A review of peripheral nerve blocks for cesarean delivery analgesia

Abstract

Peripheral nerve blocks have a unique role in postcesarean delivery multimodal analgesia regimens. In this review article, options for peripheral nerve blocks for cesarean delivery analgesia will be reviewed, specifically paravertebral, transversus abdominis plane, quadratus lumborum, iliohypogastric and ilioinguinal, erector spinae, and continuous wound infiltration blocks. Anatomy, existing literature evidence, and specific areas in need of future research will be assessed. Considerations for local anesthetic toxicity, and for informed consent for these modalities in the context of emergency cesarean deliveries, will be presented.

INTRODUCTION

Current practices for routine multimodal cesarean delivery analgesia include neuraxial anesthesia with intrathecal or epidural morphine, scheduled administration of non-opioid analgesics (acetaminophen and non-steroidal anti-inflammatory medications), and strategic use of opioids for severe breakthrough pain.^1,2 In non-obstetric surgical settings, peripheral nerve blocks are used as part of multimodal analgesic strategies. These practices are linked to reductions in opioid requirements, enhanced quality of recovery, and reductions in hospital resource utilization.^3–6 Although not performed routinely, peripheral nerve blocks play a role in cesarean delivery analgesia. Several specific blocks have been investigated to assess their potential benefit in multimodal and rescue analgesia.

In this review article, options for peripheral nerve blocks for cesarean delivery will be reviewed. Specific attention will be given to paravertebral, transversus abdominis plane (TAP), quadratus lumborum (QL), iliohypogastric (IH) and ilioinguinal (II), and continuous wound infiltration (CWI) blocks. Erector spinae plane block, a relatively new procedure, will be briefly discussed. Anatomy, existing evidence, and specific areas for future research will be assessed. Considerations will be weighed concerning local anesthetic toxicity, liposomal bupivacaine, and informed consent for these modalities in emergency cesarean delivery under general anesthesia.

METHODS

For this narrative review article, we conducted a literature search for peripheral nerve blocks in cesarean delivery using the PubMed and MEDLINE electronic databases, with the assistance of a health sciences librarian (C.B.W.) A complete search strategy including all search terms is available in online supplemental file 1. Articles were limited to those in the English language, published between January 1, 1980 and December 31, 2018. From these results, articles were selected that were most relevant to the stated objectives of evaluating anatomy, evidence for use in clinical practice, and specific areas for needed research. Limited articles published prior to 1980 were included for historical context. Additional information on informed consent considerations were gleaned from available professional society statements and from personal communications with legal experts. Online supplementary table 1 (Supplemental Digital Content) provides a detailed assessment of relevant published work according to the type of peripheral nerve block. Figure 1 provides an overview of the peripheral nerve blocks that will be the point of focus in this article.

Figure 1.

Overview of peripheral nerve blocks for postcesarean delivery pain management. PCEA, patient-controlled epidural analgesia.²

LUMBAR PARAVERTEBRAL BLOCK

Dermatomes covered and anatomy

Paravertebral lumbar sympathetic block (paravertebral nerve block) is a nerve root level block placed outside the dura mater and have also been called paraspinal epidural blocks.⁷ They can be performed using landmark-guided or ultrasound-guided techniques. Dermatomal coverage is unilateral and depends on the volume of local anesthetic injected, as well as the number of injections or levels selected.⁸ The typical maximum dermatomal spread for a single-level block with an injected volume of 5 mL is four dermatomal levels.⁹ For most abdominal surgeries, paravertebral nerve block covers innervation of the abdominal wall by the lower thoracoabdominal nerves (T6-T12).¹⁰ Those dermatomes may not always be sufficient for the Pfannenstiel incision typically used for cesarean delivery (L1).

Approach

For the Pfannensteil skin incision typically used for cesarean delivery, bilateral paravertebral lumbar block at T12-L1 should be used.¹¹ In addition, for the visceral pain associated with cesarean delivery, additional paravertebral sympathetic blockade can be added from T10-L2 vertebral levels, which corresponds to uterine innervation via the preganglionic and postganglionic sympathetic fibers of the superior and inferior hypogastric plexi (branches of the hypogastric nerve).¹²

A parasagittal in-plane approach is associated with reduced risk for epidural spread compared with a transverse in-plane approach, because the neural foramen is approached perpendicularly.^13–17 In this approach, a point 2–2.5 cm lateral to the spinous process tip is found and marked. Transverse process, costo-transverse ligament, and pleura are identified. A 21–18-gage needle is inserted at the cephalic aspect of the ultrasound probe and visualized as it is advanced toward the costo-transverse ligament. On traversing this ligament, a tactile “pop” is appreciated. After negative aspiration, 2–7 mL of the local anesthetic of choice, such as ropivacaine 0.5%–0.75% with or without epinephrine, is injected. This local anesthetic distribution can be seen within a multilevel (two or more) spread associated with anterior displacement of pleura.

