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Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers
Veterinary Anaesthesia and Analgesia xxxx, xxx, xxx
RESEARCH PAPER
Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers Mariko St Jamesa, Tatiana H Ferreiraa, Carrie A Schroedera, Karen L Hershberger-Brakerb & Kristopher M Schroederc a
Department of Surgical Sciences, School of Veterinary Medicine, University of WisconsineMadison, Madison, WI, USA
b
Department of Pathobiological Sciences, Department of Comparative Biosciences, School of Veterinary Medicine,
University of WisconsineMadison, Madison, WI, USA c
Department of Anesthesiology, School of Medicine and Public Health, University of WisconsineMadison, Madison,
WI, USA Correspondence: Tatiana H Ferreira, Department of Surgical Sciences, School of Veterinary Medicine, University of WisconsineMadison, 2015 Linden Drive, Madison, WI 53706, USA. E-mail: [email protected]
Abstract Objectives To describe the ultrasound-guided rectus sheath block technique and the anatomical spread of two volumes of methylene blue injection in dog cadavers.
analgesia for the ventral midline. This study supports the potential of the rectus sheath block for abdominal procedures, and further investigations on its clinical efficacy are warranted.
Study design Blinded, prospective, experimental cadaveric study.
Keywords abdominal wall, dog, nerve block, rectus sheath block, regional anesthesia, ultrasound.
Animals A total of eight dog cadavers weighing 8.9 ± 1.6 kg.
Introduction
Methods Ultrasound-guided rectus sheath injections were performed bilaterally 1 cm cranial to the umbilicus using 0.25 mL kge1 (low volume; LV) and 0.50 mL kge1 (high volume; HV) of 0.5% methylene blue dye. A total of 16 hemiabdomens were injected. The ultrasound image quality of the muscular and fascial plane landmarks and needle visualization were scored using a standardized scale. Cadavers were dissected to determine the distribution of the dye and to assess staining of ventral branches of the spinal nerves. Results Fewer ventral spinal nerve branches were stained in the LV group than in the HV group, at 2.00 ± 0 and 2.90 ± 0.83, respectively (p < 0.01). Ventral branches of thoracic (T) and lumbar (L) spinal nerves (T10, T11, T12, T13 and L1) were stained 25%, 100%, 75%, 25% and 0% of the time in LV group and 12.5%, 87.5%, 100.0%, 75.0% and 13.0% in HV group. A lesser extent of cranialecaudal dye distribution was observed in the LV group than in the HV group (7.1 ± 1.8 cm and 9.2 ± 1.8 cm, respectively; p ¼ 0.03). There was no significant difference in medialelateral spread of dye, number of test doses or ultrasound image quality scores between groups. Conclusions and clinical relevance The results of this study suggest that, on an anatomical basis, this easily performed block has the potential to provide effective abdominal wall
Increasing popularity of perioperative abdominal wall and fascial plane nerve blocks in both human and veterinary medicine has led to the development of various techniques targeting the spinal nerves innervating this region. For abdominal surgeries, a commonly utilized technique is the transversus abdominis plane (TAP) block, which was first described in veterinary medicine by Schroeder et al. (2011) as an ultrasound (US)-guided injection to block the innervation of the canine abdominal wall, originating from thoracic (T) 11e13 and lumbar (L) 1e3 vertebrae (Casta~ neda-Herrera et al. 2017; Hermanson et al. 2019a). These ventral spinal nerve branches traverse through the TAP before entering the rectus abdominis muscle, branching to innervate musculature, cutaneous tissue and peritoneum (Casta~ neda-Herrera et al. 2017; Evans & de Lahunta 2017; Hermanson et al. 2019a). Targeting these nerves provides somatic analgesia and reportedly decreases intra- and postoperative opioid use and improves pain scores (Gurnaney et al. 2011; Dingeman et al. 2013; Bashandy & Elkholy 2014; Flack et al. 2014; Hamill et al. 2016; Skouropoulou et al. 2018). Although the TAP block was initially described as bilateral injections performed at the umbilicus (Schroeder et al. 2011), more recently it has been suggested that a single injection into each hemiabdomen will not adequately block the abdominal 1
Please cite this article as: St James M, Ferreira TH, Schroeder CA et al. Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers, Veterinary Anaesthesia and Analgesia, https://doi.org/10.1016/j.vaa.2019.09.001
Rectus sheath block in dogs M St James et al.
wall in dogs (Bruggink et al. 2012; Portela et al. 2014; Drozdzynska et al. 2017; Johnson et al. 2018). Efficacy of the TAP block depends on the distribution of injectate in this plane; therefore, multiple injections and high volumes of local anesthetic may be required (Bruggink et al. 2012; Drozdzynska et al. 2017). Consequently, risks of systemic local anesthetic toxicity or damage to abdominal viscera or vasculature may be increased (Ferguson et al. 1996; Sviggum et al. 2012; Chin et al. 2017). Recent research in human volunteers has demonstrated that traditional TAP techniques frequently fail to provide midline cutaneous analgesia (Carney et al. 2011; Støving et al. 2016). Cutaneous sensory mapping following bilateral TAP blocks (Carney et al. 2011) and unilateral TAP blocks compared with TAP injections with saline (Støving et al. 2016) illustrated the inconsistent results of this block and lack of dermatomal distribution of the local anesthetic. An alternative technique for abdominal somatic anesthesia is the rectus sheath block (RSB). The technique was first described in the 19th century by Schleich (1899) but has recently regained popularity in human medicine as an alternative to the TAP block (Sviggum et al. 2012; Hamill et al. 2016; Yasumura et al. 2016; Chin et al. 2017). Both TAP and RSB target branches of the ventral spinal nerves. Whereas the TAP block anesthetizes the ventral spinal nerve branches more laterally, RSB targets these nerves as they enter the internal (‘posterior’) rectus sheath (RS) prior to penetrating the rectus abdominis muscle. This internal sheath is formed by the transversalis fascia and aponeuroses of the transversus abdominis (TAM) and internal oblique muscles (Bashandy & Elkholy 2014; Chin et al. 2017). In humans, local anesthetic injection at this site can provide nerve blockade of the ventral (‘anterior’) branches of the nerves originating from T7eT12; thus, RSB is indicated for umbilical and periumbilical hernia repairs, laparoscopic procedures and midline abdominal surgeries (Ferguson et al. 1996; Gurnaney et al. 2011; Dingeman et al. 2013; Bashandy & Elkholy 2014; Hamill et al. 2015; Manassero et al. 2015; Ueshima & Otake 2016). There is a slight anatomical difference in the canine internal RS. The cranial to midabdominal RS is formed by the continuation of the transversalis fascia and aponeurosis of the transversus abdominis, which is replaced by the tendinous strand of the rectus near the pelvis (Evans & de Lahunta 2017; Hermanson et al. 2019b). The canine abdominal wall is innervated by ventral spinal nerve branches originating between T11e13 and L1e3 in the dog (Casta~ neda-Herrera et al. 2017; Hermanson et al. 2019a). The smaller compartment of the RS compared with the TAP may allow further cranial and caudal spread of injectate, facilitating greater sensory blockade with a relatively smaller volume. The purpose of the present study was to describe the RSB technique in dog cadavers and the resulting dye distribution. 2
We hypothesized that RSB would be easily performed and would stain multiple ventral spinal nerve branches. Materials and methods A group of eight adult Beagle dogs (four female and four male) with mean body weight of 8.9 ± 1.6 kg (mean ± standard deviation) were frozen immediately after euthanasia for reasons unrelated to the study and thawed for 24 hours in the refrigerator for use in this study. Bilateral injections were performed using either low (0.25 mL kge1; group LV) or high volume (0.50 mL kge1; group HV) methylene blue (0.5%; Consolidated Chemical & Solvents LLC, PA, USA). Each cadaver was administered either LV or HV injections in the left or right hemiabdomen. Assignment of LV and HV to either side of each dog was randomized (randomization.com). No animal use protocol or ethical animal use approval was required for the use of canine cadavers as per the University of Wisconsin, Madison, WI, USA Institutional Animal Care and Use Committee. Injection technique for RSB Volumes for injections were based on those used for canine TAP blocks and reported volumes used for RSB in human patients (range, 0.17e1.00 mL kge1) (Ferguson et al. 1996; Schroeder et al. 2011; Bruggink et al. 2012; Sviggum et al. 2012; Bashandy & Elkholy 2014; Manassero et al. 2015; Chin et al. 2017; Drozdzynska et al. 2017). A pilot study was performed using several volumes between 0.25 and 1.00 mL kge1 in four hemiabdomens. The volumes of 0.25 and 0.50 mL kge1 were chosen for this study because no substantial differences in ventral spinal nerve branch staining and dye spread were observed among the volumes tested (data not published). In these pilot studies, a focal pocket of dye was consistently identified within the RS during dissection. Cadavers were positioned in dorsal recumbency and clipped from pubis to xiphoid, and laterally to 10 cm on either side of ventral midline. The umbilicus was identified and a transverse line was drawn across the abdomen 1 cm cranial to the center of the umbilicus. The linear array US transducer (12L-RS, 5e13 MHz; GE Healthcare, PA, USA) was initially placed in a transverse orientation midline along this mark to observe the linea alba (Fig. 1a) before sliding laterally to view the lateral extent of the rectus abdominis muscle (Fig. 1b). The image was optimized to produce a hyperechoic ‘double line’ representing the internal RS (Fig. 1), which is formed from the aponeurosis of TAM, transversalis fascia and peritoneum (Bashandy & Elkholy 2014; Chin et al. 2017; Evans & de Lahunta 2017; Hermanson et al. 2019b). Once the double line or adequate visualization of the internal RS was established, an echogenic needle (50 mm, 22 gauge; SonoTap; PAJUNK USA, GA, USA) was inserted lateral to the probe at a 30-degree angle to the
© 2019 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved., xxx, xxx
Please cite this article as: St James M, Ferreira TH, Schroeder CA et al. Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers, Veterinary Anaesthesia and Analgesia, https://doi.org/10.1016/j.vaa.2019.09.001
Rectus sheath block in dogs M St James et al.
