Ultrasound-guided subcostal oblique transversus abdominis plane block in canine cadavers

Comparative study between lateral versus latero-ventral quadratus lumborum block for perioperative analgesia in canine laparoscopic ovariectomy

OBJECTIVE

To compare the perioperative analgesic effect of lateral versus latero-ventral quadratus lumborum block (QLB) in dogs undergoing laparoscopic ovariectomy.

STUDY DESIGN

Randomized, blinded clinical study.

ANIMALS

A total of 15 client-owned female dogs undergoing laparoscopic ovariectomy.

METHODS

Animals were randomly assigned to receive a bilateral QLB, performed with 0.3 mL kg-1 ropivacaine 0.5%, either with lateral (group LQLB, n = 7) or latero-ventral approach (group LVQLB, n = 7). Dogs were premedicated intramuscularly with methadone 0.2 mg kg-1 and dexmedetomidine 3 μg kg-1. General anaesthesia was induced intravenously (IV) with propofol and maintained with isoflurane. Cardiovascular and respiratory variables were continuously monitored and recorded every 5 minutes during surgery. Fentanyl 3 μg kg-1 was administered IV if there was a 20% increase in heart rate and/or mean arterial pressure from previous values recorded 5 minutes before. Meloxicam 0.2 mg kg-1 was administered IV to all dogs during recovery. The short-form of the Glasgow Composite Pain Scale was used hourly for 8 hours post-QLB. Methadone 0.2 mg kg-1 was administered IV when pain score was ≥ 6/24. A chi-square test compared the number of dogs requiring intraoperative rescue fentanyl. A Friedman test with a Dunn's post hoc was used to evaluate the trend in postoperative pain scores within each group, and a Mann-Whitney U test compared scores between the groups at each time point; p < 0.05.

RESULTS

Significantly fewer dogs required intraoperative rescue fentanyl in group LQLB than in group LVQLB. No dog required postoperative rescue methadone, and there were no significant differences in pain scores.

CONCLUSIONS AND CLINICAL RELEVANCE

Bilateral QLB performed with lateral approach reduced the number of dogs requiring intraoperative rescue analgesia in comparison with the latero-ventral approach. No differences were detected postoperatively, possibly owing to the confounding effects of methadone, dexmedetomidine and meloxicam.

Evaluation of preoperative rectus sheath block with bupivacaine for analgesia in cats undergoing ovariohysterectomy: a cadaveric and randomized clinical study

OBJECTIVE

Phase 1: to determine the feasibility of desensitizing ventral branches of spinal nerves within the rectus sheath using an ultrasound-guided rectus sheath block (USRSB). Phase 2: to determine the effect of preoperative USRSB on intraoperative responses to surgical stimulation and postoperative pain.

STUDY DESIGN

Cadaveric study and prospective, randomized, blinded, parallel-arm clinical trial.

ANIMALS

A group of five cat cadavers and 37 shelter-owned cats undergoing ovariohysterectomy.

METHODS

Phase 1: anatomical dissection was performed on one uninjected cadaver. Abdominal walls were dissected in four cadavers (eight hemiabdomens) following bilateral USRSB using 1:1 new methylene blue and 0.5% bupivacaine (0.8 mL kg-1 total). Phase 2: preoperative bilateral USRSB was performed with 0.8 mL kg-1 of 0.25% bupivacaine (RSB) or equivalent volume of 0.9% saline (CONTROL). Intraoperative systolic arterial blood pressure (SAP), heart rate (HR), respiratory rate (fR) and vaporizer setting (vap%) were recorded before skin incision, during celiotomy and abdominal wall closure. In recovery, cats were administered robenacoxib (2 mg kg-1; CONTROL) or 0.9% saline (0.1 mL kg-1; RSB) subcutaneously. Postoperative pain was evaluated for 6 hours using the Glasgow Composite Measure Pain Scale.

RESULTS

Phase 1: spinal nerves T9-L3 were identified within the rectus sheath, and stained in 0%, 40%, 63%, 75%, 100%, 88%, 50% and 13% of hemiabdomens, respectively. Phase 2: 37 cats were included (RSB, n = 17; CONTROL, n = 20). Intraoperatively, SAP, HR and fR were not significantly different between groups. Vap% was significantly lower in RSB during celiotomy (p = 0.036) and closure (p = 0.044). Postoperatively, RSB cats were 5.3 times (95% CI 1.8-8.3) more likely to require rescue analgesia than CONTROL cats.

CONCLUSIONS AND CLINICAL RELEVANCE

During surgery, USRSB with bupivacaine offered minor benefits and provided markedly less postoperative analgesia than robenacoxib, indicating that relying on USRSB provides insufficient postoperative analgesia for ovariohysterectomy in cats.

