Ultrasound-guided transversus abdominis plane block in the dog: an anatomical evaluation

Objective To describe the ultrasound‐guided technique to the transversus abdominis plane (TAP) block in the dog and evaluate the spread of a local anesthetic/methylene blue solution. Study design Prospective experimental trial. Animals Ten adult Beagle cadavers weighing 11.1 ± 1.1 kg (mean ± SD). Methods Transversus abdominis plane (TAP) blocks were performed bilaterally by a single trained individual on unpreserved cadaver dogs using 10 mL of methylene blue/bupivacaine solution per site. Dissection of the abdominal wall was performed within 15–55 minutes of block to determine distribution of injectate and nerve involvement in the transversus abdominis fascial plane. Results The transversus abdominis fascial plane was adequately visualized via ultrasound and injected in twenty hemi‐abdominal walls. Segmental branches of T11, T12, T13, L1, L2, and L3 were adequately stained in 20%, 60%, 100%, 100%, 90%, and 30% of injections, respectively. Conclusions and clinical relevance This anatomical study suggests that the transversus abdominis plane (TAP) block would provide adequate regional anesthesia of the abdomen, potentially extending to the cranial and caudal limits of the abdomen. This supports the clinical potential of this block in veterinary medicine.     

Transversus abdominis plane block in cat cadavers: anatomical description and comparison of injectate spread using two- and three-point approaches

ObjectiveTo describe the sonoanatomy of the abdominal wall in live cats and to compare the distribution pattern of two versus three ultrasound-guided transversus abdominis plane (TAP) injections using clinically applicable volumes of lidocaine–dye solution in cat cadavers.Study designProspective anatomical study.AnimalsA total of eight client-owned healthy cats and eight cat cadavers.MethodsUltrasound anatomy of the abdominal wall, landmarks and sites for needle access were determined in live cats. Ultrasound-guided TAP injections were performed in eight thawed cat cadavers. Volumes of 0.25 or 0.16 mL kg^?1 per point of a lidocaine–dye solution were injected using either two [subcostal and preiliac (SP)] or three [subcostal, retrocostal and preiliac (SRP)] injection points, respectively. Each cadaver was then dissected to determine the injectate distribution and the number of thoracolumbar nerves stained with each approach. The target nerves were defined as the ventromedial branches of the thoracic nerves 10 (T10), T11, T12, T13 and lumbar nerves 1 (L1) and L2.ResultsSonoanatomy was consistent with anatomy upon dissection and the TAP was identified in all cadavers. A total of 16 subcostal, 16 preiliac and nine retrocostal TAP injections were performed. The overall staining success rate of the target nerves was 66.7% and 92.6% for the SP and SPR approaches, respectively (p = 0.02). The ventromedial branches of T10, T11, T12, T13, L1 and L2 were stained in 57.1%, 100.0%, 85.7%, 28.6%, 42.9% and 85.7%, and in 66.7%, 100.0%, 100.0%, 100.0%, 88.9% and 100.0% of the cases with the SP and SRP approaches, respectively.Conclusions and clinical relevanceThe SRP approach allowed a broader distribution around the target nerves, whereas a staining gap was observed at T13 and L1 with the SP approach. Further studies are necessary to investigate the analgesic effect of these approaches in a clinical setting.     

Evaluation of injection volumes for the transversus abdominis plane block in dog cadavers: a preliminary trial

ObjectiveTo evaluate staining of nerve branches after the injection of different volumes during ultrasound-guided transversus abdominis plane (TAP) block in dog cadavers.Study designProspective randomized study.AnimalsA total of 15 frozen/thawed adult dog cadavers.MethodsHemiabdomens were randomly allocated to one of four groups. In groups G0.3, G0.6 and G1.0, ropivacaine–methylene blue solution (0.3, 0.6 and 1.0 mL kg^–1 in seven, eight and eight hemiabdomens, respectively) was injected at the midpoint between the iliac crest and the last rib at the height of the shoulder. In group G0.3×2 (seven hemiabdomens), two injections (0.3 mL kg^–1) were performed, caudal to the last rib and cranial to the iliac crest at the same height. Total time for injection was recorded; after 30 minutes, cadavers were dissected and spread of dye was evaluated.ResultsAccuracy of injection site was 80% and injection time was 71 (48–120) seconds for all groups together. Craniocaudal spread was 6.4 ± 1.6, 9.1 ± 2.6, 11.4 ± 2.3 and 11.2 ± 3.8 cm for G0.3, G0.6, G1.0 and G0.3×2, respectively [G0.3 to G0.3×2 (p = 0.044) and G1.0 (p = 0.034)]. There was no difference in dorsoventral spread among groups. Number of ventral nerve branches stained was 3 (2–4), 3 (2–4), 3 (3–4) and 3 (2–4) for G0.3, G0.6, G1.0 and G0.3×2, respectively, including nerve branches from twelfth thoracic to third lumbar (L3) in different proportions among groups.Conclusions and clinical relevanceResults suggest that a single-injection TAP block, using 0.3 mL kg^–1, stains comparable number of nerve branches as higher volumes or two-point injection. Despite the volume or technique, consistent staining of the innervation of the caudal abdomen (L1–L3) was observed. Additional cadaveric studies are necessary to identify the optimal technique for complete abdominal wall staining.     

Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers

ObjectivesTo describe the ultrasound-guided rectus sheath block technique and the anatomical spread of two volumes of methylene blue injection in dog cadavers.Study designBlinded, prospective, experimental cadaveric study.AnimalsA total of eight dog cadavers weighing 8.9 ± 1.6 kg.MethodsUltrasound-guided rectus sheath injections were performed bilaterally 1 cm cranial to the umbilicus using 0.25 mL kg^–1 (low volume; LV) and 0.50 mL kg^–1 (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.ResultsFewer 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 cranial–caudal 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 = 0.03). There was no significant difference in medial–lateral spread of dye, number of test doses or ultrasound image quality scores between groups.Conclusions and clinical relevanceThe results of this study suggest that, on an anatomical basis, this easily performed block has the potential to provide effective abdominal wall 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.     

Ultrasound-guided modified subcostal transversus abdominis plane block and influence of recumbency position on dye spread in equine cadavers

ObjectiveTo describe and evaluate an ultrasound-guided modified subcostal approach for the transversus abdominis plane (TAP) block in horse cadavers in lateral or dorsal recumbency.Study designProspective, experimental cadaveric study.AnimalsStudy of one preserved foal and eight fresh adult horse cadavers.MethodsThe lateral and ventral abdominal wall of a preserved cadaver was dissected to identify the muscles and nerves. A unilateral standard TAP block technique was performed (60 mL of methylene blue dye–bupivacaine) on a fresh cadaver in right lateral recumbency. A modified subcostal technique was performed on the opposite side using a linear ultrasound transducer and in-plane approach. Injection points (two 30 mL dye) were at the level of the TAP (between the rectus abdominis and transversus abdominis muscles and ventral to the cutaneous trunci muscle) perpendicular to: 1) the mid-point between the xiphoid cartilage and umbilical scar; and 2) at a point between the caudal and middle thirds of the abdomen measured from the first injection point to the umbilical scar. The modified subcostal approach was performed in seven additional cadavers in both hemiabdomens, with three cadavers in lateral and four cadavers in dorsal recumbency. Ultrasound guidance was used with all injections.ResultsThe standard approach stained the sixteenth to eighteenth thoracic nerves (T16–T18). The modified subcostal approach performed in lateral recumbency provided greater spread (T9–T17) than dorsal recumbency (T12–T18) (p = 0.016).Conclusions and clinical relevanceThe modified subcostal TAP approach resulted in extensive staining exceeding the standard approach. The nerves stained are consistent with production of ventral abdominal wall anesthesia in horses. Clinical studies are needed to verify these findings.     

A novel ultrasound-guided lateral quadratus lumborum block in dogs: a comparative cadaveric study of two approaches

ObjectiveTo describe an ultrasound-guided lateral quadratus lumborum (LQL) block technique and the spread characteristics of lidocaine–dye injected in the LQL plane using a transversal (LQL-T) or a longitudinal (LQL-L) approach.Study designExperimental anatomic study.AnimalsA total of eight canine cadavers.MethodsBilateral ultrasound-guided injections in the fascial plane lateral to the quadratus lumborum muscle and medial to the thoracolumbar fascia (LQL plane) with the needle directed at the first lumbar (L1) transverse process were performed using lidocaine–dye (0.3 mL kg⁻¹). Anatomical dissection determined the dye distribution, sympathetic trunk staining and number of spinal nerves stained circumferentially >1 cm.ResultsThe LQL fascial plane was ultrasonographically recognized in all cadavers and filled with lidocaine–dye in all eight cadavers with the LQL-T approach and in six with LQL-L. The injectate spread ventral to the lumbar transverse processes, around the quadratus lumborum muscle and dorsal to the transversalis fascia, affecting the ventral branches of the spinal nerves and the sympathetic trunk. A median (range) of 4 (3–5) and 3 (0–4) ventral branches of the thoracolumbar nerves were dyed with LQL-T and LQL-L approaches, respectively (p = 0.04). The most cranial nerve stained was the twelfth thoracic (T12) with the LQL-T approach and T13 with LQL-L, and the most caudal was L3 with both approaches. The incidence of sympathetic trunk staining was significantly higher using LQL-T (six injections) compared with LQL-L (one injection; p = 0.04). Dye was not observed in the lumbar plexus, epidural space or abdominal cavity.Conclusions and clinical relevanceUltrasound-guided LQL-T approach resulted in a more consistent spread toward the spinal nerves and sympathetic trunk compared with LQL-L approach. Further studies are necessary to assess the LQL block effectiveness and success rate in live dogs.     