Figure 1 Transverse ultrasound (US) images of the abdominal wall of a dog cadaver (a) initial image with midline/linea alba in the middle of the US window prior to needle insertion, (b) pre-injectate US image after sliding the probe laterally to obtain the view of the lateral extent of the rectus abdominis muscle (RAM) and beginning of the transversus abdominis muscle (TAM), and (c) postinjectate US image with methylene blue dye pooling between the RAM and internal rectus sheath. D, dorsal; L, linea alba; MB, methylene blue dye; P, peritoneum; V, ventral (V). Triangles, needle; arrows, characteristic double line formed by the internal rectus sheath and peritoneum.
skin, directed dorsomedially using an in-plane approach. The needle was attached to a stopcock (three-way luer lock; Smiths Medical, OH, USA) and T-port extension (18 cm, 18 cm MicroClave; Zoetis Inc., CA, USA) primed with 0.5% methylene blue. The needle insertion point was between the lateral edge and midpoint of the rectus abdominis muscle, advancing
through the external RS, then muscle, until reaching the plane between the muscle and internal RS (Fig. 1b). To confirm correct placement, test doses were performed by administering 0.2 mL of methylene blue. If hydrodissection separated the rectus abdominis muscle from the internal RS, the needle was deemed to be accurately placed as described by Sviggum et al.
© 2019 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved., xxx, xxx
3
Please cite this article as: St James M, Ferreira TH, Schroeder CA et al. Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers, Veterinary Anaesthesia and Analgesia, https://doi.org/10.1016/j.vaa.2019.09.001
Rectus sheath block in dogs M St James et al.
(2012) and Manassero et al. (2015). If the test dose demonstrated that the needle was not in the correct location, the needle was adjusted and another test dose was administered. All test doses were administered outside the target site and redirections of the needle were recorded. When the correct target site was reached, 0.25 or 0.50 mL kge1 minus the test dose(s) volume was slowly administered in the target site (LV or HV, respectively; Fig. 1c). All injections were performed by the same individual (THF). Scoring US image quality The US image quality was scored by assessing the landmark and needle visualization. The following scoring system was used: excellent, easily distinguishable double line and clear separation of muscle layer and internal RS postinjection; good, identifiable muscle and peritoneum but no double line; poor, landmarks could not be identified. Needle imaging was described as: excellent, entire shaft and needle tip could be visualized; good, only the tip clearly visualized; poor, the needle tip was only identified after test dose injection. Anatomical dissection Dissections were performed immediately after the injections were completed. The umbilicus was marked with a metal clip prior to caudal to cranial reflection of the skin. The external and internal oblique muscles were dissected and reflected laterally. Subsequently, the rectus abdominis muscle and TAM were isolated, thereby exposing the ventral branches of the spinal nerves, with care taken to avoid disrupting any pockets of dye if they were present (Fig. 2). Dye distribution in the muscle layers and measurements of cranialecaudal and medialelateral spread were recorded. Based on previously published criteria on nerve staining, complete staining was recorded if 1 cm and the entire circumference of the nerve was stained, and partial staining was recorded when the nerve was stained <1 cm or incomplete circumferentially (Schroeder et al. 2011; Drozdzynska et al. 2017; Portela et al. 2017; Ferreira et al. 2018, 2019). Numerical values were assigned: score 2 for complete, 1 for partial and 0 for no staining. Only completely stained nerves were considered in the statistical analyses as they represent nerves presumed to be adequately blocked had local anesthetic solution been injected (Raymond et al. 1989; Schroeder et al. 2011; Portela et al. 2017; Ferreira et al. 2018, 2019). The nerve aligned with the last rib was traced to its origin to confirm identification of ventral spinal nerve branches. A single anatomist (KHB), unaware of the volume injected, performed all assessments of dye distribution and nerve staining. Finally, the abdomen was entered to determine whether methylene blue had entered the peritoneal cavity. 4
Figure 2 Dissection of a dog cadaver after injections mimicking a rectus sheath block using methylene blue dye. External and internal oblique muscles have been removed and the rectus abdominis muscle (RAM) is retracted to view the staining of thoracic and lumbar (T11, T12, T13 and L1) ventral nerve branches based on the vertebrae of origin. Dye is localized at the rectus sheath, between the RAM and transversus abdominis muscle (TAM). Cd, caudal; Cr, cranial. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
Statistical analysis Statistical analysis was performed using GraphPad Prism 7.0d (GraphPad Software Inc., CA, USA). Data were evaluated for normality using the ShapiroeWilk test. Paired t test was used for normally distributed parametric data, and ManneWhitney was used for nonparametric data. The ManneWhitney test was used to establish significance of differences between groups in quality of US images and number of test doses used. Significance was considered if p < 0.05. Results are presented as mean ± standard deviation for normally distributed data and as median (range) otherwise. Results A significantly greater number of ventral spinal nerve branches were completely stained in HV than in LV (2.9 ± 0.8 and 2 ± 0 nerve branches, respectively; p < 0.01; Table 1). Overall, the nerves T10, T11, T12, T13 and L1 were stained 12.5%, 87.5%, 100%, 75.0% and 12.5%, respectively, in HV, whereas the same nerves were stained 25%, 100%, 75%, 25% and 0%, respectively, in LV. There was no significant difference between groups for the number of test doses required [median (range); LV, 2 (1e4); HV, 1 (1e3); p ¼ 0.20]. Grossly, the dye stained the dorsal surface of the rectus abdominis muscle and ventral TAM. There was a significant difference in the physical cranialecaudal spread of injectate between the LV and HV groups (7.1 ± 1.8 and 9.2 ± 1.8 cm,
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Please cite this article as: St James M, Ferreira TH, Schroeder CA et al. Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers, Veterinary Anaesthesia and Analgesia, https://doi.org/10.1016/j.vaa.2019.09.001
Rectus sheath block in dogs M St James et al. Table 1 Staining scores of ventral nerve branches of spinal nerves after ultrasound-guided rectus sheath injections performed with two volumes of methylene blue (0.25 or 0.50 mL kge1) in eight dog cadavers Dog
1 2 3 4 5 6 7 8
Volume (mL kge1)
0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50
Spinal nerves T10
T11
T12
T13
L1
1 0 0 0 0 0 0 1 2 0 0 1 2 0 0 2
2 2 2 2 2 2 2 2 2 0 2 2 2 2 2 2
2 2 2 2 2 2 2 2 0 2 2 2 0 2 2 2
1 2 1 2 0 2 0 2 0 2 0 1 0 0 0 2
0 2 0 0 0 0 0 0 0 1 0 0 0 0 0 0
Score 2, completely stained when 1 cm of nerve stained and entire circumference of the nerve was stained; score 1, partially stained when the nerve was stained <1 cm or not completely circumferentially; score 0, not stained. L, lumbar; T, thoracic.
