BLOCK AT A GLANCE
Injection of local anesthetic (LA) into the fascial plane between the pectoral muscles and between the pectoralis minor and serratus anterior muscles.
Indications: Analgesia after breast surgery, thoracotomy, rib and clavicle fractures, and herpes zoster neuralgia
Goal: LA spread along the interfascial planes to block the pectoral nerves and lateral branches of the intercostal nerves T3-T6
Local anesthetic volume: 15 to 30 mL
Ultrasound (US)-guided pectoral nerves block (Pecs I and II) are novel fascial plane techniques introduced for analgesia after breast surgery. The techniques can be viewed as simpler alternatives to the epidural, paravertebral, or intercostal blocks, which require a greater degree of technical skills. These techniques are increasingly more commonly used due to their simplicity and documented efficacy. A recent meta-analysis concluded that the Pecs II block, in the context of multimodal analgesia, reduces opioid requirements after breast surgery. Recent evidence suggests that Pecs II is associated with a lower incidence of chronic pain after mastectomy.
Compared to the paravertebral block, Pecs I and II have several advantages: the targeted fascial planes are more superficial and easier to identify, the blocks can be performed in the supine position, and risk of complications is lower. However, the extent and quality of analgesia of Pecs I and II blocks are lower compared to paravertebral blocks, which can be used as a complete anesthetic for breast surgery.
The Pecs I was described first and consists of an interfascial injection of LA between the pectoralis major and minor muscles, targeting the medial and lateral pectoral nerves. Pecs II was then introduced as a modification to extend analgesia to the axillary fossa and upper intercostal nerves by adding a second infiltration into a deeper fascial plane between the pectoralis minor and serratus anterior muscles.
Current US images are unable to identify the small nerve branches traveling in these fascial planes. Interindividual variability in both the extent and duration of sensory block is common, which limits the reproducibility of these blocks. The block of the long thoracic nerve may interfere with nerve monitoring during axillary fossa surgery.
Infiltration of large volumes and doses of LAs in vascularized intermuscular planes carries a risk of local anesthetic systemic toxicity (LAST). The most commonly reported complications are local hematoma. However, pneumothorax may also occur, particularly during the Pecs II, due to the proximity of the intercostal muscles and pleura.
The lateral and medial pectoral nerves are branches of the brachial plexus arising from the lateral and medial cords, respectively. These branches are interconnected by the ansa pectoralis, a fine neural network. They innervate the pectoralis major and minor muscles, the acromioclavicular joint, and contribute innervation to the ribs and clavicle through the origins and insertions of the pectoral muscles.