Pioneered by Sellheim in 1905 [1], the technique for thoracic paravertebral blockade (TPVB) commonly used today was originally described by Kappis in 1919 [2]. During the early part of the 20th century, the TPVB was used as a diagnostic tool to differentiate between different causes of abdominal pain [3,4], as well as to treat conditions including angina pectoris, supraventricular tachycardias, and bronchial asthma in addition to providing relief from pain associated with surgery, traumatic injuries, herpes zoster, malignancy, and sympathetic dystrophies [5]. Despite the versatility and early enthusiasm for the TPVB, it became less frequently used during the mid-twentieth century as refinements in general anesthetic agents and monitoring techniques outpaced developments in local/regional anesthesia.

More recently, there has been renewed interest in regional techniques to overcome persistent limitations of general anesthesia (GA) and systemic opioid-based analgesic techniques. Eason and Wyatt [6] renewed interest in the TPVB specifically with their 1979 description of a technique for placing catheters within the thoracic paravertebral space (TPVS). At present, developments in ultrasound (US) imaging technology and increasing operator experience with interventional US techniques are contributing to increased TPVB use. In addition, intriguing preliminary data suggesting that TPVBs may be associated with a reduction in the recurrence rate of breast cancer following surgical excision [7] may potentially increase surgeons’ requests for TPVBs in their patients.

The TPVB has been used to provide surgical anesthesia for superficial procedures of the chest or abdomen. It is most commonly used to provide surgical anesthesia for breast surgery, including radical mastectomy procedures [8,10]. The TPVB can serve as an alternative to systemic or epidural analgesia following thoracotomy, thoracoscopy, laparotomy, open cholecystectomy, and liver or kidney surgery [11–16]. It may be especially useful in situations where epidural techniques may not be possible (such as in patients with spinal trauma [17,18] or previous posterior fusion of the thoracic spine). A paravertebral catheter can be used to provide and extend the duration of analgesia after such procedures or for painful conditions including multiple traumatic rib fractures [19,21] or herpes zoster [5,22].

Specific contraindications for TPVB are few. TVPB should be avoided in patients with ipsilateral empyema or severe disease of the contralateral lung. Contraindications to any regional anesthetic/analgesic technique (overlying infection or neoplasm, allergy to local anesthetics, patient or surgeon refusal, inability to obtain informed consent) apply to the TVPB as well. Patients who have significantly abnormal anatomy may be at an increased risk for complications such as inadvertent pleural or dural puncture. The use of TPVBs in patients with coagulopathy or receiving anticoagulant medications is controversial, and the TPVB currently is not considered safer than neuraxial techniques [23]. It is possible that that there is less potential for neurologic injury than with central neuraxial techniques. That a hematoma confined to the central neuraxial space could lead to spinal cord injury is well known. However, a hematoma in the TPVS could possibly extend to the adjoining epidural space through the intervertebral foramina and subsequently cause compression of the spinal cord. In addition, because the TPVS is within the thoracic cage (deep to the ribs/transverse processes), applying external pressure may not control bleeding, and significant blood loss into the pleural cavity could occur.

Risks specific to the TPVB include hemothorax/pneumothorax [24,26], epidural or intrathecal injection [27–30], mediastinal puncture [31,32] and systemic local anesthetic toxicity [33]. Of importance, it is possible that pneumothoraces resulting from pleural puncture during TPVB placement may be subclinical before patient discharge and develop slowly (more likely for single-injection techniques using small-gauge needles). Thus, patients should be advised to seek medical care immediately should they experience shortness of breath, and to avoid air travel or other significant changes in atmospheric pressure soon after TPVB placement.

