Ultrasound-guided continuous block of median and ulnar

Veterinary Anaesthesia and Analgesia 2020, 47, 405e413 https://doi.org/10.1016/j.vaa.2019.12.008

RESEARCH PAPER

Ultrasound-guided continuous block of median and ulnar

nerves in horses: development of the technique

Maria Teresa MR Soutoa, Denise T Fantonib, Adilson Hamajic, Marcelo Hamajic,

Cynthia P Vendruscolob, Denise A Otsukid, Ana Carolina BCF Pintob & Aline M Ambr�osiob

aDepartment of Anesthesiology, School of Medicine, University of S~ao Paulo, S~ao Paulo, SP, BrazilbSurgical Clinic Department, School of Veterinary Medicine and Animal Science, University of S~ao Paulo, S~ao Paulo,

SP, BrazilcClinical Hospital, Institute of Orthopedics and Traumatology, S~ao Paulo, SP, BrazildLIM/08, Laboratory of Anesthesiology, Laboratory of Medical Research, Clinical Hospital, School of Medicine,

University of S~ao Paulo, S~ao Paulo, SP, Brazil

Correspondence: Maria Teresa MR Souto, Department of Anesthesiology, USP Medical School, Av. Dr. Eneas de Carvalho Aguiar nº 155, 8º Andar e Pr�edio

dos Ambulat�orios - Bloco 3 - CEP 05403-000 - Cerqueira C�esar S~ao Paulo, SP, Brazil. E-mail: [email protected]

Abstract bearing in affected limbs and decreased requirement for

Objective To develop a technique for ultrasound-guidedcontinuous median and ulnar peripheral nerve block inhorses.

Study design Anatomical and prospective experimentalstudy.

Animals A total of 16 thoracic limbs from horse cadaversand 18 adult horses.

Method This study was conducted in three phases. Phase1: Dissection of median and ulnar nerves in the ante-brachial region of two cadaver limbs to identify localizinglandmarks. Description of sonoanatomy in 14 cadaverlimbs using ultrasound-guided perineural infiltration of acombination of cellulose gel (5 mL), contrast medium (4mL) and methylene blue (1 mL). Catheters were insertedbetween the perineural sheath and epineurium in six limbs,followed by computed tomography. Phase 2: Ultrasono-graphic images of the limbs of 18 healthy horses of differentbreeds were used to define an acoustic window and opti-mize the approach to nerves. Phase 3: Two case reports ofhorses with chronic pain of different etiologies. Catheterswere inserted between the epineurium and paraneuralsheath of the median and/or ulnar nerves guided by ul-trasound, followed by continuous infusion of 0.4%ropivacaine.

Results Information from phase 1 was used to direct needleinsertion, solution dispersion and catheter implantation inphase 2, which resulted in 100% technique accuracy. Inresponse to the peripheral nerve block, pain reduction wasapparent in the two clinical cases by increased weight

systemic analgesic medications. No local reactions wereobserved.

Conclusions and clinical relevance The ultrasound tech-nique allowed real-time visualization of needle, catheter anddrug dispersion and resulted in a high success rate for nerveblocks. The horses administered a median and ulnar nerveblock exhibited no discomfort or signs of infection at thecatheter insertion site. Further studies are warranted tovalidate the efficacy of this technique.

Keywords catheters, horses, indwelling, infusion pump,nerve block, ultrasonography.

Introduction

Musculoskeletal diseases are the leading causes of loss in thehorse industry. These diseases involve muscles, bones, joints,tendons and ligaments, with ligament damage being the mostclinically relevant because of slow healing and consequenttransition to chronic disorders (Broster et al. 2009; Wagner2010; Caston & Burzette 2018). Surgical trauma, especiallywith preexisting pain, may cause peripheral and central painsensitization and result in long-lasting, intractable pain syn-dromes (Hoheisel &Mense 1989; Harvey et al. 2004; Driessenet al. 2008; Guedes 2017) Diseases such as laminitis causepain refractory to conventional systemic analgesia, requiringeuthanasia in serious cases (Collins et al. 2010; Wylie et al.2012). Pain in horses is controlled by the use of non-steroidal anti-inflammatory drugs (NSAIDs), steroids, opioids,N-methyl-D-aspartate receptor blockers and anticonvulsants(Driessen 2007). Prolonged NSAID use is the most common

405

mailto:[email protected]

https://doi.org/10.1016/j.vaa.2019.12.008

Median and ulnar nerve blocks in horses MTMR Souto et al.

treatment in equine pain medicine, often causing serious sideeffects (Taylor et al. 2002; Flecknell 2008; van Weeren & deGrauw 2010; Bardell 2017). Furthermore, NSAIDs alone areineffective at controlling moderate to intense pain in humansaccording to the World Health Organization. Although opioidsare more effective than NSAIDs in controlling pain, they toocan cause adverse effects in horses (Taylor et al. 2002;Flecknell 2008; van Weeren & Back 2016).Use of regional anesthesia is popular in human medicine.

