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.     

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.     

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.     

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.     

Ultrasound-guided rectus sheath block injections in miniature swine cadavers: technique description and distribution of two injectate volumes

ObjectiveTo describe a technique for ultrasound-guided rectus sheath block in pigs and the distribution of two injectate volumes.Study designExperimental study.AnimalsA group of 11 Hanford miniature pig cadavers.MethodsThe lateral border of each rectus abdominis muscle in 10 freshly euthanized pigs was visualized with a 6-15 MHz linear ultrasound probe. A spinal needle was inserted 1 cm cranial to the umbilicus, in-plane and medial to the probe, and advanced dorsal to lateral until the tip was ventral to the internal rectus sheath. Pigs were injected bilaterally with high volume (treatment HV; 0.8 mL kg^–1) or low volume (treatment LV; 0.5 mL kg^–1) of 1:1 solution of 1% methylene blue and 0.5% bupivacaine (1 mg kg^–1) diluted with 0.9% saline. Nerve staining ≥ 1 cm circumferentially was determined by dissection 15 minutes postinjection. The Clopper–Pearson method was used to calculate 95% confidence intervals (CIs) for proportions of stained nerves. In another pig, a 1:1 solution of 1% methylene blue and 74% ioversol contrast was injected, and computed tomography performed at 15 minute intervals after injection.ResultsNerve staining for thoracic (T) spinal nerves T9, T10, T11, T12, T13 and T14 occurred 20%, 60%, 90% 100%, 100% and 50%, and 0%, 20%, 90%, 100%, 100% and 50% of the time in treatments HV and LV, respectively. More nerves were stained in treatment HV in 4/10 animals (40%, 95% CI: 12%–74%) than in treatment LV (0%, 95% CI: 0%–31%). The greatest spread of injectate occurred within the first 15 minutes after injection.Conclusions and clinical relevanceStaining of T11–T14 nerves was the same in both treatments but the higher volume stained more T9–T10 nerves. Based on dye distribution, a rectus sheath block may only provide ventral abdominal analgesia cranial to the umbilicus in pigs.     

Open approach to the ventral transversus abdominis plane in the dog: evaluation and injectate dispersion in cadavers

ObjectiveTo evaluate a direct intra-abdominal approach to injection of the ventral transversus abdominis plane (TAP) and compare the dispersion of two volumes of injectate.Study designProspective anatomic and feasibility study.AnimalsA total of 10 canine cadavers weighing 9 ± 4 kg.MethodsA ventral incision was made extending through the linea alba, from the umbilicus and extending 5 cm caudally. A single injection of an isovolumic mixture of iopamidol and new methylene blue was performed with a hypodermic needle placed within the TAP of each hemiabdomen, alternating between 0.5 mL kg^–1 in low-volume group (LV) and 1 mL kg^–1 in high-volume group (HV). Surgical staples marked the incision. Computed tomography and three-dimensional reconstruction of the tomographic images evaluated the dimensions, cranial and caudal spread beyond the incision and the total area of the injectate. Dissection determined the extent of nerve staining within the TAP adjacent to the abdominal incision. Wilcoxon signed rank (stain) or paired t test was used to compare variables between groups. Data are reported as mean ± standard deviation or median (range).ResultsInjectate spread was within the ventral TAP. Length of spread was 2.5 ± 1.6 cm greater in group HV than in group LV. There was a strong positive correlation between the surface area (p = 0.02, r = 0.71) and cranial–caudal spread of injectate (p = 0.041, r = 0.65) with volume.All but two LV injections were associated with staining of all nerves adjacent to the incision. Additional nerves caudal to the incision were stained in group HV (p = 0.02).ConclusionsThis approach to the TAP was easily performed, with volume of injectate positively influencing distribution.Clinical relevanceThis technique is easily applied and future prospective studies are warranted to determine its analgesic efficacy.     

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.     

Ultrasound-Guided Transversus Abdominis Plane Block in Shetland Ponies: A Description of a Three-Point Injection Technique and Evaluation of Potential Analgesic Effects

