Advances in Regional Obstetric Anesthesia

Abstract

Advances in obstetric regional anesthesia, particularly ultrasound-guided techniques, have significantly improved pain relief and safety during childbirth. This chapter explores the latest developments in ultrasound-assisted central neuraxial anesthesia and fascial blocks for post-cesarean analgesia. The use of ultrasound guidance in neuraxial procedures has been extensively studied, demonstrating improved success rates, reduced complications, and increased patient satisfaction. It enhances the accuracy of identifying lumbar intervertebral spaces and facilitates needle insertion, resulting in higher first-pass success rates. Additionally, ultrasound-guided fascial blocks, such as the transversus abdominis plane (TAP) block and Quadratus Lomborum Block (QLB), provide effective analgesia after cesarean section when intrathecal morphine is not feasible. This chapter summarizes the step-by-step technique for ultrasound-guided neuraxial block and fascial blocks, emphasizing the importance of incorporating ultrasound guidance into obstetric anesthesia practice based on the growing body of evidence supporting its benefits.

1. Introduction

Obstetric regional anesthesia has advanced significantly, providing effective pain relief and ensuring the safety of parturients during childbirth. Techniques such as spinal anesthesia and epidural analgesia have revolutionized childbirth care, offering comfort and safety for both mother and baby. With millions of women undergoing childbirth each year, high-quality anesthesia care is crucial for promoting safe deliveries. Technological widespread, including advanced ultrasound techniques, have enhanced precision, safety, and efficacy [1, 2, 3]. This chapter explores the latest advancements in ultrasound-assisted central neuraxial anesthesia and fascial blocks for post-cesarean analgesia.

2. Ultrasound-guided neuraxial block

The application of spinal ultrasound for lumbar puncture and neuraxial anesthesia can be attributed to early pioneers such as Bogin, Stulin, Porter, and Cork, who recognized the potential of this technology in locating relevant landmarks [4, 5, 6]. Building upon this foundation, subsequent advancements were made by Grau and colleagues, further refining the clinical application of spinal ultrasound and contributing to our current understanding of spinal sonoanatomy [7, 8, 9]. Despite notable technical improvements in epidural and spinal procedures, complications such as accidental dural puncture continue to pose concerns. Incorporating ultrasound technology into these procedures holds promise for enhancing safety, improving success rates, and minimizing complications.

In recent years, several systematic reviews and meta-analyses have contributed to the growing body of evidence supporting the use of neuraxial ultrasound. Such reviews demonstrated the superior accuracy of neuraxial ultrasound in identifying lumbar intervertebral spaces compared to landmark palpation alone [10]. Their findings also revealed a strong correlation between ultrasound-measured depth and needle insertion depth, highlighting the precision offered by ultrasound guidance.

Furthermore, it was conducted a review of 32 randomized controlled trials involving 3439 patients in general population. The findings demonstrated that pre-procedural ultrasound not only reduced the failure rate and the need for needle redirections but also increased the first-attempt success rate. Importantly, these improvements were achieved without prolonging the overall procedure time [11].

Similarly, two reviews focusing specifically on the obstetric population, also highlighted the benefits of ultrasound guidance. They found that ultrasound guidance significantly improved the first-pass success rate, with risk ratios of 1.46 (95% CI: 1.16–1.82) and 1.49 (95% CI: 1.21–1.84), respectively [12, 13].

When analyzing the prediction of preprocedural difficulty subgroups, both studies mentioned above also agreed that ultrasound assistance facilitated the first-pass success rate, with risk ratios of 1.56 (95% CI: 1.21–2.01) and 1.40 (95% CI: 1.12–1.75), respectively. Importantly, the use of ultrasound did not increase the total time taken to perform the procedure, with risk ratios of 50.12 (95% CI: −13.69–113.94) and −0.18 (95% CI: −0.86–0.49), respectively [12, 13].

All these studies consistently found a protective association between the use of ultrasound and complications related to the procedure, such as failure of anesthesia, vascular puncture, back pain, and headache. Moreover, one of these studies particularly investigated the differences between the experience of the sonographer and the operator of the procedure. The study found no significant difference between the two groups, especially after considering publication biases [12].

Despite previous descriptions, real-time ultrasound-assisted neuraxial block remains at the forefront of new research studies. Currently, it has been found to be challenging for a single operator to perform and time-consuming compared to the pre-scan technique [14, 15, 16, 17]. Furthermore, in anticipation of future advancements in standard care, color Doppler patterns was studied to visualize flow in the epidural space among patients with well-functioning epidural catheters. This pilot study proposes further investigations to identify Doppler patterns in non-functioning catheters to predict the efficacy of this method [18].