Transversus Abdominis Plane (TAP) Block in Rabbit Cadavers: Anatomical Description and Measurements of Injectate Spread Using One- and Two-Point Approaches

The aim of this study was to describe one-point (preiliac approach) and two-point (preiliac and retrocostal approach) blocks of the Transversus Abdominis Plane (TAP) on a cadaveric model. For this purpose, ultrasound-guided infiltration of the plane between the internal oblique and transversus abdominis muscles was performed and, after dissection of tissues, the areas and percentage of nerve fibers involved were analyzed. Injection into the TAP plexus of a 1 mL/kg solution of 2% lidocaine and 1% methylene blue (1:1) was performed in 30 rabbit cadavers. In fifteen rabbits (group S), the solution was inoculated at the preiliac level. In the other 15 rabbits (group D), the solution was divided into two inoculations (0.5 mL/kg at the retrocostal level and 0.5 mL/kg at the preiliac level). All cadavers were then dissected and stained spinal nerve branches were measured. Moreover, the percentage of length, height and the total area of the stained tissue were calculated. In the S group, T10, T11 and T12 nerve eminences were successfully stained in 18%, 52% and 75% of cases, respectively. Furthermore, L1, L2, L3 and L4 were stained in 95%, 100%, 60% and 40% of cases, respectively. In group D, the ventromedial eminence of T10, T11 and T12 were stained in 68.1%, 100% and 98% of cases, respectively, and L1, L2, L3 and L4 were stained in 88%, 100%, 62% and 31% of cases, respectively. In conclusion, a two-point TAP block is more effective in covering the nerve eminences of the cranial abdomen than the preiliac approach alone.

Image analysis comparison of nerve staining with food dye, methylene blue or tissue marker

OBJECTIVE

Novel locoregional techniques use dye studies to confirm successful nerve targeting. The goal was to objectively quantify and compare nerve staining characteristics of dye mixtures commonly reported in the literature using image analysis software.

STUDY DESIGN

Prospective, randomized cadaveric study.

METHODS

Thirty-six brachial plexus nerves from unpreserved pig cadavers were randomized into three groups of 12: FD (1:10 mixture of blue food dye and bupivacaine 0.5%), MB (methylene blue 1%) and TM (0.1:10 mixture of blue tissue marker and lidocaine 2%). Nerves were immersed in dye for 1, 15, 30 or 60 minutes (n = 3 each). Images of nerves before immersion (baseline) and at each time point with epineurium intact (superficial staining) and after longitudinal bisection (deep staining) were processed using image analysis software. Color saturation values were divided into quartiles (dark, medium-dark, medium-light or light). Percentage of stained nerve area in each quartile was calculated and compared using two-way anova.

RESULTS

Superficially, at minute 1, dark saturation covered 40% of nerve area in FD versus 19% in MB (p = 0.04) and 0% in TM (p < 0.0001). In bisected nerves, dark and medium-dark saturations occurred only in FD; medium-light saturation comprised anywhere from 4% to 22.5% over time in FD versus <1% at any time in MB (p = 1.000; p = 0.343; p = 0.383; p = 0.262). Deep staining was not found in TM at any point.

CONCLUSION AND CLINICAL RELEVANCE

Food dye rapidly stains superficial and deep nerve layers. Based on these characteristics, investigators can choose the appropriate dye for their study.

An Ultrasound-Guided Latero-Ventral Approach to Perform the Quadratus Lumborum Block in Dog Cadavers

The QL block is a high-level locoregional anesthesia technique, which aims to provide analgesia to the abdomen. Several approaches of the QL block have been studied to find out which one allows a greater distribution of the injectate. The aim of this study is to compare the traditional interfascial QL block (IQL) with a new latero-ventral approach (LVQL). We hypothesize that this new approach could be safer and easier to perform, since the injectate is administered more superficially and further away from vital structures. Our second objective is to assess whether a higher volume of injectate (0.6 mL/kg) could reach the ventral branches of the last thoracic nerves, leading to a blockade of the cranial abdomen. Six thawed canine cadavers (12 hemiabdomens) were used for this purpose. Both approaches were performed in all cadavers. A combination of methylene blue/iopromide was administered to each hemiabdomen, randomly assigned to the LVQL or IQL. No differences were found regarding the ease of perform the LVQL with respect to IQL. The results show that both techniques reached the ventral branches from L1 to L3, although only the IQL consistently stained the sympathetic trunk (5/6 IQL vs. 1/6 LVQL). The use of a higher volume did not enhance a more cranial distribution of the injectate.

Transversus abdominis plane block in rats: Preliminary cadaveric studies

The transversus abdominis plane (TAP) block is an ultrasound guided regional anaesthetic technique used to provide analgesia to the abdominal wall. Research in humans and cats has demonstrated that TAP blocks reduce pain and post-operative opioid requirements after abdominal surgery. To date TAP blocks have not been described in rats. The optimal technique to employ when performing TAP blocks is controversial with single point injection techniques failing to reliably provide adequate coverage of the cranial abdominal wall. It has been suggested that performing a two point injection may provide more reliable coverage of the cranial abdominal wall.The objective of this study was to determine the feasibility of performing ultrasound guided TAP blocks in rat cadavers and to evaluate whether performing a two point technique provides greater spread of injectate than a one point technique when administering the same total volume of methylene blue solution.Twenty-three, four-month-old, female Sprague Dawley rat cadavers weighing 506 ± 78 g were used. TAP blocks were performed using a total of 1 ml/kg of methylene blue solution.Overall success rates for injections were 21.7% (13.6-32.8%). Single point injection area of spread was 87.8 ± 32 mm² compared with 102.4 ± 17 mm² for the two point injection technique.Due to the low success rate the use of TAP blocks using the current technique cannot be recommended. Two point injection technique appears to provide greater spread; however, additional data is required to draw meaningful conclusions.

