Surgeries of the breast are among the most common operative procedures, and numerous options exist for perioperative anesthesia and analgesia that can affect acute perioperative pain, persistent pain, and potentially cancer recurrence. Patients who undergo breast surgery experience significant acute pain, but are also at risk of chronic pain. Up to 55% of postmastectomy patients experience chronic pain persisting for months to years.1–5 One of the best predictors of chronic pain following breast surgery is the amount of perioperative pain experienced by the patient.6–12 Although multiple options exist for control of perioperative breast surgery pain, including several newly described regional anesthesia techniques, there is insufficient understanding of the anatomy of the breast, the anatomic structures disrupted by the various breast surgeries, and the theoretical and experimental evidence supporting the use of the various analgesic options. In part I of this article, we review the anatomy of the breast and common breast surgeries, along with the potential anatomic sources of perioperative pain. We conclude with a discussion of the anatomic basis for different analgesic techniques. In part II, we present a systematic review of the evidence for the analgesic techniques including multimodal analgesia, local anesthetic infiltration, intercostal block, epidural administration, paravertebral block (PVB), brachial plexus block, and novel peripheral nerve blocks.
To determine the evidence base for perioperative breast analgesia techniques, we performed a literature search of the MEDLINE database via PubMed on November 5, 2016. The search combined terms for breast surgery, anesthesia, and analgesia. The PubMed search terms were ((“Analgesics” [MeSH] OR “analgesics” [all fields] OR “Analgesia” [MeSH] OR “analgesia” [all fields] OR “Anesthesia, Conduction” [MeSH] OR “nerve block” [all fields] OR “regional anesthesia” [all fields] OR “epidural” [all fields] OR “spinal anesthesia” [all fields] OR “neuraxial” [all fields] OR “general anesthesia” [all fields] OR “anaesthesia” [all fields] OR “anesthesia” [all fields] OR (“local” [all fields] AND “infiltration” [all fields])) AND (“Mammaplasty” [MeSH] OR “Mastectomy” [MeSH] OR “mammaplasty” [all fields] OR “mastectomy” [all fields] OR “breast surgery” [all fields] OR “chest wall” [all fields] OR “axilla*” [all fields] OR “Breast Neoplasms/surgery” [MeSH] OR “breast cancer surgery” [all fields] OR “mammary” [all fields] OR “breast augmentation” [all fields] OR “axillary surgery” [all fields])). The search was not limited by date and excluded conference abstracts. The search was replicated in the EMBASE database for articles published in journals not indexed in MEDLINE.
Articles were included if they met the following inclusion criteria: (1) randomized controlled trial (RCT) design; (2) participants were humans at least 18 years of age undergoing elective surgery on the breast (not including biopsy); (3) published in English and full text available; (4) analgesic interventions were intercostal block, interpleural block, epidural block, PVB, or novel peripheral nerve blocks; (5) outcome measures were postoperative analgesic consumption, postoperative pain scores, or duration of postoperative analgesia; and (6) minimum Jadad score of 2. Article titles and abstracts were screened, full-text articles were reviewed, and risk-of-bias assessments were performed by 2 authors independently (R.M.J.I. and R.B.M.), with any discrepancies resolved through discussion. Risk of bias was assessed using the 5-point scale described by Jadad et al.13 Articles using a study design other than RCT but meeting all other inclusion criteria were subsequently reviewed for findings not yet confirmed in RCTs.
The search strategy captured 5418 articles, of which 4407 were eliminated for failure to meet the inclusion criteria based on their titles and abstracts. Full-text review of the remaining 1011 articles eliminated an additional 965 articles that failed to meet the inclusion criteria, yielding a total of 46 articles (Fig. 1). Articles were organized according to intervention: 5 intercostal block, 0 interpleural block, 5 epidural block, 31 PVB, 1 brachial plexus block, and 4 novel peripheral nerve block.
