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Comparison of dorsoventral and ventrodorsal approaches for ultrasound-guided quadratus lumborum block in cats: a cadaver study

  • José Diogo dos-Santos
    Correspondence
    Correspondence. José Diogo dos-Santos, VetOeiras, Estrada de Oeiras nº 18, 2780-114, Oeiras, Portugal.
    Affiliations
    VetOeiras, Veterinary Hospital, Oeiras, Portugal

    CITAB, Centre for the Research and Technology of Agro-Environmental and Biological Sciences, University of Trás-os-Montes and Alto Douro, Vila Real, Portugal

    CECAV, Animal and Veterinary Research Centre UTAD, University of Trás-os-Montes and Alto Douro, Vila Real, Portugal

    Department of Veterinary Science, University Lusófona, Lisbon, Portugal
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  • Mário Ginja
    Affiliations
    CITAB, Centre for the Research and Technology of Agro-Environmental and Biological Sciences, University of Trás-os-Montes and Alto Douro, Vila Real, Portugal

    CECAV, Animal and Veterinary Research Centre UTAD, University of Trás-os-Montes and Alto Douro, Vila Real, Portugal
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  • Sofia Alves-Pimenta
    Affiliations
    CITAB, Centre for the Research and Technology of Agro-Environmental and Biological Sciences, University of Trás-os-Montes and Alto Douro, Vila Real, Portugal

    CECAV, Animal and Veterinary Research Centre UTAD, University of Trás-os-Montes and Alto Douro, Vila Real, Portugal
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  • Pablo E Otero
    Affiliations
    Universidad de Buenos Aires, Facultad de Ciencias Veterinarias, Cátedra de Anestesiología y Algiología, Buenos Aires, Argentina
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  • Lénio Ribeiro
    Affiliations
    Department of Veterinary Science, University Lusófona, Lisbon, Portugal
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  • Bruno Colaço
    Affiliations
    CITAB, Centre for the Research and Technology of Agro-Environmental and Biological Sciences, University of Trás-os-Montes and Alto Douro, Vila Real, Portugal

    CECAV, Animal and Veterinary Research Centre UTAD, University of Trás-os-Montes and Alto Douro, Vila Real, Portugal
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Open AccessPublished:May 25, 2022DOI:https://doi.org/10.1016/j.vaa.2022.05.003

      Abstract

      Objective

      To assess the feasibility of an ultrasound (US)-guided quadratus lumborum (QL)-psoas muscle (Pm) interfascial plane injection using a dorsoventral (DV) approach, and to compare needle visualization and distribution pattern between DV and ventrodorsal (VD) approaches.

      Study design

      Experimental anatomical study.

      Animals

      A total of 14 cat cadavers.

      Methods

      Bilateral in-plane US-guided injections in the QL-Pm plane were performed at the level of the second lumbar (L2) transverse process. A spinal needle was inserted using either a VD or DV approach. A total volume of 0.4 mL kg–1 of a solution of ropivacaine 0.18%, tissue dye and iohexol (350 mg mL–1), in a proportion of 3:1:1, respectively, was injected bilaterally. Spread of injectate was compared and evaluated using US, computed tomography (CT) scanning and anatomical dissection. Presence of dye on the sympathetic trunk was compared between methods using Kappa (κ) coefficient of agreement.

      Results

      The QL-Pm plane was visualized, and dye was present in the target plane using both approaches. Needle visualization in the VD approach was enhanced compared with the DV approach (p = 0.0005). Mean distribution along the sympathetic trunk was 4.8 and 4.1 segments in the VD and DV approaches, respectively, showing non-statistical differences. The ventral branches of L1, L2 and L3 were successfully stained in 11/14 and 6/14 using the VD and DV approaches, respectively. Substantial agreement (κ = 0.61) of sympathetic trunk staining was observed between CT scan and anatomical dissection. Dye was observed cranial to the diaphragm in 7/8 cases on CT with both approaches. Epidural and abdominal cavity dye distribution was not observed.

      Conclusions and clinical relevance

      The DV approach to the QL-Pm plane could be an alternative to the VD approach. Both approaches seem capable of reaching the spinal nerves, the sympathetic trunk and both splanchnic and coeliac nerves in feline cadavers.