Use of Transversus Abdominis Plane and Intercostal Blocks in Bitches Undergoing Laparoscopic Ovariectomy: A Randomized Controlled Trial

In humans and dogs, loco-regional anesthesia is associated with lower peri-operative opioid consumption and less related side effects. The combination of transversus abdominis plane (TAP) and intercostal blocks can be used to desensitize the entire abdominal wall in dogs. The aim of this study was to evaluate the effectiveness of TAP and intercostal blocks in bitches undergoing laparoscopic ovariectomy. Twenty client-owned bitches were enrolled in this double-blinded randomized controlled trial. After premedication with dexmedetomidine, methadone and ketamine, the animals were randomized into two groups. Dogs in the TAP group received intercostal blocks from T8 to T10 and a TAP block with ropivacaine. Dogs in the FEN group received a fentanyl bolus and a constant rate infusion for the entire duration of the procedure. Intra-operative cardiovascular stability, post-operative pain scores, rescue opioid requirement, dysphoria during recovery, time to attain sternal recumbency and interest in food at 6 h post-extubation were compared. Bitches in the TAP group received a statistically significant lower amount of rescue fentanyl intra-operatively and methadone post-operatively. Pain scores were lower in the TAP group until 6 h post-extubation. No difference was found for dysphoric recoveries, time to attain sternal recumbency and appetite at 6 h post-extubation. No adverse event was recorded for any of the dogs. The combination of TAP and intercostal blocks can be part of an effective multi-modal analgesic strategy in bitches undergoing laparoscopic ovariectomy.

Analgesic efficacy of ultrasound-guided transversus abdominis plane block in dogs undergoing ovariectomy

Background

In medicine, the transversus abdominis plane (TAP) block has been shown as an effective method of analgesia in several surgical procedures. In this context, this prospective, randomized, blinded study aimed to evaluate the analgesic efficacy of TAP block, guided by ultrasound in female dogs submitted to ovariectomy.

Methods

Therefore, 32 animals randomly assigned in two groups (n = 16) were used. Groups consisted of TAP block control (TBC) which received water injection (0.2 ml kg⁻¹ point), and TAP block bupivacaine (TBB) which received bupivacaine (0.2 ml kg⁻¹ point at 0.25%); both groups were submitted to four-point approach. Animals were pre-medicated with acepromazine (0.03 mg kg⁻¹) and meperidine (2 mg kg⁻¹) IM, propofol was used as anesthetic induction (3–5 mg kg⁻¹) IV, and isoflurane was used to maintain. To standardize groups, the animals received a continuous infusion of remifentanil (0.2μg kg⁻¹ min) and rocuronium (0.6 mg kg⁻¹) IV in the intraoperative period. Variables measured were the heart and respiratory rates, blood pressure, temperature, peripheral oxyhemoglobin saturation, exhaled carbon dioxide concentration, exhaled isoflurane concentration, serum cortisol, analgesia, and sedation. Before the pre-anesthetic medication (Baseline) and 1, 2, 4, 6, and 8 h after extubation, pain and sedation were assessed using a numeric rating scale (NRS), Glasgow composite measure pain scale (GCMPS-SF), and sedation scale. Moreover, serum cortisol was measured at different moments.

Results

The results show that in the intraoperative period, there was no significant difference between groups. After surgery, in TBC, 13 out of 16 animals required analgesic rescue, whereas, in TBB, this occurred only in one animal. Regarding the measurement of serum cortisol, the TBC group showed a significant difference when compared to the baseline time in the traction of the first ovary (p < 0.0001), 2 h (p = 0.0441), and 8 h (p = 0.0384) after extubation. In TBB, cortisol showed a significant increase only in the traction of the first ovary and 2 h after extubation (p < 0.0001).

Conclusion

The technique using ultrasound-guided TAP block in two points approach by hemiabdomen with 0.2 ml kg⁻¹ bupivacaine 0.25% was effective in providing post-operative analgesia in dogs undergoing ovariectomy.

An Anatomical, Sonographic, and Computed Tomography Study of the Transversus Abdominis Plane Block in Cat Cadavers

This study compared the distribution of a bupivacaine-iopamidol-dye solution following ultrasound-guided in-plane TAP injection using a 1-point (TAP-L) or 2-point (TAP-SL) approach in cat cadavers. Two cadavers were used to study the TAP sonoanatomy while eight cadavers were enrolled in a randomized, prospective, blinded investigation. Each cat randomly received a TAP-L with 0.5 mL/kg in one hemiabdomen and a TAP-SL with 0.25 mL/kg/point in the contralateral hemiabdomen. After injection, computed tomography and dissection were performed to assess contrast distribution and number of stained target nerves. TAP-SL resulted in a wider contrast spread (mm) compared with TAP-L (87 ± 7 versus 71 ± 9; p = 0.002). The prevalence of nerve staining was higher using TAP-SL than TAP-L (p = 0.001). The ventral branches of T10, T11, T12, T13, L1 and L2 were stained in 2/8, 2/8, 5/8, 7/8, 4/8 and 1/8, and in 7/8, 7/8, 8/8, 8/8, 8/8 and 1/8 using TAP-L and TAP-SL approaches, respectively. Computed tomography and dissection identified minimal injectate intraperitoneally or within the falciform ligament fat following 1 TAP-L and 2 TAP-SL. Ultrasound-guided TAP-SL provided better injectate distribution around the thoracolumbar spinal nerve branches than TAP-L.