Peripheral nerve blocks can improve analgesia, decrease theduration of hospitalization and, by decreasing the need forsystemic medication, minimize the side effects (Kapral et al.2008; Kiran et al. 2018). Use of ultrasonography allowsvisualization of the needle position and spread of the localanesthetic solution in real time. The advantages over con-ventional, blind techniques are significant, such as decreasedvolume for injection for effective blockade, reducing the risk oftoxicity from the local anesthetic, and decreased risk of intra-neural or intravascular injections or damage (Marhofer et al.1998, 2010; Kapral et al. 2008; Kiran et al. 2018). High-resolution equipment is essential, and the clinician must ac-quire experience in ultrasonography and knowledge of thelocal anatomy of the nerve to be blocked (Gray 2006; Juaneset al. 2016).Local anesthetic solution for a peripheral nerve block can be

administered as single or multiple boluses or by a continuousinfusion (Gray & Schafhalter-Zoppoth 2003; Jones et al.2007). A continuous infusion of local anesthetic is deliveredthrough a catheter inserted percutaneously, using ultrasoundto guide the tip to the nerve or plexus. The drug can be titratedaccording to the desired level of motor or sensory block(Marhofer et al. 2010). Nerve blocks are indicated in theperioperative or postoperative periods, as well as for chronicpain, because local analgesia can provide effective pain reliefwith a lower incidence of side effects compared with systemicadministration of analgesics (Capdevila et al. 2005; Ilfeld2011, 2017).Studies of continuous perineural blockade of the palmar

nerves in the distal equine thoracic limb have been published(Zarucco et al. 2007, 2010; Driessen et al. 2008; Watts et al.2011). No studies regarding continuous median andulnar nerve blockade in horses were found in the literaturesearch. The aim of this study was to describe the gross anatomyand ultrasonographic anatomy of the median and ulnarnerves at the antebrachium in horses, to identify landmarks forneedle and catheter insertion at this site and to test theseprocedures in vivo and assessing response to ropivacaineinjection. Our hypothesis was that the use of ultrasoundwould allow precise localization of the median and ulnarnerves in real time and that the adequate positioning of thecatheter with this technique could enhance the quality of theblock.

© 2020 Association of Veterinary Anaesthetists and American College406

Materials and methods

This study was approved by the Animal Ethics Committee ofthe School of Veterinary Medicine and Animal Science, Uni-versity of S~ao Paulo, Brazil (no. 7941181114) and by theAnimal Ethics Committee of the Medical School, University ofS~ao Paulo, Brazil (no. 175/14). It was conducted at the Vet-erinary Hospital of the School of Veterinary Medicine andAnimal Science of the University of S~ao Paulo, Brazil.

Animals

The study was divided into three phases. In phase 1, theanatomy of the antebrachial region containing median andulnar nerves was defined using dissection, ultrasonographyand computed tomography (CT) in horse cadavers. In phase 2,the same anatomy was studied using ultrasonography inconscious horses of different breeds. In phase 3, median andulnar nerve blocks were evaluated in two clinical equinepatients.

Phase 1

The thoracic limbs of eight horses that died for reasons unre-lated to this study were used. Immediately after death, thelimbs were disarticulated from the body at the scapula andfrozen. The limbs were slowly thawed by immersing the limbsin a container of water at room temperature for 24 hours. Theanatomy of two limbs was studied using literature guidelineson neuroanatomy of equine thoracic limbs and the aid of ananatomist (Constantinescu et al. 2004; Ashdown & Done2012). The limb was placed with the lateral side facingdown, and the skin and superficial fascia were dissectedexposing the pectoralis transversus, flexor carpi radialis, flexorcarpi ulnaris, superficial digital flexor and deep digital flexormuscles as well as the median and ulnar nerves.The other 14 thoracic limbs were examined for the sonoa-