These findings collectively emphasize the increasing pool of evidence that supports the use of pre-procedural ultrasound in neuraxial procedures. Aligned with the 2008 recommendation by the National Institute for Health and Care Excellence (NICE) endorsing the use of ultrasound-guided catheterization of the epidural space, the authors of these studies have unequivocally recommended the incorporation of preprocedural ultrasound in neuraxial procedures [19].

2.1 Technique

The authors summarized the following step-by-step description based on published material from Karmakar, Chin and Carvalho [15, 20]. It should be noted that although being an experienced ultrasound operator does not significantly impact overall success rates, some knowledge of palpation techniques, sonoanatomy, and proficiency with other ultrasound-guided procedures prior to performing neuraxial blocks is expected, considering the delicacy and sensitivity of the region.

Step 1: Begin by communicating the procedure to the patient, ensuring that they understand and provide an opportunity for consent, if applicable. Prepare the ultrasound device by attaching a low frequency curvilinear transducer and adjusting the depth settings to 7 to 10 cm. Organize the necessary devices in a proper arrangement for optimal ergonomics. Perform a thorough equipment safety check, ensuring that all instruments and drugs are appropriately diluted and ready for use.

Step 2: Assisted by another healthcare professional, position the patient in a seated position for the neuraxial procedure, ensuring that the spine is flexed optimally. Put on sterile gloves and thoroughly prepare the skin using an appropriate antiseptic solution. Place a sterile drape over the area and cover the ultrasound transducer with a sterile cap. Apply a generous amount of gel to the transducer to enhance the coupling of ultrasound waves.

Step 3: Palpate the spinous processes to locate the desired area. Instruct the patient to remain as still as possible during the examination and neuraxial anesthesia procedure. We recommend repeating the ultrasound scan and skin markings if the patent moved for any reason.

Step 4: Start your scan 4 to 5 cm lateral to the midline with the transducer longitudinally and, by convention, left side of the screen is cephalad. This will obtain the parasagittal transverse process view where these structures will appear as the “trident sign” pattern. Move transducer medially, 1 to 2 cm lateral to midline to obtain parasagittal articular process view which are seen in a “camel hump” pattern (Figure 1).

Figure 1.

On the left: Probe positioning. On the right: Camel hump pattern.

(Once you have developed proficiency in the sonoanatomy of the region, you can initiate the scan from this point)

Step 5: Gradually move the transducer towards the midline while adjusting the angle of the ultrasound beam by 5 to 10 degrees medially. This will allow you to obtain the parasagittal oblique interlaminar view, as shown in the figure, which displays a distinct “sawtooth” pattern (Figure 2). This view provides visualization of the interlaminar spaces as soft gaps. Slide the transducer up and down to identify the optimal interlaminar space for the neuraxial procedure. Once you have identified the optimal view, use a marker to indicate the interlaminar spaces by marking the midpoint of the long edge of the transducer. At this point, use the ultrasound caliper to measure the distance between the skin and the posterior complex. Remember to release the pressure on the transducer when measuring.

Figure 2.

Sawtooth pattern.

Step 6: Rotate the transducer horizontally and medially by 90 degrees to obtain the transverse approach to the spinous process, allowing you to determine the midline. Slide the transducer up or down until you reach the desired interspace. Angling the ultrasound beam by 5 to 10 degrees cephalad will reveal the “bat sign,” as shown in the Figure 3. The “bat sign” is an important reference for spinal ultrasound as it depicts the major anatomical landmarks and targets for neuraxial anesthesia. These include the posterior complex (top of bat’s head), anterior complex (bottom of the bat), and the transverse processes (wings of the bat). Select the interspace that provides the clearest view of the “bat sign” to ensure optimal visualization of the posterior and anterior complexes. Align the midpoint of the transducer’s long edge with the patient’s midline and use a marker to trace a line that intersects with the horizontal line from the parasagittal view. The crossing of these two lines indicates the site for needle insertion.

Figure 3.

Bat sign.

Step 7: Use the caliper tool on the ultrasound device to measure the depth of needle insertion from the skin to the posterior complex. Take note of the angle of the ultrasound beam and visually memorize it so that you can replicate this angle during needle insertion.

Step 8: Proceed with the neuraxial procedure following standard practices, using the marked reference points to guide needle insertion and angle. Keep in mind that ultrasound measurements typically underestimate depth by up to 10 mm, with a median underestimation of 3 mm.