      Keywords

      Introduction

      In veterinary medicine, the use of ultrasound (US)-guided interfascial plane blocks is becoming popular for the management of perioperative pain, as these techniques are easy to perform and have low complication rates (
      • Portela D.A.
      • Romano M.
      • Briganti A.
      Retrospective clinical evaluation of ultrasound guided transverse abdominis plane block in dogs undergoing mastectomy.
      ;
      • Argus A.P.V.
      • Freitag F.A.V.
      • Bassetto J.E.
      • Vilani R.G.
      Quadratus lumbar block for intraoperative and postoperative analgesia in a cat.
      ;
      • Asorey I.
      • Sambugaro B.
      • Bhalla R.J.
      • Drozdzynska M.
      Ultrasound-guided serratus plane block as an effective adjunct to systemic analgesia in four dogs undergoing thoracotomy.
      ;
      • Portela D.A.
      • Romano M.
      • Zamora G.A.
      • et al.
      The effect of erector spinae plane block on perioperative analgesic consumption and complications in dogs undergoing hemilaminectomy surgery: a retrospective cohort study.
      ;
      • Salvatierra D.N.
      • Linares M.E.
      • Motta L.
      • Martinez M.
      Ultrasound-guided erector spinae interfascial plane block for spinal surgery in three cats.
      ). They consist of an US-guided injection of local anaesthetic into an interfascial plane, which is intended to target different nerves or structures (
      • Freitag F.A.
      • Bozak V.L.
      • do Carmo M.P.
      • et al.
      Continuous transverse abdominal plane block for analgesia in three dogs with abdominal pain.
      ;
      • Skouropoulou D.
      • Lacitignola L.
      • Centonze P.
      • et al.
      Perioperative analgesic effects of an ultrasound-guided transversus abdominis plane block with a mixture of bupivacaine and lidocaine in cats undergoing ovariectomy.
      ;
      • Teixeira L.G.
      • Pujol D.M.
      • Pazzim A.F.
      • et al.
      Combination of transversus abdominis plane block and serratus plane block anesthesia in dogs submitted to masctetomy.
      ;
      • Garbin M.
      • Portela D.A.
      • Bertolizio G.
      • et al.
      Description of ultrasound–guided quadratus lumborum block technique and evaluation of injectate spread in canine cadavers.
      ,
      • Garbin M.
      • Portela D.A.
      • Bertolizio G.
      • et al.
      A novel ultrasound-guided lateral quadratus lumborum block in dogs: a comparative cadaveric study of two approaches.
      ;
      • Alaman M.
      • Bonastre C.
      • Blasa I.
      • et al.
      Description of a novel ultrasound-guided approach for a dorsal quadratus lumborum block: a canine cadaver study.
      ;
      • dos-Santos J.D.
      • Ginja M.
      • Alves-Pimenta S.
      • et al.
      A description of an ultrasound-guided technique for a quadratus lumborum block in the cat: a cadaver study.
      ;
      • Viscasillas J.
      • Terrado J.
      • Marti-scharfhausen R.
      • et al.
      A modified approach for the ultrasound-guided quadratus lumborum block in dogs: A cadaveric study.
      ). In humans, interfascial plane blocks carry a lower risk of nerve damage and they are easier to perform compared with neuraxial techniques (
      • Chin K.J.
      • Barrington M.J.
      Erector spinae block: A magic bullet for.
      ;
      • Machi A.
      • Joshi G.P.
      Interfascial plane blocks.
      ). Previous research in animals demonstrated a reduction in perioperative opioid consumption when regional anaesthesia was included in multimodal analgesia protocols (
      • Portela D.A.
      • Romano M.
      • Briganti A.
      Retrospective clinical evaluation of ultrasound guided transverse abdominis plane block in dogs undergoing mastectomy.
      ;
      • Skouropoulou D.
      • Lacitignola L.
      • Centonze P.
      • et al.
      Perioperative analgesic effects of an ultrasound-guided transversus abdominis plane block with a mixture of bupivacaine and lidocaine in cats undergoing ovariectomy.
      ;
      • Argus A.P.V.
      • Freitag F.A.V.
      • Bassetto J.E.
      • Vilani R.G.
      Quadratus lumbar block for intraoperative and postoperative analgesia in a cat.
      ;
      • Portela D.A.
      • Romano M.
      • Zamora G.A.
      • et al.
      The effect of erector spinae plane block on perioperative analgesic consumption and complications in dogs undergoing hemilaminectomy surgery: a retrospective cohort study.
      ;
      • Salvatierra D.N.
      • Linares M.E.
      • Motta L.
      • Martinez M.
      Ultrasound-guided erector spinae interfascial plane block for spinal surgery in three cats.
      ). In addition, lower postoperative pain scores and stress responses were observed (
      • Portela D.A.
      • Romano M.
      • Briganti A.
      Retrospective clinical evaluation of ultrasound guided transverse abdominis plane block in dogs undergoing mastectomy.
      ,
      • Portela D.A.
      • Romano M.
      • Zamora G.A.
      • et al.
      The effect of erector spinae plane block on perioperative analgesic consumption and complications in dogs undergoing hemilaminectomy surgery: a retrospective cohort study.
      ;
      • Skouropoulou D.
      • Lacitignola L.
      • Centonze P.
      • et al.
      Perioperative analgesic effects of an ultrasound-guided transversus abdominis plane block with a mixture of bupivacaine and lidocaine in cats undergoing ovariectomy.
      ).
      The US-guided quadratus lumborum (QL) block is an interfascial plane block that was first described in humans, and consists of the injection of local anaesthetic between the QL and psoas muscles (Pm) (
      • El-Boghdadly K.
      • Elsharkawy H.
      • Short A.
      • Chin K.J.
      Quadratus lumborum block nomenclature and anatomical considerations.
      ;
      • Dam M.
      • Moriggl B.
      • Hansen C.K.
      • et al.
      The pathway of injectate spread with the transmuscular quadratus lumborum block: A cadaver study.