respectively; p ¼ 0.03; Table 2). No intra-abdominal staining was observed in any of the cadavers. The US-guided RSB injections were easily performed in all 16 hemiabdomens. Visualization of landmarks was excellent in
all but three hemiabdomens; these were scored as good, two of which belonged to the same animal. No needle redirections were required to perform the RSB technique. Across all dogs, an average of 2 ± 1 minute was spent identifying the target site, administering test doses and injecting dye. The mean depth of the needle on US image was 0.5 ± 0.2 cm. Discussion The aim of the present study was to develop and describe a canine RSB technique and evaluate the distribution of two volumes of dye (0.25 and 0.50 mL kge1). The results demonstrate that the canine RS can be easily identified and targeted using ultrasonography and an in-plane technique. The distribution of dye using 0.50 mL kge1 consistently produced staining of the dorsal surface of the rectus abdominis muscle, RS and ventral surface of the TAM; additionally, more ventral nerve branches were stained using HV than using LV of the dye. Innervation of the canine abdominal wall is variable but is generally provided by spinal nerves originating at T11e13 and L1e3 (Casta~ neda-Herrera et al. 2017; Hermanson et al. 2019a). Although more extensive cranialecaudal spread with a greater number of fully stained nerves occurred in group HV, neither volume used in this study would be expected to provide adequate blockade of the full canine abdomen using a single-level injection bilaterally. Additionally, there can be variability where the nerves enter and branch in the rectus abdominis muscle, which may also affect the efficacy of the block (Bashandy & Elkholy 2014). The RSB targets the ventral
Table 2 Evaluation of ultrasound (US) quality and US needle visualization during US-guided rectus sheath injections of methylene blue (0.25 or 0.50 mL kge1) in eight dog cadavers Dog
Volume (mL kge1)
US landmark visualization
US needle visualization
Cranialecaudal spread (cm)
Medialelateral spread (cm)
Number of nerves stained
1
0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50
Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Good Excellent Good Good Excellent Excellent Excellent Excellent
Good Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent
9.3 12.5 5.8 8.0 9.5 7.0 7.0 10.3 8.5 10.4 6.3 9.0 5.0 7.5 5.5 8.9
4.5 5.0 4.0 3.5 2.8 4.0 3.4 3.4 6.3 5.0 6.0 6.0 4.0 3.0 2.5 5.0
2 4 2 3 2 3 2 3 2 2 2 2 2 2 2 4
2 3 4 5 6 7 8
Spread of dye and number of nerves stained were determined after dissection. US landmark visualization: excellent, easily distinguishable double line and clear separation of muscle layer and internal rectus sheath postinjection; good, identifiable muscle and peritoneum but no clear double line; poor, unable to identify landmarks. Needle visualization: excellent, complete visualization of the tip and shaft; good, clear visualization of only the tip; poor, position of tip only identified after test dose.
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5
Please cite this article as: St James M, Ferreira TH, Schroeder CA et al. Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers, Veterinary Anaesthesia and Analgesia, https://doi.org/10.1016/j.vaa.2019.09.001
Rectus sheath block in dogs M St James et al.
branches of the spinal nerves as they transverse the RS and enter the rectus abdominis muscle before branching into cutaneous, muscular and peritoneal nerves (Sviggum et al. 2012; Bashandy & Elkholy 2014; Murouchi et al. 2015; Casta~ neda-Herrera et al. 2017; Chin et al. 2017; Evans & de Lahunta 2017; Hermanson et al. 2019a). Thus, RSB should be performed in the lateral portion of the rectus abdominis muscle, where these nerves are most likely to penetrate the RS. Nerves scored as partially stained were recorded but not reported here because they are unlikely to be effectively blocked. Different numbers of completely or partially stained nerves may have been obtained had the RSB been performed in vivo, as functioning physiologic processes may enhance the distribution of the injected local anesthetic. The efficacy of nerve blocks depends on the concentration, volume and exposed length of the nerves to the local anesthetic (Raymond et al. 1989; Fenten et al. 2015). Similar to current recommendations for a four or more quadrant approach to the TAP block (Portela et al. 2014; Drozdzynska et al. 2017; Johnson et al. 2018), the RSB may also require multiple-level injections per side to provide adequate coverage of the abdominal wall. However, the requirement of additional injections increases the risk of adverse events, such as damage to the vasculature or viscera. The RSB technique used in the present study required little technical skill as the linea alba, rectus abdominis muscle and RS were readily identified, and no needle redirections were necessary. It is important to note that the double line is only meant to be appreciated as a landmark for the internal RS rather than a target; injectate should be deposited immediately superficial to the internal RS and not within the double line. Advancing the needle immediately superficial to the double line and administering a test dose of injectate was adequate for rapid assessment of whether the needle was in the correct site. In the majority of clinical canine patients, the anatomic landmarks for the TAP block are easily and clearly identified. However, variability in animal body condition may contribute to poorly defined abdominal wall musculature, resulting in difficult recognition of the TAP. Additional oblique hyperechoic lines in the abdominal wall have also been described by Mirra et al. (2018) when performing US-guided TAP injections in calf cadavers, though these were suspected to be tendinous intersections of the rectus abdominis muscle. In clinical situations where there may be unexpected ultrasonographic findings, such as poor demarcation of muscle layers or wall defects, the option of performing RSB may be beneficial for ease and confidence of the target site identification. An anatomic evaluation of the TAP by Casta~ neda-Herrera et al. (2017) identified an additional fascial plane near the site of the TAP in all the canine abdomens examined. A similar distinct fascial layer has been identified in human cadavers (Rozen et al. 6
2008). Authors of both studies postulated that if local anesthetic was erroneously placed above this plane, the extent of nerve blockade could be diminished as the neurovascular structures lay deep to this fascia (Rozen et al. 2008; Casta~ nedaHerrera et al. 2017). This finding may further complicate the seemingly straightforward TAP block and may contribute to the clinically and anecdotally reported variability in efficacy (Carney et al. 2011; Gurnaney et al. 2011; Dingeman et al. 2013; Flack et al. 2014; Hamill et al. 2015; Støving et al. 2016; Chin et al. 2017). Comparatively, the anatomic simplicity of the RS and the lack of variability in muscle and fascial layers allow easy visualization and decreased risk of erroneous injection. The major limitation of the present study is the use of thawed cadavers. Distribution of local anesthetic likely differs in live animals versus cadavers, and may be further affected by changes in tissue composition after freezing. The use of methylene blue in this study is assumed to accurately reproduce the spread of local anesthetic solution in cadavers; however, this may be different from the RSB performed in vivo. Additionally, the antinociceptive success of the dermatomal coverage of the RSB is unknown. Further studies in live animals with sensory function testing are necessary. Dog cadavers from a single breed with similar body condition and weight were used in this study. These features may have overestimated the ease of performing this technique compared with the variety of breeds and body conditions presented in clinical practice. However, there are few other anatomical structures that would be present in the US window when performing RSB; therefore, the authors predict that mastery of this approach will require minimal regional anesthesia or ultrasonographic experience. In humans, RSB has been used for various procedures, such as abdominal laparoscopies (Murouchi et al. 2015; Yasumura et al. 2016), exploratory laparotomies for abdominal cancers (Bashandy & Elkholy 2014), umbilical hernia repair (Manassero et al. 2015) and pediatric abdominal surgery (Hamill et al. 2016). Use of RSB may be considered over the TAP block, as analgesia provided by TAP blocks may be inconsistent for midline incisions (Carney et al. 2011; Støving et al. 2016). Although the TAP block provides sensory blockade via ventral nerve branches, the anatomical finding of extensive nerve communication in the form of plexi within the TAP (Rozen et al. 2008) may explain inconsistent dermatomal coverage (Carney et al. 2011; Støving et al. 2016). Numerous studies with RSB in humans have demonstrated varying degrees of improvement in postoperative pain scoring (Dingeman et al. 2013; Bashandy & Elkholy 2014; Hamill et al. 2015) and/or decreased perioperative opioid use (Gurnaney et al. 2011; Bashandy & Elkholy 2014; Flack et al. 2014). Therefore, use of RSB for animals undergoing similar abdominal procedures, such as hernia repair,
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Please cite this article as: St James M, Ferreira TH, Schroeder CA et al. Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers, Veterinary Anaesthesia and Analgesia, https://doi.org/10.1016/j.vaa.2019.09.001
Rectus sheath block in dogs M St James et al.
