Lumbosacral plexus block using a combination of ultrasound-guided lateral pre-iliac and parasacral approaches in cats

ObjectiveTo describe an ultrasound-guided lateral pre-iliac (LPI) and parasacral (PS) approach in feline cadavers (phase I) and compare the perioperative analgesic use and complications in cats administered LPI and PS blocks (group PNB) or epidural anesthesia (group EPI) for pelvic limb surgery (phase II).Study designExperimental uncontrolled, anatomic and retrospective cohort study.AnimalsA group of eight feline cadavers and 52 medical records.MethodsBilateral LPI and PS approaches with 0.1 mL kg^–1 of dye to stain the femoral and obturator nerves and the lumbosacral trunk, respectively, were performed on each cadaver. Nerve staining effect was evaluated upon dissections (phase I). Perioperative analgesics use, and complication rates were retrospectively compared between groups PNB and EPI (phase II). Continuous data were compared using the Mann–Whitney U test and the prevalence of events with Fisher’s exact test. Differences were considered significant when p < 0.05.ResultsDissections revealed that the LPI approach stained 94% and 75% of the femoral and obturator nerves, respectively. The PS approach stained 100% of the lumbosacral trunks. Cats enrolled in group PNB (n = 23) were administered lower doses of intraoperative opioids than those in group EPI (n = 25) (p = 0.006). Intraoperative rescue analgesia was required in 60% and 17.4% of cats enrolled in groups EPI and PNB, respectively (p = 0.003). Group PNB required more intraoperative anticholinergics than group EPI (p = 0.02). There were no differences in postoperative pain scores, analgesic use and complication rates.Conclusions and clinical relevanceThe ultrasound-guided LPI and PS approach stained the femoral/obturator nerves and the lumbosacral trunk, respectively, in feline cadavers. Furthermore, PNB was associated with lower intraoperative opioid use and similar postoperative pain and analgesic use compared with epidural anesthesia in a cohort of cats undergoing surgery of the pelvic limb.     

Comparison of three ultrasound guided approaches to the lumbar plexus in dogs: a cadaveric study

ObjectiveTo assess the accuracy of contrast material injection and the dispersion of injectate following ultrasound guided injections at the level of L6 and L7, in canine cadavers.Study designProspective, randomized, experimental study.AnimalsTwenty nine mixed breed canine cadavers (28.9 ± 6.0 kg).MethodsThree ultrasound-guided approaches to the lumbar plexus (LP) were compared: 1) a dorsal pre-iliac approach at the level of L6; 2) a lateral paravertebral approach at mid-L6; and 3) a lateral paravertebral approach at mid-L7. An isovolumic mixture of iodine-based contrast with new methylene blue (0.1 mL kg⁻¹) was injected bilaterally in the juxta-foraminal region along the L6 or L7 nerve root. Computed tomography was performed followed by segmentation and 3D reconstruction of the lumbar spine and contrast material volumes using dedicated software. Distances between contrast material and the fifth through seventh lumbar foraminae, and length of femoral (FN) and obturator (ON) nerve staining were measured and compared between approaches (p < 0.05).ResultsInjectate moved cranial and caudal to the site of injection, and dispersed into an ovoid shape between the quadratus lumborum, iliopsoas and psoas minor muscles. Injections at L7 resulted in significantly closer contrast proximity to the L6 and L7 foraminae (p < 0.001). Femoral nerve staining was similar for all approaches, ON staining was more consistent after L7 injections (p < 0.001).Conclusion and clinical relevanceAn ultrasound-guided lateral paravertebral approach to the LP proved very practical and accurate, with easy visualization of the plexus and associated nerves. To ensure that the ON is covered by injectate, an approach at the level of L7 is recommended. Further studies are necessary to determine if this correlates with clinically effective local anesthesia.     

Ultrasound-guided thoracic paravertebral injection in dogs: a cadaveric study

Objective

To describe ultrasound-visualized anatomy and the spread characteristics of a dye injected in the thoracic paravertebral (TPV) space under ultrasound guidance.

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.     

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.     

Mandibular nerve block in juvenile Nile crocodile: a cadaveric study

ObjectiveTo develop a technique for performing the mandibular nerve block in Nile crocodiles.Study designExperimental cadaveric study.AnimalsA total of 16 juvenile Nile crocodile heads.MethodsTo study the course of the mandibular nerve, one head was dissected. Computed tomography (CT) examination was performed in two heads to identify useful landmarks. Thereafter, a hypodermic needle was inserted through the external mandibular fenestra of 17 hemimandibles (13 heads), and a mixture of methylene blue and iohexol was injected. Injection volumes were 0.5 (n = 7) and 1.0 mL (n = 10) for hemimandibles < 15 and ≥ 15 cm long, respectively. Iohexol spread and nerve staining with methylene blue were assessed with CT and anatomical dissection, respectively. Data were analysed with one-sample t test or Mann–Whitney U test. Significance was set at p < 0.05.ResultsBoth anatomical dissection and imaging confirmed the external mandibular fenestra as a useful anatomical landmark for needle insertion. The CT images acquired after needle positioning confirmed that its tip was located on the medial bony mandibular surface formed by the fusion of the angular and coronoid bones in 100% cases. In all the hemimandibles, the rostrocaudal spread of contrast was > 23 mm. The length of the stained mandibular nerve in the temporal region and of the stained medial branch of the mandibular nerve, as well as the dorsoventral and mediolateral spread of iohexol, was greater in group 1.0 than in group 0.5 (p < 0.001). The caudal spread of iohexol was greater in group 1.0 than in group 0.5 (p = 0.01).Conclusions and clinical relevanceThe technique developed in this study is feasible. Both injection volumes resulted in staining of the mandibular nerve. The spread of contrast in the anatomical region of interest may result in successful sensory block.     