Part I: Anatomy of the Breast, Surgical Disruption, and the Anatomic Basis for Regional Analgesia Techniques
Innervation of the Breast and Superficial Tissues
Several distinct nerves innervate the breast and surrounding tissues. The majority of the cutaneous sensation to the breast is derived from the intercostal nerves. Upon exiting the intervertebral foramina, the thoracic spinal nerves divide into dorsal and ventral rami. The dorsal rami innervate the skin and muscles over the medial back (Fig. 2). The ventral rami pass through the paravertebral space and become the intercostal nerves, which travel in the intercostal space just below the inferior border of the superior rib and are accompanied by an intercostal vein and artery. Much like the abdominal musculature, the intercostal region is composed of 3 muscle planes.14 From superficial to deep, the muscular planes are formed by the external intercostal muscle, the internal or intermediate intercostal muscle, and an innermost layer composed of the subcostal (posterior), innermost intercostal, and transversus thoracis (anterior) muscles. The intercostal nerves travel in the plane between the innermost layer and the internal intercostal muscle (Fig. 2).15 Near the midpoint between the spine and sternum, at approximately the angle of the rib and midaxillary line, a lateral cutaneous branch arises from the intercostal nerve and pierces the internal intercostal, external intercostal, and serratus anterior muscles (SAMs).15 The lateral cutaneous branches then divide into anterior and posterior divisions that provide cutaneous innervation to the lateral chest (Figs. 2–4). The continuation of the intercostal nerve terminates as an anterior cutaneous branch (ACB) by piercing the fascial extension of the external intercostal muscle close to the lateral edge of the sternum, providing cutaneous innervation to the medial chest and sternum (Figs. 2–4).15–17 In many texts, the anterior division of the lateral cutaneous branch is referred to as the anterior branch. We have used the term “anterior division” in order to avoid confusion with the terminal portion of the intercostal nerve, the ACB.
The breast is essentially a subcutaneous organ that receives innervation from anterior and lateral cutaneous branches of intercostal nerves, as well as supraclavicular nerves. Published descriptions of the specific nerves involved and their courses vary significantly, likely because of both anatomic variability and differences in research methodology. The most commonly described pattern of innervation of the medial breast is by the ACBs of the T2 through T5 intercostal nerves with variable involvement of T1 and T6 and innervation of the lateral breast by the lateral cutaneous branches of the T2 through T5 intercostal nerves with variable involvement of T1, T6, and T7 (Figs. 3, 4).16–20 The first intercostal nerve rarely gives off a lateral cutaneous branch. Both the lateral and anterior branches of different intercostal nerves frequently communicate with each other throughout their course, producing a variable pattern of innervation that does not adhere to strict dermatomal segmentation.
The relationship of the cutaneous nerves of the breast to the underlying muscles is important as surgeons must avoid these nerves, and anesthesiologists seek to block them. After piercing the internal and external intercostal muscles, the lateral cutaneous branches of the intercostal nerves penetrate through the slips of origin of the SAM. The anterior divisions of these nerves course over the lateral edge of the pectoralis major (PM) muscle to reach the cutaneous tissue of the chest (Figs. 3, 4). The T4 and T5 lateral cutaneous branches may also give rise to a deep branch that pierces the PM muscle before reaching the breast.17
The nipple-areola complex (NAC) is innervated by both anterior and lateral branches of the intercostal nerves T3 through T4, with variable contribution from T2 and T5. The exact innervation of the NAC is still controversial because of numerous anatomic variations and the difficulty in dissecting this area.21 The most common descriptions of NAC innervation detail a comingling of the terminal branches of the anterior divisions of the lateral cutaneous branches of the T4 and T5 intercostal nerves and the terminal branches of the ACBs.17–19,22
Special consideration should be given to the course of the lateral cutaneous branch arising from the T2 intercostal nerve, termed the intercostobrachial nerve. As with the other lateral cutaneous branches, this nerve branches off the intercostal nerve around the angle of the rib. The lateral aspect of the T2 rib lies in the axilla. After piercing the intercostal and SAMs, the majority of the lateral cutaneous branch of T2 travels laterally along the floor of the base of the axilla to reach the upper medial arm (Fig. 5). The intercostobrachial nerve provides cutaneous innervation to the axillary tail of the breast, the axilla, and the medial upper arm. The extrathoracic anatomy of this nerve is highly variable. It may receive contributions from other intercostal branches (T1, T3, and even T4) and can have a variety of anastomoses with branches of the brachial plexus, including the medial antebrachial cutaneous nerve, posterior cutaneous nerve of the forearm, and rarely with the pectoral nerves.23–25 This nerve is often implicated in postmastectomy pain, particularly after axillary dissection or lymph node sampling.26,27 Its variable anatomy may account for the conflicting reports of post–nerve injury symptoms.
In addition to the innervation of the breast tissue and skin from the intercostal nerves, a small portion of the superior breast skin may be innervated by the supraclavicular nerves, although this description has been disputed.16,17,28 These nerves originate from the superficial cervical plexus and eventually travel in the subcutaneous tissue to pass over the clavicle and reach the superior aspect of the breast (Figs. 3, 4).
Innervation of the Chest Wall
Although the cutaneous innervation of the breast is derived from the intercostal nerves with a small contribution from the supraclavicular nerves, the brachial plexus supplies the innervation to the muscles of the chest wall (other than the intercostal muscles, which derive their innervation from the intercostal nerves). The majority of the breast tissue is immediately anterior to the pectoralis muscles. The upper portion of the PM muscle is supplied by the lateral pectoral nerve (LPN), whereas the medial pectoral nerve (MPN) innervates the pectoralis minor (Pm) muscle and the lower portion of PM.29,30 These nerves arise from the brachial plexus at variable locations and take a variable course to the pectoralis muscles (Fig. 6). The LPN is derived from the C5–7 nerve roots and arises most frequently from the anterior division of the upper trunk of the brachial plexus or from the lateral cord, from which it derives its name.31 The MPN is derived from the C7–T1 nerve roots and usually arises from the medial cord.