      ). This block is effective in a variety of abdominal surgical procedures in humans, such as caesarean section (
      • Mænchen N.
      • Hansen C.K.
      • Dam M.
      • Børglum J.
      Ultrasound-guided transmuscular quadratus lumborum (TQL) block for pain management after caesarean section.
      ;
      • Tamura T.
      • Yokota S.
      • Ando M.
      • et al.
      A triple-blinded randomized trial comparing spinal morphine with posterior quadratus lumborum block after cesarean section.
      ;
      • Xu M.
      • Tang Y.
      • Wang J.
      • Yang J.
      Quadratus lumborum block for postoperative analgesia after cesarean delivery: a systematic review and meta-analysis.
      ), nephrectomy (
      • Chakraborty A.
      • Goswami J.
      • Patro V.
      Ultrasound-guided continuous quadratus lumborum block for postoperative analgesia in a pediatric patient.
      ;
      • Elsharkawy H.
      • Ahuja S.
      • DeGrande S.
      • et al.
      Subcostal approach to anterior quadratus lumborum block for pain control following open urological procedures.
      ;
      • Zhu M.
      • Qi Y.
      • He H.
      • et al.
      Analgesic effect of the ultrasound-guided subcostal approach to transmuscular quadratus lumborum block in patients undergoing laparoscopic nephrectomy: a randomized controlled trial.
      ;
      • Saleh A.H.
      • Abdallah M.W.
      • Mahrous A.M.
      • Ali N.A.
      Quadratus lumborum block (transmuscular approach) versus transversus abdominis plane block (unilateral subcostal approach) for perioperative analgesia in patients undergoing open nephrectomy: a randomized.
      ), cholecystectomy (
      • Baytar C.
      • Yilmaz C.
      • Karasu D.
      • Topal S.
      Comparison of ultrasound-guided subcostal transversus abdominis plane block and quadratus lumborum block in laparoscopic cholecystectomy: A prospective, randomized, controlled clinical study.
      ) and abdominal hernia repair (
      • Carvalho R.
      • Segura E.
      • Loureiro M.C.
      • Assunção J.P.
      Quadratus lumborum block in chronic pain after abdominal hernia repair: case report.
      ). In humans, anatomical variability and varied medical requirements have led to the description of multiple approaches to reach the same target plane. In the case of the QL block, injection can be performed through a lateral approach (termed QL1;
      • Akerman M.
      • Pejčić N.
      • Veličković I.
      A review of the quadratus lumborum block and ERAS.
      ), a posterior approach (termed QL2;
      • Akerman M.
      • Pejčić N.
      • Veličković I.
      A review of the quadratus lumborum block and ERAS.
      ) or a transmuscular approach (termed QL3;
      • Akerman M.
      • Pejčić N.
      • Veličković I.
      A review of the quadratus lumborum block and ERAS.
      ). Similarly, in canine cadavers, an injection in the QL-Pm interfascial plane has been described through transverse (
      • Garbin M.
      • Portela D.A.
      • Bertolizio G.
      • et al.
      Description of ultrasound–guided quadratus lumborum block technique and evaluation of injectate spread in canine cadavers.
      ,
      • Garbin M.
      • Portela D.A.
      • Bertolizio G.
      • et al.
      A novel ultrasound-guided lateral quadratus lumborum block in dogs: a comparative cadaveric study of two approaches.
      ), longitudinal (
      • Garbin M.
      • Portela D.A.
      • Bertolizio G.
      • et al.
      A novel ultrasound-guided lateral quadratus lumborum block in dogs: a comparative cadaveric study of two approaches.
      ) and dorsal approach (
      • Alaman M.
      • Bonastre C.
      • Blasa I.
      • et al.
      Description of a novel ultrasound-guided approach for a dorsal quadratus lumborum block: a canine cadaver study.
      ). Recently, a dorsoventral (DV) approach performed through the epaxial muscles, with the needle passing the transverse process until it reached the QL-Pm interfascial plane, was described in dogs (
      • Viscasillas J.
      • Terrado J.
      • Marti-scharfhausen R.
      • et al.
      A modified approach for the ultrasound-guided quadratus lumborum block in dogs: A cadaveric study.
      ).
      A cadaver study performed in cats showed that the use of 0.4 mL kg–1 of solution injected in a ventrodorsal (VD) approach to the QL-Pm interfascial plane was effective in staining the sympathetic trunk, coeliac ganglia, splanchnic nerves and ventral branches of the spinal nerves from the first lumbar (L1) to the third lumbar (L3) (
      • dos-Santos J.D.
      • Ginja M.
      • Alves-Pimenta S.
      • et al.
      A description of an ultrasound-guided technique for a quadratus lumborum block in the cat: a cadaver study.
      ). The VD approach to QL has been also reported in a cat in vivo, as an effective technique for the provision analgesia for cystotomy (
      • Argus A.P.V.
      • Freitag F.A.V.
      • Bassetto J.E.
      • Vilani R.G.
      Quadratus lumbar block for intraoperative and postoperative analgesia in a cat.
      ). However, the efficacy of this technique for the provision of somatic and visceral analgesia of the abdomen in veterinary medicine is still to be proven. In order to use the QL block technique routinely in clinical cases, the cat’s anatomy should be considered, and the most appropriate approach for each animal and procedure should be selected.
      We hypothesized that an US-guided injection into the QL-Pm interfascial plane of feline cadavers may be achieved using either a DV or a VD approach. It was also hypothesized that both approaches would result in the spread of injectate along the sensory nerves of the abdominal wall and visceral organs. To test these hypotheses, this study assessed the feasibility of an US-guided QL block using a DV approach in feline cadavers. We evaluated needle visualization using the DV and VD approaches, and we compared the distribution pattern of a contrast medium-dye solution with computed tomography (CT) and gross anatomical dissection using the two approaches.

