS-II block is therefore used for more extensive breast surgery, including mastectomy with or without axillary clearance. 2 The SPB 3 is a more recent addition to the family of thoracic interfascial nerve blocks and involves a single injection of 0.4 mL/kg of local anesthetic into the myofascial plane between the latissimus dorsi and the serratus anterior muscle more posteriorly and at the level of the fifth rib. 3 Local anesthetic spreads in the serratus plane, deep to the latissimus dorsi, and along the lateral chest wall to affect the lateral cutaneous branches of the second to ninth intercostal nerves and possibly the long thoracic and thoracodorsal nerves. 3,4 A clear understanding of the sonoanatomy of the thoracic wall is a prerequisite to effectively using a PECS or SPB. The following section describes the gross anatomy, ultrasound scan technique, and sonoanatomy of the thoracic wall relevant for the thoracic interfascial nerve blocks. Because these blocks are frequently used for breast surgery, a brief description of the innervation of the breast is also included.
Muscles: Muscles involved with thoracic interfascial nerve blocks are pectoralis major, pectoralis minor, serratus anterior, intercostal muscles, and the latissimus dorsi.
Pectoralis major: The pectoralis major muscle is a triangular, fan-shaped muscle that makes up the bulk of the anterior chest wall (Figs. 10–1 and 10–2). It has two parts: the clavicular head and the sternocostal head (Fig. 10–1). The clavicular head originates from the medial half of the clavicle, and the sternocostal head arises ...