Ultrasound-guided pectoral plane nerve block—PECS I represents a reasonable alternative to paravertebral nerve block and thoracic epidural block to provide surgical anesthesia for surgeries involving the pectoralis major muscle including the insertion of breast expanders, subpectoral prostheses, implantable drug delivery systems including ports and reservoirs, pacemaker and implantable defibrillator insertions, and repair of chest wall trauma (Fig. 89.1). This technique has great clinical utility in both children and adults when managing acute postoperative and posttrauma pain in the area of the pectoralis major muscle. PECS I block may also be used in combination with paravertebral block following mastectomy to facilitate physical therapy to maintain upper extremity function.

The anatomic basis for the PECS I, PECS II, and serratus anterior plane blocks is the fact that the fascias at the pectoral level create potential compartments that can contain local anesthetics when injected within the facial compartments. Because the nerves contained within these fascial compartments traverse these fascial compartments, they are amenable to neural blockade at various points along their paths. Since these fascial compartments can potentially prevent the spread of local anesthetic to block other nerves, repositioning of the needle tip into adjacent fascial compartments may be required in order to provide complete anesthesia and analgesia to the regions, especially to the lateral breast. The primary target of the PECS I block is the medial and lateral pectoral nerves whose fibers arise from the medial cord of the brachial plexus and provide innervation to the pectoralis major and minor muscles (Fig. 89.2). The medial pectoral nerve passes behind the first segment of the axillary artery and vein, while the lateral pectoral nerve passes across the axillary artery and vein. There are communicating branches between the medial and lateral pectoral nerves that pass in front of the axillary artery to provide motor, nociceptive, and proprioceptive information from both nerves (Fig. 89.3). The thoracoacromial artery arises from the second portion of the axillary artery and is proximity to the medial and lateral pectoral nerves (Fig. 89.4).

To perform ultrasound-guided pectoral plane nerve block— PECS I, the patient is placed in the supine position with the arms resting comfortably by the patient’s side (Fig. 89.5). A total of 10 mL of local anesthetic is drawn up in a 12-mL sterile syringe. If the painful condition being treated is thought to have an inflammatory component, 40 to 80 mg of depot steroid is added to the local anesthetic. The middle of the clavicle is identified by palpation, and a linear high-frequency ultrasound transducer is then placed in the transverse plane just below the previously identified midpoint of the clavicle with the inferior portion of the transducer pointed inferomedially toward the patient’s axilla (Fig. 89.6). Under continuous ultrasound imaging, the transducer is slowly moved inferolaterally to identify the pectoralis major and pectoralis minor muscles as well as the thoracoacromial vessels that lie in the plane between the two muscles. Color Doppler may help identify the thoracoacromial vessels as will slight lateral rotation of the inferior portion of the transducer. The bright sunset line of the pleura should also be identified to allow the operator to avoid placing the needle too deeply.