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 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.     

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 posterior extraconal block in the dog: anatomical study in cadavers

Objective

To describe a novel ultrasound-guided posterior extraconal block in the dog.

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.     

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.     

A non-inferiority study comparing the ultrasound-guided parasacral with a novel greater ischiatic notch plane approach in canine cadavers

ObjectiveTo describe the gross and ultrasound anatomy of the parasacral region and an ultrasound-guided greater ischiatic notch (GIN) plane approach aimed at staining the lumbosacral trunk (LST) in canine cadavers. To evaluate if the ultrasound-guided GIN plane approach is non-inferior to the previously described ultrasound-guided parasacral approach at staining the LST.Study designProspective, randomized, non-inferiority experimental anatomic study.AnimalsA total of 17 (23.9 ± 5.2 kg) mesocephalic canine cadavers.MethodsAnatomic and echographic landmarks, and the feasibility of performing a GIN plane technique were evaluated using two canine cadavers. The remaining 15 cadavers had each hemipelvis randomly assigned to be administered either parasacral or GIN plane injection of 0.15 mL kg^–1 dye solution. The parasacral region was dissected after injections to assess the staining of LST, cranial gluteal nerve, pararectal fossa and pelvic cavity. The stained LST were removed and processed for histological evaluation of intraneural injections. A one-sided z-test for non-inferiority (non-inferiority margin –14%) was used to statistically evaluate the success of the GIN plane versus the parasacral approach. Data were considered statistically significant when p < 0.05.ResultsThe GIN plane and parasacral approach stained the LST in 100% and 93.3% of the injections, respectively. The success rate difference between treatments was 6.7% [95% confidence interval, –0.6 to 19.0%; p < 0.001 for non-inferiority]. The GIN plane and parasacral injections stained the LST for 32.7 ± 16.8 mm and 43.1 ± 24.3 mm, respectively (p = 0.18). No evidence of intraneural injection was found.Conclusions and clinical relevanceThe ultrasound-guided GIN plane technique resulted in nerve staining that was non-inferior to the parasacral technique and may be considered an alternative to the parasacral approach to block the LST in 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.     

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.     

Tumescent local anesthesia with ropivacaine in different concentrations in bitches undergoing mastectomy: plasma concentration and post‐operative analgesia

ObjectiveTo compare two concentrations of ropivacaine administered for tumescent local anesthesia (TLA) in dogs undergoing mastectomy.Study designProspective randomized clinical study.AnimalsSeventeen bitches of various breeds, aged 12 ± 2 years and weighing 10 ± 6.5 kg requiring total unilateral or bilateral mastectomy.MethodsDogs were premedicated with acepromazine (0.04 mg kg^?1) and morphine (0.4 mg kg^?1) intramuscularly. Anesthesia was induced with propofol (2.5 mg kg^?1) and midazolam (0.2 mg kg^?1) intravenously, followed by intubation and maintenance with isoflurane and TLA. Dogs were randomly allocated to receive TLA either with 0.1% ropivacaine (group G1) or with 0.05% ropivacaine (group G05). TLA was performed by insertion of a multihole needle under the skin and infusion of ropivacaine and lactated Ringer’s solution at a fixed volume of 15 mL kg^?1. Ropivacaine concentrations in arterial blood were measured by high-performance liquid chromatography. Post-operative pain was assessed using two scales (University of Melbourne pain scale and a modified composite measure pain scale) and von Frey filaments, 4 hours after TLA and at 1 hour intervals until sensitivity was regained. A score above 30% of the maximum possible score was considered a positive indicator of pain.ResultsPeak plasma concentrations of ropivacaine were measured 240 minutes after TLA in G1. Low concentrations were measured in G05 for 60 minutes, with subsequent increase. Analgesic rescue and return of sensitivity occurred at 7 ± 2.3 and 7 ± 1.9 hours (mean ± SD) after TLA for G1 and G05, respectively.Conclusions and clinical relevanceTumescent local anesthesia with ropivacaine provided satisfactory post-operative analgesia that lasted for several hours, with no difference in duration between the concentrations. No serious side effects were attributed to TLA. Results indicated that 0.05% ropivacaine provided adequate analgesia for mastectomy, however, more studies are required to support this conclusion.     