      Materials and methods

      This study was approved by the commission on ethics (Doc14-CE-UTAD-2020). Sample size was calculated by comparing paired differences of the presence of dye on sympathetic trunk segments, in order to achieve a power of 80% and a level of significance of 5% (two sided), for the detection of an effect size of 0.863 between pairs. A total of 14 mixed-breed cat cadavers were used, all of which had died or were euthanized for reasons unrelated to this study. The specimens were preserved in frozen storage within the first 24 hours following death and thawed at room temperature for at least 24 hours before use. Weight and body condition score (BCS) evaluated on a scale from 1 to 9 (
      • Laflamme D.
      Development and validation of a body con- dition score system for cats: a clinical tool.
      ) were recorded for each cadaver. No anatomical changes were observed. An US-guided bilateral injection of an anaesthetic–dye solution into the QL-Pm interfascial plane was performed at the level of second lumbar vertebra (L2) in both the hemiabdomens of all cadavers using either a VD or a DV approach (Fig. 1). The approach used on each hemiabdomen and the order of injection was assigned using a random sequence generator (
      • Haahr M.
      Random.org: True random number service.
      ). Arbitrarily, yellow and green dye were used for the right and left hemiabdomens, respectively. A CT scan was performed after each injection in eight randomly selected cadavers (Fig. 1), using a random sequence generator (
      • Haahr M.
      Random.org: True random number service.
      ). Presence of dye on the sympathetic trunk and thoracolumbar spinal nerves was specifically assessed through gross anatomical dissection of all cadavers. The injection approach used on each side was blinded from the anatomical evaluators, BC and SAP (Veterinary Anatomy professors).
      Figure 1
      Figure 1Schematic diagram showing the number of cat cadavers used for the quadratus lumborum-psoas muscle interfascial plane injection. A ventrodorsal (VD) or dorsoventral (DV) approach was used in 28 hemiabdomens. Arbitrarily, yellow and green dye solution was injected in the right and left sides, respectively. A computed tomography (CT) scan was performed in eight randomly selected cadavers 10 minutes after injection. Gross anatomical dissection was performed in all cat cadavers. US, ultrasound.

      Preparation of injectate

      The injected solution consisted of a combination of 0.5% ropivacaine (Ropivacaine 5 mg mL–1; BBraun Medical Inc., Germany), tissue marking dye yellow or green (Shandon tissue marking dye; Richard-Allan Scientific, MI, USA) and iohexol (Omnipaque 350 mg mL–1; GE Healthcare, Spain) in a 3:1:1 proportion, respectively, reaching a final concentration of 0.18% ropivacaine.

