Ultrasound Verification of Laparoscopic-Assisted Transversus Abdominis Plane Blocks in Children Undergoing Laparoscopic Procedures

Introduction

Transversus abdominis plane (TAP) blocks are commonly administered preoperatively to minimize postoperative pain in both adult and pediatric patients undergoing abdominal surgery. ¹ TAP blocks were first described by Rafi in 2001, wherein local anesthetic was injected into the fascial plane between the transversus abdominis (TA) and internal oblique (IO) muscle through the lumbar triangle of Petit guided only by surface anatomy. ² More recently, ultrasound-guided TAP blocks have become the goldstandard by which TAP blocks are administered, combining tactile feedback with visual direction from the ultrasound. Studies of ultrasound-guided TAP blocks in children have shown lower pain scores and postoperative analgesia requirements.^3,4

TAP blocks placed with laparoscopic assistance (L-TAP) were first described in 2011 as a safer and less time consuming, although semiblinded technique. ⁵ After the creation of pneumoperitoneum and under laparoscopic visualization, a needle is introduced externally through the abdominal sidewall. Similar to the previously described blind “2-pop” technique, laparoscopy enables direct vision and avoidance of peritoneal penetration. Once the injection of the local anesthetic is commenced, a bulge can be seen as the TA muscle and overlying peritoneum are deflected internally. This is known as the “Doyle's internal bulge sign.”

The original description of the procedure, however, did not confirm the appearance of Doyle's sign correlated with actual delivery of local anesthetic into the correct transversus abdominus plane. Subsequent studies, primarily in adult patients, evaluating the efficacy of laparoscopically placed TAP blocks rely on the technique introduced by Doyle, and assume proper delivery into the transversus abdominal plane, without confirmation otherwise (i.e., ultrasound). ⁶

Laparoscopically placed TAP blocks have continued to gain popularity among adult surgeons, despite the lack of evidence to-date, verifying a bulge visualized on laparoscopy results in the administration of anesthetic into the correct tissue plane. ⁵ Few studies to date have evaluated the delivery or efficacy of L-TAP blocks in children undergoing laparoscopic procedures.^5,7 As a preliminary step preceding any study to evaluate the efficacy of L-TAP blocks among children, we felt it necessary to verify the accuracy of surgeon placed L-TAP blocks. The purpose of our study was to verify whether local anesthetic administered through L-TAP blocks in children undergoing laparoscopic procedures were routinely delivered into the correct neurofascial plane.

Materials and Methods

L-TAP block procedure

Surgeons who participated in the study were given a short introduction to the study and the technique using visual aids. Surgeons needed to complete 5 L-TAPs under study staff supervision before they were allowed to participate in the study, to allow them to become comfortable with the technique.

The block procedure was performed as described by Doyle and colleagues ⁵ : after establishing pneumoperitoneum and entering the abdomen laparoscopically, surgeons identified the lateral-most point on either side of the abdomen to perform bilateral L-TAP blocks without risking injury to underlying bowel or viscera. This lateral point, between the mid- and anterior-axillary lines, was marked with a surgical marking pen. The level selected corresponded to the location of trocars and largest incision, which was usually at the level of the umbilicus. A sterile ultrasound probe was placed over the site marking before the L-TAP block and a preblock ultrasound image was acquired by the research team. Then after removing the ultrasound probe from the surgical field, the block was performed.

Around 0.25% bupivacaine was used according to weight-based dosing (1 mL/kg up to a maximum dose of 30 mL), divided between the two sides. Blocks were placed using visual feedback from laparoscopy, watching for the downward deflection of the TA and peritoneum (Fig. 1). ⁵ Immediately following placement of the block, a postblock ultrasound image was acquired over the site of the injection. Surgeons were blinded entirely from the ultrasound images during the procedure to avoid bias.

OPEN IN VIEWER

FIG. 1.