Both nerves depart the axilla to travel medially toward the pectoralis muscles.29,30,32–35 The LPN crosses the lateral and superior border of the Pm muscle to enter the plane between the PM and Pm muscles, usually alongside the pectoral artery (Figs. 6, 7).36 This fascial plane and artery are often used as sonographic landmarks to locate the LPN. The LPN provides numerous branches that penetrate the deep surface of the PM muscle and supply the innervation to the superior and medial aspect of the muscle. The MPN usually travels deep (posterior) to the Pm muscle, supplying its innervation, before coursing anteriorly to supply innervation to the inferior portion of the PM. The MPN may pierce the Pm muscle or emerge from beneath the inferior edge of the muscle to reach the PM, or both (Figs. 6, 7). Although these nerves do not innervate the subcutaneous tissue of the breast, they still play an important role in breast surgical pain. Disruption, stretching, or spasm of the pectoral muscles or associated fascia can be a significant source of myofascial pain after breast surgery.37,38 Although often labeled simply as motor nerves, they have been described to carry both nociceptive and proprioceptive fibers.39 In addition to proprioception, all of the motor nerves to the chest wall carry postganglionic fibers from the cervical and thoracic ganglion, which may be another mechanism for communication of pain.40 Aside from injury to the tissues supplied by the nerves, traction, radiation, or other direct nerve injury may play a role in postsurgical neuropathic pain.40
Two other important nerves in the region of the axilla and lateral chest wall are the long thoracic and thoracodorsal nerves (TDNs), both of which originate from the brachial plexus. The long thoracic nerve (LTN) arises from the C5–7 nerve roots. Upon reaching the infraclavicular region, it runs along the lateral chest wall superficial to the SAM, which it innervates (Fig. 6). Disruption of the SAM during breast reconstruction (making a pocket for an implant) can result in myofascial pain to the chest wall radiating to the subscapular region.38
The TDN is derived from the C6–8 nerve roots and arises from the posterior cord of the brachial plexus. It exits the posterior wall of the axilla to travel along the anterior and lateral portion of the latissimus dorsi muscle in close proximity to the subscapular artery, where it innervates the latissimus dorsi muscle (Figs. 6, 7). Similar to the LTN, injury to this nerve has been implicated in postmastectomy pain.38,40
Breast Surgery and Tissue Disruption
Knowledge of the precise anatomic location of tissue disruption for each type of breast surgery is imperative in developing a perioperative analgesic plan. Operations involving the breast can differ substantially with regard to the tissues that are removed or compromised. Breast cancer procedures are discussed first.
Excisional Breast Surgery
Lumpectomy involves excision of a wedge of subcutaneous breast tissue. A partial (segmental or quadrantectomy) mastectomy is performed if more breast tissue warrants removal. This procedure is performed for tumors that are too large for lumpectomy, for patients who cannot tolerate radiation, or if more than 1 distinct area of the breast is involved. As with a lumpectomy, only subcutaneous breast tissue is removed.41 Depending on whether surgery is performed medial or lateral to the nipple, the anterior or lateral cutaneous branches of the intercostal nerves (respectively) will contribute to the innervation of the operative area. A total (simple) mastectomy involves removing the entire subcutaneous breast tissue and varying amounts of overlying skin. The underlying fascia of the PM muscle is not disrupted.42 Similar to lumpectomies and partial mastectomies, the intercostal nerves are responsible for the innervation to the surgical area. When developing a plan for perioperative analgesia, it is important to determine if an axillary dissection or sentinel node biopsy will be performed in conjunction with a partial or total mastectomy. Surgery in the axilla is in the territory of the intercostobrachial nerve (lateral cutaneous branch of T2), which may require separate blockade, depending on the chosen analgesic approach.