ovariohysterectomy, laparoscopic procedures and exploratory laparotomy, is expected to show the same benefit. Many of these procedures do not require an incision extending the length of the abdomen and thus may not require multiple injections per hemiabdomen. As many small animal surgical approaches involve an incision in the ventral midline, it is possible that the TAP block does not provide adequate analgesia to the surgical site, similar to the findings in humans, and RSB may be more useful (Carney et al. 2011; Støving et al. 2016). Future clinical studies of RSB are supported by the clinical use of TAP blocks in small animal practice and studies demonstrating improved pain scores and/or reduced opioid use, as the target nerves are similar (Portela et al. 2014; Skouropoulou et al. 2018). As RSB likely carries less risk of pelvic limb weakness than the TAP block, its use in large animals should be explored. A cadaveric study by Baldo et al. (2018) demonstrated staining of the major psoas, quadratus lumborum and several lumbar nerve branches in ponies following a bilateral TAP block, which could lead to pelvic limb weakness in vivo. Pelvic limb weakness resulting in recovery and postoperative injury has potentially fatal consequences in large animals. RSB provides a limited compartment for local anesthetic, far from the site of the lumbar plexus or pelvic musculature. Thus, cadaveric and experimental studies are warranted before use in clinical patients. Other possible complications of RSB include hematoma formation from epigastric vessel damage, peritoneal perforation and block failure (Ferguson et al. 1996). No peritoneal injections were noted during this study, further supporting the clinical evaluation of RSB. Conclusion The injection for RSB was easily and consistently performed in dogs using an US-guided in-plane technique. The higher volume utilized in this study demonstrated greater nerve staining; thus, 0.5 mL kge1 of local anesthetic demonstrates potential for clinical application. The results of this study justify further investigations into clinical efficacy and different combinations of volumes and injection sites in order to better define its use. Acknowledgements No specific grant from funding agencies in the public, commercial or not-for-profit sectors was received for this research. Authors' contributions MSJ and THF: study design, data collection, statistical analyses, data interpretation, manuscript preparation. CAS: execution of the study, data interpretation, manuscript preparation. KHB: study design, execution of the study, data
collection. KMS: execution of the study, data collection, data interpretation. All authors approved the final manuscript for publication. Conflict of interest statement The authors declare no conflict of interest. References Baldo CF, Almeida D, Wendt-Hornickle E, Guedes A (2018) Transversus abdominis plane block in ponies: a preliminary anatomical study. Vet Anaesth Analg 45, 392e396. Bashandy GMN, Elkholy AHH (2014) Reducing postoperative opioid consumption by adding an ultrasound-guided rectus sheath block to multimodal analgesia for abdominal cancer surgery with midline incision. Anesth Pain Med 4, e18263. Bruggink SM, Schroeder KM, Baker-Herman TL, Schroeder CA (2012) Weight based volume of injection influences cranial to caudal spread of local anesthetic solution in ultrasound-guided transversus abdominis plane blocks in canine cadavers. Vet Surg 41, 455e457. Carney J, Finnerty O, Rauf J et al. (2011) Studies on the spread of local anaesthetic solution in transversus abdominis plane blocks. Anaesthesia 66, 1023e1030. Casta~ neda-Herrera FE, Buritic a-Gaviria EF, Echeverry-Bonilla DF (2017) Anatomical evaluation of the thoracolumbar nerves related to the transversus abdominis plane block technique in the dog. Anat Histol Embryol 46, 373e377. Chin KJ, McDonnell JG, Carvalho B et al. (2017) Essentials of our current understanding: abdominal wall blocks. Reg Anesth Pain Med 42, 133e183. Dingeman RS, Barus LM, Chung HK et al. (2013) Ultrasonographyguided bilateral rectus sheath block vs local anesthetic infiltration after pediatric umbilical hernia repair: a prospective randomized clinical trial. JAMA Surg 148, 707e713. Drozdzynska M, Monticelli P, Neilson D, Viscasillas J (2017) Ultrasound-guided subcostal oblique transversus abdominis plane block in canine cadavers. Vet Anaesth Analg 44, 183e186. Evans HE, de Lahunta A (2017) The skeletal and muscular systems. In: Guide to the Dissection of the Dog (8th edn). Evans HE, de Lahunta A (eds). Elsevier, USA. pp. 6e95. Fenten MG, Schoenmakers KPW, Heesterbeek PJC et al. (2015) Effect of local anesthetic concentration, dose and volume on the duration of single-injection ultrasound-guided axillary brachial plexus block with mepivacaine: a randomized controlled trial. BMC Anesthesiol 15, 130e138. Ferguson S, Thomas V, Lewis I (1996) The rectus sheath block in paediatric anaesthesia: new indications for an old technique? Paediatr Anaesth 6, 463e466. Ferreira TH, Teixeira LBC, Schroeder CA et al. (2018) Description of an ultrasound-guided thoracic paravertebral block technique and the spread of dye in dog cadavers. Vet Anaesth Analg 45, 811e819. Ferreira TH, St James M, Schroeder CA et al. (2019) Description of an ultrasound-guided erector spinae plane block and the spread of dye in dog cadavers. Vet Anaesth Analg 46, 516e522.