Ultrasound and laparoscopic views of the abdomen (1) preinsufflation, with EO, IO, and TA muscles. (2A, 2B) Postinsufflation and before block administration; shadowing/reflecting pattern below the peritoneum caused by pneumoperitoneum. (3A, 3B) Postblock images that show Doyle's internal bulge sign of the TA and peritoneum; asterisk (*) indicates spread of local anesthesia between TA and IO. White arrow (⇒) indicates peritoneum. EO, external oblique; IO, internal oblique; TA, transversus abdominis. Color images are available online.

Results

Fifty-one patients were enrolled over the course of this study, all of whom, but one underwent bilateral L-TAP blocks for a total of 101 blocks completed. Eight blocks done by surgical residents were excluded from the study, as the residents had not done five prior L-TAPs under study staff supervision. A total of 93 blocks were included for analysis. The mean age of patients enrolled was 5.9 ± 5.7 years. The mean weight was 25.4 kg (range 2.64–118.8 kg), with an average BMI of 18.2 ± 6.4 kg/m². A summary of the patient demographics and procedures performed can be found in Table 1. The most common procedure performed was a laparoscopic inguinal hernia repair (n = 19, 5 of those being bilateral).

Nine surgeons participated in the study, including seven pediatric surgery attendings and two pediatric surgery fellows. Each surgeon performed an average of 10.3 ± 14.4 L-TAP blocks (range 1–38 blocks). There were no reported complications from the L-TAP blocks within the 4-month follow-up period.

Intraoperative ultrasound images and laparoscopic images are presented in Figure 1. The reviewers had a 77.4% correlation when reviewing the ultrasound images; Cohen's Kappa = 0.539, indicating moderate agreement or inter-rater reliability. ⁸ Blocks that were partially in the correct plane were counted as a successful block. The distribution of nine blocks (9.7%) was found by the reviewers to be indeterminate.

The overall accuracy was found to be 57.5%, with 53.5 of the 93 blocks confirmed on ultrasound to be within the correct plane. Attending surgeons were able to place the L-TAP block in the correct plane in 58.0% ± 3.8% of cases. The most common distribution in a “missed” L-TAP block was within the IO muscle (n = 21). There were only 4.5 blocks that were graded as being too deep (within the TA muscle or preperitoneal space). The distribution of L-TAP blocks is summarized in Table 2.

Discussion

TAP blocks are widely used in both pediatric and adult abdominal surgeries as part of multimodal analgesic regimens. This is the first published study that has objectively verified the distribution of local anesthetic after a surgically placed TAP block in children. In our series of 93 L-TAP blocks, ∼58% of blocks were placed in the desired plane. Ultrasound verification of distribution was achieved with minimal interruption to the procedure, and blinded reviewers were able to reliably grade preblock and postblock ultrasound images.

Surgeons who participated in this study had no formal training in regional anesthesia techniques and learned to perform blocks based on their understanding of TAP anatomy and observation of surgical colleagues' techniques. The overall accuracy of the L-TAP blocks placed by attending pediatric surgeons was 58%. More longitudinal testing is needed to determine if accuracy improves with regular practice and feedback. The vast majority of incorrectly placed L-TAP blocks was injected too superficially, either within the IO muscle belly or between the oblique muscles. While this may not be ideal for postoperative pain reduction, it shows a trend that can be corrected through feedback and education.

Furthermore, a single preblock and postblock ultrasound image may be underestimating our accuracy with L-TAP blocks; a single view may miss part of the injection that is within the correct plane, but dissipated out of the view of the ultrasound probe. The probe was only placed on the premarked site and did not scan additional areas of the abdomen for block distribution. The probe was only applied after administration of the block, not concurrently during the block, so as not to interfere with the laparoscopic visualization of the block. Future L-TAP training can be done with live ultrasound as a visual aid to ensure more accurate placement of the anesthetic.