Performing bilateral blocks could theoretically increase the risks for several reasons: bilateral sympathetic blockade can produce hemodynamic effects (bradycardia and hypotension) similar to epidural techniques [34], the increased doses of local anesthetics used to achieve bilateral blockade may increase the risk of systemic local anesthetic toxicity [33,35], and there is a risk of bilateral hemothorax/pneumothorax. Rostral or caudal spread of anesthetic within the paravertebral space can produce a block of cervical or lumbar nerve roots causing a motor, sensory, or sympathetic block of the arm (cervical plexus or stellate ganglion block) or leg [36,37]. The inferior boundary of the TPVS is controversial, however, as the origin of the psoas muscle may prevent spread below T12. In addition, anesthetic fluid injected in the lower part of the TPVS could spread via the epidural space to effect a lumbar plexus block [38], or via the transversalis fascia to the celiac ganglion, and produce splanchnic vasodilation and hypotension [39].

The TPVS is a wedge-shaped triangular space located on both sides of the thoracic vertebral column. The anterolateral boundary is formed by the parietal pleura and the base (medial boundary) is formed by the posterolateral aspect of the vertebral body, intervertebral disc, and the intervertebral foramina. The posterior border is formed by the superior costotransverse ligament, which extends from the lower border of the transverse process above to the upper border of the transverse process below. The TPVS communicates with the epidural space medially via the intervertebral foramina, and at the tips of the transverse processes the TPVS is continuous with the intercostal space laterally. The TPVS contains the proximal intercostal nerves (as continuation of the ventral rami), the dorsal rami, the sympathetic chain, the intercostal vessels, the endothoracic fascia, and adipose tissue (Fig. 1A) [37,40].

Fig. 1 Anatomy of the thoracic paravertebral space (TPVS). (A) Diagram showing the anatomy of the TPVS. (Reprinted from Karmakar MK. Thoracic paravertebral block. Anesthesiology 2001;95(3):771–80; with permission.) (B) Surface anatomy for thoracic paravertebral block (TPVB). Spinous processes are outlined. Dotted lines are 2.5 cm lateral to the midline. The prominent spinous process of C7 (marked C7) is a consistent surface landmark. The angle of the scapula corresponds roughly to the T7/8 interspace (marked with a horizontal line).

For anesthesia and/or analgesia of the chest and/or abdominal wall, blocks can be performed from the first thoracic to the first lumbar spinal level. Local anesthetics spread easily to adjacent levels and occasionally spread to the contralateral space via the prevertebral fascia or to the epidural space medially [41,43]. The extent of rostral/caudad spread of local anesthetic is determined by the volume of fluid injected for single-injection techniques as well as the number of levels blocked for multiple-injection techniques [44,45]. Local anesthetics placed within the TPVS act on somatic fibers as well as the sympathetic chain. As a result, TPVBs can have greater hemodynamic effects (such as vasodilation or bradycardia) than more peripheral truncal blocks, such as those of individual intercostal nerves [46].

Several studies have shown improved early recovery for patients undergoing breast surgery with TPVBs with sedation as compared with patients undergoing similar procedures under GA [8–10,61–63]. Patients in the TPVB/sedation groups had significantly less rest and/or dynamic pain, nausea, and sedation. In addition, patients in the TPVB/sedation groups were able to be discharged home earlier than patients who had received GA. Although the risk of complications from the TPVB was generally low in these studies, one pneumothorax was reported (in a series of 100 patients) [61], so caution is warranted in settings where surgical backup may not be available if urgent thoracostomy is necessary. A 1% risk of pneumothorax may be unacceptably high for elective minor procedures, especially in an ambulatory setting.

TPVB/sedation has also been compared with GA for other types of surgical procedures including inguinal hernia repair [64,65], ventral hernia repair [11], and endovascular abdominal aortic aneurysm (AAA) repair [66]. For these procedures, patients had similar improvements in pain control and early recovery. In addition, TPVB/sedation was associated with a reduced risk of hypotension in patients undergoing endovascular AAA repair compared with GA, suggesting that this type of anesthetic may be a good alternative for patients who may not tolerate GA.

Two studies have compared TPVBs to spinal anesthesia (SA) for inguinal hernia repair [67,68]. Both studies found that patients in the TPVB group had longer anesthesia-related times and block onset times. The TPVB groups required higher doses of propofol for sedation during surgery, but these differences were not clinically significant. Both studies also found that patients in the TPVB group had lower postoperative pain scores, longer times to first-rescue analgesic dose, shorter time to recovery of ambulation, and faster discharge from the postanesthesia care unit (PACU). In the study that reported rates of urinary retention [68], no patients in the TPVB group (30 patients) required bladder catheterization, compared with 5 patients (of 30) in the SA group.