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Rectus sheath block in dogs M St James et al. Flack SH, Martin LD, Walker BJ et al. (2014) Ultrasound-guided rectus sheath block or wound infiltration in children: a randomized blinded study of analgesia and bupivacaine absorption. Paediatr Anaesth 24, 968e973. Gurnaney HG, Maxwell LG, Kraemer FW et al. (2011) Prospective randomized observer-blinded study comparing the analgesic efficacy of ultrasound-guided rectus sheath block and local anaesthetic infiltration for umbilical hernia repair. Br J Anaesth 107, 790e795. Hamill JK, Liley A, Hill AG (2015) Rectus sheath block for laparoscopic appendicectomy: a randomized clinical trial. ANZ J Surg 85, 951e956. Hamill JK, Rahiri JL, Liley A, Hill AG (2016) Rectus sheath and transversus abdominis plane blocks in children: a systematic review and meta-analysis of randomized trials. Paediatr Anaesth 26, 363e371. Hermanson JW, de Lahunta A, Evans HE (2019a) The spinal nerves. In: Miller and Evans’ Anatomy of the Dog (5th edn). Hermanson JW, de Lahunta A, Evans HE (eds). Elsevier, USA. pp. 728e743. Hermanson JW, de Lahunta A, Evans HE (2019b) The muscular system. In: Miller and Evans’ Anatomy of the Dog (5th edn). Hermanson JW, de Lahunta A, Evans HE (eds). Elsevier, USA. pp. 252e258. Johnson EK, Bauquier SH, Carter JE et al. (2018) Two-point ultrasound-guided transversus abdominis plane injection in canine cadavers e a pilot study. Vet Anaesth Analg 45, 871e875. Manassero A, Bossolasco M, Meineri M et al. (2015) Spread patterns and effectiveness for surgery after ultrasound-guided rectus sheath block in adult day-case patients scheduled for umbilical hernia repair. J Anaesthesiol Clin Pharmacol 31, 349e353. Mirra A, von Rotz A, Schmidhalter M et al. (2018) Ultrasoundguided lateral and subcostal transversus abdominis plane block in calves: a cadaveric study. Vet Anaesth Analg 45, 384e391. Murouchi T, Iwasaki S, Yamakage M (2015) Chronological changes in ropivacaine concentration and analgesic effects between transversus abdominis plane block and rectus sheath block. Reg Anesth Pain Med 40, 568e571. Portela D, Romano M, Briganti A (2014) Retrospective clinical evaluation of ultrasound guided transverse abdominis plane
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block in dogs undergoing mastectomy. Vet Anaesth Analg 41, 319e324. Portela DA, Campoy L, Otero PE et al. (2017) Ultrasound-guided thoracic paravertebral injection in dogs: a cadaveric study. Vet Anaesth Analg 44, 636e645. Raymond SA, Steffensen SC, Gugino LD, Strichartz GR (1989) The role of length of nerve exposed to local anesthetics in impulse blocking action. Anesth Analg 68, 563e570. Rozen WM, Tran TMN, Ashton MW et al. (2008) Refining the course of the thoracolumbar nerves: a new understanding of the innervation of the anterior abdominal wall. Clin Anat 21, 325e333. Schroeder CA, Snyder LBC, Tearney CC et al. (2011) Ultrasoundguided transversus abdominis plane block in the dog: an anatomical evaluation. Vet Anaesth Analg 38, 267e271. Schleich DL (1899) Schmerzlose Operationen (4th edn). Springer, Germany. pp. 240e248. Skouropoulou D, Lacitignola L, Centonze P et al. (2018) Perioperative analgesic effects of an ultrasound-guided transversus abdominis plane block with a mixture of bupivacaine and lidocaine in cats undergoing ovariectomy. Vet Anaesth Analg 45, 374e383. Støving K, Rothe C, Rosenstock CV et al. (2016) Cutaneous sensory block area, muscle-relaxing effect, and block duration of the transversus abdominis plane block: a randomized, blinded, and placebo-controlled study in healthy volunteers. Reg Anesth Pain Med 40, 355e362. Sviggum HP, Niesen AD, Sites BD, Dilger JA (2012) Trunk blocks 101: transversus abdominis plane, ilioinguinaliliohypogastric, and rectus sheath blocks. Int Anesthesiol Clin 50, 74e92. Ueshima H, Otake H (2016) Correspondence: Optimal site for the rectus sheath block. J Clin Anesth 35, 228e229. Yasumura R, Kobayashi Y, Ochiai R (2016) A comparison of plasma levobupivacaine concentrations following transversus abdominis plane block and rectus sheath block. Anaesthesia 71, 544e549. Received 1 June 2019; accepted 5 September 2019. Available online xxx
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Please cite this article as: St James M, Ferreira TH, Schroeder CA et al. Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers, Veterinary Anaesthesia and Analgesia, https://doi.org/10.1016/j.vaa.2019.09.001
RESEARCH PAPER
Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers Mariko St Jamesa, Tatiana H Ferreiraa, Carrie A Schroedera, Karen L Hershberger-Brakerb & Kristopher M Schroederc a
Department of Surgical Sciences, School of Veterinary Medicine, University of WisconsineMadison, Madison, WI, USA
b
Department of Pathobiological Sciences, Department of Comparative Biosciences, School of Veterinary Medicine,
University of WisconsineMadison, Madison, WI, USA c
Department of Anesthesiology, School of Medicine and Public Health, University of WisconsineMadison, Madison,
WI, USA Correspondence: Tatiana H Ferreira, Department of Surgical Sciences, School of Veterinary Medicine, University of WisconsineMadison, 2015 Linden Drive, Madison, WI 53706, USA. E-mail: [email protected]
Abstract Objectives To describe the ultrasound-guided rectus sheath block technique and the anatomical spread of two volumes of methylene blue injection in dog cadavers.
analgesia for the ventral midline. This study supports the potential of the rectus sheath block for abdominal procedures, and further investigations on its clinical efficacy are warranted.
Study design Blinded, prospective, experimental cadaveric study.
Keywords abdominal wall, dog, nerve block, rectus sheath block, regional anesthesia, ultrasound.
Animals A total of eight dog cadavers weighing 8.9 ± 1.6 kg.
Introduction
Methods Ultrasound-guided rectus sheath injections were performed bilaterally 1 cm cranial to the umbilicus using 0.25 mL kge1 (low volume; LV) and 0.50 mL kge1 (high volume; HV) of 0.5% methylene blue dye. A total of 16 hemiabdomens were injected. The ultrasound image quality of the muscular and fascial plane landmarks and needle visualization were scored using a standardized scale. Cadavers were dissected to determine the distribution of the dye and to assess staining of ventral branches of the spinal nerves. Results Fewer ventral spinal nerve branches were stained in the LV group than in the HV group, at 2.00 ± 0 and 2.90 ± 0.83, respectively (p < 0.01). Ventral branches of thoracic (T) and lumbar (L) spinal nerves (T10, T11, T12, T13 and L1) were stained 25%, 100%, 75%, 25% and 0% of the time in LV group and 12.5%, 87.5%, 100.0%, 75.0% and 13.0% in HV group. A lesser extent of cranialecaudal dye distribution was observed in the LV group than in the HV group (7.1 ± 1.8 cm and 9.2 ± 1.8 cm, respectively; p ¼ 0.03). There was no significant difference in medialelateral spread of dye, number of test doses or ultrasound image quality scores between groups. Conclusions and clinical relevance The results of this study suggest that, on an anatomical basis, this easily performed block has the potential to provide effective abdominal wall
Increasing popularity of perioperative abdominal wall and fascial plane nerve blocks in both human and veterinary medicine has led to the development of various techniques targeting the spinal nerves innervating this region. For abdominal surgeries, a commonly utilized technique is the transversus abdominis plane (TAP) block, which was first described in veterinary medicine by Schroeder et al. (2011) as an ultrasound (US)-guided injection to block the innervation of the canine abdominal wall, originating from thoracic (T) 11e13 and lumbar (L) 1e3 vertebrae (Casta~ neda-Herrera et al. 2017; Hermanson et al. 2019a). These ventral spinal nerve branches traverse through the TAP before entering the rectus abdominis muscle, branching to innervate musculature, cutaneous tissue and peritoneum (Casta~ neda-Herrera et al. 2017; Evans & de Lahunta 2017; Hermanson et al. 2019a). Targeting these nerves provides somatic analgesia and reportedly decreases intra- and postoperative opioid use and improves pain scores (Gurnaney et al. 2011; Dingeman et al. 2013; Bashandy & Elkholy 2014; Flack et al. 2014; Hamill et al. 2016; Skouropoulou et al. 2018). Although the TAP block was initially described as bilateral injections performed at the umbilicus (Schroeder et al. 2011), more recently it has been suggested that a single injection into each hemiabdomen will not adequately block the abdominal 1
Please cite this article as: St James M, Ferreira TH, Schroeder CA et al. Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers, Veterinary Anaesthesia and Analgesia, https://doi.org/10.1016/j.vaa.2019.09.001
Rectus sheath block in dogs M St James et al.
