American Society of Regional Anesthesia and Pain Medicine August 2016 - 43

Figure 3:

Figure 4:

thoracic nerve, vascular injury, local anesthetic toxicity, pleural
puncture, and pneumothorax. The PECS II and serratus plane block
involve the visualization of the pectoralis minor, serratus anterior
muscles, and 4th to 5th ribs. The placement of local anesthetic is
either on the superficial or deep borders of the serratus muscle
respectively, near the 4th, 5th or 6th ribs.16-19

nerve innervates the serratus anterior muscles. Local anesthetic
placement, either superficial or deep to the serratus muscles, will
produce the dermatomal anesthesia to the chest wall, T2-T6.19

Anatomy. The PECS I-II and serratus anterior plane blocks, under
US guidance, involve the visualization of the pectoralis major, the
pectoralis minor, serratus anterior muscles, intercostal muscles,
and the 4th and 5th ribs. These can be described as three separate
techniques, although the scanning technique can allow the
opportunity to perform these in combination with local anesthetic
placement in the described planes. The PEC I injection allows for
blockade of the lateral pectoral nerve and medial pectoral nerves
(Figure 3). The lateral pectoral nerve (lateral anterior thoracic
nerve) arises from the lateral cord, with components from C5,
C6, and C7 nerve roots. It innervates the superior one-third of the
pectoralis major muscle. The medial pectoral nerve (medial anterior
thoracic nerve) arises from the medial cord, with components from
C6, C7, C8, and T1 nerve roots. It innervates and pierces through
the pectoralis minor muscle with subsequent innervation to the
inferior two-thirds of the pectoralis major. The lateral pectoral
nerve will run near and adjacent to the thoracoacromial artery.
The probe placed beneath the clavicle, in a similar position to the
infraclavicular block, will demonstrate the pectoralis muscles.
With slight rotation of the probe and moving laterally along the
anterior axillary line to the 4th and 5th ribs, the lateral edge of
the pec minor, the serratus anterior muscles, and the ribs can be
found under US guidance. Here, the course of the thoracodorsal
and the long thoracic nerve also may be found. The thoracodorsal
nerve innervates the latissimus dorsi muscle, and the long thoracic

Technique. The PECS blocks can be performed prior to or after
surgery for analgesia. One consideration is that there may be a
significant amount of subcutaneous air postoperatively, which will
make US guidance extremely difficult. Performing the blocks before
surgery can result in preemptive analgesia and decrease opioid
consumption.
The block is performed with the patient in the supine position
and under US guidance. A similar position of the arm to the
infraclavicular block (elbow flexed and shoulder abducted) seems
to work best for visualization of appropriate anatomy in the PECS
I block.20 In this position, the probe can be placed inferior to the
clavicle and at the "12 to 1 o'clock" orientation of the breast. The
use of a linear probe and a beveled tip needle with an in-plane
needle technique will allow for injection between the pectorals
muscles and will accomplish the PEC I block (Figure 3). For the
PEC II block, one can scan laterally and inferiorly along the breast
contour in the anterior axillary line to visualize the lateral edge of
the pec minor muscle, the serratus anterior muscle, and the 4th rib
(Figure 4). In the PECS II block, local anesthetic will be deposited
between the 4th rib and the serratus muscle. The serratus
plane block is performed near the midaxillary line, and the local
anesthetic placement is between the latissimus dorsi muscle and
the serratus muscle along the 4th and 5th ribs.17 As for the choice
of local anesthetic, in the PECS blocks, analgesic results are easily
obtained with the choice of volume over concentration (ie, a lower
concentration 0.2-0.25% of a longer-acting drug and a higher
volume 20-30 cc bilaterally). One can often visualize both pectoral

American Society of Regional Anesthesia and Pain Medicine
2016

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