Needle visualization with the parasagittal in-plane approach can be poorer than the transverse in-plane approach due to the steep angle of insertion. Therefore, some practitioners recommend performing these blocks using a transverse in-plane approach. To perform the transverse in-plane approach, key landmarks are identified as noted above. The tip of the transverse process is positioned in the middle of the ultrasound image. The needle is inserted 2–2.5 cm lateral to the transverse process so that adequate needle visualization can be achieved. The needle is directed between the transverse process and the pleura, and injection is performed under direct visualization. Pleural displacement is noted to confirm correct placement.

Advantages and disadvantages

The major advantage of paravertebral nerve blocks is that analgesia can be provided in patients for whom neuraxial analgesia could be complicated, such as neuraxial anatomical abnormalities or spine surgery with instrumentation.¹⁸ For non-incisional (visceral) pain after cesarean delivery, the paravertebral block of sympathetic chain ganglion offers unique advantages to other abdominal wall blocks that only target cutaneous nerves. Duration of analgesia with typical agents is 9–12 hours, and repeat procedure may be needed if catheter-based techniques are not used.¹⁸ In contrast to epidural analgesia, patients with paravertebral blocks may be ambulatory and have fewer side effects (urinary retention and hypotension), although a meta-analysis in thoracotomy patients was unable to make definitive conclusions on differences in side effects between epidural and paravertebral blockade.^19,20 Paravertebral blocks require some skill to perform and can be associated with unintentional epidural or intrathecal injections of medications. These considerations, along with wider-spread clinical comfort in the performance of neuraxial blockade for obstetric patients, may explain why limited studies thus far have been performed in cesarean delivery patients.

Current evidence and future research directions

Randomized control trials comparing the efficacy between the epidural analgesia and paravertebral nerve blocks for cesarean delivery analgesia are lacking. Published literature has focused on paravertebral nerve blocks for labor analgesia, which can provide some insight into their potential role for cesarean delivery analgesia. Existing literature is limited to case reports of specific patients for whom traditional epidural analgesia was contraindicated. In one case, a patient with spina bifida occulta and tethered cord with non-palpable spinous processes had a paravertebral nerve block with 0.375% bupivacaine and pudendal nerve block for labor analgesia, which provided adequate analgesia.²¹ A patient with Harrington rods and non-palpable spinous process with multiple failed epidural attempts during her previous childbirth, received bilateral paravertebral nerve block with 15 mL of 0.375% with 1:400 000 epinephrine and a pudendal block, and reported adequate labor analgesia.²¹

As much of the evidence of use of paravertebral block (PVB) cited above is anecdotal, further evidence is necessary before this block can be unequivocally recommended for analgesia for cesarean deliveries.

TRANSVERSUS ABDOMINIS PLANE BLOCK

Dermatomes covered and anatomy

The TAP block is a field block of the thoracolumbar nerves (maximum dermatomal coverage, T6-L1; often cited, T10-T12), which run in the fascial plane between the internal oblique muscle and the transversus abdominis muscles^22,23 (figure 2). The anterior primary rami course between the internal oblique and the transversus abdominis muscles, and subsequently branch into the lateral and anterior cutaneous nerves at approximately the midaxillary line.

Figure 2.

Schematic illustration of tissue planes and related anatomy for (A) transversus abdominis plane (TAP) and (B) quadratus lumborum (QL) blocks. QLT, quadratus lumborum transmuscular.

Approach

Two approaches for TAP predominate. The landmark-guided technique utilizes the “double pop” technique via the triangle of Petit to determine the site and depth of insertion of the needle. This anatomic space is bordered anteriorly by the external oblique muscle, posteriorly by the edge of the latissimus dorsi, and inferiorly by the iliac crest.^23,24 The “double pop” refers to the feeling of the needle piercing through the fascial plane of the external oblique muscle and then through the fascial plane of the internal oblique muscle.²³ In the ultrasound-guided lateral technique, the transducer is placed perpendicular to the midaxillary line between the costal margin and the iliac crest²³ to identify the three muscles layers (from superficial to deep): external oblique, internal oblique, and transversus abdominis muscle. Using an in-plane approach, the needle tip and injection ideally enters the TAP at the midaxillary line. Ultrasonographic images of the fascial plane between internal oblique and transversus abdominus muscle for TAP may appear different in non-pregnant and postcesarean delivery patients (figure 3).

Figure 3.

Ultrasound images comparing tissue planes for transversus abdominis plane (TAP) and quadratus lumborum (QL) blocks in non-pregnant patient (A) and immediately postcesarean delivery (B). Note the tissue distortion (flattened-appearing muscular planes) and air artifacts (arrows) that occur after cesarean delivery, which may introduce visualization and technique challenges for abdominal wall nerve blockade in this patient population. *Target for TAP block. **Target for QL block (QL1). ***Target for QL block (QL2). EOM, external oblique muscle; IOM, internal oblique muscle; QL, quadratus lumborum muscle; TA, transversus abdominis muscle.