wall in dogs (Bruggink et al. 2012; Portela et al. 2014; Drozdzynska et al. 2017; Johnson et al. 2018). Efficacy of the TAP block depends on the distribution of injectate in this plane; therefore, multiple injections and high volumes of local anesthetic may be required (Bruggink et al. 2012; Drozdzynska et al. 2017). Consequently, risks of systemic local anesthetic toxicity or damage to abdominal viscera or vasculature may be increased (Ferguson et al. 1996; Sviggum et al. 2012; Chin et al. 2017). Recent research in human volunteers has demonstrated that traditional TAP techniques frequently fail to provide midline cutaneous analgesia (Carney et al. 2011; Støving et al. 2016). Cutaneous sensory mapping following bilateral TAP blocks (Carney et al. 2011) and unilateral TAP blocks compared with TAP injections with saline (Støving et al. 2016) illustrated the inconsistent results of this block and lack of dermatomal distribution of the local anesthetic. An alternative technique for abdominal somatic anesthesia is the rectus sheath block (RSB). The technique was first described in the 19th century by Schleich (1899) but has recently regained popularity in human medicine as an alternative to the TAP block (Sviggum et al. 2012; Hamill et al. 2016; Yasumura et al. 2016; Chin et al. 2017). Both TAP and RSB target branches of the ventral spinal nerves. Whereas the TAP block anesthetizes the ventral spinal nerve branches more laterally, RSB targets these nerves as they enter the internal (‘posterior’) rectus sheath (RS) prior to penetrating the rectus abdominis muscle. This internal sheath is formed by the transversalis fascia and aponeuroses of the transversus abdominis (TAM) and internal oblique muscles (Bashandy & Elkholy 2014; Chin et al. 2017). In humans, local anesthetic injection at this site can provide nerve blockade of the ventral (‘anterior’) branches of the nerves originating from T7eT12; thus, RSB is indicated for umbilical and periumbilical hernia repairs, laparoscopic procedures and midline abdominal surgeries (Ferguson et al. 1996; Gurnaney et al. 2011; Dingeman et al. 2013; Bashandy & Elkholy 2014; Hamill et al. 2015; Manassero et al. 2015; Ueshima & Otake 2016). There is a slight anatomical difference in the canine internal RS. The cranial to midabdominal RS is formed by the continuation of the transversalis fascia and aponeurosis of the transversus abdominis, which is replaced by the tendinous strand of the rectus near the pelvis (Evans & de Lahunta 2017; Hermanson et al. 2019b). The canine abdominal wall is innervated by ventral spinal nerve branches originating between T11e13 and L1e3 in the dog (Casta~ neda-Herrera et al. 2017; Hermanson et al. 2019a). The smaller compartment of the RS compared with the TAP may allow further cranial and caudal spread of injectate, facilitating greater sensory blockade with a relatively smaller volume. The purpose of the present study was to describe the RSB technique in dog cadavers and the resulting dye distribution. 2
We hypothesized that RSB would be easily performed and would stain multiple ventral spinal nerve branches. Materials and methods A group of eight adult Beagle dogs (four female and four male) with mean body weight of 8.9 ± 1.6 kg (mean ± standard deviation) were frozen immediately after euthanasia for reasons unrelated to the study and thawed for 24 hours in the refrigerator for use in this study. Bilateral injections were performed using either low (0.25 mL kge1; group LV) or high volume (0.50 mL kge1; group HV) methylene blue (0.5%; Consolidated Chemical & Solvents LLC, PA, USA). Each cadaver was administered either LV or HV injections in the left or right hemiabdomen. Assignment of LV and HV to either side of each dog was randomized (randomization.com). No animal use protocol or ethical animal use approval was required for the use of canine cadavers as per the University of Wisconsin, Madison, WI, USA Institutional Animal Care and Use Committee. Injection technique for RSB Volumes for injections were based on those used for canine TAP blocks and reported volumes used for RSB in human patients (range, 0.17e1.00 mL kge1) (Ferguson et al. 1996; Schroeder et al. 2011; Bruggink et al. 2012; Sviggum et al. 2012; Bashandy & Elkholy 2014; Manassero et al. 2015; Chin et al. 2017; Drozdzynska et al. 2017). A pilot study was performed using several volumes between 0.25 and 1.00 mL kge1 in four hemiabdomens. The volumes of 0.25 and 0.50 mL kge1 were chosen for this study because no substantial differences in ventral spinal nerve branch staining and dye spread were observed among the volumes tested (data not published). In these pilot studies, a focal pocket of dye was consistently identified within the RS during dissection. Cadavers were positioned in dorsal recumbency and clipped from pubis to xiphoid, and laterally to 10 cm on either side of ventral midline. The umbilicus was identified and a transverse line was drawn across the abdomen 1 cm cranial to the center of the umbilicus. The linear array US transducer (12L-RS, 5e13 MHz; GE Healthcare, PA, USA) was initially placed in a transverse orientation midline along this mark to observe the linea alba (Fig. 1a) before sliding laterally to view the lateral extent of the rectus abdominis muscle (Fig. 1b). The image was optimized to produce a hyperechoic ‘double line’ representing the internal RS (Fig. 1), which is formed from the aponeurosis of TAM, transversalis fascia and peritoneum (Bashandy & Elkholy 2014; Chin et al. 2017; Evans & de Lahunta 2017; Hermanson et al. 2019b). Once the double line or adequate visualization of the internal RS was established, an echogenic needle (50 mm, 22 gauge; SonoTap; PAJUNK USA, GA, USA) was inserted lateral to the probe at a 30-degree angle to the
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Please cite this article as: St James M, Ferreira TH, Schroeder CA et al. Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers, Veterinary Anaesthesia and Analgesia, https://doi.org/10.1016/j.vaa.2019.09.001
Rectus sheath block in dogs M St James et al.
Figure 1 Transverse ultrasound (US) images of the abdominal wall of a dog cadaver (a) initial image with midline/linea alba in the middle of the US window prior to needle insertion, (b) pre-injectate US image after sliding the probe laterally to obtain the view of the lateral extent of the rectus abdominis muscle (RAM) and beginning of the transversus abdominis muscle (TAM), and (c) postinjectate US image with methylene blue dye pooling between the RAM and internal rectus sheath. D, dorsal; L, linea alba; MB, methylene blue dye; P, peritoneum; V, ventral (V). Triangles, needle; arrows, characteristic double line formed by the internal rectus sheath and peritoneum.
skin, directed dorsomedially using an in-plane approach. The needle was attached to a stopcock (three-way luer lock; Smiths Medical, OH, USA) and T-port extension (18 cm, 18 cm MicroClave; Zoetis Inc., CA, USA) primed with 0.5% methylene blue. The needle insertion point was between the lateral edge and midpoint of the rectus abdominis muscle, advancing
through the external RS, then muscle, until reaching the plane between the muscle and internal RS (Fig. 1b). To confirm correct placement, test doses were performed by administering 0.2 mL of methylene blue. If hydrodissection separated the rectus abdominis muscle from the internal RS, the needle was deemed to be accurately placed as described by Sviggum et al.
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3
Please cite this article as: St James M, Ferreira TH, Schroeder CA et al. Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers, Veterinary Anaesthesia and Analgesia, https://doi.org/10.1016/j.vaa.2019.09.001
Rectus sheath block in dogs M St James et al.