Occurrence and clinical management of urethral obstruction in male cats under primary veterinary care in the United Kingdom in 2016

BackgroundUrethral obstruction (UO) has a negative effect on welfare of cats.ObjectivesThis study aimed to determine incidence, case management, and outcomes of UO in cats in primary‐care practice in the United Kingdom.AnimalsAll male cats under veterinary care within the VetCompass database in 2016.MethodsA retrospective cohort study was performed. The electronic records of all male cats with a clinical note during the study period were searched for UO cases and were manually reviewed for inclusion. Additional demographic and clinical information were extracted on cases.ResultsFrom the study cohort of 237 825 male cats, there were 1293 incident cases. The estimated UO incidence risk during 2016 was 0.54 (95% CI: 0.51‐0.57). Demographic and clinical data were available for 1108 cases. Antibiotics were administered to 641/1108 (57.9%) cases. Overall repeat catheterization rate was 253/854 (29.6%). Repeat catheterization at 48 hours was less frequent in patients with indwelling catheters (10.1%) vs those that had a catheter placed and then immediately removed (14.8%; P = .04). Death during a UO episode was 329/1108 (29.6%), and 285/329 (88.0%) deaths involved euthanasia.Conclusions and Clinical ImportanceAntibiotics were commonly prescribed in cats for treatment of UO despite minimal evidence in the clinical records of bacterial cystitis. Repeat catheterization was common and case fatality rate during a UO episode was high. Repeat catheterization within 48 hours of elective removal of a urethral catheter was less common in cats that had previously had indwelling catheters. The majority of cats requiring repeat catheterization survived until the end of the study.     

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.     

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.     

An ultrasound-guided subparaneural approach to the sciatic nerve in the dog: a cadaver study

ObjectiveTo describe the gross and microscopic anatomy of the sciatic nerve paraneural sheath and to report an ultrasound (US)-guided subparaneural approach to the sciatic nerve in dogs, comparing two different volumes of injectate.Study designProspective, randomized, anatomical study.AnimalsA group of nine middle-sized adult Mongrel canine cadavers (18 limbs).MethodsThe sciatic nerves of three pelvic limbs of two canine cadavers were identified, exposed and isolated between the greater trochanter and the popliteal fossa for gross anatomical and microscopic examination. An additional three pelvic limbs were surgically dissected on the lateral surface of the limb; the sciatic nerves were isolated, and a 26 gauge over-the-needle catheter was inserted through the paraneural sheath under direct visualization. A methylene blue solution was then slowly injected into the subparaneural compartment through the catheter under US visualization using an 8–13 MHz linear-array transducer. Subsequently, 12 pelvic limbs (six cadavers) were randomly allocated to one of two groups; using US-guided percutaneous subparaneural approach, either 0.1 or 0.05 mL kg^–1of a 1:1 solution of methylene blue and 0.5% bupivacaine was injected. The spread of the dye solution and the amount of nerve staining were macroscopically scored. The stained sciatic nerves with their sheaths were then harvested for microscopic examination.ResultsThe paraneural sciatic nerve sheath was easily identified distinct from the nerve trunk both macroscopically and with US visualization, and microscopically. Complete staining was achieved in five of six (83.3%) sciatic nerves in each group; no difference was found in the amount of staining between the two groups. Microscopically, no signs of sciatic nerve intraneural injection were observed.Conclusions and clinical relevanceThe US-guided subparaneural injection of 0.05 mL kg^–1 of a dye injectate resulted in satisfactory nerve staining without evidence of sciatic nerve intraneural injection.     

Ultrasound‐guided retrobulbar nerve block in horses: a cadaveric study

Objective To develop an ultrasound‐guided technique for retrobulbar nerve block in horses, and to compare the distribution of three different volumes of injected contrast medium (CM) (4, 8 and 12 mL), with the hypothesis that successful placement of the needle within the retractor bulbi muscle cone would lead to the most effective dispersal of CM towards the nerves leaving the orbital fissure. Study design Prospective experimental cadaver study. Animals Twenty equine cadavers. Methods Ultrasound‐guided retrobulbar injections were performed in 40 cadaver orbits. Ultrasound visualization of needle placement within the retractor bulbi muscle cone and spread of injected CM towards the orbital fissure were scored. Needle position and destination of CM were then assessed using computerized tomography (CT), and comparisons performed between ultrasonographic visualization of orbital structures and success rate of injections (intraconal needle placement, CM reaching the orbital fissure). Results Higher scores for ultrasound visualization resulted in a higher success rate for intraconal CM injection, as documented on the CT images. Successful intraconal placement of the needle (22/34 orbits) resulted in CM always reaching the orbital fissure. CM also reached the orbital fissure in six orbits where needle placement was extraconal. With 4, 8 and 12 mL CM, the orbital fissure was reached in 16/34, 23/34 and 28/34 injections, respectively. Conclusion and clinical relevance The present study demonstrates the use of ultrasound for visualization of anatomical structures and needle placement during retrobulbar injections in equine orbits. However, this approach needs to be repeated in controlled clinical trials to assess practicability and effectiveness in clinical practice.     

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.     

Maxillary nerve blocks in horses: an experimental comparison of surface landmark and ultrasound-guided techniques

Objective

The aim of this preliminary proof-of-concept study was to evaluate and compare the success and complication rate of infiltration of the maxillary nerve of cadaver heads using previously described surface landmarks, standard ultrasound and a novel needle guidance positioning ultrasound system (SonixGPS).

Preliminary study of a teaching model for ultrasound-guided peripheral nerve blockade and effects on the learning curve in veterinary anesthesia residents

Objective

To evaluate the use of an experimental colloid model for teaching veterinary anesthesia residents ultrasound-guided technique for nerve blockade.