      US-guided scanning and injection

      With the cadaver positioned in lateral recumbency, the hair of the thoracic and lumbar regions was clipped and the skin was scrubbed. US gel (Dahlhausen, Germany) was applied to facilitate acoustic coupling. An anaesthetist (JDS; veterinarian) experienced in US-guided regional anaesthesia performed the US study using a linear array probe (6–14 MHz L14-6NE; Mindray, Guangdong, China) attached to a portable US machine (M8; Mindray).
      For the DV approach, the US transducer was initially positioned caudal to the last rib and perpendicular to the animal’s long axis, with its mark facing dorsally. Then, the transducer was moved slightly caudally until the transverse process of L2 was identified. Subsequently, a slight ventral displacement of the transducer allowed visualization of the belly of the QL and Pm muscles ventral to the transverse process of L2, and of the QL-Pm interfascial plane. Additionally, the aponeurosis of the abdominal wall muscles were also noted (Fig. 2). After visualization of the QL-Pm plane, a 22 gauge, 75 mm spinal needle (Spinocan; BBraun Medical Inc.) attached to 10 cm prefilled extension line (Discofix 3; BBraun Medical Inc.) was introduced in-plane and advanced dorsoventrally through the erector spinae muscles. It passed over the transverse process of L2 until its tip reached the interfascial plane between the QL and Pm muscles (Fig. 3a) After confirming the desired position of the tip of the needle by injection of a test dose of 0.3 mL of saline solution, 0.4 mL kg–1 of the prepared solution was injected.
      Figure 2
      Figure 2(a) Ultrasound image of musculature visible while performing a lateral quadratus lumborum (QL)-psoas muscle (Pm) interfascial plane injection in cat cadavers. (b) The schematic drawing of ultrasound (US)-guided landmarks to perform the injection in QL-Pm interfascial plane. The graphical representation of needle identifies the ventrodorsal (VD) and dorsoventral (DV) approaches. Ao, aorta; L2, second lumbar.
      Figure 3
      Figure 3A feline cadaver positioned in right lateral recumbency demonstrating the approach to a quadratus lumborum injection. The transducer is positioned caudal to the last rib and orientated perpendicular to the animal’s long axis, with its mark facing dorsally. (a) Ultrasound probe and needle orientation using the dorsoventral approach. The needle is introduced in-plane through the epaxial musculature and advanced dorsolaterally to ventromedially. (b) Ultrasound probe and needle orientation using the ventrodorsal approach. The needle is introduced in-plane and advanced ventrodorsally.
      For the VD approach, the US transducer was positioned in the same fashion as for the DV approach and the same structures were identified. After visualization of the QL-Pm plane, a 22 gauge, 75 mm spinal needle (Spinocan; BBraun Medical Inc.) attached to a 10 cm prefilled extension line (Discofix 3; BBraun Medical Inc.) was introduced in-plane and advanced ventrodorsally through the lateral aspect of the abdominal wall until its tip reached the interfascial plane between the QL and Pm muscles (Fig. 3b). Confirmation of location of the tip of the needle and final injected volume was performed in the same manner as described for the DV approach.
      The quality of needle visualization was rated as ‘excellent’ when the entire needle shaft and tip could be visualized, ‘good’ when the tip, but not the entire shaft, could be visualized but the shaft only partially, and ‘poor’ when only the tip could be visualized. US visualization of the hydrodissection between QL and Pm muscles was also recorded.

      Computed tomography scanning

      A CT scan (Brivo CT 325; General Electric Healthcare, NY, USA) of the region between the ninth thoracic (T9) and the seventh lumbar (L7) vertebrae was performed 10 minutes after each injection. Images were acquired with the cats positioned in dorsal recumbency with their thoracic and pelvic limbs extended. Slice thickness was set to 1.00 mm, collimator pitch was 1.0, mA was automated, kVp was 120; standard soft tissues, and bone reconstruction algorithms were selected.
      The CT evaluator (MG; Radiology professor) recorded the presence of contrast in the QL-Pm interfascial plane (yes/no), sympathetic trunk (based on vertebral space landmarks), epidural space (yes/no), diaphragm (yes/no), and intra-abdominal cavity (yes/no). For imaging analysis, Horos software version 3.3.6 (Horos Project, MD, USA) was used.

      Gross anatomical dissection

      Anatomical evaluations were performed after CT scanning by two researchers (BC and SAP) with experience in dissection. With the cats positioned in dorsal recumbency, an incision of the linea alba and sternotomy was performed to explore the abdominal and thoracic cavities, respectively. The aortic hiatus and the diaphragmatic region were evaluated for presence of dye. The content of the retroperitoneal space was carefully inspected. The presence of dye on the sympathetic trunk, coeliac ganglia, splanchnic major and minor nerves was recorded. Additionally, the spinal nerves between T9 and L7 were identified and examined for the presence of dye. Cadavers were then placed in lateral recumbency, and dissection of the abdominal muscles was performed. The extent of stain dispersion on the sympathetic trunk was evaluated using an equivalent segment of a vertebral body. The ventral branches of the spinal nerves were identified and followed until their emergence from the corresponding intervertebral foramen, where the presence of dye was also noted. Spread of dye on the sublumbar musculature was also evaluated, and finally a laminectomy was performed to evaluate the epidural dye distribution. Nerves were considered successfully stained when the dye solution was distributed around their circumference to a length greater than 0.6 cm (
      • Raymond S.A.
      • Steffensen S.C.
      • Gugino L.D.
      • Strichartz G.R.
      The role of length of nerve exposed to local anesthetics in impulse blocking action.
      ). Data and images from gross anatomical dissection were collected for further analysis.

      Statistical analysis

      Statistical analysis was performed using SPSS version 26 (IBM SPSS Statistic; IBM Corp., NY, USA). Median and 95% median confidence interval values (95% CI) were calculated for the variables weight and BCS. Mean and standard deviation (SD) were calculated for the variable presence of dye on sympathetic trunk segments. To assess homogeneity of variance, a Levene test was used. To compare the presence of dye on sympathetic trunk segments between the DV and VD approaches, a one-way analysis of variance was used. In order to assess proportion comparisons, the z test (https://www.medcalc.org, MedCalc Software Ltd, Belgium) was applied for the evaluation of the data related to the quality of needle visualization within each category (excellent, good and poor), and after Bonferroni correction the alpha level was set at < 0.017. Agreement of the presence of dye on the sympathetic trunk obtained from the CT scan and anatomical dissection was evaluated using Cohen’s Kappa test. The Kappa coefficient of agreement (κ) was graded as follows: slight agreement for values below 0.2, fair agreement for values between 0.21 and 0.4, moderate agreement for values between 0.41 and 0.6, substantial agreement for values between 0.61 and 0.8 and almost perfect agreement for values higher than 0.81 (
      • Landis J.R.
      • Koch G.G.
      The measurement of observer agreement for categorical data.
      ).