Development of Enhanced Recovery After Surgery (ERAS) protocols in veterinary medicine through a one-health approach: the role of anesthesia and locoregional techniques

Enhanced Recovery After Surgery (ERAS) is a new and emerging concept in human medicine that involves rethinking the preoperative, intraoperative, and postoperative periods. The ultimate, overarching aim is to improve patient outcome following surgery and, thus, return to a normal daily routine as soon as possible. The development and implementation of locoregional anesthetic techniques in humans is one of the key elements driving these protocols. In veterinary medicine, we are no exception: the rapidly growing interest, development, and refinement of these techniques in our veterinary species is changing the way we think of anesthesia and analgesia. The potential real benefits are yet to be determined, as this concept is implemented into our veterinary hospitals in general, and our surgical patients in particular, in a more systematic and routine way. In this article, we will introduce the reader to the concept of ERAS protocols and the role of regional anesthesia in some common surgical procedures.

Local and Regional Anaesthetic Techniques in Canine Ovariectomy: A Review of the Literature and Technique Description

Simple Summary

This review stems from a general trend of increasing attention toward surgical nociception in the veterinary field. Indeed, veterinarian anaesthetists are becoming more careful in relieving perioperative nociception, improving the analgesic protocols and therefore optimising surgical outcomes. Canine ovariectomy is a common surgical procedure with a moderate level of pain. Therefore, intraoperative analgesia is very important because pain causes various systemic inflammatory effects that slow patient recovery. This review aims to collect all recent information about local and regional anaesthetic/analgesic techniques in a review of the literature describing the technique utilised. In addition, the present review aims to provide practical guidelines for veterinary practitioners to improve the anaesthetic techniques in canine neutering through an overview of the available literature. In fact, the methods described, considering the relative simplicity of execution, can be used in daily routine practice.

Abstract

Canine ovariectomy is an elective surgery with a moderate level of pain. Despite its relative simplicity, it requires surgical pain management. This study aimed to collect all recent information about local and regional anaesthetic/analgesic techniques in a review of the literature describing the technique utilised. The various procedures described in this review use local anaesthetics to improve analgesia in the routine systemic anaesthetic protocol. The approach described in this paper is called multimodal analgesia and is used in addition to the normal standard anaesthetic protocol. These techniques proved effective in minimising responses to the surgical stimulus and ensured adequate intraoperative and postoperative analgesia. The routine use of multimodal analgesia is considered a useful alternative for pain management in canine ovariectomy, in that it minimises patient suffering, improves the recovery of rescue analgesia, increases drug savings, and improves animal outcomes. In addition, the use of these local and regional techniques ensures satisfactory analgesic coverage that lasts for the first hours postoperatively.

Effect of needle type on plane block spread in a cadaveric porcine model

INTRODUCTION

Plane blocks are an increasingly common type of regional anaesthesia technique in the perioperative period. Increased spread of local anaesthesia during plane blocks is thought to be related to an increased area of pain coverage. This study sought to assess differences in injectate spread comparing Tuohy needles with standard insulated stimulating block needles.

METHODS

10 Yorkshire-Cross porcine cadavers were used in this study. Immediately following euthanasia, the cadavers underwent bilateral ultrasound-guided transversus abdominis plane (TAP) block injection with radiopaque contrast dye, with one side placed with a 20 g Tuohy needle, and the other side with a 20 g insulated stimulating block needle. Injectate spread was assessed using plain film X-ray and area of spread was measured to compare differences.

RESULTS

All 10 animals underwent successful ultrasound-guided TAP block placement. In all 10 animals, the area of contrast spread was greater with the Tuohy than stimulating needle. Wilcoxon signed-rank test was used to analyse the difference between the groups. The average difference between the two sides was 33.02% (p=0.002).

CONCLUSIONS

This is the first study to demonstrate differences in injectate spread with different needle types. This suggests enhanced spread with Tuohy needle compared with standard block needle, and may encourage its use during plane blocks.

Ultrasound-Guided Lateral Transversus Abdominis Plane (TAP) Block in Rabbits: A Cadaveric Study

The aims of the study were to describe the ultrasonographic-guided lateral TAP block in rabbit cadavers and evaluate the spread of a lidocaine/methylene blue solution through a single fascial infiltration. The US-guided block and anatomical dissections were performed in 17 New Zealand rabbit cadavers. The probe was placed perpendicular to the column, one centimetre ventrally to the transverse processes, halfway between the iliac crest and the costal margin. External oblique (EO), internal oblique (IO), and transversus abdominis (TA) muscles were visualised, and 1 mL/kg of lidocaine 2% plus methylene blue 1% was injected. After dissection, the branches of spinal nerves stained were measured. Moreover, the percentage of length and height of the area marked were calculated. A good visualisation of the TAP was obtained in all 34 hemiabdomens. T11 nerve eminence was successfully stained in 52% of cases. T12, L1, and L2 were stained in 75%, 95%, and 100% of cases, respectively. L3 and L4 were stained in 60% and 40% of cases, respectively. The lateral TAP block with a single point of injection can be easily performed in rabbits, but it is not sufficient to cover the nerve eminences of the cranial abdomen. The two-point TAP block (lateral and subcostal) could represent a better option, particularly when large surgical incisions are required.

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

OBJECTIVE

To evaluate a direct intra-abdominal approach to injection of the ventral transversus abdominis plane (TAP) and compare the dispersion of two volumes of injectate.