natomy study. The limbs were placed with the lateral sidefacing down and the limb in extension. Ultrasonography wasperformed using a multifrequency linear transducer (13e6MHz, model HFL38x; FUJIFILM SonoSite Inc., WA, USA)configured with nerve preset and a SonoSite M-turbo model(FUJIFILM SonoSite Inc.). The transducer was positionedtransversely to the limb (short axis) to identify the median andulnar nerves and all structures adjacent to them. Initially,echogenic needles (22 gauge, 0.70 � 50 mm; Stimuplex ultra;B Braun Melsungen, Germany) were placed between theepineurium and paraneural sheath of both nerves in theantebrachial region. The needles were inserted percutaneouslyat an angle of approximately 60 degrees between the trans-ducer and the limb in a proximal to distal direction. The so-lution for ultrasound-guided perineural infiltration wasmethylene blue (1 mL; ADVantage, SP, Brazil), iodine-based

of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rightsreserved., 47, 405e413


contrast (4 mL; Omnipaque; GE Healthcare, SP, Brazil) andcellulose-based thermic gel (5 mL; Termogel Industria e Com-ercio de Produtos de Est�etica Ltda, SP, Brazil), of which 4 mLwas injected over 2e3 minutes on the perineural sheaths ofthe ulnar nerve and 6 mL on the median nerve.In two of the 14 limbs, a Tuohy needle from an epidural

anesthesia kit (19 gauge; Sigma-Aldrich; Becton DickinsonIndústrias Cirúrgicas Ltda, MG, Brazil) was used to facilitatecatheter introduction for the tomography study. The catheters(BD Durasafe Plus 19 gauge; Becton Dickinson IndústriasCirúrgicas Ltda) were filled with the same solution previouslydescribed to prevent air from being injected, which wouldimpair sonographic visualization of structures. Prior to cath-eter placement, the Tuohy needle was inserted in the spacebetween the epineurium and paraneural sheath and 4 mL ofsolution was injected to expand the space, facilitating catheterplacement. The catheter was inserted 5 cm beyond the end ofthe Tuohy needle; the Tuohy needle was gently removed andthe distal (external) end of the catheter was sealed with a cap.The distal end was glued in the wings of a butterfly needle andsutured to the skin for fixation in the limb avoidingdisplacement.The limb was placed with the lateral side down and in

extension on the CT table [Multislice Philips MX 8000 IDT 16channels device; Philips Medical Systems (Cleveland) Inc., OH,USA] The CT images were rendered in three-dimensional (3D)images to evaluate catheter position by examining contrastagent in between the epineurium and paraneural sheath of themedian and ulnar nerves. To directly view the nerves and so-lution dispersion, two limbs were frozen after CT and then cuttransversely in 1 cm slices from olecranon base to distal radiususing a band saw.

Phase 2

A total of 18 healthy horses, Arabian (n ¼ 6), Brazilian SportHorse (n ¼ 6) and American Quarter Horse (n ¼ 6), werestudied. The Arabian horses were obtained from the School ofVeterinary Medicine and Animal Science, University of S~aoPaulo, and the other 12 horses were owned by clients whovolunteered for the study. None of these animals showedanatomical changes resulting from diseases or accidents thatwere detrimental to ultrasound study. During examination, allhorses were standing with weight bearing on all four limbs andmanually restrained only with a halter and rope. The medialand caudal regions of the antebrachium in each animal werecleaned with alcohol and soaked in ultrasound gel to reducetransducer friction with hair, minimizing acoustic noise andimproving image quality. The same ultrasound equipment andtransducer employed in phase 1 was used. The externalanatomical reference points for the median and ulnar nerveswere the transverse pectoral muscle and caudal tuberosity of

© 2020 Association of Veterinary Anaesthetists and American College of Veterinareserved., 47, 405e413

the olecranon, respectively. The distance from these anatom-ical points to the transducer position immediately above thetarget nerve was measured using a ruler graduated in centi-meters. Subsequently, the depth of the nerve, i.e., distance fromthe skin to the epineurium and paraneural sheath as well asthe nerve area were measured using the ultrasound monitor(in mm and mm2), respectively.