      Results

      A total of 14 adult cat cadavers were studied (eight males and six females) which had a median body weight of 2.8 kg (95% CI 2.2–3.3) and a median BCS of 4 (95% CI 3–4). A total of 28 injections were performed (14 on each hemiabdomen).

      US scanning and injection

      The QL-Pm interfascial plane was correctly visualized using both approaches as a hyperechoic line. In the VD approach, the needle was visualized passing through the aponeurosis of the transversus abdominis muscle and the thoracolumbar fascia until reaching the QL-Pm interfascial plane (Fig. 2). With the DV approach, the needle was observed passing through the epaxial musculature, over the transverse process of L2 until it reached the QL-Pm interfascial plane (Fig. 2).
      Results of needle visualization are summarized in Table 1. The hydrodissection performed by the injectate was correctly visualized between the QL and Pm muscles in all animals using both approaches.
      Table 1Quality of needle visualization with the dorsoventral (DV) or ventrodorsal (VD) approaches in a total of 14 cat cadavers. Excellent, entire shaft and tip could be visualized; Good, only partial shaft visualized with clear tip visualization; Poor, only the tip was clearly visualized. Significant at α < 0.017 (∗) and non-significant at α > 0.017 (NS)
      VDDVp
      Excellent71.42% (10/14)7.14% (1/14)0.0005∗
      Good28.57% (4/14)57.14% (8/14)0.1260NS
      Poor0% (0/14)35.71% (5/14)0.0135∗

      Computed tomography scanning

      In all cadavers and with both approaches, contrast medium was detected in the QL-Pm interfascial plane, surrounding the QL muscle in its ventral and lateral quadrants. Dye distribution observed along the sympathetic trunk is summarized in Table S1. Dye was observed cranial to the diaphragm in 7/8 cats with both approaches. Epidural and abdominal cavity dye distribution was not observed.

      Anatomical dissection

      Dye was observed within the QL-Pm interfascial space in all cadavers. In addition, stain was observed surrounding the QL muscle in its ventral and lateral aspects. An extensive lateral spread of dye between the transversus abdominis, and the internal oblique muscles was also noted in all cats. Dye was identified in the retroperitoneal space staining the parietal pleura in all cadavers (Fig. 4a). Using the VD and DV approaches, dye crossed the diaphragm through the endothoracic fascia and reached the extrapleural thoracic space in 13/14 and 11/14 injections, respectively (Fig. 5). Distribution of dye along the sympathetic nerves is summarized in Table S2. The sympathetic trunk was stained in a mean (±SD) of 4.8 ± 0.8 and 4.1 ± 0.9 segments in the VD and DV approaches, respectively (p = 0.064; Fig. 5). The ventral branches of the L1, L2 and L3 lumbar spinal nerves were successfully stained in 11/14 and 6/14 injections using the VD and DV approaches, respectively. Dye reached the thirteenth thoracic (T13) spinal nerve in 7/14 and 3/14 injections, and the fourth lumbar spinal nerve in 5/14 and 4/14 using the VD and DV approaches, respectively (Fig. 5). In three cases in which the DV approach was used, no ventral branches were stained.
      Figure 4
      Figure 4Anatomical structures of the sublumbar musculature in a cat cadaver following removal of the thoracic and abdominal viscera the s. (a) Coloured dye is distributed along the sympathetic trunk, with the spread of dye on to the ventral branches of the thoracic and lumbar spinal nerves, its limits are marked by needles. Yellow dye was used as standard for the right hemiabdomen and green dye for the left hemiabdomen. (b) Schematic drawing (a) illustrating dye distribution on the sympathetic trunk and ventral branches. L1, first lumbar; L2, second lumbar; L3, third lumbar; L4, fourth lumbar; T9, ninth thoracic; T10, tenth thoracic; T11, eleventh thoracic; T12, twelfth thoracic; T13, thirteenth thoracic vertebrae.
      Figure 5
      Figure 5Characteristics of the spread of dye observed upon anatomical evaluation of 14 cat cadavers, after injection of 0.4 mL kg–1 of dye between the quadratus lumborum and psoas muscles. The left side shows the stained nerves with ventrodorsal (VD) approach, whereas the right side shows the nerves stained with the dorsoventral (DV) approach. The lines ending with squares represent the segment number of the sympathetic trunk, and the dotted lines ending with arrows represent the number of ventral branches stained. L1, first lumbar; L2, second lumbar; L3, third lumbar; L4, fourth lumbar; T12, twelfth thoracic; T13, thirteenth thoracic vertebrae.
      Analysis of the distribution of injectate on the sympathetic trunk observed on CT scanning and anatomical dissection showed a substantial agreement between methods (κ = 0.61).