Several studies have shown that TPVBs provide better pain control than systemic opioid-based analgesics following many types of surgical procedures of the chest and abdomen, including breast surgery [69,70], thoracotomy or thoracoscopy [13,71,72], laparoscopic or open cholecystectomy [12,73], open hepatic resection [16] or radiofrequency ablation of liver masses [74], transhepatic biliary drainage procedures [75], and major kidney surgery [15]. These studies all showed that compared with patients receiving systemic opioid-based analgesics alone, patients who received TPVBs had lower pain scores, decreased opioid consumption, and a lower incidence of postoperative nausea and vomiting (PONV). The duration of analgesia from single-injection techniques may be short-lived, however, as one study found no differences in pain scores between groups following patient discharge from the PACU [70]. This result suggests that continuous techniques may be more effective [76], but there have been no comparisons of single-injection with continuous techniques to date.

Few trials have compared TPVBs and local infiltration of local anesthetic or more selective peripheral nerve blocks. One trial found that compared with continuous wound infusions of ropivacaine, single-injection ropivacaine TPVBs provided superior early pain control and a lower incidence of PONV following modified radical mastectomy, but patients with wound infusions had lower pain scores 16 and 24 hours after surgery [77]. A continuous TPVB group was not included for comparison. Two studies have compared TPVBs with ilioinguinal/iliohypogastric (II/IH) blocks for pain control following inguinal hernia repair under GA [78,79]. In both studies TPVBs were performed before surgery and II/IH blocks were performed during surgery. Both of the studies found that patients in the TPVB group had lower pain scores and required fewer opioid analgesics, and neither study reported any complications in either group.

Numerous trials have compared TPVBs with thoracic epidural analgesia (TEA) following major thoracic surgery. In a recent meta-analysis, Davies and colleagues [80] pooled data from 10 trials involving a total of 520 patients, and found no significant differences between study groups’ pain scores from 4 to 8, 24, or 48 hours postoperatively with similar doses of supplemental morphine usage between groups at all time points. The TPVB groups had lower risks of pulmonary complications (odds ratio [OR] 0.36), urinary retention (OR 0.23), nausea and vomiting (OR 0.47), and hypotension (OR 0.23). In addition, the TPVB groups had lower block failure rates (OR 0.28). All differences were highly statistically significant (P values .03 to <.0001). It was concluded that TPVBs provided similar pain relief compared with TEA but have a more favorable side effect profile. These findings are in agreement with those of an earlier systematic review of regional techniques for post-thoracotomy analgesia by Joshi and colleagues [81], which found that TPVBs provided similar pain relief to TEA but was associated with a lower risk of pulmonary complications and hypotension. Of note, this study found that TPVBs were associated with lower rates of pulmonary complications than systemic analgesic regimens, whereas TEA was not. In another systematic review, Scarci and colleagues [82] reported that compared with TEA, TPVBs were associated with improved pulmonary function, lower plasma cortisol concentrations, shorter operative times, lower rates of technical failure or catheter displacement, and a reduction in the incidence and severity of hypotension. In a recent meta-regression analysis of different TPVB techniques for post-thoracotomy analgesia, Kotze and colleagues [45] analyzed 25 trials involving a total of 763 patients, and found that higher doses of local anesthetic were associated with improved pain control and faster recovery of pulmonary function. These investigators also found that compared with intermittent bolus dosing, regimens involving continuous infusions of local anesthetic provided better pain relief, whereas the addition of adjuvants such as clonidine or fentanyl did not improve the analgesic effect of the TPVB.