A radical mastectomy is a more extensive breast cancer operation involving removal of the entire breast, nipple, axillary lymph nodes, and pectoralis muscles. More commonly, a mastectomy and sentinel node biopsy are performed, or alternatively, a modified radical mastectomy, which includes a mastectomy and an axillary dissection but preserves the pectoralis muscles, is performed.43 The borders of dissection extend superiorly to the clavicle, medially to the sternum, inferiorly to the most caudal extent of breast tissue (on the costal margin below the inframammary fold), and laterally in the axilla to the border of the latissimus dorsi. The fascia of the PM muscle forms the deep margin of the dissection and is removed during the procedure, which may constitute a source of postoperative myofascial pain.44 The dissection also frequently involves removal of breast tissue or lymph nodes that reside between the inferior edge of the PM muscle and the Pm muscle. This is important as the MPN can be injured, resulting in partial denervation of the PM muscle.32,33 In addition, manipulation and stretching of the pectoralis muscles may be another source of perioperative myofascial pain. One or 2 drains may be placed through separate inferior-lateral incisions and can be additional sources of pain below the dermatomes associated with the breast. Mastectomy requires general anesthesia or an advanced regional block with sedation. In contrast to pain from simple mastectomy, brachial plexus–derived nerves (lateral and medial pectoral, thoracodorsal, long thoracic) can also contribute to perioperative modified radical mastectomy pain (Fig. 7).
Reconstructive Breast Surgery
Because of the disfiguring nature of breast cancer surgery, surgical reconstruction to restore a natural breast appearance is frequently performed in conjunction with breast cancer procedures.45 In reconstructions with an implant, a tissue expander is usually placed beneath the PM muscle and anterior to the Pm. Laterally, the SAM may be elevated to cover the inferolateral pole of the implant.46 The inflatable bladder is expanded over days to weeks to slowly stretch the overlying PM muscle, fascia, and skin. In a second operation, the temporary expander is replaced by a long-term implant. It is important to identify whether a tissue expander will be placed after a total mastectomy. Unlike total mastectomy without a tissue expander, this procedure will involve blunt dissection of a pocket for the expander between the pectoral muscles. Creation of the pocket can be a source of additional periprocedure and chronic pain due to direct disruption of the pectoral nerves or lateral cutaneous branches of the intercostal nerves or due to stretching or injury to the fascia of the serratus anterior or pectoral muscles. Women who undergo breast cancer surgery with immediate reconstruction have a higher prevalence of chronic pain when compared with women who undergo mastectomy without reconstruction (49% and 31%, respectively).12 An important consideration in developing a perioperative analgesic plan for breast surgery with reconstruction is the involvement of not only the intercostal nerves, but also the pectoral nerves and possibly the LTN (Fig. 7).
With implant reconstruction, a sheet of mesh or acellular dermal matrix is often used to provide internal support to the implant and to extend the lower border of the PM muscle. This allows the muscle to be held in place against the chest wall at the desired inframammary fold and provides an additional source of coverage material for the lower pole of the implant. This material is sewn directly to the chest wall, with sutures placed in rib periosteum or deep chest wall fascia, often creating a significant source of postoperative discomfort. Analgesia is targeted to the level of the sixth and seventh intercostal spaces (at the level of the inframammary fold) to address pain from these sutures.
Another type of reconstruction, either delayed or immediate, involves a free or pedicle flap to recreate breast volume.45 The most common procedures include transverse rectus abdominis myocutaneous flaps, either performed as a pedicled or free flap; deep inferior epigastric artery perforator as a free flap; and latissimus dorsi myocutaneous flaps as a pedicled flap. When developing a perioperative analgesic plan, the donor site for the flap must be considered in addition to the breast surgery itself. For example, a patient undergoing total mastectomy with immediate pedicled transverse rectus abdominis myocutaneous flap reconstruction may experience more postoperative pain from the abdominal wall donor site than from the mastectomy site.47,48 This is due to the resection of the rectus muscle and closure of the rectus sheath (primarily or with synthetic mesh).
When a traditional latissimus dorsi flap is used for breast reconstruction, an ellipse of skin is harvested from the back over the lower thoracic region to act as the donor site. The entire latissimus muscle is then elevated from a pocket that extends subcutaneously from the mid–lumbar region inferiorly to the tip of the scapula superiorly and from the paraspinous muscle fascia medially to the posterior axillary line laterally. The flap is passed through a tunnel near the axilla to the anterior chest. Any indwelling anesthetic catheter would need to cover the entire hemiback to the posterior midline on the side of the flap. It is also important to note that this muscle is innervated by the TDN, a branch of the brachial plexus.