STUDY DESIGN

Prospective anatomic and feasibility study.

ANIMALS

A total of 10 canine cadavers weighing 9 ± 4 kg.

METHODS

A ventral incision was made extending through the linea alba, from the umbilicus and extending 5 cm caudally. A single injection of an isovolumic mixture of iopamidol and new methylene blue was performed with a hypodermic needle placed within the TAP of each hemiabdomen, alternating between 0.5 mL kg^-1 in low-volume group (LV) and 1 mL kg^-1 in high-volume group (HV). Surgical staples marked the incision. Computed tomography and three-dimensional reconstruction of the tomographic images evaluated the dimensions, cranial and caudal spread beyond the incision and the total area of the injectate. Dissection determined the extent of nerve staining within the TAP adjacent to the abdominal incision. Wilcoxon signed rank (stain) or paired t test was used to compare variables between groups. Data are reported as mean ± standard deviation or median (range).

RESULTS

Injectate spread was within the ventral TAP. Length of spread was 2.5 ± 1.6 cm greater in group HV than in group LV. There was a strong positive correlation between the surface area (p = 0.02, r = 0.71) and cranial-caudal spread of injectate (p = 0.041, r = 0.65) with volume. All but two LV injections were associated with staining of all nerves adjacent to the incision. Additional nerves caudal to the incision were stained in group HV (p = 0.02).

CONCLUSIONS

This approach to the TAP was easily performed, with volume of injectate positively influencing distribution.

CLINICAL RELEVANCE

This technique is easily applied and future prospective studies are warranted to determine its analgesic efficacy.

Ultrasound-guided modified subcostal transversus abdominis plane block and influence of recumbency position on dye spread in equine cadavers

OBJECTIVE

To describe and evaluate an ultrasound-guided modified subcostal approach for the transversus abdominis plane (TAP) block in horse cadavers in lateral or dorsal recumbency.

STUDY DESIGN

Prospective, experimental cadaveric study.

ANIMALS

Study of one preserved foal and eight fresh adult horse cadavers.

METHODS

The lateral and ventral abdominal wall of a preserved cadaver was dissected to identify the muscles and nerves. A unilateral standard TAP block technique was performed (60 mL of methylene blue dye-bupivacaine) on a fresh cadaver in right lateral recumbency. A modified subcostal technique was performed on the opposite side using a linear ultrasound transducer and in-plane approach. Injection points (two 30 mL dye) were at the level of the TAP (between the rectus abdominis and transversus abdominis muscles and ventral to the cutaneous trunci muscle) perpendicular to: 1) the mid-point between the xiphoid cartilage and umbilical scar; and 2) at a point between the caudal and middle thirds of the abdomen measured from the first injection point to the umbilical scar. The modified subcostal approach was performed in seven additional cadavers in both hemiabdomens, with three cadavers in lateral and four cadavers in dorsal recumbency. Ultrasound guidance was used with all injections.

RESULTS

The standard approach stained the sixteenth to eighteenth thoracic nerves (T16-T18). The modified subcostal approach performed in lateral recumbency provided greater spread (T9-T17) than dorsal recumbency (T12-T18) (p = 0.016).

CONCLUSIONS AND CLINICAL RELEVANCE

The modified subcostal TAP approach resulted in extensive staining exceeding the standard approach. The nerves stained are consistent with production of ventral abdominal wall anesthesia in horses. Clinical studies are needed to verify these findings.

Combined caudal retrocostal and lateral ultrasound-guided approach for transversus abdominis plane injection: A descriptive pilot study in pig cadavers

Transversus abdominis plane (TAP) block is a regional anesthetic technique used to desensitize the abdominal wall in several species. This study aimed to describe the anatomical characteristics of the abdominal wall and to identify a feasible approach for an US-guided TAP injection that would result in adequate staining of the relevant nerves in the abdominal wall in pig cadavers. Fresh cadavers from five Landrace pigs (age, 12 weeks; body weight, 35.5 ± 1.6 kg) were used. One pig (n = 1) was anatomically dissected, and four pigs (n = 4; i.e., 8 hemiabdomens) were used for TAP injections and evaluation of dye spread. The volume of 0.3 mL/kg/injection point of methylene blue was injected bilaterally. In the caudal retrocostal approach, the injection was performed ventral to the most caudal part of the costal arch. In the lateral approach, the injection was performed between the last rib and iliac crest. A needle was inserted in plane for the caudal retrocostal and the lateral approach caudocranially and craniocaudally, respectively. Successful staining was defined as presence of dye on the nerve for a length of >1 cm in its entire circumference. The TAP was found between different muscle layers in the described anatomical regions. In the caudal retrocostal approach the TAP was found between the external abdominal oblique and transversus abdominis muscle bellies. In the lateral approach the TAP was found between the internal abdominal oblique and transversus abdominis muscles. The approach combining lateral and caudal retrocostal injections at the studied volume stained a median of 5 (3–6) target nerves from the fourth-last thoracic nerve to L2 (six nerves). Combined caudal retrocostal and lateral TAP injections of 0.3 mL/kg/injection point, resulted in staining of target nerve branches which supply the periumbilical and caudal abdominal wall in pig cadavers.