Phase 3

Case 1

AnAmerican Quarter Horse stallion aged 10 years andweighing480 kg was admitted with osteoarthrosis of the right meta-carpophalangeal joint of >3 months duration. The horse was inpain despite multimodal medication treatment with phenylbu-tazone, dipyrone, morphine and ketamine. The lameness scorewas 4/5 according to the American Association of Equine Prac-titioners (AAEP) scale (Baxter& Stashak 2011), a score of 8 on avisual analog scale (VAS) (Breivik et al. 2008) and a score of 7 onthe horse grimace scale (HGS; Dalla Costa et al. 2016). The re-sponses to an ultrasound-guided median nerve block with ropi-vacaine (5 mL 0.4%; ropivacaine 0.75% diluted with sterilewater) (Crist�alia Produtos Químicos e Farmaceuticos Ltda, SP,Brazil) were AAEP ¼ 1, VAS ¼ 0 and HGS ¼ 0. The horse wasanesthetized for surgical arthrodesis of the first and secondinterphalangeal joints. Before the beginning of the surgery, acatheter was inserted using the technique described for the me-dian nerve and a bolus of 5 mL of 0.4% ropivacaine was injected.After recovery from anesthesia andwith the animal standing, thecontinuous infusion of 0.4% ropivacaine was initiated with theaid of an elastomeric infusion pump (Homepump C-Ser-ieseElastomeric Balloon Pump, 100 mL; Halyard Health Inc.,GA, USA) at an infusion rate of 2 mL houre1. A filter (BectonDickinson Indústrias Cirúrgicas Ltda) was attached to the distalend of the indwelling catheter. The elastomeric pump wasbraided into the mane and then wrapped with tape.

Case 2

A Lusitano stallion aged 2 years and weighing 285 kg wasadmitted with a 2 month history of chronic laminitis of the leftthoracic limb. There was a 7 degree rotation and exposure ofthe third phalanx. The horse exhibited minimal weight bearingand remained in lateral recumbency for most of the time. Painscores were: AAEP ¼ 5, VAS ¼ 10 and HGS ¼ 8. Scores afterultrasound-guided median nerve block (4 mL of 0.4% ropiva-caine) were: AAEP¼ 2, VAS¼ 5 and HGS¼ 6. An ulnar nerveblock was performed 15 minutes later and the scores were:AAEP ¼ 2, VAS ¼ 3 and HGS ¼ 2. With the horse anes-thetized, catheters were inserted in the median and ulnarnerves for continuous infusion of 0.4% ropivacaine with twosimilar elastomeric pumps and rate described for case 1.

ry Anesthesia and Analgesia. Published by Elsevier Ltd. All rights 407


Statistical analysis

Data are described as mean ± standard deviation. Althoughdistribution of variables was analyzed using the D’Agostinotest and some of the variables had normal distribution, becauseof the small number of samples, a nonparametric test wasperformed. For comparing breeds, variables were analyzedusing KruskaleWallis test with Dunn’s post hoc test whenappropriate. A significance level of 5% was used (p < 0.05). Allstatistical tests were performed using GraphPad Prism 5(GraphPad Software, CA, USA).

Results

Phase 1

The median nerve could be observed after reflecting the skin,superficial fascia and muscles. The ulnar nerve is located su-perficially on the flexor carpi ulnaris muscle, closely connectedwith its fascia and can often be confused with this structure(Fig. 1a). This nerve can be approached distal to the olecranonon the caudal aspect of the antebrachium, being located closelyto the collateral ulnar vein and artery (Fig. 1a). By contrast,the median nerve can be approached on the medial side of thethoracic limb and is clearly observable during dissection fromthe proximal region of the antebrachium, beneath the pec-toralis transversus muscle, to distal portion of the radius, al-ways positioned caudally to this bone (Fig. 1b). The mediannerve is located underneath the flexor carpi radialis muscle inthe middle third of the antebrachium, in the distal portion ofthe pectoralis transversus muscle, and can be easily observedwhen the flexor carpi radialis muscle is displaced cranially.Moreover, this nerve is closely connected with the median

Figure 1 (a) Caudal view and (b) medial view of the antebrachial region oflexor muscle; 3, deep digital flexor muscle; 4, median nerve; 5, medianmuscle.


artery and vein, and this anatomical correlation was observedin all dissections (Fig. 1b).

Sonoanatomy (in vitro)

The transducer was positioned transversely to the limb toapproach the two nerves. The short axis images showed thatthe median and ulnar nerves are visualized as a triangular oroval hyperechoic structure with a dotted honeycomb appear-ance (Fig 2a, b). The median nerve is in close proximity to themedian vein and artery, blood vessels that are easily identifiedand provide landmarks for locating the nerve (Fig. 2a). Theulnar nerve has the same sonographic characteristics as themedian nerve, but its location requires greater image inter-pretation by the clinician. The ulnar nerve is located on thesuperficial digital flexor muscle and is differentiated frommuscle fibers by the adjacent blood vessels (Fig. 2b).In 1 cm cross sections of frozen thoracic limbs, frozen gel

dispersion was visually observed demonstrating precise injec-tion between the epineurium and paraneural sheath. Geldispersion causes expansion between the epineurium andparaneural sheath surrounding the nerve and, according tohuman literature, is considered proof for correct paraneuralaccess technique (Hadzic et al. 2016; Fig. 3).