Advantages and disadvantages

TAP in cesarean delivery is useful as a primary mode of analgesia in women not receiving neuraxial morphine for any reason.¹ The ultrasonographic anatomy to perform the block is typically identifiable, even after cesarean delivery. The major disadvantage of TAP is that it does not provide visceral analgesia (table 1). This omission likely explains why multiple studies have failed to show superiority of TAP compared with standard multimodal analgesia with intrathecal morphine (ITM) (vide infra).

Table 1.

Comparison of peripheral nerve block techniques for cesarean delivery. Dermatomes covered, skin incision type addressed, volume of local anesthetics required, and other considerations are presented and compared between techniques

Technique	Dermatomes	Skin incision type	Anatomic alterations in obstetric patient	Injectate volume requirements	Somatic analgesia	Visceral analgesia	Adjacent vascularity	Major risks	Notes	References
Paravertebral (PVB)	Variable; can address thoracolumbar dermatomes	Pfannenstiel Vertical midline	No changes likely	5–10 mL per side Multiple Injections of small volumes (3—4 mL) at contiguous levels preferred over single large-volume Injection	Yes	Yes	Yes (thoracic segmental arteries, abdominal branches of lumbar arteries)	Pneumothorax; epidural or Intrathecal Injections	Few high-quality studies for cesarean analgesia; superiority to neuraxial morphine unknown; parasagittal in-plane approach can minimize risk for epidural spread, but requires skill to maintain needle visualization	15 80 81
TAP (TAP)	T10-L1*	Pfannenstiel Vertical midline	Postdelivery changes In tissue planes may occur	20–30 mL per side	Yes	Not reliable; parietal peritoneum only	Yes (abdominal branches of lumbar arteries)	Local anesthetic toxicity; organ Injury; hematoma	Not superior to neuraxial morphine; may have benefit In breakthrough pain despite multimodal analgesia or Inability to receive neuraxial morphine	82 83
QL(QL) QL1 (lateral)	T7-L1		Postdelivery changes In tissue planes may occur	20–30 mL per side	Yes	Not reliable; depends on posterior spread into paravertebral space (QL2 provides more reliable spread into paravertebral space)	Yes (abdominal branches of lumbar arteries)	Local anesthetic toxicity; organ Injury; hematoma	Compared with TAP, QL1 and QL2 are deep nerve blocks; risks include infection, hematoma, organ injury	36 84
QL2 (posterior)	T7-L1	Pfannenstiel Vertical midline	Postdelivery changes In tissue planes may occur	20–30 mL per side	Yes
QLT transmuscular)	T10-L4		Postdelivery changes In tissue planes may occur	20–30 mL per side	Yes				Superiority to neuraxial morphine unknown
QLI (Intramuscular)	T7-T12		No changes likely	20–30 mL per side	Yes
II-IH (II-IIH)	L1	Pfannenstiel	Postdelivery changes in tissue planes may occur	10mL per side	Yes	No	Yes (smaller branches of lumbar arteries)	Intra-arterial Injection; partial block If Improper Injection	Not superior to neuraxial morphine; possible benefit In breakthrough pain despite multimodal analgesia or in absence of neuraxial morphine	85 86
CWI (CWI)	Variable	Pfannenstiel Vertical midline	No changes likely	10mL bolus 2–5mL/hour infusion rate; maximum infusion rates 14mL/hour	Yes	No	No	Local anesthetic toxicity; variable analgesia; high infusion rates can lead to leakage around the wound	Not superior to neuraxial morphine; may have benefit in breakthrough pain despite multimodal analgesia or inability to receive neuraxial morphine	50 56
Erector Spinae Plane (ESP)	Variable	Pfannenstiel	No changes likely	20–25 mL per side	Yes	No	No	Local anesthetic toxicity; variable analgesia; possible motor block	Only case reports currently available	59 60

^*Anterior TAP performed medial to the anterior superior iliac spine.

QL, quadratus lumborum; TAP, transversus abdominis plane.

Current evidence and future research directions

Studies on postcesarean TAP in the absence of ITM show benefit compared with placebo or no intervention. McDonnell et al demonstrated significant reductions in opioid requirements with landmark-based TAP in the absence of ITM.²⁴ TAP lowered 48 hours morphine use with the largest differences in the first 0–12 hours (33 mg vs 6 mg). However, the pain scores at rest and with movement (visual analog scale) were not consistently reduced across time points. Similarly, other studies have found reduced mean breakthrough pain medication (opioid and tramadol) requirement as well as prolonged time-to-first-analgesic request^24–27; however, reduction in pain was not consistent across studies. Two meta-analyses showed no difference in pain scores at rest and pain scores at 24 hours postoperatively with TAP versus no TAP.^28,29 However, one meta-analysis found a reduction in opioid use and in pain scores with movement at 24 hours²⁸. Another meta-analysis showed lower pain scores at rest (6 and 12 hours) and with movement (6 and 12 hours) associated with postcesarean TAP.²⁹ Overall, the studies suggest that in the absence of ITM, TAP results in less opioid requirement and possibly lower pain scores in the first 12 hours after cesarean delivery.