In a prospective trial of 20 patients undergoing open cholecystectomy, patients were randomly assigned to receive either a continuous TPVB or TEA for postoperative pain control [83]. There were no differences between groups with regard to postoperative hemodynamic stability or pulmonary function; however, patients in the TPVB group had higher pain scores and required more opioid analgesics than patients in the TEA group. One trial compared left-sided TPVB with TEA for pain control following elective robotic-assisted coronary artery bypass grafting via a left-sided minithoracotomy approach [84]. There were no differences in outcomes between groups with regard to pain control, hemodynamic stability, or complications. There was a trend toward improved pulmonary function in the TPVB group, but this did not reach statistical significance.

Additional studies have also suggested that TPVBs may reduce the risk of chronic postsurgical pain (CPSP) following breast surgery. In a 1-year follow-up study of patients enrolled in a previous study comparing TPVB/sedation to GA for surgical anesthesia for breast surgery, Kairaluoma and colleagues [85] found that patients who had received TPVBs had significantly decreased prevalence of pain symptoms as well as a decreased intensity of pain with movement and at rest. Iohom and colleagues [86] studied the effect of TPVB on acute and chronic pain following breast surgery with axillary clearance; they followed patients for 10 weeks postoperatively and found that patients who received GA and TPVBs were less likely to develop CPSP than patients who received GA and systemic analgesics alone (0/14 in the TPVB group, 12/14 in the GA group, P = .009). This study also investigated the role that nitric oxide production could play in the development of CPSP, but no correlation between perioperative plasma nitric oxide levels and risk of subsequent CPSP was demonstrated. However, the results of this study could be confounded by the fact that patients in the TPVB group also received parecoxib after induction of GA and celecoxib for up to 5 days postoperatively, whereas patients in the GA group did not.

One of the most intriguing outcomes examined recently is the potential effect TPVBs may have on the rates of breast cancer recurrence. A recent retrospective analysis [7] of patients undergoing surgical excision of malignant breast lesions showed a significant reduction in the rates of local recurrence during a 36-month follow-up period (6% vs 24%, P = .007). This effect could be caused by a blunted stress response to surgery, as patients undergoing breast cancer surgery with TPVBs have been shown to have lower serum concentrations of glucose, cortisol, and C-reactive protein than patients treated with systemic opioids [87]. However, in this study TPVBs did not reduce the serum levels of the vascular endothelial growth factor (VEGF) or prostaglandin-E2 (PGE2). Others have proposed that the TPVB leads to a reduction in substance P production with decreased tumor cell proliferation and neoangiogenesis via activation of tumor neurokinin-1 receptors [88], though they have not yet tested these hypotheses in vitro or in vivo. It does appear that the TPVB may indeed contribute to the lower rates of recurrence, as serum from patients with TPVBs undergoing excision of malignant breast lesions inhibited proliferation of estrogen-receptor negative breast cancer cells in vitro [89]. The authors wish to emphasize that although these findings are very intriguing, confirmation with large-scale prospective studies is necessary. The design of these studies has been proposed [90], and patient recruitment is currently under way.

Although there are good data supporting the use of TPVBs over TEA for pain relief after thoracic surgery and the use of TPVBs over systemic analgesics following abdominal surgery, additional studies comparing bilateral TPVBs with TEA for abdominal procedures could be valuable. Comparisons of continuous TPVBs and continuous wound infusion techniques could also help determine the relative efficacy and efficiency, as well as the risks of these modalities. The use of single- or multiple-injection techniques for performing TPVBs remains controversial, and additional studies comparing these may help clarify the advantages and risks of the two. Additional comparisons between TPVBs and more distal blocks such as TAP or II/IH blocks could also be helpful.

Comparisons between US-guided and traditional approaches (or combinations of the two) are needed before definitive conclusions regarding the relative merits and risks of either modality can be drawn. Improvements in US imaging technology and needle/catheter design may allow for more consistent visualization of anatomic structures and aid the correct placement of needles/catheters within the TVPS. Increasing operator experience may increase the understanding of relative advantages and disadvantages of various US-guided approaches, and lead to more standardization of techniques.

Prospective studies are needed to confirm the preliminary finding of decreased chronic pain as well as local recurrence rates following surgical excision of malignant breast lesions (a multicenter trial is currently under way), as well as to determine the underlying mechanisms for these potential beneficial effects.