CT scan (in vitro)

Using 3D-reconstructed CT images, placement of the cathetersbetween the epineurium and paraneural sheath and filling ofthe space with injectate was confirmed (Fig. 4). After dissec-tion, the length of the nerves that indicated contrast dispersionwas 8e10 cm.

f the left thoracic limb of a horse. 1, ulnar nerve; 2, superficial digitalvein and artery; 6 flexor carpi radialis muscle; 7, flexor carpi ulnaris


Figure 2 In vivo ultrasound images of the antebrachial region of the left thoracic limb of a horse with the transducer (green dot) placedtransversely to the limb identifying (a) the median nerve (short axis), (b) the ulnar nerve (short axis, caudal approach). In (b), A is the site formeasurement of nerve depth (0.56 cm in this horse). (For interpretation of the references to color in this figure legend, the reader is referred to theWeb version of this article.)

Figure 3 Cross-section of the proximal third of the right antebrachium of a horse. (a) 1, radius; 2, ulna; 3, median nerve; 4, median vein; 5,median artery; DDFM, deep digital flexor muscle; FCRM, flexor carpi radialis muscle; FCUM, flexor carpi ulnaris muscle; SDFM, superficial digitalflexor muscle. (b) 1, ulna; 2, ulnar nerve; DDFM, deep digital flexor muscle; SDFM, superficial digital flexor muscle. The yellow area indicates thedelineation of the perineural tissue of the nerves soaked with the gel solution.


Phase 2

The external measurements made in phase 1 established spe-cific areas for approaching each nerve in the three breeds(Fig. 5). The internal depth measurements served as guidancefor the introduction of the needle between the epineurium andparaneural sheath (Fig. 2b).


The Brazilian Sport Horses, Arabians and American QuarterHorses were aged 11.2 ± 2.8, 3.8 ± 0.8 and 17.7 ± 4.3 years,mean ± standard deviation, and weighed 554.5 ± 39.5, 346.7± 13.9 and 571.7 ± 32.1 kg, respectively.The distance from the distal portion of the pectoralis trans-

versus muscle to the median nerve was not statisticallydifferent among breeds (Table 1). The same distance to the


Figure 4 Computed tomography, 3D reconstruction of the left thoracic limb of a horse. (a) Contrast filling the space between the paraneuralsheath and epineurium of the ulnar and median nerves after ultrasound-guided infiltration. (b) Medial view of the antebrachial region of the rightthoracic limb of a horse. The blue area indicates the contrast dyeing of the median nerve which is beneath the flexor carpi radialis muscle (FCRM).

Figure 5 Anatomical reference points and positioning of the trans-ducer to define the specific area to approach the median (a) and theulnar (b) nerve of a horse. TPM, transverse pectoral muscle.


ulnar nerve was shorter in Arabians than in American QuarterHorses (p ¼ 0.007). The depth of the median nerve in theaccess area was not statistically different among breeds(Table 1). By contrast, the depth of the ulnar nerve in Amer-ican Quarter Horses was greater than that in the other twobreeds (p ¼ 0.005). The access area to the median nerve wasgreater in Brazilian Sport Horses than in American QuarterHorses (p ¼ 0.045).


Phase 3

Insertion of catheters

To implant the catheters, the two horses were anesthetized.Xylazine 10% (0.6 mg kge1; Equisedan; J.A Saúde Animal, SP,Brazil) was injected intravenously (IV) and 10 minutes later,anesthesia was induced with IV ketamine (2.2 mg kge1; Dop-alen; Ceva Saúde Animal, SP, Brazil) and diazepam (0.05 mgkge1; Compaz; Crist�alia Produtos Químicos e FarmaceuticosLtda). Anesthesia was maintained in case 1 with isoflurane(Isoforine; Crist�alia Produtos Químicos e Farmaceuticos Ltda)and in case 2 with infusions of ketamine (2.2 mg kge1 houre1)and 5% guaifenesin (100 mg kge1 houre1; EGG PPU; J.A SaúdeAnimal). Each horse was positioned in lateral recumbency withthe affected limb dependent. The hair was clipped from themedial surface of the antebrachium and the skin asepticallyprepared using alcoholic solution of 2% chlorhexidine. A layer of2% lidocaine hydrochloride acoustic gel (Xylestesin geleia;Crist�alia Produtos Químicos e Farmaceuticos Ltda) was appliedto the area; using a sterile protected probe (Nipro Safe Derme 30mm, 8Å~12 cm;NiproMedical Corporation do Brasil, SP, Brazil),the specific area for catheter implantation was located with thepreviously described technique. The Tuohy needle was coupledto a 60 cm infuser extender and a 20 mL syringe, prefilled with0.4% ropivacaine hydrochloride solution. With the transducerkept transversely over the specific area to approach the twonerves, the needle was introduced percutaneously at approxi-mately 60 degrees, out of plane. After dilation of the space be-tween the epineurium and paraneural sheath with 5 mL ofropivacaine, the catheter was introduced and advanced 5 cm