Mammoplasty refers to a group of procedures aimed at changing the shape and/or size of the breast, typically by augmentation or reduction. In primary breast augmentation, implants are generally placed via 1 of 4 skin incisions: periareolar, inframammary, transaxillary, or less commonly transumbilical. The transaxillary approach requires special consideration because of possible injury to the intercostobrachial nerve in the axilla, which may result in acute and chronic axillary pain.49 The implant is generally placed in 1 of 2 pockets—behind the breast parenchyma and superficial to the PM muscle, or deep to the PM muscle. As with tissue expanders, creation of a pocket posterior to the PM muscle can be a source of postoperative myofascial pain. The dissection required for the pocket involves disruption of the PM muscle and its attachments to the cartilaginous portion of the ribs. In some cases, the muscle fibers of the PM are split to access the plane posterior to the PM and anterior to the Pm muscle. Unlike tissue expander placement, the implant will usually be placed at its final size and not inflated over time. In addition to direct manipulation and disruption to the muscles and fascia, the stretch of the PM muscle after implant placement can be substantial. The major source of pain from submuscular breast augmentation is myofascial and is transmitted by the pectoral nerves. Postoperative pain from the stretching and disruption of the pectoral muscles is common, and many surgeons prescribe muscle relaxants to ameliorate it.50 Creation of the submuscular pocket may also directly disrupt the pectoral nerves and/or the lateral cutaneous branches of the intercostal nerves. As with breast cancer surgery, breast augmentation procedures can lead to persistent pain. In one study, 9.5% of patients reported moderate to severe persistent pain after submuscular breast augmentation, 75% reported sensory changes over the breast, and 38% met criteria for neuropathic pain.51
Other Cosmetic Breast Surgeries
Two additional procedures to be considered are reduction mammoplasty and mastopexy. In these procedures, a volume of breast tissue is removed, while the areola and nipple are spared. From a perioperative analgesic standpoint, these procedures are similar to a simple mastectomy because only cutaneous and subcutaneous breast tissue is involved, and the pectoral muscles are not disrupted. The incisions vary but typically involve the periareolar region and inferior pole of the breast.
The various surgical procedures and the relevant innervation are summarized in Figure 8.
Anatomic Basis of Analgesic Procedures
The goals of perioperative analgesia are to provide or supplement operative anesthesia, reduce immediate postoperative pain, and reduce the incidence of chronic pain. Regional anesthesia modalities have gained popularity for breast surgery due to the recent focus on reducing the requirement for inpatient surgery, inpatient length of stay, and the incidence of persistent postsurgical pain. We now discuss the anatomic basis of various procedures for the control of perioperative breast pain, as summarized in Figure 8. A discussion of how to perform the various blocks is beyond the scope of this review.
Intercostal Nerve Blocks
Local anesthetic can be deposited near intercostal nerves to provide a band of anesthesia targeted to a specific dermatomal area. Multiple intercostal nerves must be blocked to achieve coverage for breast surgery, depending on the tissue disrupted (eg, T2–T7). Classically, 3 to 5 mL of local anesthetic solution is injected at each thoracic level.52 If only the medial breast is involved, intercostal blocks may be performed at any point along the intercostal nerve course, including at the exit point of the ACB just medial to the sternum. If the lateral breast is involved, intercostal blocks must be performed proximal to the origin of the lateral cutaneous branches of the intercostal nerves at the midaxillary line. Intercostal blocks should be combined with other approaches if the surgery involves myofascial pain, as thoracic intercostal blocks do not anesthetize nerves derived from the brachial or cervical plexuses.
The most common levels for placement of epidural injections or catheters for breast analgesia is T3–5. Similar to intercostal blocks, thoracic epidural anesthesia (TEA) without cervical spread would not block the branches of the brachial or cervical plexus that may contribute to perioperative breast surgery pain.
The paravertebral space can be accessed to block the thoracic spinal nerves as they exit the intervertebral foramina. Local anesthetic deposited in this space can spread multiple levels superior and/or inferior, as well as into the intercostal space laterally, the contralateral paravertebral space, and the epidural space medially.53 This technique generally results in ipsilateral blockade of somatic and sympathetic nerves and can serve as the sole anesthetic for breast surgery, as long as blockade of the supraclavicular nerves, pectoral nerves, or other brachial plexus branches is not required (similar to TEA).
Brachial Plexus and Novel Peripheral Nerve Blocks
Alternative regional techniques have been proposed in an effort to provide equivalent or improved analgesia with a lower risk of adverse events and greater suitability for outpatient surgery (see part II for the evidence base behind claims of efficacy and safety for each technique). Initial efforts were aimed at blocking some or all of the peripheral nerves of brachial plexus origin that provide sensory innervation to the breast: LPN, MPN, LTN, and TDN. Subsequent efforts have aimed to expand the utility of these novel blocks by simultaneously anesthetizing the cutaneous branches of the intercostal nerves.