(2012) and Manassero et al. (2015). If the test dose demonstrated that the needle was not in the correct location, the needle was adjusted and another test dose was administered. All test doses were administered outside the target site and redirections of the needle were recorded. When the correct target site was reached, 0.25 or 0.50 mL kge1 minus the test dose(s) volume was slowly administered in the target site (LV or HV, respectively; Fig. 1c). All injections were performed by the same individual (THF). Scoring US image quality The US image quality was scored by assessing the landmark and needle visualization. The following scoring system was used: excellent, easily distinguishable double line and clear separation of muscle layer and internal RS postinjection; good, identifiable muscle and peritoneum but no double line; poor, landmarks could not be identified. Needle imaging was described as: excellent, entire shaft and needle tip could be visualized; good, only the tip clearly visualized; poor, the needle tip was only identified after test dose injection. Anatomical dissection Dissections were performed immediately after the injections were completed. The umbilicus was marked with a metal clip prior to caudal to cranial reflection of the skin. The external and internal oblique muscles were dissected and reflected laterally. Subsequently, the rectus abdominis muscle and TAM were isolated, thereby exposing the ventral branches of the spinal nerves, with care taken to avoid disrupting any pockets of dye if they were present (Fig. 2). Dye distribution in the muscle layers and measurements of cranialecaudal and medialelateral spread were recorded. Based on previously published criteria on nerve staining, complete staining was recorded if 1 cm and the entire circumference of the nerve was stained, and partial staining was recorded when the nerve was stained <1 cm or incomplete circumferentially (Schroeder et al. 2011; Drozdzynska et al. 2017; Portela et al. 2017; Ferreira et al. 2018, 2019). Numerical values were assigned: score 2 for complete, 1 for partial and 0 for no staining. Only completely stained nerves were considered in the statistical analyses as they represent nerves presumed to be adequately blocked had local anesthetic solution been injected (Raymond et al. 1989; Schroeder et al. 2011; Portela et al. 2017; Ferreira et al. 2018, 2019). The nerve aligned with the last rib was traced to its origin to confirm identification of ventral spinal nerve branches. A single anatomist (KHB), unaware of the volume injected, performed all assessments of dye distribution and nerve staining. Finally, the abdomen was entered to determine whether methylene blue had entered the peritoneal cavity. 4
Figure 2 Dissection of a dog cadaver after injections mimicking a rectus sheath block using methylene blue dye. External and internal oblique muscles have been removed and the rectus abdominis muscle (RAM) is retracted to view the staining of thoracic and lumbar (T11, T12, T13 and L1) ventral nerve branches based on the vertebrae of origin. Dye is localized at the rectus sheath, between the RAM and transversus abdominis muscle (TAM). Cd, caudal; Cr, cranial. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
Statistical analysis Statistical analysis was performed using GraphPad Prism 7.0d (GraphPad Software Inc., CA, USA). Data were evaluated for normality using the ShapiroeWilk test. Paired t test was used for normally distributed parametric data, and ManneWhitney was used for nonparametric data. The ManneWhitney test was used to establish significance of differences between groups in quality of US images and number of test doses used. Significance was considered if p < 0.05. Results are presented as mean ± standard deviation for normally distributed data and as median (range) otherwise. Results A significantly greater number of ventral spinal nerve branches were completely stained in HV than in LV (2.9 ± 0.8 and 2 ± 0 nerve branches, respectively; p < 0.01; Table 1). Overall, the nerves T10, T11, T12, T13 and L1 were stained 12.5%, 87.5%, 100%, 75.0% and 12.5%, respectively, in HV, whereas the same nerves were stained 25%, 100%, 75%, 25% and 0%, respectively, in LV. There was no significant difference between groups for the number of test doses required [median (range); LV, 2 (1e4); HV, 1 (1e3); p ¼ 0.20]. Grossly, the dye stained the dorsal surface of the rectus abdominis muscle and ventral TAM. There was a significant difference in the physical cranialecaudal spread of injectate between the LV and HV groups (7.1 ± 1.8 and 9.2 ± 1.8 cm,
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Please cite this article as: St James M, Ferreira TH, Schroeder CA et al. Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers, Veterinary Anaesthesia and Analgesia, https://doi.org/10.1016/j.vaa.2019.09.001
Rectus sheath block in dogs M St James et al. Table 1 Staining scores of ventral nerve branches of spinal nerves after ultrasound-guided rectus sheath injections performed with two volumes of methylene blue (0.25 or 0.50 mL kge1) in eight dog cadavers Dog
1 2 3 4 5 6 7 8
Volume (mL kge1)
0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50
Spinal nerves T10
T11
T12
T13
L1
1 0 0 0 0 0 0 1 2 0 0 1 2 0 0 2
2 2 2 2 2 2 2 2 2 0 2 2 2 2 2 2
2 2 2 2 2 2 2 2 0 2 2 2 0 2 2 2
1 2 1 2 0 2 0 2 0 2 0 1 0 0 0 2
0 2 0 0 0 0 0 0 0 1 0 0 0 0 0 0
Score 2, completely stained when 1 cm of nerve stained and entire circumference of the nerve was stained; score 1, partially stained when the nerve was stained <1 cm or not completely circumferentially; score 0, not stained. L, lumbar; T, thoracic.
respectively; p ¼ 0.03; Table 2). No intra-abdominal staining was observed in any of the cadavers. The US-guided RSB injections were easily performed in all 16 hemiabdomens. Visualization of landmarks was excellent in
all but three hemiabdomens; these were scored as good, two of which belonged to the same animal. No needle redirections were required to perform the RSB technique. Across all dogs, an average of 2 ± 1 minute was spent identifying the target site, administering test doses and injecting dye. The mean depth of the needle on US image was 0.5 ± 0.2 cm. Discussion The aim of the present study was to develop and describe a canine RSB technique and evaluate the distribution of two volumes of dye (0.25 and 0.50 mL kge1). The results demonstrate that the canine RS can be easily identified and targeted using ultrasonography and an in-plane technique. The distribution of dye using 0.50 mL kge1 consistently produced staining of the dorsal surface of the rectus abdominis muscle, RS and ventral surface of the TAM; additionally, more ventral nerve branches were stained using HV than using LV of the dye. Innervation of the canine abdominal wall is variable but is generally provided by spinal nerves originating at T11e13 and L1e3 (Casta~ neda-Herrera et al. 2017; Hermanson et al. 2019a). Although more extensive cranialecaudal spread with a greater number of fully stained nerves occurred in group HV, neither volume used in this study would be expected to provide adequate blockade of the full canine abdomen using a single-level injection bilaterally. Additionally, there can be variability where the nerves enter and branch in the rectus abdominis muscle, which may also affect the efficacy of the block (Bashandy & Elkholy 2014). The RSB targets the ventral
Table 2 Evaluation of ultrasound (US) quality and US needle visualization during US-guided rectus sheath injections of methylene blue (0.25 or 0.50 mL kge1) in eight dog cadavers Dog
Volume (mL kge1)
US landmark visualization
US needle visualization
Cranialecaudal spread (cm)
Medialelateral spread (cm)
Number of nerves stained
1
0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50 0.25 0.50
Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Good Excellent Good Good Excellent Excellent Excellent Excellent
Good Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent
9.3 12.5 5.8 8.0 9.5 7.0 7.0 10.3 8.5 10.4 6.3 9.0 5.0 7.5 5.5 8.9
4.5 5.0 4.0 3.5 2.8 4.0 3.4 3.4 6.3 5.0 6.0 6.0 4.0 3.0 2.5 5.0
2 4 2 3 2 3 2 3 2 2 2 2 2 2 2 4
2 3 4 5 6 7 8
Spread of dye and number of nerves stained were determined after dissection. US landmark visualization: excellent, easily distinguishable double line and clear separation of muscle layer and internal rectus sheath postinjection; good, identifiable muscle and peritoneum but no clear double line; poor, unable to identify landmarks. Needle visualization: excellent, complete visualization of the tip and shaft; good, clear visualization of only the tip; poor, position of tip only identified after test dose.