Table 1 Specific area to approach the nerves, and median and ulnar nerve depths (mean ± standard deviation) for the Brazilian Sport Horse(n ¼ 6), Arabian (n ¼ 6) and American Quarter Horse (n ¼ 6)

Breed Specific area to approach the nerves (cm2) Skinenerve depth (cm)

Median nerve Ulnar nerve Median nerve Ulnar nerve

Brazilian Sport Horse 7.7 ± 1.9 17.4 ± 2.0 2.18 ± 0.19 0.46 ± 0.05y

Arabian 7.7* ± 1.3 15.2 ± 1.7 1.86 ± 0.29 0.45 ± 0.19z

American Quarter Horse 9.2* ± 1.5 20.8 ± 2.4 2.19 ± 0.27 0.84 ± 0.22yz

Specific area to approach the nerves: the external anatomical reference points for the median and ulnar nerves were the transverse pectoral muscle and the caudal tuberosity ofthe olecranon, respectively.*Significant difference between indicated breeds (p < 0.05). ySignificant difference in skinenerve distance between indicated breeds (p < 0.05). zSignificant difference inskinenerve distance between indicated breeds (p < 0.05).


beyond the end of the needle. After catheter placement, theTuohy needlewas removed and the catheter was glued to plasticbutterfly needlewings and then sutured to the skinwith number0 nylon (Fig. 6c). After anesthesia recovery, an elastomericinfusion pump was connected to each catheter and the infusionstarted. Infusions were maintained for 24 and 10 days for cases1 and 2, respectively.

Figure 6 (a) Insertion of perineural catheter into median nerve of an anesintroduction of Tuohy needle at an angle of 60 degrees. (b) Ultrasonograpdispersion of the anesthetic between the epineurium and paraneural sheatvein. (c) Medial view of the right thoracic limb. A butterfly needle plastic wwith a cap is attached to the external end of the catheter to avoid contrecovering from anesthesia for arthrodesis surgery. The elastomeric pumpwrapped with tape is connected to a filter which is connected to the deliv


Clinical case outcomes

In both the clinical cases, the nerve blocks achieved by infusionof ropivacaine through the indwelling catheter(s) providedadequate analgesia helping the animals to recover theirnormal mobility. The horses were discharged from the hospital.Follow-up for horses 1 and 2 was after 7 months and 2 years,respectively. Although horse 1 did not return to sporting life

thetized horse. Positioning of ultrasound probe in the specific area withhic image. The yellow circle indicates the needle tip, the blue area theh. FCRM, flexor carpi radialis muscle; MN, median nerve; MV, medianing is glued to the catheter and fixed to the skin with a suture; a filteramination. (d) Horse with a continuous peripheral nerve block aftercontaining ropivacaine (black arrow) is braided into the mane and

ery catheter.



owing to the underlying disease, it maintained breeding ac-tivity with a good quality of life. The second horse was able toenter into dressage training.

Discussion

The anatomical knowledge was valuable to determine nerveposition and adjacent structures. The sonoanatomy studyestablished a specific area for approaching the nerves andidentified the depth of each nerve during needle and catheterinsertion. The results of this study demonstrated that nervevisualization requires the use of high-frequency transducers10e15 MH (Helen et al. 2015) to provide excellent resolution,allowing discrimination of nerve architecture. The ultrasono-graphic nerve appearance on short axis varies with theanatomical location and intraneural amount of connectivetissue. The median and ulnar nerves have the appearance of ahoneycomb with internal hyperechoic spots, surrounded byhyperechoic perineural tissue. Knowledge of nerve appearancein specific areas of this approach allows the clinician to identifythe nerves and adequately perform the technique (Helen et al.2015; Hadzic et al. 2016). Knowledge of the nerve depthmeasurements promotes a greater accuracy when performingthe nerve blocks, especially when performing the blockswithout ultrasound assistance. In fact, a study of blind nerveblocks of the median and ulnar nerves in horses has indicatedthat the needle is frequently inserted deeper than needed toreach the nerve (Schumacher et al. 2013).No ultrasonographic signs of vascular or neural lesions were