3. Ultrasound guided fascial blocks

Cesarean sections often result in moderate-to-severe pain, which can impede recovery, mother-child bonding, and breastfeeding. Multimodal analgesia is crucial for effective postoperative pain management and faster recovery [21]. Intraoperative interventions such as long-acting intrathecal opioids is well known to enhance analgesia after cesarean delivery. But, when such strategy is not feasible, more commonly when spinal anesthesia is contradicted, local analgesia infiltration and abdominal nerve blocks have been found to improve postoperative pain relief [22, 23]. Recommendations by the PROSPECT Working Group [22] and by Enhanced Recovery After Surgery (ERAS) 2019 guideline [23] have guided pain management for cesarean sections with efforts to reduce opioid use and implement enhanced recovery protocols in recent years.

Intrathecal morphine has consistently demonstrated its superiority over fascial blocks for postoperative pain management after cesarean section in various settings, as supported by multiple randomized trials and meta-analyses. High doses of intrathecal morphine have been shown to provide longer-lasting analgesia, albeit with a potential increase in side effects [24, 25, 26]. However, in cases where the use of intrathecal morphine is not feasible for cesarean delivery, two fascial blocks can be considered for multimodal analgesia and opioid sparing strategy. These include the Transversus Abdominal Plane Block and Quadratus Lumborum Block. These fascial blocks must be performed bilaterally to cover the cesarean incision and provide adequate analgesia.

There is a limited number of studies directly comparing these techniques with each other. In a 2021 systematic review, despite the low quality evidence, it was found that both TAP Block and QL Block were efficient in reducing pain scores when compared to control groups. Nevertheless, no significant difference was observed between the two techniques in terms of their analgesic efficacy [27]. Further high-quality studies are needed to provide more conclusive evidence on the comparative effectiveness of these fascial blocks for postoperative pain management after cesarean section.

This chapter section will approach each Fascial Block with its rationale and technique. The choice of the technique to use is up to the provider.

3.1 Ultrasound guided transversus abdominal plane block (TAP)

The transversus abdominis plane is a fascial plane located superficially to the transversus abdominis muscle, which is the innermost muscular layer of the anterolateral abdominal wall. The TAP block involves anesthesia of the upper and lower TAP plexuses, formed by the communication of intercostal, subcostal, and L1 segmental nerves.

Since 2021, a group of experts in Regional Anesthesia has worked towards standardizing the terminology for abdominal fascial blocks [28]. One important change is that what was previously known as the Posterior TAP block is now referred to as the Lateral Quadratus Lumborum Block. This standardization requires us to consider the benefits of this approach on the following section of this chapter [29].

As a result of this standardization, Ultrasound-assisted TAP block can be performed using three different approaches: subcostal, transverse abdominal plane, and midaxillary approaches [28]. While each approach has its own specific technique, they all share a common goal of distributing large volumes of local anesthetics within the transverse abdominal plane.

The subcostal approach is believed to provide analgesia for the T6-T9 nerves, while the transverse abdominal plane targets analgesia for the T10-T12 nerves. The midaxillary approach aims to provide analgesia for the lower abdomen, including the L1 nerve. Given our focus on post-cesarean delivery analgesia, we will only describe the midaxillary TAP Block approach.

3.1.1 Technique

Step 1: Begin by communicating the procedure to the patient, ensuring that they understand and provide an opportunity for consent, if applicable. Prepare the ultrasound device by attaching either a linear or curvilinear transducer and adjusting the depth settings accordingly. Organize the necessary devices in a proper arrangement for optimal ergonomics. Perform a thorough equipment safety check, ensuring that all instruments and drugs are appropriately diluted and ready for use.

TAP blocks are better achieved with high volumes of local anesthetics, with the minimum accepted volume being 15 ml for each side. Select the dosage to achieve the maximum safe dose for the patient’s size.

Step 2: TAP Block may be performed by only one provider with the patient on the supine position. Put on sterile gloves and thoroughly prepare the skin using an appropriate antiseptic solution. Place a sterile drape over the area and cover the ultrasound transducer with a sterile cap. Apply a generous amount of gel to the transducer to enhance the coupling of ultrasound waves.

Step 3: Place the transducer transversely on the mid-axillary line of the abdomen and scan the region up and down between the costal margin and the iliac crest. Typically, three muscle layers can be seen: the external and internal obliques, as well as the transverse abdominis muscles (Figure 4).

Figure 4.