In 2001, Rafi [91] described a percutaneous technique to deposit local anesthetic solution via the iliolumbar triangle of Petit to produce an “abdominal field block.” Based on their findings from cadaveric anatomic studies as well as clinical and imaging studies in volunteers, in 2007 McDonnell and Laffey [92] coined the term “transversus abdominis plane” block (commonly abbreviated as TAP block) to describe this novel block. Since that that time, the TAP block has been increasingly used by anesthesiologists as a means of providing postoperative somatic analgesia for adult and pediatric patients undergoing a wide array of abdominal surgical procedures (see later discussion).

The TAP block has been shown to be effective for reducing pain following many types of abdominal surgery including cesarean delivery [93], open retropubic prostatectomy [94], appendectomy [95], abdominal hysterectomy [96], vertical midline laparotomy with colon resection [97], and laparoscopic cholecystectomy [98]. To date, large series of prospective studies examining use of the TAP block for surgical anesthesia have not been published. The efficacy of the TAP block for providing analgesia after surgical procedures involving incisions above the umbilicus remains unclear (see Anatomy section).

There are no specific contraindications for the TAP block. Standard contraindications to any regional anesthetic technique (see TPVB section) also apply to the TAP block. In theory, the TAP block would not be possible in patients with syndromes characterized by an absence of abdominal musculature such as the prune belly syndrome. Because it is a relatively superficial block, bleeding should be controlled by applying external pressure. For this reason, the TAP block could be performed in patients with bleeding disorders or who are taking anticoagulant medications. The risk of hematoma formation does exist, but is not associated with potential risk of the permanent spinal cord injury and paraplegia associated with a central neuraxial hematoma.

Specific risks of the TAP block are predominantly related to intraperitoneal needle placement with injury to intra-abdominal organs. Jankovic and colleagues [99] reported a case of inadvertent intraperitoneal catheter placement without injury to viscera, and Farooq and Carey [100] reported a case of liver trauma during TAP block. Both cases involved blocks performed using a posterior, landmark-based “2-pop” technique.

The ventral rami of spinal nerve roots T6 to L1 give rise to the thoracolumbar nerves, which subsequently course through the lateral abdominal wall within a potential space defined superiorly by the costal margin, inferiorly by the iliac crest, medially by the lateral border of the rectus abdominis muscle (linea semilunaris), superficially by the internal oblique muscle, and deep by the transversus abdominis muscle (Fig. 4A). The lumbar triangle of Petit is defined by the posterior border of the external oblique muscle anteriorly, and the lateral border of the latissimus dorsi muscle posteriorly. The base of the triangle is defined by the iliac crest (Fig. 4B). Jankovic and colleagues [101] performed an anatomic study in cadavers to more precisely describe the position and size of the triangle. These investigators found that the triangle is more posterior than previous descriptions of McDonnell and Rafi (mean distance posterior to mid-axillary line 9.3 cm, range 4–15.1 cm). It was also noted that the thoracolumbar nerves were not in the TAP in this posterior location, but had entered the TAP at the level of the mid-axillary line. Small branches of the subcostal arteries within the triangle in 16 of 24 specimens were also noted. Rozen and colleagues [102] performed detailed dissections of the TAP in 20 cadaveric hemi-abdominal walls. These investigators demonstrated an extensive fascial layer between the internal oblique and transversus abdominis in all specimens. This layer was not adherent to the internal oblique, and bound down the thoracolumbar nerves on its deep surface to the transversus abdominis below. Segmental nerves T6 to T9 were observed to enter the TAP between the midline and anterior axillary line. At the level of the anterior axillary line, the segmental nerves of T9 to L1 had branched extensively, with every segmental origin contributing to at least 2 nerves within the TAP. Multiple locations were found where there was extensive communication between segmental nerves. Interconnections between subcostal and intercostal nerves (T6–T9) within the TAP form an “intercostal plexus,” while T9 to L1 contribute to plexi lateral to the deep circumflex iliac artery (“TAP plexus”) and alongside the deep inferior epigastric artery located within the rectus abdominis muscle (“rectus sheath plexus”).