Colic surgery is one of the most painful procedures carried out in horses. Common strategies to alleviate immediate postsurgical abdominal pain include the administration of potent systemic analgesics; however, these may cause unwanted adverse effects such as cardiovascular depression, ileus, and ataxia. The administration of local anesthetics at the incision site in form of an ultrasound-guided subcostal transversus abdominis plane (TAP) block may therefore be preferred to provide adequate analgesia without significant side effects. To date, no technique for a TAP block in horses undergoing median celiotomy has been described. The objective of the study was to develop a TAP block technique, which will lead to the desensitization of the ventrolateral abdominal wall and adjacent skin area of experimental Shetland Ponies using bupivacaine 0.125%. This is a prospective, blinded, self-controlled trial. A cadaver study was performed to determine the ideal injection points and the volume required to stain the nerves responsible for the sensation of the ventrolateral abdominal wall and skin in Shetland pony cadavers (i.e., T9–L 2). Subsequently, using the ideal injectate volume and the landmarks obtained in the first phase of the study, six Shetland ponies received a bilateral TAP injection, either with a local anesthetic solution (bupivacaine 0.125%) or with saline in a randomized, crossover, blinded fashion. Effectiveness was determined over a 4 hour postinjection time, by using a pinprick technique. Significant differences were found to the responses of the pinprick evaluation between the bupivacaine- and saline-treated sides after 30 minutes of TAP block injection. Reported “learned behavior” could have affected the results of the pinprick testing. The TAP block technique reported in this study using bupivacaine 0.125% appeared effective in desensitizing the lower abdomen of ponies for up to 2 hours. Further research is required to apply this technique in horses undergoing celiotomy. Potentially larger volumes and/or higher concentrations of bupivacaine may be necessary to provide longer duration of action of the block.     

Evaluation of ultrasound-guided pecto-intercostal block in canine cadavers

ObjectiveTo describe the technique for performing an ultrasound-guided pecto-intercostal fascial (PIF) block and compare two volumes of injectate in canine cadavers.Study designProspective experimental cadaveric study.AnimalsA total of 11 canine cadavers (11.8 ± 1.9 kg).MethodsParasternal ultrasound-guided injections were performed within the PIF plane, between the deep pectoral and external intercostal muscles, at the intercostal space between ribs four and five. Each hemithorax was injected with 0.25 mL kg^–1 (treatment low volume, LV) or 0.5 mL kg^–1 (treatment high volume, HV) of 1% methylene blue dye. Treatments were randomly assigned to either right or left hemithorax, with each cadaver injected with both treatments, for a total of 22 injections. Anatomical dissections were performed to determine staining of ventral cutaneous branches of intercostal nerves, surrounding nerves and musculature and spread of injectate. The presence or absence of intrathoracic puncture was also noted.ResultsThe PIF plane was identified and injected in each hemithorax. No significant differences between treatments LV and HV were found for number of ventral cutaneous nerve branches stained or any other analyzed variable. The ventral cutaneous branches of intercostal nerves (T3–T8) were variably stained, and the most commonly stained nerves were T5 (6 and 10), T6 (8 and 9) and T7 (2 and 7) in treatments LV and HV, respectively. Staining outside the immediate parasternal region was noted in both treatments, with greater spread away from the parasternal region in treatment HV. No intrathoracic staining was found.Conclusions and clinical relevanceUltrasound-guided PIF injections resulted in staining of ventral cutaneous branches and parasternal musculature; however, the spread observed was inadequate to provide effective analgesia to the sternum. In vivo studies are warranted to investigate this regional anesthetic technique in veterinary patients.     

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.     

Development of a lateral ultrasound-guided approach for the proximal radial,ulnar, median and musculocutaneous (RUMM) nerve block in cats

ObjectiveTo describe a lateral ultrasound (US)-guided approach to the radial, ulnar, median and musculocutaneous (RUMM) nerves through a single proximal in-plane insertion in cats and to determine whether one or two injection points are required to successfully stain all the target nerves.Study designProspective study.AnimalsA total of eight client-owned healthy cats and 12 cat cadavers.MethodsIn live cats, the US anatomy of the brachium, the landmarks and the site for needle accesses were determined. Then, 12 thawed feline cadavers were used to assess the spread of dye solution and nerve staining following the US-guided proximal-lateral-humeral RUMM injection using one and two injection points. Each cadaver was injected with 0.15 mL kg^–1 of a 0.25% new methylene blue solution in either a single injection aimed for the radial nerve of one limb (G1) or via two sites delivering 0.1 mL kg^–1 and 0.05 mL kg^–1 aimed for the radial and musculocutaneous nerves of the opposite limb, respectively (G2). Upon dissection, staining of the target nerves around their circumference for length of >1 cm was considered successful.ResultsSonoanatomy was consistent with anatomy upon dissection and target nerves were identified in all cadavers. Staining was 100% successful for the radial, median and ulnar nerves in both groups, and 41.7% and 100% for the musculocutaneous nerve in G1 and G2, respectively.Conclusions and clinical relevanceThis novel lateral US-guided approach for the proximal RUMM nerve block allowed a good identification of the nerves and related structures, and it provided a consistent muscular structure through which the needle could be easily guided. An injection performed in two aliquots (within the caudal and cranial compartments of the neurovascular sheath) appeared to be necessary to successfully stain all the target nerves.     