Can TAP either replace or enhance ITM for postcesarean delivery analgesia? A 2016 meta-analysis by Champaneria et al²⁸ evaluated studies which compared TAP to control (14 studies), TAP to ITM (two studies) and TAP with ITM to ITM alone (four studies). For pain at rest, TAP was more effective than control for early pain but was less effective than ITM. Adding TAP to ITM did not augment pain relief over the first 24 hours. When the authors evaluated pain with movement, TAP was again more effective than control in the first 24 hours, and ITM again was more effective at six and 24 hours postoperatively. Adding TAP to ITM reduced pain at 6 hours, but not at 24 hours postoperatively. Finally, when opioid requirements were evaluated, TAP reduced morphine consumption effectively for up to 24 hours, while the comparison of TAP to ITM revealed reduced opioid requirements among the ITM patients, but only at some time points. The addition of TAP to ITM produced no additional effect in terms of opioid consumption in the sole trial that measured this parameter.²⁸ Altogether, the best available evidence suggests that TAP is effective for postoperative analgesia when ITM is not possible or desired, such as when general anesthesia is required for cesarean delivery.

The ideal dose for postcesarean TAP has been questioned, given that local anesthetic plasma levels have been shown to exceed toxic levels after TAP.^30,31 Singh et al compared two doses of local anesthetics in three intervention groups: ITM with placebo, versus ITM with TAP using high-dose ropivacaine (3 mg/kg, max 300 mg), versus ITM with TAP using low-dose ropivacaine (1.5 mg/kg, max 150 mg).³² Notably, the volumes of injectate were identical (60 mL) between high and low dose ropivacaine groups. No difference in pain scores at rest at 24 hours, with movement at 24 hours or breakthrough pain medication requirements were found between the high-dosage and low-dosage groups.³² Pain scores with movement at 6 and 12 hours were lower in the high-dose group. Several case reports and cohort studies have been published describing neurological symptoms consistent with local anesthetic systemic toxicity after TAP for cesarean delivery.^30,33–35 Ng et al conducted a meta-analysis comparing studies which evaluated a high dose versus low dose local anesthetic. The authors classified doses in bupivacaine equivalents and determined high-dose as greater than 50 mg per block per side, and low-dose as less than or equal to 50 mg. The results showed that low-dose and high-dose groups had similar postoperative analgesia and opioid-sparing effects (opioid consumption, time-to-first request, 24 hours pain scores).³⁴ Therefore, there may be no increased benefit of local anesthetic after a certain dose threshold, and low-dose strategies for postcesarean TAP may reduce local anesthetic toxicity risk without compromising analgesic efficacy.

QUADRATUS LUMBORUM BLOCK

Dermatomes and anatomy

The QL block is a peripheral nerve block technique first described using ultrasound to trace the transversus abdominis more posteriorly until the transversus aponeurosis appears.³⁶ The anatomy is best understood by appreciating the layers that surround the QL muscle (figure 2). The thoracolumbar fascia surrounds the QL muscle, as well as several other muscles of the back and is composed of the anterior, middle, and posterior layers. The anterior layer is anterior to the QL muscle, the middle layer is located between the erector spinae and the QL muscle, and the posterior layer of thoracolumbar fascia encloses the erector spinae.³⁶ Large-volume injections of local anesthetic, typically a long-acting amide such as ropivacaine or bupivacaine 0.125%–0.375% (15–30 mL per side, 0.2–0.4 mL/kg), injected into any of these fascial planes affect the adjacent nerve fibers, such as the lateral cutaneous branches of the IH, II, and subcostal nerves, with potential to track into the paravertebral space. This posterior spread into the paravertebral space can potentially affect the sympathetic chain, conferring visceral as well as somatic analgesia (table 1). The dermatological spread of the different approaches to QL block are somewhat variable. Ultrasonographic identification of tissue planes for QL may appear different in non-pregnant versus postcesarean delivery patients (figure 3).

Approach

There are currently four described QL block approaches (figure 2).³⁶ The first approach, QL1 or commonly known as the lateral QL, is an injection deep to the transversus abdominis aponeurosis. The second approach, QL2, also referred to as posterior QL, is an injection deep to the erector spinae muscle, with deposition of local anesthetic posterior to the QL muscle. The transmuscular (QLT) or anterior approach is an injection into the plane between the psoas major muscle and the QL muscle. Finally, for the intramuscular QL (QLI) described in the pediatric population, local anesthetic is injected directly into the QL muscle.³⁷ Dermatome spread varies somewhat with the different QL block approaches. The QL1 and QL2 approach reportedly affect dermatomes T7 to L1, the transmuscular version covers T10 to L4, and the intramuscular technique covers T7 to T12³⁶ (table 1).