Lumbar erector spinae plane block: an anatomical and dye distribution evaluation of two ultrasound-guided approaches in canine cadavers

ObjectiveTo examine the anatomy of the lumbar epaxial region and to describe two different ultrasound-guided approaches for the lumbar erector spinae plane (ESP) block in dogs.Study designAn anatomical and experimental cadaver study.AnimalsA group of 19 canine cadavers.MethodsThe anatomy was described following dissection of two cadavers. Bilateral ultrasound-guided ESP injections with 0.4 mL kg^–1 of contrast dye were performed in 17 adult Beagle cadavers using either transversal (TVS) or parasagittal (PST) approaches. Computed tomography was performed to measure the total length of the contrast dye column and the epidural, intravascular, hypaxial and intra-abdominal migration. Dissections were performed to assess the spread of the contrast dye and to determine the degree of staining of the dorsal branches of the spinal nerves (DBSN). Mann–Whitney U and chi-square tests were used to compare data between groups.ResultsUsing both techniques, the contrast dye was observed within the ESP compartment. There was no difference in the total length of the contrast dye column between TVS and PST approaches (p = 0.056). Using the TVS approach, multisegmental staining of the DBSN was visible with 100% (17/17) of injections, while complete staining of the DBSN was achieved at 94% of the injection sites. Using the PST approach, these values were 29% (5/17) and 23% (4/17), respectively. The TVS approach stained more DBSN than the PST approach (p = 0.001), with a median (range) of 2 (2–3) versus 0 (0–3) DBSN, respectively. Using the TVS approach, epidural and intravascular migration were present in 2/17 (p = 0.485) and 3/17 (p = 0.227) injections, respectively.Conclusions and clinical relevanceBoth ultrasound-guided approaches resulted in a spread of the contrast dye within the ESP compartment. Although there were no differences in the total length of the contrast dye column, the TVS approach was superior to the PST approach in staining DBSN.     

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 the potential efficacy of an ultrasound-guided adductor canal block technique in dog cadavers

Objective

To evaluate an ultrasound-guided technique for adductor canal (AC) block by describing the distribution of methylene blue around the AC, popliteal fossa, saphenous, tibial and common fibular nerves in dog cadavers.

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.     

In-plane ultrasound-guided peribulbar block in the dog: an anatomical cadaver study

ObjectiveTo describe a novel in-plane ultrasound (U/S)-guided temporal approach to peribulbar block in dogs.Study DesignProspective experimental cadaver study.AnimalsA group of 10 Beagle cadavers.MethodsAfter describing the U/S anatomy, peribulbar injection was performed bilaterally in 10 thawed Beagle cadavers by two randomly assigned operators. A 5–8 MHz microconvex U/S probe was positioned caudal to the orbital ligament in the longitudinal plane. Using an in-plane technique, methylene blue dye was injected in five dogs (10 eyes total), while methylene blue dye and iohexol contrast mixture (50:50) were injected in the remaining five dogs. Injection volume was 0.2 mL cm^?1 of cranial length. A computed tomography (CT) scan was performed on dogs injected with dye and contrast to identify spread of contrast. Dissection to visualize dye spread in the orbit was performed in all dogs. Injection success was defined as spread of contrast into the peribulbar space. The pattern of distribution of contrast-dye was also assessed. Comparisons between operator and bilateral injections were assessed using a Student t test (p < 0.05). All other data are reported as number (n/N) and percentage (%).ResultsPeribulbar spread was noted in 19/20 injections (95%) on dissection. CT imaging (five dogs) illustrated peribulbar contrast spread in 9/10 injections (90%), with mixed peribulbar/retrobulbar spread for the remaining injection. Contrast was present at the rostral alar foramen in 4/10 (40%) injections, orbital fissure in 5/10 (50%), oval foramen in 1/10 (10%), maxillary nerve in 3/10 (30%) and intracranial in 5/10 (50%). Coverage of the maxillary nerve was noted on 3/20 (15%) injections on dissection. No further dye spread was noted.Conclusions and clinical relevanceThis technique demonstrated peribulbar spread of injectate in 100% of injections for the 10 canine cadavers studied. Further studies are required to evaluate this technique clinically.     

Description of an ultrasound-guided thoracic paravertebral block technique and the spread of dye in dog cadavers

Objectives

To describe an ultrasound-guided thoracic paravertebral block and determine the distribution after injection of two volumes of methylene blue in dog cadavers.