Brachial plexus blocks. The LPN, MPN, and TDN typically arise from the anterior division of the upper trunk or lateral cord, medial cord, and posterior cord, respectively. Thus, infraclavicular brachial plexus block at the level of the cords would be expected to block these brachial plexus components of breast analgesia, and possibly the LTN as it courses along the lateral chest wall. In contrast, interscalene block at the level of the C5–7 nerve roots would be expected to block the LTN, but only partial blockade of the LPN, MPN, and TDN because of absence of reliable C8 and T1 nerve root block. It is important to note that interscalene block is not expected to provide axillary analgesia, because sensory innervation of the axilla is derived primarily from the intercostobrachial nerve (T2 intercostal nerve). Because of its proximity to the axilla, infraclavicular block typically does result in block of the intercostobrachial nerve and axilla. Bigeleisen and Wilson54 demonstrated 77% and 87% incidence of intercostobrachial nerve block with 10 mL volume infraclavicular block via a medial and lateral approach, respectively. Although anatomically possible, the extent to which infraclavicular block provides local anesthetic spread along the chest wall to anesthetize the lateral cutaneous branches of the intercostal nerves other than the intercostobrachial nerve, and thus provide breast analgesia, has not been adequately studied. With the possible exception of infraclavicular blocks, brachial plexus blocks alone will not anesthetize the thoracic intercostal nerves supplying the breast and would not be sufficient for complete breast analgesia.
Pecs I block. Novel blocks have recently been introduced in an effort to anesthetize key nerves derived from the brachial plexus, avoid blocking the brachial plexus nerves that innervate the arm, and block the cutaneous branches of the intercostal nerves. Blanco55 was the first to describe a novel ultrasound-guided interfascial plane block, the Pecs I block, targeting the LPN and MPN via an injection between the PM and Pm muscles (eg, 0.25% bupivacaine 0.4 mL/kg). Distribution of local anesthetic in this plane is expected to anesthetize the LPN as it courses between the PM and Pm muscles and the MPN as it courses anteriorly through or at the lateral margin of the Pm muscle, with the goal of reducing postoperative muscle spasm and myofascial pain from the pectoralis muscles (eg, surgeries involving the pectoral muscles, including tissue expander and subpectoral prostheses placement).55 Note that evidence is needed to support this theoretical mechanism of chest wall analgesia (see part II).
Pecs II block. In order to expand the utility of interfascial peripheral nerve blocks for breast surgery, Blanco et al56 proposed a modification of the Pecs I block, called the Pecs II block. This block is performed with ultrasound guidance at the level of ribs 2–4. Pecs II block consists of 2 injections, one deep injection between the Pm muscle and the SAM with 20 mL bupivacaine 0.25% and one superficial injection identical to the Pecs I block (between the PM and Pm muscles) with 10 mL bupivacaine 0.25%. Both injections can be made via one skin puncture site and often via 1 needle pass. The terminology of this block (named the Pecs II block or modified Pecs I block by Blanco) has led to some confusion as some authors have erroneously used “Pecs II” to describe the deep injection alone.
The addition of the deep injection (between the Pm muscle and the SAM) targets 3 distinct nerve groups: the anterior divisions of the lateral cutaneous branches of the intercostal nerves that pierce the external intercostal muscle and SAM at approximately the midaxillary line, the LTN that courses along the superficial surface of the SAM, and the TDN that courses along the deep surface of the latissimus dorsi muscle. Of note, in an effort to improve interfascial spread and spare the LTN, Pérez et al57 proposed a modification of the Pecs II block, wherein the deep injection is performed deep to the SAM rather than superficial to the SAM. Sparing of the LTN would allow for postoperative assessment given the risk of surgical injury to this nerve during axillary dissection.57
The ACBs of the intercostal nerves (terminal portion of the intercostal nerves exiting near the sternum) would not be expected to be anesthetized with a Pecs II block unless local anesthetic were to diffuse deep to the SAM and the external and internal intercostal muscles to reach the intercostal nerve. Thus, a Pecs II block alone would be expected to leave sensory innervation of the medial breast intact.
Serratus plane block. Blanco et al58 described another variation of the Pecs blocks, termed the serratus plane block (SPB), with the goal of providing extended intercostal nerve coverage. This block is performed more distal and lateral than Pecs II block, overlying the fifth rib at the midaxillary line. The latissimus dorsi muscle is visualized with ultrasound overlying the SAM. Identification of the thoracodorsal artery can verify the plane between the 2 muscles. Local anesthetic (eg, bupivacaine 0.125% 0.4 mL/kg) can be deposited either superficial or deep to the SAM, in an attempt to provide sensory block of the T2–T9 dermatomes.58
De la Torre et al59 and Alfaro–de la Torre and Fajardo-Pérez60 have developed a nearly identical block termed the serratus-intercostal fascial block that involves deposition of local anesthetic deep to the SAM, between the SAM and external intercostal muscle. It is important to understand that SPB replaces only the deep injection of Pecs II block (between the Pm muscle and SAM), necessitating addition of a Pecs I block to cover the LPN (eg, for subpectoral device implantation).57
Similar to the Pecs II block, the SPB likely blocks only the lateral cutaneous branches of the intercostal nerves, thus failing to anesthetize the medial breast. It is unclear if the local anesthetic diffuses through the SAM and external interocostal and internal intercostal muscles to reach the intercostal nerve proximal to the origin of the lateral cutaneous branch. Closer proximity to the intercostal nerves is one of the theoretical advantages of injection deep to the SAM, but this remains insufficiently studied.