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 dorsal approach for the brachial plexus block in common kestrels (Falco tinnunculus): a cadaver study

ObjectiveTo develop an ultrasound-guided dorsal approach to the brachial plexus and to investigate the nerve distribution and staining of a dyed injectate in common kestrel (Falco tinnunculus) cadavers.Study designProspective, cadaver study.AnimalsA group of three common kestrel cadavers (six wings).MethodsAll cadavers were fresh-frozen at –20 °C and thawed for 10 hours at room temperature before the study. The cadavers were placed in sternal recumbency and their wings were abducted. A 8–13 MHz linear-array transducer was placed over the scapulohumeral joint, at the centre of a triangle formed by the scapula and the humerus. The brachial plexus was identified between the scapulohumeralis muscle and the pectoralis major muscle, as hypoechoic structures lying just cranially to the axillary vessels. After ultrasound-guided brachial plexus identification, a 22 gauge, 50 mm insulated needle was advanced in-plane using ultrasound visualization. A volume of 0.5 mL kg^–1 of a 3:1 (2% lidocaine:methylene blue) solution was injected. Following cadaver dissection, the pattern of the spread was assessed, and the extent of nerve staining was measured with a calliper and deemed adequate if more than 0.6 cm of the nerve staining was achieved.ResultsThe brachial plexus was clearly identified in all wings with the dorsal approach. After dye injection, all the branches of the brachial plexus defined as nerves 1–5 (N1, N2, N3, N4 and N5) were completely stained in five (83%) and partially stained in one (17%) of the six wings.Conclusions and clinical relevanceThe ultrasound-guided dorsal approach allows a clear visualization of the brachial plexus structure. The injection of 0.5 mL kg^–1of a lidocaine/dye solution produced complete nerve staining in most cases. Further in vivo studies are mandatory to confirm the clinical efficacy of this locoregional anaesthesia technique in common kestrels (Falco tinnunculus).     

Description of an ultrasound-guided rectus sheath block injection technique and the spread of dye in calf cadavers

ObjectivesTo describe an ultrasound-guided rectus sheath (RS) block technique in calves with injections of methylene blue and assess the extent of injectate spread and nerve staining in calf cadavers.Study designProspective, experimental, blinded cadaveric study.AnimalsA total of 16 calf cadavers weighing 30.7 ± 7.1 kg.MethodsUsing an ultrasound-guided, in-plane technique, each cadaver was injected with both a low (LV; 0.25 mL kg^–1) and high (HV; 0.5 mL kg^–1) volume of methylene blue dye. Volumes were randomly assigned to the left or right hemiabdomen. Ultrasound imaging was scored based on landmarks and needle visualization, and duration to perform injections were assessed. Dissections were performed immediately after injections. Staining of ventral branches of spinal nerves and the extent of dye spread were recorded by an anatomist unaware of treatment allocation.ResultsThe number of nerves stained in treatments LV and HV were 2.3 ± 1.7 and 4.4 ± 1.3, respectively (p = 0.0001). Branches of thoracic nerves T7–13 and lumbar nerves L1–2 were completely stained 6.3%, 6.3%, 31.3%, 62.5%, 56.3%, 37.5%, 31.3%, 6.3% and 0%, respectively, in treatment LV and 0%, 12.5%, 50%, 93.8%, 100%, 93.8%, 62.5%, 25% and 6.3%, respectively, in treatment HV. Ultrasound imaging was scored excellent in most cadavers and needle visualization deemed excellent in all injections. The mean duration to perform RS injections in both treatments was 2 (range, 1–6) minutes.Conclusions and clinical relevanceNerve staining results from treatment HV suggest that this RS injection technique could be clinically useful in ventral midline surgical procedures, including umbilical procedures, in calves. This study supports future clinical trials in calves.     

Anatomical Evaluation of the Thoracolumbar Nerves Related to the Transversus Abdominis Plane Block Technique in the Dog

Transversus abdominis plane (TAP) is a fascial plane containing the thoracolumbar nerve branches that innervate the abdominal wall. Limited information is available on the anatomical organization of these nerve branches in the dog, which is of great importance for the success of the TAP block anaesthetic technique. The aim of this study was to describe the origin and conformation of thoracolumbar nerves running through the TAP in 20 hemi‐abdominal walls of 10 adult mongrel dog cadavers with an average body weight of 12.6 kg (range: 9.6‐15.6). The abdominal walls were dissected from superficial to deep direction, the skin and both obliquus externus abdominis and obliquus internus abdominis muscles were dissected and reflected dorsally to expose the transversus abdominis muscle and the thoracolumbar nerve branches located in this plane. The anatomical features of ventral nerve branches were described. The thoracic nerve branches: T7–T12 and costoabdominalis; and the lumbar nerve branches: iliohypogastricus cranialis, iliohypogastricus caudalis, ilioinguinalis and cutaneus femoris lateralis were identified in all the cadavers. Anatomical variations related to the presence or absence within the TAP of the T7, T8 and T9 nerve branches were found. These variations should be taken into account when planning the TAP block technique in dogs.