Fig. 4 Anatomy of the transversus abdominis plane (TAP). (A) Diagram shows anatomy of the TAP and needle trajectory in the TAP between the internal oblique and the transversus abdominis muscles. Ext Oblique, external oblique muscle; Int Oblique, internal oblique muscle; Transversus, transversus abdominis muscle. (Data from Ecole Polytechnique Fédérale de Lausanne, Switzerland, Visible Human Web Server. Available at: http://visiblehuman.epfl.ch) (Reprinted from Tran TM, Ivanusic JJ, Hebbard P, et al. Determination of spread of injectate after ultrasound-guided transversus abdominis plane block: a cadaveric study. Br J Anaesth 2009;102(1):123–7; with permission.) Note the location of the US transducer on the abdominal wall and the tangential (relative to the peritoneal cavity) trajectory of the needle inserted from the medial aspect of the transducer. (B) Surface anatomy for TAP block via the posterior approach. The lumbar triangle of Petit (shaded) is defined by the external oblique muscle (EO) anteriorly, the latissumus dorsi muscle (LD) posteriorly, and the iliac crest (IC) inferiorly. The needle insertion site is the center of the triangle.

McDonnell and colleagues [103] evaluated the spread of injectate within the TAP both in a cadaver model and using radiographic imaging in healthy volunteers. These investigators reported a sensory block extending from T7 to L1 dermatomes in the volunteers, and have reported satisfactory analgesia with this technique even for surgical procedures using a vertical midline incision extending above the umbilicus [97]. However, Hebbard [104] and Shibata and colleagues [105] performed separate retrospective audits and, based on their experiences, suggested that the TAP block performed just above the iliac crest does not reliably provide sensory analgesia above the umbilicus. Hebbard described a new “oblique subcostal” approach to the TAP, and reported that this modified approach resulted in a more cephalad distribution of the block [106]. Tran and colleagues [107] and Barrington and colleagues [108] confirmed these findings in separate studies examining the distribution of dye injected into the TAP of cadavers. These studies found that the spread of dye was limited to the T10-L1 nerve roots with the originally described US-guided posterior TAP approach, but from T9 to T11 if a US-guided subcostal approach was used. Multiple-injection techniques within the TAP (as the needle was advanced from medial to lateral) were found to be more likely to involve the T7 and T8 segmental nerves.

Lee and colleagues [109] recently published an observational study of patients receiving bilateral US-guided TAP blocks for analgesia following major abdominal surgery. Patients received the TAP blocks via either a posterior or oblique subcostal approach. This study found that patients in the oblique subcostal group had a larger number of affected dermatomal segments, and that the oblique subcostal approach was more likely to block more cephalad segments (median block height T8 vs T10 in the posterior-approach group, P = .001).

The TAP block is a compartment or field block, and the end points for all of the techniques described in this section are not determined by placing the needle’s tip in close proximity to the individual thoracolumbar nerves themselves. For this reason (and because it is predominantly used for postoperative analgesia rather than surgical anesthesia), the TAP block can be performed in patients under GA or SA. The TAP block is a unilateral block extending from the mid-axillary line to the ipsilateral rectus abdominis muscle, and procedures involving midline or bilateral incisions require a TAP block on each side.

Ultrasound-guided technique

With a linear-array, high-frequency transducer placed in an axial orientation on the lateral abdominal wall (Fig. 5A), the US image can show the subcutaneous tissues, the internal and external oblique muscles, the transversus abdominis muscle, and the peritoneum and viscera (Fig. 5B). The muscular layers of the lateral abdominal normally have a characteristic “3-stripe” appearance. The internal and external oblique muscles usually have a characteristic striated appearance, whereas the transversus abdominis usually appears relatively hypoechoic (dark) and homogeneous. Walter and colleagues [111] reported variability of the layers of the abdominal wall in Petit’s area, and the best US image may be obtained with the transducer somewhat more anterior than directly over the triangle. The implications of injecting anesthetic anterior to the triangle remain unclear.