Transversus abdominis plane block in cat cadavers: anatomical description and comparison of injectate spread using two- and three-point approaches

OBJECTIVE

To describe the sonoanatomy of the abdominal wall in live cats and to compare the distribution pattern of two versus three ultrasound-guided transversus abdominis plane (TAP) injections using clinically applicable volumes of lidocaine-dye solution in cat cadavers.

STUDY DESIGN

Prospective anatomical study.

ANIMALS

A total of eight client-owned healthy cats and eight cat cadavers.

METHODS

Ultrasound anatomy of the abdominal wall, landmarks and sites for needle access were determined in live cats. Ultrasound-guided TAP injections were performed in eight thawed cat cadavers. Volumes of 0.25 or 0.16 mL kg^-1 per point of a lidocaine-dye solution were injected using either two [subcostal and preiliac (SP)] or three [subcostal, retrocostal and preiliac (SRP)] injection points, respectively. Each cadaver was then dissected to determine the injectate distribution and the number of thoracolumbar nerves stained with each approach. The target nerves were defined as the ventromedial branches of the thoracic nerves 10 (T10), T11, T12, T13 and lumbar nerves 1 (L1) and L2.

RESULTS

Sonoanatomy was consistent with anatomy upon dissection and the TAP was identified in all cadavers. A total of 16 subcostal, 16 preiliac and nine retrocostal TAP injections were performed. The overall staining success rate of the target nerves was 66.7% and 92.6% for the SP and SPR approaches, respectively (p = 0.02). The ventromedial branches of T10, T11, T12, T13, L1 and L2 were stained in 57.1%, 100.0%, 85.7%, 28.6%, 42.9% and 85.7%, and in 66.7%, 100.0%, 100.0%, 100.0%, 88.9% and 100.0% of the cases with the SP and SRP approaches, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

The SRP approach allowed a broader distribution around the target nerves, whereas a staining gap was observed at T13 and L1 with the SP approach. Further studies are necessary to investigate the analgesic effect of these approaches in a clinical setting.

Description of different ultrasound guided transversus abdominis plane block in pig cadavers - A pilot study

OBJECTIVE

To develop an ultrasound (US)-guided transversus abdominis plane (TAP) block in pigs.

STUDY DESIGN

Prospective, descriptive, experimental study.

ANIMALS

A total of 26 hemi-abdomens belonging to 13 Seghers Hybrid cadavers.

METHODS

The study consisted of two parts. In part 1, a preliminary anatomical understanding of the abdominal wall innervation in pigs was established (two hemi-abdomens of one pig). Part 2 was divided into three phases, and a US-guided TAP technique using methylene blue dye (0.3 mL kg^-1 for each hemi-abdomen) was developed. In chronological order, a pilot study (phase I) was conducted to establish good injection points (four hemi-abdomens). In phase II a two-point injection technique (10 hemi-abdomens) was performed. A cranial injection was made at two-thirds of the distance between the xyphoid process and the iliac crest, immediately ventral to the rib arch. A caudal injection was performed ventral to the last rib. In phase III a three-point injection technique was performed (10 hemi-abdomens) with an extra injection point halfway between the cranial and caudal injection point. Staining of the different nerves was recorded during dissection.

RESULTS

In part 1 the nerves innervating the pig's abdominal wall, thoracic vertebrae 12-16 (T12-16) and lumbar vertebrae 1-3 (L1-3), were identified. In part 2, data from the pilot study, adequate nerve staining with the two- or three-point injection technique, were obtained in T12 (29 versus 45% respectively), T13 (29 versus 100%), T14 (73 versus 45%), T15 (75 versus 78%), T16 (58 versus 78%), L1 (100 versus 75%), L2 (88 versus 84%) and L3 (23 versus 0%).

CONCLUSIONS AND CLINICAL RELEVANCE

US-guided TAP block can be used in swine but only a moderate success rate for adequate nerve staining was achieved in this study. Further studies are necessary to determine a correct injection volume and assess clinical intra- and postoperative efficacy.

Evaluation of injection volumes for the transversus abdominis plane block in dog cadavers: a preliminary trial

OBJECTIVE

To evaluate staining of nerve branches after the injection of different volumes during ultrasound-guided transversus abdominis plane (TAP) block in dog cadavers.

STUDY DESIGN

Prospective randomized study.

ANIMALS

A total of 15 frozen/thawed adult dog cadavers.

METHODS

Hemiabdomens were randomly allocated to one of four groups. In groups G0.3, G0.6 and G1.0, ropivacaine-methylene blue solution (0.3, 0.6 and 1.0 mL kg^-1 in seven, eight and eight hemiabdomens, respectively) was injected at the midpoint between the iliac crest and the last rib at the height of the shoulder. In group G0.3×2 (seven hemiabdomens), two injections (0.3 mL kg^-1) were performed, caudal to the last rib and cranial to the iliac crest at the same height. Total time for injection was recorded; after 30 minutes, cadavers were dissected and spread of dye was evaluated.