Advantages and disadvantages

QL block has been associated with reduced postoperative opioid consumption and pain scores in patients undergoing cesarean delivery, but these studies have been challenging to interpret given the lack of study groups receiving standardized multimodal analgesia with neuraxial morphine. Blanco et al showed that posterior approach QL (QL2) injection of 0.125% bupivacaine at 2 mL/kg compared with saline placebo after cesarean delivery reduced morphine used at 6 and 12 hours, diminished morphine requests at 6, 12, 24, and 48 hours, and lowered pain scores during movement and at rest (not significant at 24 hours).³⁸ One study of patients randomly assigned to QL1 with ropivacaine 0.375% versus control, concluded that there were significant differences in morphine consumption, time-to-first-request for postoperative opioid, and the median of the pain numeric rating scale within 48 hours postoperatively.³⁹ In a comparison of the effects of TAP and QL blocks in cesarean delivery, patients receiving posterior approach QL (QL2) used less morphine than patients receiving TAP at 12, 24, and 48 hours, but there was no significant difference at 4 or 6 hours. The QL group also had fewer morphine demands at 6, 12, 24, and 48 hours. There was no significant difference in visual analog scales between the groups at rest or movement.⁴⁰

In contrast to TAP, the QL territory is in closer proximity to the vertebral column; therefore, QL blocks can be associated with paravertebral spread, although unreliably so. This paravertebral spread can enhance visceral analgesia but can also confer greater hemodynamic changes. Uptake in the systemic circulation through highly vascularized muscle bed of the QL block can be concerning for local systemic anesthetic toxicity.³⁷

Current evidence and future research directions

Randomized control trials to date^38,40 in cesarean deliveries under spinal anesthesia have reported QL to be superior to spinal anesthesia alone, and to TAP block with spinal anesthesia. Blanco et al⁴⁰ compared QL and TAP blocks after cesarean delivery, with both receiving 0.125% bupivacaine 0.2 mL/kg in each side for a total of 0.4 mL/kg. Patients receiving QL block had lower morphine doses than TAP (p<0.005) at 12, 24, and 48 hours. Calculated total pain relief at rest and with movement were similar in both groups. It is worth noting that studies to date have been limited by the absence of spinal anesthesia containing ITM and standardized postpartum multimodal analgesia. Due to this limitation, no conclusions can be made about the superiority of QL to current clinical practice standards. High-quality research is needed to assess the utility of QL as a routine part of a multimodal analgesic regimen that includes neuraxial anesthesia with morphine, and to assess the ideal approach to QL block (QL1, QL2, QLT, or QLI) for cesarean delivery analgesia.

ILIOINGUINAL-ILIOHYPOGASTRIC BLOCK

Dermatomes covered/anatomy

The II and IH nerves arise from L1 nerve root and pierce the transversus abdominis muscles superior and medial to the anterior superior iliac spine (ASIS).⁴¹ The IH nerve provides sensory innervation to the skin over the inguinal region. The II nerve enters the inguinal canal and provides sensory innervation to the skin of the scrotum or labia majora and medial thigh.⁴¹ The ventral branch pierces the internal oblique muscle providing innervation to the internal and external oblique muscles, then pierces the external oblique muscles and provides sensory innervation of the suprapubic region.⁴¹ Although the classic teaching states the II and IH nerves arise from L1, cadaver studies suggest the II nerve originates from L1 in 65% of specimens but can arise from nerves extending from T12 to L3; the IH nerve can originate from T11 to L1.⁴²

Approach

The landmark technique for II-IH nerve block is based on the above anatomy. The needle is inserted 1–2 cm medial and 1–2 cm superior to the ASIS.⁴¹ A “pop” is felt as the needle enters the space between the internal oblique and transversus; alternatively, a first “pop” is felt with a piercing of the external oblique and a second “pop” is felt with piercing of the internal oblique.⁴¹ Local anesthetic is deposited between the internal oblique and transversus abdominis muscles. Bell et al developed a multi-injection technique to facilitate better spread of the local anesthetic.⁴³ Ultrasound imaging can also be used to perform an II-IH nerve block, in which the transducer is positioned on the line between the ASIS and the umbilicus; local anesthetic is deposited between the transversus abdominis and internal oblique muscle planes.

Advantages and disadvantages

Complications associated with II-IH block include lateral femoral cutaneous or femoral nerve blockade from medication tracking below the inguinal ligament, and rarely, bowel perforation. Disadvantages of the multi-injection “double pop” technique include technical difficulty and uncertainty associated with this landmark or blind technique.