      Discussion

      The results of this study indicated adequate distribution of injectate along the spinal nerves and sympathetic trunk, and therefore the feasibility of a DV approach to the QL-Pm interfascial plane in cat cadavers.
      In this study, the recognition of ultrasonographic reference points (i.e., transverse process of L2, QL and Pm muscles) was possible in all cadavers. However, the VD approach enhanced needle visualization compared with the DV approach (p = 0.0005). Differences observed between VD and DV approaches may be explained by the different needle pathways towards the QL-Pm interfascial space. With the VD approach, it was easier to maintain the needle in-plane, allowing a better visualization. Conversely, with the DV approach, the needle must be advanced through the epaxial muscles and over the transverse process of L2 to reach the QL-Pm interfascial space. This may require additional needle movements, which hinders its visualization. Good visualization of the needle is very important as vital structures such as the kidneys, aorta, peritoneum and intestines may be easily contacted by the needle if visualization is poor or inaccurate (
      • Elsharkawy H.
      • El-Boghdadly K.
      • Barrington M.
      Quadratus lumborum block.
      ). Monitoring the needle trajectory and tip prior to injecting the drug significantly increases the level of safety and efficacy of the technique (
      • Akerman M.
      • Pejčić N.
      • Veličković I.
      A review of the quadratus lumborum block and ERAS.
      ). The results of this study indicate that the VD approach may provide better needle visualization than the DV. However, caution should be taken to avoid any visceral injury using both approaches.
      The results of this study were more consistent in the VD group in terms of ventral branches stained. However, the DV approach may be a more useful and safer alternative to the VD approach where visualization of the target plane or landmarks is poor, in cases of increased intra-abdominal pressure (renal/adrenal masses, pregnancy) or in presence of abdominal wall abnormalities. The DV approach may be particularly helpful when a rescue block is performed postoperatively, where access to the flank region may be restricted by dressings and drains (
      • Cumming J.
      Rectus sheath catheter entrapment - Manufacturer’s reply.
      ), for example, after a caesarean section (
      • Mænchen N.
      • Hansen C.K.
      • Dam M.
      • Børglum J.
      Ultrasound-guided transmuscular quadratus lumborum (TQL) block for pain management after caesarean section.
      ) or abdominal hernia repair (
      • Ahmed A.
      • Fawzy M.
      • Nasr M.A.R.
      • et al.
      Ultrasound-guided quadratus lumborum block for postoperative pain control in patients undergoing unilateral inguinal hernia repair, a comparative study between two approaches.
      ).
      The CT evaluation provided confirmation in all cases, for both approaches, that the contrast medium was located in the QL-Pm interfascial plane. Even though CT imaging was only performed in eight cadavers, it was useful to compare the distribution along the sympathetic trunk between the two approaches. The results of this study agree with those described in cats (
      • dos-Santos J.D.
      • Ginja M.
      • Alves-Pimenta S.
      • et al.
      A description of an ultrasound-guided technique for a quadratus lumborum block in the cat: a cadaver study.
      ) and in dogs (
      • Garbin M.
      • Portela D.A.
      • Bertolizio G.
      • et al.
      Description of ultrasound–guided quadratus lumborum block technique and evaluation of injectate spread in canine cadavers.
      ).
      Substantial agreement was observed between CT scans and anatomical dissection when the cranio-caudal extent of the sympathetic trunk staining was evaluated (κ = 0.61). The high level of agreement between these methods reinforces the use of anatomical dissection as a method of evaluating the spread of dye in cadavers. This is because the chance of a result being affected by tissue manipulation is minimized, and it also supports the use of CT imaging as a noninvasive method to determine distribution in vivo.
      The fact that more than one approach can be used to reach the same target is important since this allows the anaesthetist to select the most suitable technique in each animal. The results of this anatomical study demonstrate that using either the VD or the DV approach, the injectate may reach not only the ventral branches of the spinal nerves and the sympathetic trunk, but also the splanchnic major and minor nerves and the coeliac ganglia. However, use of the VD approach resulted in more consistent distribution of the contrast/dye solution to the ventral branches of the lumbar nerves (10/14) compared with the use of the DV approach (6/14). In humans, the posteroanterior needle trajectory was frequently associated with an increase in the dispersion of dye between the fascial planes of the abdominal wall muscles (
      • Yang H.M.
      • Park S.J.
      • Yoon K.B.
      • et al.
      Cadaveric evaluation of different approaches for quadratus lumborum blocks.
      ). However, our results allow us to conclude that the needle trajectory used in the DV approach does not increase dispersion in that interfascial plane. There is even less dispersion over the ventral branches of the spinal nerves when compared with the VD approach.
      In cats, in order to achieve analgesia of the entire abdominal wall, desensitization of the dermatomes from eleventh thoracic to L3 is necessary (
      • Skouropoulou D.
      • Lacitignola L.
      • Centonze P.
      • et al.
      Perioperative analgesic effects of an ultrasound-guided transversus abdominis plane block with a mixture of bupivacaine and lidocaine in cats undergoing ovariectomy.
      ). In this study, the innervation of the abdominal wall was not entirely stained with either approach, and therefore this technique would not provide analgesia of the entire abdominal wall. The spread of dye along the QL-Pm interfascial plane, associated fasciae and nerve structures we observed after anatomical dissection was similar to that reported in other studies in cats (
      • dos-Santos J.D.
      • Ginja M.
      • Alves-Pimenta S.
      • et al.
      A description of an ultrasound-guided technique for a quadratus lumborum block in the cat: a cadaver study.
      ), dogs (
      • Garbin M.
      • Portela D.A.
      • Bertolizio G.
      • et al.
      Description of ultrasound–guided quadratus lumborum block technique and evaluation of injectate spread in canine cadavers.
      ,
      • Garbin M.
      • Portela D.A.
      • Bertolizio G.
      • et al.
      A novel ultrasound-guided lateral quadratus lumborum block in dogs: a comparative cadaveric study of two approaches.
      ;
      • Viscasillas J.
      • Terrado J.
      • Marti-scharfhausen R.
      • et al.
      A modified approach for the ultrasound-guided quadratus lumborum block in dogs: A cadaveric study.
      ) and human cadavers (
      • Elsharkawy H.
      • El-Boghdadly K.
      • Barrington M.
      Quadratus lumborum block.
      ).
      The mean distribution of stain on the sympathetic trunk segments did not differ between the VD and DV approaches (p = 0.064). Thus, these results revealed that there are no differences in dye distribution to the ventral spinal nerves and sympathetic trunk between the two approaches we tested. The consistent presence of dye on the minor splanchnic nerves, coeliac ganglion and on the sympathetic trunk from the level of T13 to L3 suggest that both techniques may provide visceral analgesia, especially for the cranial and medial abdomen (
      • Ranson S.W.
      • Billingsley P.R.
      The thoracic truncus sympathicus, rami communicantes and splanchnic nerves in the cat.
      ;
      • Akerman M.
      • Pejčić N.
      • Veličković I.
      A review of the quadratus lumborum block and ERAS.
      ;
      • Ribeiro A.A.C.M.
      • de Souza R.R.
      • Barbosa J.
      • Fernandes Filho A.
      Estudo anatômico dos gânglios celíaco, celiacomesentérico e mesentérico cranial e de suas conexões no gato doméstico.
      ). The difference in the distribution of dye obtained with these two techniques may have been affected by poor needle visualization with the DV technique, which hindered the accuracy of administration in the QL-Pm interfascial plane.
      When performing bilateral blocks, the concentration of the local anaesthetic should be calculated to avoid surpassing the toxic dose. In this study, the final volume of 0.4 mL kg–1 of 0.18% ropivacaine was selected based on its potential clinical applicability. Future studies would be required to evaluate the distribution of different injectate volumes. Likewise, further clinical trials are necessary to evaluate the clinical efficacy and duration of analgesia using both techniques in this species.
      This study has some limitations. Firstly, owing to the use of cadavers in this investigation, the distribution of the contrast medium-dye–ropivacaine combination may not accurately reflect the distribution of local anaesthetic in vivo. The density, viscosity and temperature of a mixed solution differ from that of local anaesthetic solutions, and this may have affected the flow and spread results. The echogenicity of the muscles and interfascial planes may be altered in cadavers after freezing and thawing processes, and consequently, the recognition of the target structures may be different in living cats. Further studies with a larger sample size and different operators are warranted to confirm the results of this study.