Comparison between two approaches for the transversus abdominis plane block in canine cadavers

ObjectiveTo compare the dye distribution following either two lateral abdominal or one lateral abdominal and one subcostal ultrasound-guided transversus abdominis plane (TAP) injections of a clinically relevant volume of dye solution in dogs.Study designRandomized cadaveric study.AnimalsA total of eight canine cadavers.MethodsOn one side of each cadaver, two TAP injections were performed on the lateral aspect of the abdomen (approach LL), caudal to the last rib and cranial to the iliac crest. On the contralateral hemiabdomen, one subcostal (caudal to the costal arch) and one lateral abdominal injection (between last rib and iliac crest), were performed (approach SL). Side allocation was randomly determined. A spinal needle was introduced in-plane to the transducer for each injection of methylene blue (0.25 mL kg^?1). All cadavers were dissected to assess dye distribution and number of stained target nerves.ResultsAll injections were performed in the TAP. The proportion of target nerve staining was 53.5% versus 80.4% with approaches LL and SL, respectively (p = 0.005). Approach LL stained the first lumbar (L1) spinal nerve in 100% of injections and ninth thoracic (T9), T10, T11, T12, T13 and L2 were stained in 0%, 0%, 37.5%, 62.5%, 87.5% and 87.5% of injections, respectively. Approach SL stained T11, L1 and L2 in 100% of injections and T9, T10, T12 and T13 were stained in 37.5%, 87.5%, 75% and 62.5% of injections, respectively. Approach SL resulted in greater staining of nerves cranial to T12 compared with approach LL. The two approaches were equivalent in staining nerves caudal to T12.Conclusions and clinical relevanceApproach SL provided a broader distribution of the injected solution than approach LL, which may result in a larger blocked area in live animals undergoing celiotomy.     

Two-point ultrasound-guided transversus abdominis plane injection in canine cadavers – a pilot study

Objective

This study evaluated the spread of a two-point transversus abdominis plane (TAP) injection in canine cadavers. Compared with previous techniques, the two-point TAP injection was developed to increase the consistency of local anaesthetic spread to the nerve segments T11, T12, L1, L2 and L3.

Ultrasound-guided superficial serratus plane block in dog cadavers: an anatomical evaluation and volume dispersion study

ObjectiveTo evaluate the anatomy of the serratus plane in dogs to establish the optimal landmarks for a superficial serratus plane (SSP) block and evaluate ropivacaine–methylene blue solution dispersion with three volumes of injection.Study designProspective experimental cadaveric study.AnimalsA formaldehyde solution-preserved dog cadaver and 15 frozen/thawed adult dog cadavers.MethodsThe thoracic wall of the formaldehyde-preserved cadaver was dissected. An SSP injection was performed on each hemithorax of the cadavers, with the ultrasound transducer placed over the fourth and fifth ribs, at the level of the shoulder joint. A needle was inserted in-plane in a caudocranial direction until it could be visualized between the serratus ventralis thoracis and latissimus dorsi muscles. Dog cadavers were injected with a ropivacaine–methylene blue solution at 0.3, 0.6 and 1.0 mL kg^–1 and were dissected to determine the spread of the dye.ResultsThe thoracic wall muscles identified in the formalinized cadaver were the cutaneous trunci, latissimus dorsi, external abdominal oblique, serratus ventralis thoracis, scalenus, serratus dorsalis cranialis and external intercostal. The nerves identified in the SSP included the lateral cutaneous branches of intercostal nerves, intercostobrachial nerves and long thoracic nerve. The solution was successfully injected at the SSP in 26 of 29 (89.7%) attempts. Dermatomal dye spread, median (range), was 4 (3–6), 4 (2–5) and 5 (4–8) for 0.3, 0.6 and 1.0 mL kg^–1, respectively, with no significant difference among them.Conclusions and clinical relevanceInjections for an SSP block were easily performed under ultrasound guidance, using the fourth and fifth ribs at the level of the shoulder joint as reference landmarks. An injected volume of 0.3 mL kg^–1 may be sufficient for hemithorax analgesia in dogs. Further studies in dogs are required to determine the utility of this technique.     