RESULTS

Accuracy of injection site was 80% and injection time was 71 (48-120) seconds for all groups together. Craniocaudal spread was 6.4 ± 1.6, 9.1 ± 2.6, 11.4 ± 2.3 and 11.2 ± 3.8 cm for G0.3, G0.6, G1.0 and G0.3×2, respectively [G0.3 to G0.3×2 (p = 0.044) and G1.0 (p = 0.034)]. There was no difference in dorsoventral spread among groups. Number of ventral nerve branches stained was 3 (2-4), 3 (2-4), 3 (3-4) and 3 (2-4) for G0.3, G0.6, G1.0 and G0.3×2, respectively, including nerve branches from twelfth thoracic to third lumbar (L3) in different proportions among groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that a single-injection TAP block, using 0.3 mL kg^-1, stains comparable number of nerve branches as higher volumes or two-point injection. Despite the volume or technique, consistent staining of the innervation of the caudal abdomen (L1-L3) was observed. Additional cadaveric studies are necessary to identify the optimal technique for complete abdominal wall staining.

Comparison between two approaches for the transversus abdominis plane block in canine cadavers

OBJECTIVE

To compare the dye distribution following either two lateral abdominal or one lateral abdominal and one subcostal ultrasound-guided transversus abdominis plane (TAP) injections of a clinically relevant volume of dye solution in dogs.

STUDY DESIGN

Randomized cadaveric study.

ANIMALS

A total of eight canine cadavers.

METHODS

On one side of each cadaver, two TAP injections were performed on the lateral aspect of the abdomen (approach LL), caudal to the last rib and cranial to the iliac crest. On the contralateral hemiabdomen, one subcostal (caudal to the costal arch) and one lateral abdominal injection (between last rib and iliac crest), were performed (approach SL). Side allocation was randomly determined. A spinal needle was introduced in-plane to the transducer for each injection of methylene blue (0.25 mL kg^-1). All cadavers were dissected to assess dye distribution and number of stained target nerves.

RESULTS

All injections were performed in the TAP. The proportion of target nerve staining was 53.5% versus 80.4% with approaches LL and SL, respectively (p = 0.005). Approach LL stained the first lumbar (L1) spinal nerve in 100% of injections and ninth thoracic (T9), T10, T11, T12, T13 and L2 were stained in 0%, 0%, 37.5%, 62.5%, 87.5% and 87.5% of injections, respectively. Approach SL stained T11, L1 and L2 in 100% of injections and T9, T10, T12 and T13 were stained in 37.5%, 87.5%, 75% and 62.5% of injections, respectively. Approach SL resulted in greater staining of nerves cranial to T12 compared with approach LL. The two approaches were equivalent in staining nerves caudal to T12.

CONCLUSIONS AND CLINICAL RELEVANCE

Approach SL provided a broader distribution of the injected solution than approach LL, which may result in a larger blocked area in live animals undergoing celiotomy.

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

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

Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers

OBJECTIVES

To describe the ultrasound-guided rectus sheath block technique and the anatomical spread of two volumes of methylene blue injection in dog cadavers.

STUDY DESIGN

Blinded, prospective, experimental cadaveric study.

ANIMALS

A total of eight dog cadavers weighing 8.9 ± 1.6 kg.

METHODS

Ultrasound-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.

RESULTS

Fewer 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 RELEVANCE

The 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.

Two-point ultrasound-guided transversus abdominis plane injection in canine cadavers - a pilot study

OBJECTIVE

This study evaluated the spread of a two-point transversus abdominis plane (TAP) injection in canine cadavers. Compared with previous techniques, the two-point TAP injection was developed to increase the consistency of local anaesthetic spread to the nerve segments T11, T12, L1, L2 and L3.

STUDY DESIGN

Prospective experimental trial.

ANIMALS

Five fresh canine cadavers.

METHODS

Two-point TAP injections were performed under ultrasound guidance by a single trained individual in canine cadavers (15.7-43.0 kg). Each hemi-abdomen was infiltrated and evaluated independently for a total of 10 evaluations of the technique. The first injection was performed at the level of the costo-chondral junction of the thirteenth rib, and the second injection was performed cranial to the tuber coxae. Each injection comprised 0.3 mL kg^-1 methylene blue solution (0.0015 mg mL^-1). Ten minutes after the injections, abdominal wall dissection was performed, and any nerves stained for a minimum of 10 mm along their long axis were identified and recorded.

RESULTS

During all injections, separation of the internal oblique and transversus abdominis muscles was observed on ultrasound. On dissection, branches of T12, T13, L1, L2 and L3 were adequately stained in 30%, 100%, 100%, 90% and 90% of injections, respectively. No staining of branches of T11 occurred in any of the cadavers. In one hemi-abdomen, branches of L1 and L3, but not L2, were stained.

CONCLUSIONS AND CLINICAL RELEVANCE

This study indicates that the two-point TAP injection delivers consistent dye dispersion to adequately stain branches of T13, L1, L2 and L3, with no coverage of T11 and poor coverage of T12, in fresh canine cadavers. An in vivo study using local anaesthetic should be performed to evaluate the analgesic efficacy of this technique in mid to caudal abdominal surgeries.

Regional anesthetic techniques for the pelvic limb and abdominal wall in small animals: A review of the literature and technique description

Increasing interest in using peripheral nerve blocks in small animals is evident, given the numerous studies published recently on this topic in important veterinary journals. Initially, research was focused on intraoperative analgesia to the pelvic limb, and several descriptions of lumbosacral plexus, femoral and sciatic nerve blocks have been described in studies. There is recent interest in developing techniques for somatosensory blockade of the abdominal wall. This article is the second part of a two-part review of regional anesthesia (RA) in small animals, and its aim is to discuss the most relevant studies in the veterinary literature, where objective methods of nerve location have been used, and to illustrate in pictures the currently used techniques for providing RA to the abdominal wall and the pelvic limb in small animals.