      Conclusions

      In conclusion, an US-guided DV approach to the QL-Pm interfascial plane is feasible in feline cadavers; however, the VD approach resulted in better needle visualization. Injectate spread was detected in the spinal nerves, sympathetic trunk and both splanchnic and coeliac nerves using the VD and DV approaches. So, the DV approach may be an alternative to the VD approach in cases of increased intra-abdominal pressure or abdominal wall abnormalities.

      Acknowledgements

      This work was supported by the projects UIDB/CVT/00772/2020, LA/P/0059/2020, UIDB/04033/2020 and UIDB/CVT/00772/2020 funded by the Portuguese Foundation for Science and Technology (FCT), and Scientific Employment Stimulus (FCT) - Institutional Call - CEECINST/00127/2018 UTAD.

      Authors' contributions

      JDS: performed the ultrasound procedures, participated in the design and execution of the study, data interpretation. MG: evaluator of CT scans analysis; SAP: dissected, reported and photographed the cadavers. PEO: study conception and design, data interpretation. LR: data interpretation. BC: study conception and design, dissected the cadavers of the study, data interpretation. All authors contributed to writing of the manuscript, the critical revision of the paper and approved the final manuscript.

      Conflict of interest statement

      The authors declare no conflict of interest.

      Supporting Information.

      The following are the Supplementary data to this article:

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