On the left: Probe positioning. On the right: Sonoanatomy of the region.

Step 4: Insert the needle in-plane, adjacent to the midaxillary line, and advance it internally and posteriorly. As you advance the needle, you may feel two distinct pops as the needle point passes through the fascia. Once the tip is placed above the TAP, inject the previously selected dosage of local anesthetics, observing the real-time volume spread into the desired space.

Step 5: Repeat the process on the other side.

3.2 Ultrasound guided quadratus Lumborum block

The quadratus lumborum (QL) is a muscle of the posterior abdominal wall dorsolateral to the psoas major muscle. Originating from the iliac crest and iliolumbar ligament, the QL muscle assists in lateral flexion of the lumbar spine. The QL block has gained popularity in different abdominal surgeries as a tool for multimodal analgesia because of its theoretical efficiency over visceral pain [30].

In a 2020 meta-analysis, which reviewed 12 studies involving 904 patients undergoing cesarean delivery, quadratus lumborum block (QLB) was found to significantly reduce opioid (intravenous morphine) consumption during the first 24 hours by 14.1 mg (95% CI 20.8 to 7.5 mg) and 48 hours by 20.8 mg (95% CI 33.1 to 8.5 mg) compared to placebo or no block. Additionally, QLB demonstrated a significant reduction in 12-hour pain scores at rest and during movement [30].

Similarly, QLB reduced opioid consumption compared to controls and provided better pain control at 6 and 12 hours postoperatively. While no significant differences in pain scores were noted at 24 hours, QLB was effective in reducing dynamic pain at 6 hours and both static pain and opioid consumption at 6 and 12 hours [31].

The terminology for QL Blocks, similar to TAP Blocks, has been standardized by a group of experts in Regional Anesthesia [28]. This standardization has led to the recognition of three possible approaches for achieving adequate analgesia: Anterior Quadratus Lumborum Block, Lateral Quadratus Lumborum Block, and Posterior Quadratus Lumborum Block [32, 33]. However, clinical studies directly comparing these three methods are lacking, and only cadaveric studies have suggested variations in the spread of local anesthetics with each approach [33].

Given that the Posterior Quadratus Lumborum Block is the most extensively studied approach for providing analgesia after cesarean delivery [34, 35], we will now review its step-by-step technique.

3.2.1 Technique

Step 1: Begin by communicating the procedure to the patient, ensuring that they understand and provide an opportunity for consent, if applicable. Prepare the ultrasound device by attaching preferably low frequency curvilinear transducer and adjusting the depth settings accordingly. Organize the necessary devices in a proper arrangement for optimal ergonomics. Perform a thorough equipment safety check, ensuring that all instruments and drugs are appropriately diluted and ready for use.

Local anesthetic dosage in the range of 0.2 to 0.4 ml/kg of 0.2 to 0.5% ropivacaine or 0.1 to 0.25% bupivacaine per side is recommended. The operator will need to adjust dosage to ensure toxic thresholds are not exceeded, particularly when bilateral blocks are performed.

Step 2: QL Block may be performed by only one provider with the patient on lateral decubitus or supine with a lateral tilt. Put on sterile gloves and thoroughly prepare the skin using an appropriate antiseptic solution. Place a sterile drape over the area and cover the ultrasound transducer with a sterile cap. Apply a generous amount of gel to the transducer to enhance the coupling of ultrasound waves.

Step 3: Place the transducer transversely on the posterior axillary line of the abdomen at the L4 level. Visualize the “shamrock sign” where the transverse process serves as the stem, and the psoas, quadratus lumborum, and erector spinae muscles form the leaves. Utilize color Doppler to ensure safe needle trajectory, avoiding any large vessels along the way (Figure 5).

Figure 5.

On the left: Probe positioning. On the right sonoanatomy of the region.

Step 4: Insert the needle in-plane and advance it internally and posteriorly. Position the needle tip posterior to the QL muscle within the fascia adjacent to the erector spinae muscle. To confirm proper needle tip placement, inject 2 ml of saline before administering the total dose. Monitor the spread of local anesthetic as you inject slowly.

Step 5: Repeat the process on the other side.

4. Conclusion

Anesthesia care, over the past two decades, has integrated the use of ultrasound-guided procedures. The combination of professional expertise with the use of ultrasound guidance, can further elevate the level of care and ensure the well-being of their patients. As we look to the future, the continuous evolution of ultrasound technology and its increasing availability hold the promise of even greater advancements in safety, comfort, and positive outcomes for patients globally.