Current evidence and future research directions

The II nerve block covers the L1 dermatome and has been studied as a target for analgesia after cesarean deliveries. Bunting published one of the first studies in 1988 describing bilateral II nerve blocks in 26 patients who had general anesthesia for cesarean deliveries.⁴⁴ The study showed pain scores were lower through the first 24 hours in the patients who received II nerve block. In addition, they showed the opioid requirements were significantly less in the intervention group at 24 hours.⁴⁴ In contrast, a subsequent study⁴⁵ comparing II-IH blocks done prior to incision and after incision for cesarean delivery, showed that patients who received II-IH had no difference in morphine consumption in the first 24 hours compared with those who did not receive a nerve block. However, the study was limited by an almost 50% failure rate of blocks placed prior to surgery, compared with no failed blocks in those placed after surgery. Bunting used a single injection technique for the II nerve blocks while Bell described the “multilevel II-IH (II-IH) block” methodology.⁴³ In Bell et al’s study, patients underwent neuraxial anesthesia (without ITM), followed by postoperative II-IH blocks with a reported 95% in block success rate. They also reported a significant reduction in intravenous patient controlled analgesia (PCA) morphine use in 24 hours in the II-IH intervention group, however they found no difference pain scores or in side effects including itching and nausea.⁴³ Sakalli et al utilized Bell’s technique in cesarean delivery under general anesthesia and similarly demonstrated reduced tramadol consumption in the II-IH group and reduced pain scores at rest for 24 hours and with movement in the first 8 hours.⁴⁶ In both Sakalli and Bell’s studies, there was no difference in nausea, vomiting, pruritus, and sedation between study groups.

Other investigators have compared TAP versus II-IH⁴⁷ blocks as well as combined II-TAP (I-TAP) blocks.⁴⁸ In one study, TAP showed reduced tramadol consumption compared with II-IH blocks after cesarean delivery with spinal anesthesia that did not include ITM.⁴⁷ Patients with failed blocks were excluded from this study, making the conclusions more robust. The I-TAP block combines the compartment block of TAP with the specific nerves of the II-IH block, thereby providing more reliable coverage of the L1 dermatome that is often lost by TAP alone (TAP block is estimated to fail in provision of L1 sensory block in >50% of patients).⁴⁸ In a prospective, triple-blind, placebo-controlled randomized trial, the combined I-TAP demonstrated reduced opioid use compared with placebo at all time points. It also reduced pain scores at rest and with movement in the first 24 hours postoperatively.⁴⁸ There was no difference in sedation, nausea, vomiting, or pruritus between the groups; however, there was one report of a femoral nerve palsy after II-IH nerve blockade.⁴⁸ While more evidence is needed before IH-II blocks can be recommended as a reliable technique for cesarean delivery analgesia, the availability of other peripheral blocks with a greater degree of dermatomal spread (and potential visceral effect) suggests that research time and effort are better spent in other areas.

CONTINUOUS WOUND INFILTRATION

CWI is an analgesic technique that uses a catheter, typically multiorifice, placed at the surgical site and connected to an elastomeric infusion pump that delivers a constant, fixed-rate infusion of medications to surrounding nerves.⁴⁹ CWI does not provide analgesia in a dermatomal distribution but rather provides cutaneous analgesia to nerves surrounding the catheter. The surgeon typically places the catheter proximal to the nerves innervating the surgical site, prior to surgical closure, and tunnels the catheter subcutaneously to prevent catheter migration and infection. For cesarean delivery, catheter placement is either between rectus fascia and subcutaneous tissue, or deep to the fascia.⁵⁰ Local anesthetics are most commonly infused, but anti-inflammatory agents such as diclofenac have also been described.⁵¹

Advantages and disadvantages

Single-shot wound infiltration may provide adequate analgesia, but effectiveness is limited by the pharmacokinetic properties of the selected drug, making prolonged analgesia less reliable. CWI allows continuous administration of local anesthetic with or without non-steroidal anti-inflammatory drugs throughout the postpartum period for up to 4 days.⁵² As with any indwelling catheter, risks for infection and catheter migration can occur. One major disadvantage of CWI is the unknown plasma concentration of local anesthetic during continuous infusion, which could theoretically lead to local anesthetic systemic toxicity, although this complication is unlikely given the low concentration and infusion rates often associated with CWI. Another disadvantage is that the placement of the catheter by the surgeon may not be reliably near affected nerve beds, causing variability in analgesia. Finally, the infusion rates and volumes to achieve analgesia often cause leaks around the wound site, which may lead to patient and provider dissatisfaction.

Current evidence and research directions needed

CWI with spinal anesthesia for cesarean delivery has been associated with reduced opioid consumption.⁵¹ In a prospective, double blind, randomized control trial, ITM (100 mcg) with saline subfascial CWI and intrathecal saline (control) with ropivacaine CWI both resulted in increased duration of postoperative analgesia by an average of 100 min compared with control (both saline ITM and CWI), but there was no statistically significant difference between ITM and CWI for pain and opioid consumption outcomes.⁵³ In a randomized control trial of 58 women undergoing elective cesarean delivery, CWI was associated with lower pain scores during rest at 2, 6, and 48 hours post partum compared with epidural morphine, and CWI patients had lower incidence of nausea, vomiting, pruritus, and urinary retention.⁵⁴ Lavand’homme et al showed that CWI using diclofenac was as effective as CWI with 0.2% ropivacaine with systemic diclofenac for reduced postcesarean pain and reduced systemic morphine requirements.⁵¹ In a different study, CWI deep to the fascia was compared with CWI superficial to the fascia, with the former group reporting significantly reduced pain at rest and lower total postoperative morphine consumption.⁵⁵

In contrast to these studies that demonstrate benefit of CWI, a randomized control trial compared ITM combined with saline CWI infusion to 48 hours CWI with either ropivacaine or saline (no ITM). The study found that ITM reduced opioid consumption by 46% in the first 24 hours postoperatively compared with ropivacaine CWI, and that ropivacaine CWI did not reduce pain or opioid requirements compared with saline CWI.⁵⁶ These findings suggest that there remains additional analgesic benefit to ITM by addressing visceral pain as well as incisional pain, whereas CWI is effective in addressing incisional pain alone.