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Please cite this article as: St James M, Ferreira TH, Schroeder CA et al. Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers, Veterinary Anaesthesia and Analgesia, https://doi.org/10.1016/j.vaa.2019.09.001
Rectus sheath block in dogs M St James et al.
branches of the spinal nerves as they transverse the RS and enter the rectus abdominis muscle before branching into cutaneous, muscular and peritoneal nerves (Sviggum et al. 2012; Bashandy & Elkholy 2014; Murouchi et al. 2015; Casta~ neda-Herrera et al. 2017; Chin et al. 2017; Evans & de Lahunta 2017; Hermanson et al. 2019a). Thus, RSB should be performed in the lateral portion of the rectus abdominis muscle, where these nerves are most likely to penetrate the RS. Nerves scored as partially stained were recorded but not reported here because they are unlikely to be effectively blocked. Different numbers of completely or partially stained nerves may have been obtained had the RSB been performed in vivo, as functioning physiologic processes may enhance the distribution of the injected local anesthetic. The efficacy of nerve blocks depends on the concentration, volume and exposed length of the nerves to the local anesthetic (Raymond et al. 1989; Fenten et al. 2015). Similar to current recommendations for a four or more quadrant approach to the TAP block (Portela et al. 2014; Drozdzynska et al. 2017; Johnson et al. 2018), the RSB may also require multiple-level injections per side to provide adequate coverage of the abdominal wall. However, the requirement of additional injections increases the risk of adverse events, such as damage to the vasculature or viscera. The RSB technique used in the present study required little technical skill as the linea alba, rectus abdominis muscle and RS were readily identified, and no needle redirections were necessary. It is important to note that the double line is only meant to be appreciated as a landmark for the internal RS rather than a target; injectate should be deposited immediately superficial to the internal RS and not within the double line. Advancing the needle immediately superficial to the double line and administering a test dose of injectate was adequate for rapid assessment of whether the needle was in the correct site. In the majority of clinical canine patients, the anatomic landmarks for the TAP block are easily and clearly identified. However, variability in animal body condition may contribute to poorly defined abdominal wall musculature, resulting in difficult recognition of the TAP. Additional oblique hyperechoic lines in the abdominal wall have also been described by Mirra et al. (2018) when performing US-guided TAP injections in calf cadavers, though these were suspected to be tendinous intersections of the rectus abdominis muscle. In clinical situations where there may be unexpected ultrasonographic findings, such as poor demarcation of muscle layers or wall defects, the option of performing RSB may be beneficial for ease and confidence of the target site identification. An anatomic evaluation of the TAP by Casta~ neda-Herrera et al. (2017) identified an additional fascial plane near the site of the TAP in all the canine abdomens examined. A similar distinct fascial layer has been identified in human cadavers (Rozen et al. 6
2008). Authors of both studies postulated that if local anesthetic was erroneously placed above this plane, the extent of nerve blockade could be diminished as the neurovascular structures lay deep to this fascia (Rozen et al. 2008; Casta~ nedaHerrera et al. 2017). This finding may further complicate the seemingly straightforward TAP block and may contribute to the clinically and anecdotally reported variability in efficacy (Carney et al. 2011; Gurnaney et al. 2011; Dingeman et al. 2013; Flack et al. 2014; Hamill et al. 2015; Støving et al. 2016; Chin et al. 2017). Comparatively, the anatomic simplicity of the RS and the lack of variability in muscle and fascial layers allow easy visualization and decreased risk of erroneous injection. The major limitation of the present study is the use of thawed cadavers. Distribution of local anesthetic likely differs in live animals versus cadavers, and may be further affected by changes in tissue composition after freezing. The use of methylene blue in this study is assumed to accurately reproduce the spread of local anesthetic solution in cadavers; however, this may be different from the RSB performed in vivo. Additionally, the antinociceptive success of the dermatomal coverage of the RSB is unknown. Further studies in live animals with sensory function testing are necessary. Dog cadavers from a single breed with similar body condition and weight were used in this study. These features may have overestimated the ease of performing this technique compared with the variety of breeds and body conditions presented in clinical practice. However, there are few other anatomical structures that would be present in the US window when performing RSB; therefore, the authors predict that mastery of this approach will require minimal regional anesthesia or ultrasonographic experience. In humans, RSB has been used for various procedures, such as abdominal laparoscopies (Murouchi et al. 2015; Yasumura et al. 2016), exploratory laparotomies for abdominal cancers (Bashandy & Elkholy 2014), umbilical hernia repair (Manassero et al. 2015) and pediatric abdominal surgery (Hamill et al. 2016). Use of RSB may be considered over the TAP block, as analgesia provided by TAP blocks may be inconsistent for midline incisions (Carney et al. 2011; Støving et al. 2016). Although the TAP block provides sensory blockade via ventral nerve branches, the anatomical finding of extensive nerve communication in the form of plexi within the TAP (Rozen et al. 2008) may explain inconsistent dermatomal coverage (Carney et al. 2011; Støving et al. 2016). Numerous studies with RSB in humans have demonstrated varying degrees of improvement in postoperative pain scoring (Dingeman et al. 2013; Bashandy & Elkholy 2014; Hamill et al. 2015) and/or decreased perioperative opioid use (Gurnaney et al. 2011; Bashandy & Elkholy 2014; Flack et al. 2014). Therefore, use of RSB for animals undergoing similar abdominal procedures, such as hernia repair,
© 2019 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved., xxx, xxx
Please cite this article as: St James M, Ferreira TH, Schroeder CA et al. Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers, Veterinary Anaesthesia and Analgesia, https://doi.org/10.1016/j.vaa.2019.09.001
Rectus sheath block in dogs M St James et al.
ovariohysterectomy, laparoscopic procedures and exploratory laparotomy, is expected to show the same benefit. Many of these procedures do not require an incision extending the length of the abdomen and thus may not require multiple injections per hemiabdomen. As many small animal surgical approaches involve an incision in the ventral midline, it is possible that the TAP block does not provide adequate analgesia to the surgical site, similar to the findings in humans, and RSB may be more useful (Carney et al. 2011; Støving et al. 2016). Future clinical studies of RSB are supported by the clinical use of TAP blocks in small animal practice and studies demonstrating improved pain scores and/or reduced opioid use, as the target nerves are similar (Portela et al. 2014; Skouropoulou et al. 2018). As RSB likely carries less risk of pelvic limb weakness than the TAP block, its use in large animals should be explored. A cadaveric study by Baldo et al. (2018) demonstrated staining of the major psoas, quadratus lumborum and several lumbar nerve branches in ponies following a bilateral TAP block, which could lead to pelvic limb weakness in vivo. Pelvic limb weakness resulting in recovery and postoperative injury has potentially fatal consequences in large animals. RSB provides a limited compartment for local anesthetic, far from the site of the lumbar plexus or pelvic musculature. Thus, cadaveric and experimental studies are warranted before use in clinical patients. Other possible complications of RSB include hematoma formation from epigastric vessel damage, peritoneal perforation and block failure (Ferguson et al. 1996). No peritoneal injections were noted during this study, further supporting the clinical evaluation of RSB. Conclusion The injection for RSB was easily and consistently performed in dogs using an US-guided in-plane technique. The higher volume utilized in this study demonstrated greater nerve staining; thus, 0.5 mL kge1 of local anesthetic demonstrates potential for clinical application. The results of this study justify further investigations into clinical efficacy and different combinations of volumes and injection sites in order to better define its use. Acknowledgements No specific grant from funding agencies in the public, commercial or not-for-profit sectors was received for this research. Authors' contributions MSJ and THF: study design, data collection, statistical analyses, data interpretation, manuscript preparation. CAS: execution of the study, data interpretation, manuscript preparation. KHB: study design, execution of the study, data
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Please cite this article as: St James M, Ferreira TH, Schroeder CA et al. Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers, Veterinary Anaesthesia and Analgesia, https://doi.org/10.1016/j.vaa.2019.09.001