Fig. 5 Sonoanatomy for posterior-approach TAP block. (A) US transducer placement for posterior-approach TAP block. A high-frequency, linear-array probe is placed transversely on the anterolateral abdominal wall. To perform the block using an in-plane technique, the needle is usually inserted from the medial aspect of the transducer and directed laterally. (B) US image of the muscular layers of the anterolateral abdominal wall below the level of the umbilicus. EO, external oblique muscle; IO, internal oblique muscle; TA, transversus abdominis muscle; PC, peritoneal cavity. The medial and lateral aspects of the image are labeled. Local anesthetic should be injected below the fascia overlying the transversus abdominis muscle (marked with arrowheads) to act on the nerves traveling within the TAP.

For the posterior approach to the TAP block, the US transducer is positioned axially over the iliac crest along the mid-axillary line (see Fig. 5A). The transducer’s position is adjusted as necessary until the classic 3-stripe image of the muscular layers of the abdominal wall is obtained (see Fig. 5B). This 3-stripe image may be more difficult to find in obese patients, as the muscles are deeper due to abundant overlying adipose tissue, and the muscles may be atrophic and as a result relatively thin. If the 3-stripe image is difficult to obtain, the transversus abdominis muscle can often be identified by first locating the peritoneal cavity, then looking superficially. Peristaltic movements of the intestine can be seen within the peritoneal cavity, and the transversus abdominis is the muscular layer directly overlying the parietal peritoneum, though in very obese patients a thick layer of preperitoneal fat can be mistaken for the transversus abdominis muscle. Alternatively, the transducer can initially be placed more medially over the rectus abdominis muscle. By scanning laterally, the posterior capsule of the rectus sheath can be demonstrated, dividing to envelop the transversus abdominis and internal oblique muscles. The anterior capsule can be seen splitting to envelop the external and internal oblique muscles (the internal oblique muscle’s fascial aponeurosis contributes to both the anterior and posterior capsules of the rectus sheath above the level of the arcuate line).

An in-plane needle approach is typically used, and the needle is usually inserted from the medial aspect of the transducer (see Figs. 4 and 5); this results in a tangential needle trajectory that may decrease the likelihood of puncturing the peritoneum (see Fig. 4A). Once the needle’s tip penetrates the fascia (seen as a hyperechoic line) between the internal oblique and transversus abdominis muscles, local anesthetic is injected incrementally into the TAP. The local anesthetic may initially be seen spreading into the substance of the transversus abdominis muscle itself. In this case, the needle should be withdrawn slightly so that the local anesthetic spreads in the TAP. The local anesthetic must be deposited deep to the fascia that binds the thoracolumbar nerves onto to the transversus abdominis muscle, which will lift off from the transversus abdominis as more fluid is injected. The key to a successful block is not to accept anesthetic spread above this fascial layer, as the thoracolumbar nerves are below it. The needle should under no circumstances be advanced through the transversus abdominis, as injury to intraperitoneal structures could result.

Because this is a compartment block, reducing the volume of local anesthetic could theoretically decrease the extent of local anesthetic distribution within the TAP. Indeed, most of the studies that have investigated the spread of fluid within the TAP have used injectate volumes of 15 to 20 mL. (see earlier discussion). If bilateral blocks are planned or if there is concern over the potential risk of systemic local anesthetic toxicity, larger volumes of anesthetic fluid with lower concentrations can be used rather than smaller volumes with higher concentrations.

A catheter can be placed within the space created by the fluid in the TAP if a continuous block is planned. For continuous blocks, the authors prefer to distend the space with a small volume of saline first, then dose the block through the catheter, thus ensuring that the resulting block derives from the correct placement of the catheter, minimizing the risk of secondary block failure.