Blocks of the ACBs of the intercostal nerves. In order to target the ACBs of the intercostal nerves, de la Torre et al59 described the pectointercostal fascial block (PIFB). This ultrasound-guided block is performed at the medial aspect of the breast, 2 to 3 cm lateral to the sternal border at the level of the fourth rib. The PM muscle is visualized superficial to the external intercostal muscle, and local anesthetic is deposited between these 2 muscles.
In a similar approach, Ueshima and Kitamura61 described the transversus thoracis muscle plane (TTP) block. This block is performed in the parasternal location; however, the local anesthetic is deposited in a deeper interfascial plane between the transversus thoracis muscle (deep) and the internal intercostal muscle (superficial).61 Potential anatomic disadvantages of this approach are the very close proximity to the pleura (because TTP is very thin)15 and the internal thoracic artery (because it travels in the same plane between the transverse thoracis muscle and the internal intercostal muscle approximately 1 cm lateral to the sternum).62 The extent of local anesthetic spread and subsequent analgesia following PIFB and TTP block require further study.
It is important to recognize the anatomic limitations of the individual interfascial approaches. None of these approaches are expected to block the supraclavicular nerves that may supply a small portion of the superior breast.63 Only the PIFB and TTP block anesthetize the ACBs of the intercostal nerves that supply the medial aspect of the breast. Thus, combinations of blocks are necessary to provide complete analgesia for many surgical procedures.59
With a sophisticated understanding of the anatomy relevant to breast surgery and analgesia, combinations of various blocks will likely provide postoperative analgesia and even surgical anesthesia for a wide variety of operations (Fig. 8). Before adopting these promising blocks, a review of the evidence for their efficacy and safety is warranted.
Part II: Systematic Review of the Evidence for Regional Analgesia Techniques for Breast Surgery
Intercostal Nerve Blocks
Five studies evaluating intercostal nerve block with a median Jadad score of only 2 (range, 2–3) were included in the review. Of these 5 studies, 3 demonstrated improved analgesia in patients receiving intercostal blocks (Table 1).64–66 The role of intercostal nerve blocks in contemporary practice is questionable, given the mixed results, the risks associated with these multilevel blocks, and the presence of alternative peripheral approaches including local anesthetic infiltration and the novel interfascial peripheral nerve blocks. High-quality studies to directly compare intercostal nerve blocks to these alternative techniques, with attention to both analgesic benefit and adverse effects, are needed to clarify the utility of intercostal blocks for patients undergoing breast surgery.
Five studies evaluating TEA with a median Jadad score of 3 were included in the review. Of these 5 studies, 2 studies71,72 utilized continuous postoperative local anesthetic infusion, 2 studies69,70 utilized epidural anesthesia in the operating room only, and 1 study68 utilized epidural morphine alone (Table 2). Three studies69,70,72 demonstrated effective surgical anesthesia with epidural block for modified radical mastectomy or mastectomy. All 5 studies demonstrated analgesic benefit with an epidural technique, although only 2 utilized a double-blind design. In the studies utilizing continuous postoperative epidural infusion, analgesic benefit persisted until epidural discontinuation (second postoperative day).71,72 In addition to reductions in pain scores and analgesic consumption, epidural anesthesia resulted in shorter hospital stay,71 faster achievement of postanesthesia care unit discharge readiness,72 and improved patient satisfaction.69,70,72 Although the evidence supports the ability of epidural technique to provide both surgical anesthesia and postoperative analgesia, concerns regarding adverse events and logistic constraints have prevented this technique from becoming common practice for breast surgery.
Thirty-one studies of PVB with a median Jadad score of 3 (range, 2–5) were included in the review. Of these, 10 studies73–81 used a single injection at 1 level, 11 studies83–86,88–91 utilized a single injection at multiple levels, and 10 studies9,94–102 utilized continuous infusions (Table 3). Single-level injections were performed at T2–T4, and multilevel injections were performed at 3 to 7 levels ranging from C7–T7. Twenty-three studies compared PVB to alternative analgesic approaches (ie, general anesthesia, intravenous opioids, local infiltration). All but 1 of these 24 studies101 identified analgesic benefit of PVB as indicated by pain scores, analgesic consumption, or time to first analgesic. It should be noted that only 4 of the 23 positive studies used a double-blind design.