observed during ultrasound-guided infiltrations. Advantages touse of ultrasound in regional anesthesia include direct visual-ization of nerves, recognition of anatomical variations, obser-vation of the distribution of local anesthetic solution and aprobable reduction in the risk of intraneural and intravascularinjection (Gray 2006).There are several limitations of this study. Implementation of

these techniques for nerve blocks requires general anesthesiafor the horse and access to high-definition ultrasound equip-ment. Furthermore, in this study, only ropivacaine wasadministered to two horses; ropivacaine and other local anes-thetics with long durations of action should be tested in alarger number of horses.

Conclusions

The results of this study demonstrate that an ultrasound-guided technique facilitates precise insertion of catheterswithin the paraneural sheaths of the median and ulnar nervesin horses. Continuous infusion of ropivacaine for 24 and 10days in two horses achieved satisfactory continuous nerveblock. Practice is required to acquire proficiency in this tech-nique. Further clinical studies are necessary to prove true


benefit of this technique in other diseases affecting the thoraciclimbs of horses.

Acknowledgments

This study was financed in part by the Coordenaç~ao deAperfeiçoamento de Pessoal de Nível Superior, Brasil (CAPES) -Finance Code 001, which provided a grant for the post-graduate student. We thank the collaborators Crist�alia Pro-dutos Químicos e Farmaceuticos Ltda, B Braun Laboratory, BDBecton Dickinson and Industria Cirurgica Ltda for providingsome of the materials used in this project.

Authors’ contributions

MTMRS, CPV and DTF: anatomy, ultrasound, needling, in vitroand in vivo catheter fixation and preparation of the manuscript.AH and MH: guidance and training in ultrasound-guidedregional anesthesia. DAO: statistical analysis. ACBCFP:computed tomography study. AMA: research supervision.

Conflict of interest statement

The authors declare no conflict of interest.

References

Ashdown RR, Done SH (2012) Color Atlas of Veterinary AnatomyVol 2 e The Horse (2nd edn). Elsevier, Brazil. pp. 55e109.

Bardell D (2017) Managing orthopaedic pain in horses. In Pract 39,420e427.

Baxter GM, Stashak TS (2011) Examination for lameness: History,visual exam, palpation, and manipulation. In: Adams and Sta-shak’s Lameness in Horses (6th edn). Baxter GM (ed.). Wiley-Blackwell, USA. pp. 109e150.

Breivik H, Borchgrevink PC, Allen SM et al. (2008) Assessment ofpain. Br J Anaesth 101, 17e24.

Broster CE, Burn CC, Barr AR, Whay HR (2009) The range andprevalence of pathological abnormalities associated with lame-ness in working horses from developing countries. Equine Vet J41, 474e481.

Capdevila X, Pirat P, Bringuier S et al. (2005) Continuous periph-eral nerve blocks in hospital wards after orthopedic surgery: amulticenter prospective analysis of the quality of postoperativeanalgesia and complications in 1,416 patients. Anesthesiology103, 1035e1045.

Caston SS, Burzette RG (2018) Demographics, training practices,and injuries in lower level event horses in the United States.J Equine Vet Sci 62, 25e31.

Collins SN, Pollitt C, Wylie CE, Matiasek K (2010) Laminitic pain:parallels with pain states in humans and other species. Vet ClinNorth Am Equine Pract 26, 643e671.

Constantinescu GM, Wilson DA, Constantinescu IA, Konig HE(2004) The anatomoclinical approach to the nerves of thoraciclimbo of the horses for performing nerve block anesthesia. WienTier€arztl Monatsschr 91, 30e41.


http://refhub.elsevier.com/S1467-2987(20)30011-8/sref1









































Dalla Costa E, Stucke D, Dai F et al. (2016) Using the horse grimacescale (HGS) to assess pain associated with acute laminitis inhorses (Equus caballus). Animals 6, E47.

Driessen B (2007) Pain: systemic and local/regional drug therapy.Clin Tech Equine Pract 6, 135e144.

Driessen B, Scandella M, Zarucco L (2008) Development of atechnique for continuous perineural blockade of the palmarnerves in the distal equine thoracic limb. Vet Anaesth Analg 35,432e448.

Flecknell P (2008) Analgesia from a veterinary perspective. Br JAnaesth 101, 121e124.

Gray AT (2006) Ultrasound-guided regional anesthesia: currentstate of the art. Anesthesiology 104, 368e373.