Specific questions about the use of CWI as a means of cesarean delivery analgesia remain. Although CWI for other open abdominal surgeries has been found to be cost beneficial compared with intravenous or epidural anlagesia,⁵⁷ studies on cost-effectiveness of CWI compared with other modalities for cesarean delivery analgesia such as ITM, TAP, or QL are lacking. Additional research is also needed to answer specific questions in the obstetric population, including infection risks associated with CWI catheters in high risk patient populations (eg, obesity, emergent cesarean deliveries), local anesthetic plasma concentrations after cesarean delivery, best concentration and rate of wound infusion, and ideal adjuncts to local anesthetic infusions.

ERECTOR SPINAE PLANE BLOCK

This relatively new truncal block involves deposition of local anesthetic in the plane anterior to the erector spinae muscles and superficial to the transverse processes of thoracic or lumbar vertebrae, resulting in considerable spread in both cephalo-caudad and medial-lateral directions. Although spread to the dorsal rami of nearby segmental nerves is assured, involvement of ventral rami is more variable.⁵⁸ Application of this block for analgesia after cesarean delivery has been limited. Only two case reports have been published to date suggesting favorable results, with one describing potential risk for motor block.^{59 60}

LOCAL ANESTHETIC SYSTEMIC TOXICITY

Local anesthetic systemic toxicity remains an ever-present risk with truncal regional anesthesia blocks, even in the era of ultrasound guidance. For obstetric patients, this complication is particularly important given known physiological changes of pregnancy that lead to increased risk for local anesthetic toxicity, specifically decreased protein binding, increased tissue blood flow and vascular engorgement.^61,62

Although injections of local anesthetics directed into intermuscular planes or other spaces (such as those discussed in this article) are not over-represented among causes of local anesthetic systemic toxicity, episodes of toxicity have been reported.³⁵ The relatively large volumes often required for fascial plane blocks, coupled by instillation into vascular tissue beds, may increase risk. In a review of cases of local anesthetic systemic toxicity from 2014 to 2016, 47 cases were reported, ten of which required cardiac life support, and nine of which received lipid emulsion therapy, with two deaths noted.⁶³ Among these cases of toxicity, 17% were associated with tissue infiltration. Only a few of the reported cases were related to TAP blocks, and none related to QL blocks; however, these truncal blocks likely made up a small fraction of the total denominator of blocks in the reviewed time period.

Truncal regional blocks all carry risk for local anesthetic systemic toxicity, although the relative likelihood of this complication compared between these abdominal wall blocks is not known. Murouchi et al assessed plasma concentrations of ropivacaine after both TAP and QL blocks performed for laparoscopic ovarian surgery and found that systemic absorption was nearly twice as high for the TAP injections.⁶⁴ However, the TAP and QL groups received different concentrations (ropivacaine 0.5% for TAP vs 0.375% for QL) which may explain these findings. In cesarean deliveries, TAP has been associated with peak plasma levels higher than recommended levels for toxicity, resulting in several occurrences of seizures or neurological symptoms consistent with neurotoxicity up to 40–90 min after the proce-dure.30 31 34 35

Given these findings, coupled with the risk for local anesthetic toxicity in this patient population, it may be prudent to monitor patients after any truncal regional anesthesia block (at our institution, we monitor these patients in a postanesthesia care unit bed with blood pressure, pulse oximetry, ECG, and 1:1 nursing). A period of monitoring for 40–90 min after performance of these blocks may be wise.

LIPOSOMAL BUPIVACAINE

Interest in liposomal bupivacaine for cesarean delivery peripheral nerve blocks has grown. Liposomal bupivacaine is a prolonged-release (up to 72 hours) formulation of bupivacaine approved by the US Federal Drug Administration for postoperative analgesia by single-dose infiltration.⁶⁵ Because of the advantages of prolonged analgesia without a catheter requirement, questions have been raised on its role in cesarean delivery analgesia.

The sparse available data on liposomal bupivacaine in this population have been methodologically limited and conflicting in results. Two retrospective studies, one on intra-incisional liposomal bupivacaine and one on liposomal bupivacaine TAP blocks, showed reduced postoperative opioid requirements and postcesarean pain scores.^65,66 In contrast, a randomized control trial by Prahbu et al⁶⁷ compared liposomal bupivacaine and placebo by fascial and skin infiltration, prior to fascial closure. The findings showed no differences in pain and opioid consumption between the groups in the first 48 hours postoperatively. The pain scores in both groups were much lower than institutional norms (pain scores of around 2, whereas institutional pain scores are typically around 5), suggesting a potential observer bias.