The sonoanatomy of the abdominal wall in the subcostal region is usually similar. However, local anesthetic can be deposited between the posterior capsule and the belly of the rectus abdominis muscle (similar to the rectus sheath block, see later discussion) if the transversus abdominis muscle (normally posterior to the rectus abdominis muscle at this level) cannot be identified in this location. For the subcostal approach, the US transducer is placed obliquely below the costal margin (Fig. 6A) along the lateral border of the rectus muscle (linea semilunaris). The muscular layers are again demonstrated (Fig. 6B). The transversus muscle may be located more medially at this level. Usually it is demonstrated posterior to the belly of the rectus abdominis muscle. If the transversus cannot be identified, local anesthetic can be injected between the belly of the rectus and the posterior capsule of the rectus sheath. A multiple-injection technique with injections both in this location and in the TAP along the costal margin described above may result in more extensive spread of local anesthetic [108]. This spread may be due to the injections being both medial and lateral to the anterior axillary line (see Anatomy section). Catheter placement may be performed in a manner similar to that described earlier for the posterior TAP block. The location of the catheter should be selected based on the dermatomal levels involved in the surgical incision.

Fig. 6 Sonoanatomy for oblique subcostal-approach TAP block. (A) Oblique US transducer position for US imaging of the subcostal TAP. The transducer is placed on the anterior abdominal wall along the inferior costal margin, medial to the anterior axillary line. As for the posterior-approach TAP block, an in-plane technique is usually used and the needle is inserted from the medial aspect of the transducer and directed laterally. (B) US image of the muscular layers of the subcostal anterolateral abdominal wall. EO, external oblique muscle; IO, internal oblique muscle; TA, transversus abdominis muscle; PC, peritoneal cavity. The medial and lateral aspects of the image are labeled. Local anesthetic should be injected below the fascia overlying the transversus abdominis muscle (marked with arrowheads) to act on the nerves traveling within the TAP.

In several small prospective randomized controlled trials, the TAP block has been shown to improve pain control and decrease opioid consumption following several abdominal surgical procedures, including large bowel resection via a vertical midline incision [97], cesarean delivery through a Pfannenstiel incision [93], abdominal hysterectomy through a low transverse incision [96], open appendectomy [95], and laparoscopic cholecystectomy with all port sites at or below the umbilicus [98,112]. Several other case reports and case series have reported reduced pain scores and decreased morphine consumption compared with historical controls for other abdominal procedures such as retropubic prostatectomy [94].

Petersen and colleagues [113] recently conducted a systematic review of studies that have examined the effect of the TAP block on postoperative pain. These investigators identified 7 prospective studies involving a total of 364 patients. The studies overall had good methodological quality (median score 5/5, range 2–5) and validity (median score 14/16, range 2–15) as evaluated by the Oxford Quality and Oxford Pain Validity Scales. Three studies involved blocks performed using the traditional landmark-based technique. Four studies involved US-guided blocks. In 6 studies, bilateral blocks were performed. Meta-analysis of patient outcomes was performed, and significant reductions in pain scores at rest and with movement, as well as morphine consumption during the first 24 hours postoperatively, were demonstrated for patients in the TAP block groups. Of note, subgroup analysis revealed a significant difference in reduction of morphine consumption between landmark-based and US-guided blocks. Landmark-based blocks resulted in a greater reduction in mean morphine consumption (−38 mg vs −11 mg). It is not clear if this difference was due to a difference in the location of injection with the 2 techniques, or if it reflects specific differences related to the surgical procedures included in these trials.

The TAP block has not been used extensively for surgical anesthesia, and comparisons with GA or SA for suitable surgical procedures such as inguinal or umbilical hernia repair could be helpful. To date, no study has formally compared the various approaches for the TAP block (eg, posterior vs subcostal). Studies comparing different techniques (eg, landmark-based with LOR vs ultrasonography) could help define their relative efficacy, success rates, and other advantages and/or limitations. Direct comparisons between TAP blocks and TPVBs or neuraxial techniques such as TEA are also needed [114] to evaluate their relative success rates, analgesic effects, side effect profiles, the incidence of complications or side effects, and to reveal any additional advantages of efficiency into daily clinical practice. Although one study has shown increased plasma levels of local anesthetic following US-guided TAP blocks [110], the pharmacokinetics of various local anesthetics within the TAP remains unclear. The effect of adding epinephrine to local anesthetics on plasma levels has not been investigated. No study to date has evaluated the effects of adding adjuvants such as opioids, bicarbonate, or clonidine to the local anesthetic solution.