Gray AT, Schafhalter-Zoppoth I (2003) Ultrasound guidance forulnar nerve block in the forearm. Reg Anesth Pain Med 28,335e339.

Guedes A (2017) Pain management in horses. Vet Clin North AmEquine Pract 33, 181e211.

Hadzic A, Carrera A, Clark T et al. (2016) Ultrasound-guidedforearm blocks. In: Hadzic’s Peripheral Nerve Blocks and Anat-omy for Ultrasound-guided Regional Anesthesia (2nd edn).Hadzic A, Carrera A, Clark T et al. (eds). The McGraw-HillCompanies Inc., USA. pp. 385e395.

Harvey RJ, Depner UB, W€assle H et al. (2004) GlyR alpha3: anessential target for spinal PGE2-mediated inflammatory painsensitization. Science 304, 884e887.

Helen L, O’Donnell BD, Moore E (2015) Nerve localization tech-niques for peripheral nerve block and possible future directions.Acta Anaesthesiol Scand 59, 962e974.

Hoheisel U, Mense S (1989) Long-term changes in dischargebehaviour of cat dorsal horn neurones following noxious stimu-lation of deep tissues. Pain 36, 239e241.

Ilfeld BM (2011) Continuous peripheral nerve blocks: a review ofthe published evidence. Anesth Analg 113, 904e925.

Ilfeld BM (2017) Continuous peripheral nerve blocks: an update ofthe published evidence and comparison with novel, alternativeanalgesic modalities. Anesth Analg 124, 308e335.

Jones E, Vi~nuela-Fernandez I, Eager RA et al. (2007) Neuropathicchanges in equine laminitis pain. Pain 132, 321e331.

Juanes JA, Alonso P, Hern�andez F et al. (2016) Anatomical-ultra-sound visor for regional anaesthesia. J Med Syst 40, 158.

Kapral S, Greher M, Huber G et al. (2008) Ultrasonographicguidance improves the success rate of interscalene brachialplexus blockade. Reg Anesth Pain Med 33, 253e258.


Kiran KGV, Gurram R, Fultambkar G et al. (2018) Evaluation ofultrasound guided versus nerve stimulator technique of inter-scalene brachial plexus block: insights from Indian multi-superspecialty hospital. Int J Res Med Sci 6, 2503e2507.

Marhofer P, Harrop-Griffiths W, Kettner SC, Kirchmair L (2010)Fifteen years of ultrasound guidance in regional anaesthesia: part1. Br J Anaesth 104, 538e546.

Marhofer P, Schr€ogendorfer K, Wallner T et al. (1998) Ultrasono-graphic guidance reduces the amount of local anesthetic for 3-in-1 blocks. Reg Anesth Pain Med 23, 584e588.

Schumacher J, Schramme MC, Schumacher J, DeGraves FJ (2013)Diagnostic analgesia of the equine digit. Equine Vet Educ 25,408e421.

Taylor PM, Pascoe PJ, Mama KR (2002) Diagnosing and treatingpain in the horse. Where are we today? Vet Clin North AmEquine Pract 18, 1e19.

van Weeren PR, de Grauw JC (2010) Pain in osteoarthritis. VetClin North Am Equine Pract 26, 619e642.

van Weeren PR, Back W (2016) Musculoskeletal disease in agedhorses and its management. Vet Clin North Am Equine Pract 32,229e247.

Wagner AE (2010) Effects of stress on pain in horses and incor-porating pain scales for equine practice. Vet Clin North AmEquine Pract 26, 481e492.

Watts AE, Nixon AJ, Reesink HL et al. (2011) Continuous peripheralneural blockade to alleviate signs of experimentally induced severeforelimb pain in horses. J Am Vet Med Assoc 238, 1032e1039.

Wylie CE, Collins SN, Verheyen KL, Newton JR (2012) Risk factorsfor equine laminitis: a systematic review with quality appraisal ofpublished evidence. Vet J 193, 58e66.

Zarucco L, Driessen B, Scandella M et al. (2007) Continuous peri-neural block of the palmar nerves: a new technique for pain reliefin distal equine forelimb. Clin Tech Equine Pract 6, 154e164.

Zarucco L, Driessen B, Scandella M et al. (2010) Sensory nerveconduction and nociception in the equine lower forelimb duringperineural bupivacaine infusion along the palmar nerves. Can JVet Res 74, 305e313.

Received 15 April 2019; accepted 29 December 2019.

Available online 6 February 2020

















































































































Documents

Ultrasound-guided continuous block of median and ulnar