In summary, published evidence on liposomal bupivacaine has been limited by biases including retrospective methodology and observer (“Hawthorne”) effects. Based on the available evidence, no definitive recommendations can be currently made about routine use of liposomal bupivacaine in cesarean delivery peripheral nerve blocks. Future trials on this topic should consider: (1) the inclusion of a third non-intervention arm to reduce observer bias or placebo effects; (2) non-inferiority study designs; (3) a focus on subgroups known to be susceptible to more pain, such as those women who could not receive neuraxial morphine.

ETHICS AND INFORMED CONSENT

Components of informed consent include: (1) ability (capacity) to make the decision; (2) disclosure of information on benefits and risks of the proposed treatment, test, or procedure, including the relative likelihood that benefits and risks will occur; (3) patient comprehension of the relevant information; (4) voluntary consent without coercion or duress.^68,69 The foundation of informed consent discussions is physician or provider beneficence, and patient autonomy.^69,70

In the context of peripheral nerve blocks for cesarean delivery analgesia, the contentious question about informed consent centers primarily around obtaining it in emergent cesarean deliveries performed under general anesthesia without neuraxial morphine. In such a setting, the advantages of performing these blocks immediately postoperatively without obtaining consent include improved postpartum pain control and reduced opioid requirements. However, the risks of the blocks would be adopted without having disclosed those risks to the patient or surrogate. The disadvantages of waiting to perform the blocks until specific consent can be obtained is pain and suffering experienced by the patient, and a potential for impaired decision-making capacity. Impaired capacity can result from postoperative duress from pain, and/or polypharmacy during and after general anesthesia leading to potentially impaired judgement.

In some emergent cesarean deliveries, emergency consent is invoked; that is, the situation does not require obtaining informed consent, because immediate treatment is required to preserve “life or limb” and to prevent serious health impairment. In determining the appropriate approach to informed consent, specifically for peripheral nerve blocks in these situations, the focus is on the emergent nature of the clinical situation (personal conversation, Chaton Turner, Esq, December 11, 2018). In an emergency, obtaining informed consent is arguably not required for any aspect of treatment provided in the context of that emergency, by virtue of emergency consent. However, to the extent that the peripheral nerve block is not necessary for the safe conclusion of the procedure, then the question is whether the provision of the regional blocks was consistent with standard of care. In emergent situations, decision-makers can rely on the care provider who is offering them options that are within practice standards. These considerations are, fundamentally, a healthcare industry question of what a professional practice “standard” is, as opposed to an element for decision-makers to weigh.

Often, practice standards are gleaned from professional society consensus statements or guidelines. The American Society of Anesthesiologists (ASA) has provided some decision aids for neuraxial and regional anesthesia,⁷¹ but these do not explicitly state recommendations for performance of regional anesthesia in the setting of emergent cesarean deliveries. The ASA Guidelines for the Ethical Practice of Anesthesiology⁷² encourages the provision of, “the process of informed decision-making, especially regarding the choice of anesthetic technique,” but makes no specifications for considerations in the context of emergencies. The 2016 ASA and Society for Obstetric Anesthesia and Perinatology Practice Guidelines for Obstetric Anesthesia make no statements on informed consent, emergencies, or supplemental peripheral nerve blocks for postcesarean analgesia.⁷³ With respect to cesarean delivery analgesia in emergencies, patients and the medical community may benefit from a professional consensus on the appropriateness of providing abdominal wall blocks in these situations.

In summary, the requirement for obtaining informed consent from the patient to provide postcesarean analgesia by peripheral nerve block in emergency cesarean deliveries, is a caseby-case determination. The determination about whether to obtain informed consent from a surrogate (vs waiting to obtain informed consent directly from the patient) to provide supplemental peripheral nerve blocks in a case of emergency general anesthesia, is dependent on the anesthesia provider’s consideration of the block as a standard or reasonable modality to offer in that context. Currently, no professional guidelines exist about how to handle this specific situation.

CONCLUSIONS

Current available evidence supports that peripheral nerve blocks for cesarean delivery offers the greatest benefit in cases where standard multimodal analgesia with neuraxial morphine or non-opioid analgesics have failed, or where neuraxial morphine can not be given (eg, cesarean delivery under general anesthesia). Low-concentration, high-volume approaches to abdominal wall blocks may reduce the risk for local anesthetic toxicity without sacrificing analgesia and monitoring for 40–90 min after truncal wall blocks is advisable. Research is needed to identify the roles of paravertebral nerve blocks and erector spinae blocks for cesarean delivery analgesia. Considerations on informed consent to provide peripheral nerve blocks for analgesia in emergent cesarean deliveries are best made on individual basis.