Effect of contrast and local anesthetic on dye spread following transversus abdominis plane injection in dog cadavers

ObjectiveTo determine whether the addition of bupivacaine or contrast medium to methylene blue dye would affect dye distribution following ultrasound (US)-guided transversus abdominis plane (TAP) injections.Study designProspective, randomized, blinded cadaveric study.AnimalsA total of 29 fresh Beagle dog cadavers.MethodsEach hemiabdomen (n = 58) was randomized into one of three groups: group M, 1% methylene blue; group MB, 50:50 mixture of 1% methylene blue and 0.5% bupivacaine; group MC, 25:75 mixture of 1% methylene blue and contrast agent (iohexol). TAP injections (0.5 mL kg^–1) were performed bilaterally by a trained individual followed by dissection of the abdominal walls. Craniocaudal and dorsoventral spread along tissue planes was measured. Staining of branches of the thoracic and lumbar spinal nerves was considered successful when dye on the nerve was >10 mm. One-way anova with post hoc Tukey test was used to compare craniocaudal and dorsoventral spread and Kruskal–Wallis test to compare incidence of nerve staining among groups.ResultsTAP injections were successful in 52 out of 58 hemiabdomens. Dorsoventral spread was greater for group M (60 ± 10 mm) compared with MC (49 ± 9 mm; p = 0.01) but not MB (52 ± 9 mm; p = 0.09). No difference was found in craniocaudal spread or number of nerves stained among groups.Conclusion and clinical relevanceThe significant difference found in spread of tissue staining between methylene blue alone and methylene blue mixed with contrast in the TAP blocks should be kept in mind when interpreting dye-based cadaveric regional anesthesia studies.     

Description of a novel ultrasound-guided approach for a dorsal quadratus lumborum block: a canine cadaver study

ObjectiveTo describe an ultrasound-guided approach to the dorsal aspect of the quadratus lumborum muscle (D-QL) and to evaluate the spread of methylene blue dye in canine cadavers.Study designProspective, experimental anatomical study.AnimalsA total of 12 canine cadavers.MethodsThe ultrasonographic landmarks and injection technique for the D-QL approach were determined in two cadavers. Correct needle tip position was confirmed by computed tomography. Bilateral ultrasound-guided injections were performed in 10 cadavers between the QL muscle, the vertebral body and the ventrocaudal aspect of the transverse process of the first lumbar vertebra (L1) using two volumes of methylene blue: low volume (LV) 0.3 mL kg^–1 or high volume (HV) 0.5 mL kg^–1. Staining of the main thoracolumbar trunk, dorsal and ventral branches of the thoracic (T) and lumbar (L) spinal nerves, sympathetic trunk and epidural space were assessed following dissection. Data between groups were compared using Mann–Whitney U test. Data are presented as median (range).ResultsThe ventral branches of spinal nerves T12, T13, L1, L2, L3 and L4 were stained in 10%, 70%, 100%, 90%, 60%, 0% and 30%, 100%, 100%, 100%, 50% and 30% after LV and HV injections, respectively. Multisegmental spread of the sympathetic trunk was found on 3 (3–4) and 5 (3–6) vertebral spinal levels following LV and HV injections, respectively (p = 0.005). The T13 segment of the sympathetic trunk was stained after all HV injections. Epidural spread was found in 20% and 30% of LV and HV injections, respectively.Conclusions and clinical relevanceThe injection of HV versus LV dye using the D-QL approach provided more consistent staining of the thoracolumbar nerve structures which innervate the abdominal wall and viscera. Clinical studies are required to evaluate the analgesic efficacy of the D-QL block for abdominal procedures in dogs in vivo.     

Ultrasound-guided erector spinae plane block in canine cadavers: relevant anatomy and injectate distribution