The optimal dosing strategy with PVB for breast surgery (single injection, single injection with additives, or continuous infusion) remains unclear. The reported duration of analgesic benefit for patients with single-injection PVB varied between studies, with evidence of analgesia as late as postoperative day 3.80
Additional outcomes were reported in several studies. Seven studies reported an improvement in postoperative nausea and vomiting,73,75,78,83,84,90,92 and 2 reported shortened length of hospital stay.84,90 In addition, 4 studies (only 2 of which were double-blind) demonstrated an improvement in pain incidence or characteristics at 1 to 12 postoperative months.9,76,101,103
In summary, the literature supports PVB as an effective perioperative analgesic technique for breast surgery. Paravertebral block can also provide surgical anesthesia and may decrease nausea and vomiting, hospital stay, and chronic postsurgical pain. The use of paravertebral catheters has not reliably been demonstrated to be superior to a single-injection technique at 1 or multiple levels. Similar to epidurals, the safety of PVBs for outpatient surgery is a concern, given the trend toward outpatient performance of breast surgeries. Outpatient breast surgery with ambulatory paravertebral catheters has been described, but its analgesic benefit has not been demonstrated.97,100 Finally, further studies comparing PVB to local anesthetic infiltration are needed.
Brachial Plexus and Novel Peripheral Nerve Blocks
Brachial Plexus Blocks
One brachial plexus block study104 with a Jadad score of 3 was included in the review (Table 4). Kaya et al104 demonstrated analgesic benefit of relatively large-volume (30 mL) interscalene block alone for modified radical mastectomy. In addition, Sundarathiti et al70 included an interscalene block as a supplement to TEA, but the study design prevents an assessment of the specific impact of the interscalene block (Table 2). In summary, although 1 study lends some support to the theoretical benefit of brachial plexus blocks, the undesirable upper-extremity block that results has prevented the incorporation of these approaches into clinical practice.
Interfascial Plane Blocks
No RCTs of Pecs I block were identified in our review. Four Pecs II block studies with a median Jadad score of 3 were included in our review105–108 (Table 4). Bashandy and Abbas106 investigated Pecs II block versus no block for modified radical mastectomy in an observer-blinded study. They demonstrated reduced pain scores in the first 24 hours, reduced opioid consumption in the first 12 hours, less nausea and vomiting, less sedation, and shorter postanesthesia care unit and hospital stay in patients receiving Pecs II block. In an unblinded study, Wahba and Kamal105 compared Pecs II block to single-injection, 1-level T4 paravertebral for modified radical mastectomy under general anesthesia. They demonstrated reduced analgesic consumption at 24 hours, longer time to first analgesic request, and some reduction in pain scores in the first 12 hours with Pecs II block. Despite the use of levobupivacaine in both blocks, pain scores were higher at 16 and 24 hours in the Pecs II block group, suggesting shorter duration of effect with Pecs II than PVB despite improved early analgesia. Eldeen107 demonstrated that Pecs II blocks can provide effective surgical anesthesia for lumpectomy without axillary lymph node dissection and a sensory block extending to a mean of 16.6 hours when using bupivacaine 0.5% combined with low-dose dexmedetomidine.
No RCTs of SPB, PIFB, or TTP block were identified in our review.
The biggest impact of interfascial peripheral nerve blocks could be their relative ease to perform and potentially low risk profile. Because of the peripheral nature of these blocks, sympathetic blockade is not expected, risk of serious bleeding is likely low, and, as with other ultrasound-guided interfascial blocks, performance of the block in both awake and anesthetized patients may be safe. Although the novel interfascial blocks hold promise, there is a clear paucity of high-quality evidence supporting the analgesic efficacy and addressing the safety of these approaches. Randomized controlled trials comparing the various technical approaches to one another and comparing the interfascial blocks to alternative techniques (especially local anesthetic infiltration and PVB) are needed.
Acute pain following breast surgery is common, and numerous options exist for perioperative analgesia. An understanding of the anatomy of the breast and the anatomic structures disrupted by various surgical procedures will aid in selecting the appropriate perioperative analgesic technique and evaluating new techniques as they are described in the literature. We summarize the innervation, surgical procedures, and analgesic procedures in Figure 8 and the evidence for each of the analgesic procedures in Table 5. Both epidural and PVBs have been shown to provide effective analgesia for breast surgery. Paravertebral block has consistently been demonstrated to enhance analgesia while improving additional aspects of postoperative recovery, but further RCTs comparing PVB directly to local anesthetic infiltration are needed. Novel interfascial peripheral nerve blocks show promise as they may be easier to perform, may decrease risk, may be more suitable for outpatient procedures, and may even provide more complete analgesia by blocking both intercostal and brachial plexus–derived nerves. Although enticing, these assertions remain unproven. Randomized trials are needed to determine the safety and efficacy of the newer peripheral blocks, especially as compared with alternative analgesic techniques.
The authors thank Anna Getselman, executive director, Health Sciences Library, Columbia University Medical Center, for her significant contributions to the literature review.
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