Overall, the benefit of TAP blocks has been studied extensively in adults, with strong evidence that TAP blocks reduce postoperative opioid requirements and improve pain scores.^9–12 Pediatric studies on the topic are limited, although the evidence supports similar benefits in children for both open and laparoscopic procedures. Carney et al. demonstrated a 50% reduction in postoperative morphine administration with landmark-based TAP blocks compared to placebo in children undergoing open appendectomy. ¹³ Using ultrasound-guided TAP blocks in children three to seven years of age, Al-Sadek et al. found patients had at least a 25% decrease in pain scores and 33% decrease in postoperative analgesia requirements compared to randomized controls. ³

Another randomized study evaluating children undergoing laparoscopic appendectomies found that patients receiving ultrasound-guided TAP blocks had better self-reported pain scores with equivalent morphine requirements when compared to patients who received local infiltration of local anesthesia. ⁴ Sahin et al. randomized children undergoing inguinal hernia repair to receive either ultrasound-guided TAP blocks or local wound infiltration; the time to first analgesic was significantly longer in the group who received TAP blocks. ¹⁴ Furthermore, Suresh et al. found that there is a dose-dependent relationship between the TAP block anesthetic and duration of analgesia in pediatric patients. ¹⁵

Although L-TAP blocks have gained popularity among adult surgeons, few studies have compared the efficacy of L-TAP blocks with conventional ultrasound-guided blocks. Fields et al. randomized adults undergoing laparoscopic ventral hernia repairs to receive L-TAP versus placebo injections; patients who received L-TAP used less opioids than controls at 6 hours postoperatively. ⁶ A recently published randomized controlled trial of adults undergoing laparoscopic cholecystectomy found equivalent efficacy in terms of opioid consumption and pain relief, but shorter block time in the L-TAP group versus ultrasound guided. ¹⁶ This study, similar to previous studies, assumes the L-TAP block is delivered into the correct plain and lacks an objective method for verifying the distribution of the local anesthetic.

Prospective studies involving laparoscopic TAP blocks in children are limited. Our group recently reported the results of a randomized-controlled trial comparing laparoscopic TAP blocks and ultrasound-guided TAP blocks. That study found that laparoscopically placed TAP blocks had equivalent efficacy in postoperative pain scores and narcotic usage. ¹⁷ As with prior studies, that study utilized Doyle's sign to place TAP blocks laparoscopically. The results of this study suggest that that Doyle's sign may not always result in radiographically correct placement. As researchers continue to assess the reliability of Doyle's sign in laparoscopic TAP blocks, this study raises the question of the necessity of perfect placement of anesthetic in the TAP plane for pain relief. One possible benefit of L-TAP blocks is the more rapid diffusion of local anesthetic within the neurofascial plane due to the increased intra-abdominal pressure exerted by insufflation for laparoscopy, which is not present with traditional TAP blocks.

In this study, we demonstrated that ultrasound can be used reliably to determine the distribution of an L-TAP block in children; however, it is unclear if the ultrasound accuracy correlates with postoperative pain relief. Further studies are needed to compare ultrasound images with pain scores or postoperative analgesic use in pediatric patients who receive L-TAP blocks. It is also critical to consider whether pneumoperitoneum established before performing an L-TAP block may act as an additional safeguard from injury for the underlying bowel or viscera in younger children with thinner abdominal walls.

The study does have limitations. As mentioned previously, the ultrasound probe was placed only in one location after block administration. This could miss properly placed blocks that had already begun to dissipate within the TAP plane. Concurrent US image capture may help better determine whether blocks were initially delivered into the correct TAP plane. This was not performed for this due to technical confounding issues. The placement of the probe to capture a sufficient image created an indentation resembling a Doyle's sign, thereby interfering with the surgeon's ability to properly visualize the actual Doyle's sign. In addition, the ultrasound could not capture dynamic video, only static images for interpretation by the anesthesiologist.

Other limitations include the surgeon training. Our study team considered training surgeons first with real-time ultrasound feedback to correlate proper block placement by ultrasound with Doyle's sign visualization before study initiation. However, we felt this would not simulate real-world clinical practice in the community. Future studies can address whether this additional training would improve accuracy and analgesic efficacy.

Conclusion

This is the first study to utilize intraoperative ultrasound as a way to objectively verify the distribution of local anesthetic after an L-TAP block in children. Our initial experience suggests that surgeons have nearly 60% accuracy with L-TAP blocks, with minimal training. Further studies will be needed to compare clinical outcomes in those receiving L-TAP blocks and those receiving ultrasound-guided TAP blocks.