ObjectiveTo investigate the distribution and nerve staining of two volumes of lidocaine–dye solution after ultrasound-guided erector spinae plane (ESP) injections in canine cadavers.Study designExperimental cadaveric study.AnimalsA total of nine canine cadavers.MethodsESP injections were performed between the longissimus thoracis muscle and the dorsolateral edge of the ninth thoracic transverse process. Two cadavers were transversally cryosectioned after unilateral ESP injections [0.6 mL kg^–1; high volume (HV)]. In seven cadavers, bilateral ESP injections with HV or low volume (0.3 mL kg^–1; LV) were performed. Gadodiamide was added to the injectate for two cadavers and magnetic resonance imaging (MRI) was performed pre- and post-injection. Injectate distribution and nerve staining of the branches of the spinal nerves were recorded after gross anatomical dissection. The thoracic paravertebral and epidural spaces were examined for dye solution.ResultsCryosections, MRI and gross dissections showed that the injectate spread dorsally to the transverse processes, over the ventromedial aspect of the longissimus thoracis muscle where the medial and lateral branches of the dorsal branches of the spinal nerves are located. LV and HV stained a median (range) of 4 (2–7) and 4 (3–8) medial branches, respectively (p = 0.52). LV and HV stained 4 (2–5) and 5 (4–7) lateral branches (p = 0.26), respectively. Ventral branches were not stained, and dye was not identified in the epidural or paravertebral spaces.Conclusionsand clinical relevance Medial and lateral branches were consistently stained over several spinal segments. The number of nerves stained was not different with HV or LV, and the ventral branches of the spinal nerves were not stained in any cadaver. ESP block may find a clinical application to desensitize structures innervated by the medial and lateral branches of the dorsal branches of the thoracic spinal nerves.     

Mm. scaleni of the Ox (Bos taurus L)*)

The Mm. scaleni of 20 bovine cadavers were dissected and their attachments and nerve supply are described and illustrated. The literature is reviewed and the principles of subdividing the muscles are discussed. The emerging roots of the brachial plexus rather than the axillary vessels are taken as the dividing line between the middle and ventral scalene muscles. This principle can also be applied to the other domesticated species. Fascicles formerly described as M. iliocostalis cervicis are grouped with the M. scalenus medius as its Pars superficialis on the ground of their nerve supply. The scalene muscles are innervated by the ventral branches of spinal nerves C4—T2. The subdivisions and innervation in the ox are as follows: 1. M. scalenus dorsalis, C5—T2. 2. M. scalenus medius: Pars superficialis, C4—C8; Pars profunda, C8. 3. M. scalenus ventralis, C4—T2.     

Endoscope‐Assisted Thoracolumbar Lateral Corpectomy

Objective: To report an endoscope‐assisted lateral approach to expose the intervertebral foramen and disk and perform lateral corpectomy of thoracolumbar disks in dogs. Study Design: Cadaver study. Animals: Fresh canine cadavers (n=6). Methods: A thoracic (T10–T11) and a lumbar (L3–L4) lateral approach were made on 6 fresh canine mixed breed cadavers. Through a limited skin incision, musculature was dissected and retracted using a neurosurgical self‐retaining retractor and lateral corpectomy performed. The approach and bone removal, both performed under endoscopic control, were assessed. Results: The foramen and intervertebral disk were clearly observed in all specimens without any iatrogenic injury of the ventral and dorsal nerve branches. Access to the foramen was possible in all specimens; in the thoracic area the head of the rib was always partially excised to observe the intervertebral disk medially. Lateral corpectomy was easily performed in all cadavers and spinal cord observation was good. Extension to foraminotomy or mini hemilaminectomy could easily be performed through the same limited approach. Conclusion: Endoscopic exploration provided a good viewing of the intervertebral disk and/or foramen. An endoscope‐assisted thoracolumbar lateral corpectomy could effectively be performed through a limited approach to the thoracolumbar disks and allowed good ventral spinal cord assessment.     

Ultrasonographic study of a modified axillary approach to block the major branches of the brachial plexus in dogs

ObjectiveTo provide ultrasonographic mapping of the axillary region of dogs to facilitate identification of the major branches of the brachial plexus in relation to the axillary artery.Study designProspective study.AnimalsA total of two dog cadavers and 50 client-owned, healthy dogs weighing >15 kg.MethodsIn Phase 1, anatomical dissections were performed to identify the relation of the major brachial plexus nerves to the axillary artery. In Phase 2, with the dogs in dorsal recumbency with thoracic limbs flexed naturally, the axillary space was scanned using a linear array probe oriented on the parasagittal plane until the axis transverse to nerves was found. Then, the transducer was rotated to a slight lateral angle approximately 30° to midline. The examination aimed to identify the axillary artery and the musculocutaneous, radial, median and ulnar nerves in addition to determining their position and distribution in four predefined sectors.ResultsThe musculocutaneous nerve was observed in all animals cranial to the axillary artery. The radial, ulnar and median nerves were distributed around the axillary artery, with >90% on the caudal aspect of the axillary artery (sectors 1 and 2).Conclusions and clinical relevanceUltrasonography identified the location of the brachial plexus nerves near the studied sectors, providing useful guidance for performing a brachial plexus nerve block.