Ultrasound-guided lateral and subcostal transversus abdominis plane block in calves: a cadaveric study

OBJECTIVE

To describe and assess the ultrasound-guided transversus abdominis plane (TAP) block feasibility in calf cadavers, to compare two injection volumes and to evaluate possible undesired solution spreads.

STUDY DESIGN

Prospective, descriptive, anatomic study.

ANIMALS

A group of 15 bovine cadavers weighing 47±11 kg (mean±standard deviation).

METHODS

Lateral (n = 24) and subcostal (n = 12) TAP block approaches were assessed. For each approach, two volumes (0.2 or 0.4 mL kg^-1) of toluidine blue and contrast medium were injected using both sides of the animals. Nerve staining was assessed by anatomical dissection and spread of injectate by contrast-enhanced computed tomography. Objective and subjective technique feasibility was evaluated by a specific score (poor, good, excellent).

RESULTS

Using the lateral approach, 58%, 92% and 25% and 75%, 83% and 25% of the thirteenth thoracic, first and second lumbar nerves were stained by 0.2 and 0.4 mL kg^-1, respectively. Craniocaudal and dorsoventral solution spread and number of blocks that adequately stained an individual nerve were not significantly different between the volumes. Using the subcostal approach, 67%, 83%, 67%, 67% and 50%, and 83%, 100%, 83%, 83% and 50% of the eighth, ninth, tenth, eleventh, twelfth thoracic nerves were stained by 0.2 and 0.4 mL kg^-1, respectively. With both techniques, no intraspinal and one intraperitoneal spread were observed. Objective and subjective feasibility score was excellent for both approaches in the majority of the cases.

CONCLUSIONS AND CLINICAL RELEVANCE

TAP injections were easy to perform with both techniques in calf cadavers. The volume of injectate did not influence spread. The authors conclude that a combination of the two approaches is necessary, but perhaps not sufficient, to stain all of the nerves innervating the ventral abdominal wall. Further studies are required to refine the technique and evaluate its efficacy in preventing nociception in calves.

Transversus abdominis plane block in ponies: a preliminary anatomical study

OBJECTIVE

To describe a single-site transversus abdominis plane (TAP) block technique in horses.

STUDY DESIGN

Prospective, descriptive, experimental anatomical study.

ANIMALS

Four adult pony cadavers.

METHODS

Freshly euthanized ponies were positioned in dorsal recumbency. A 6-13 MHz linear ultrasonic probe was used to scan the abdominal wall bilaterally midway between the last rib and iliac crest in search of the TAP location. By modifying the technique to accommodate the equine anatomy, the TAP was successfully visualized with the transducer positioned in a transverse plane with its side indicator over the intercept of two lines, one connecting the most cranial aspect of the iliac crest and the most caudal extent of the last rib and another originating just caudal to the umbilicus and extending laterally. Each hemiabdomen was injected with 0.5 mL kg^-1 of a 1:1 solution of 1% methylene blue and 0.5% bupivacaine via a 21 gauge 10 cm stimulating needle inserted ventral-dorsally and in plane with the ultrasound beam. Approximately 3 hours after injection, the abdomen was dissected and nerves stained over 1 cm in length were identified.

RESULTS

Staining was evident from the fourteenth thoracic (T14) to the third lumbar (L3) nerves. The ventral branches of the fifteenth to the eighteenth thoracic nerves (T15-T18) and first and second lumbar nerves (L1 and L2) were stained in three, six, eight, eight, eight and seven of eight injections, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Nerves T16-L2 had over 75% success rate in staining, suggesting that this technique would block transmission from T16 to L2, assuming that staining indicates potential nerve block. Dorsal spread occurred in three of eight hemiabdomens. Further studies developing techniques for the cranial abdomen and adjusting volume and concentration of injectate are warranted.

Perioperative analgesic effects of an ultrasound-guided transversus abdominis plane block with a mixture of bupivacaine and lidocaine in cats undergoing ovariectomy

OBJECTIVE

To evaluate the perioperative analgesic effects of a transversus abdominis plane (TAP) block with a mixture of lidocaine and bupivacaine administered to cats undergoing ovariectomy.

STUDY DESIGN

Controlled, randomized, prospective, blinded clinical study.

ANIMALS

A group of 20 healthy cats.

METHODS

Robenacoxib (2 mg kg^-1) was administered subcutaneously 0.5 hour before intramuscular (IM) administration of ketamine (5 mg kg^-1), methadone (0.1 mg kg^-1) and dexmedetomidine (0.01 mg kg^-1). General anesthesia was induced with intravenous (IV) propofol and maintained with isoflurane. An ultrasound-guided TAP block was performed by injecting 0.5% bupivacaine (0.2 mL kg^-1) diluted in a total volume of 1.5 mL 2% lidocaine bilaterally (TAP group, n = 10) or the same volume of saline solution bilaterally in controls (CTR group, n = 10). During surgery, a 20% increase in heart rate and respiratory frequency was treated with IV fentanyl (0.001 mg kg^-1). Before premedication and at 1, 2, 3, 4, 6, 8, 12, 16, 20 and 24 hours after extubation, pain was assessed with a simple descriptive pain scale, that ranged from 0 (no pain) to 4 (intense pain). For pain scores ≥3, IM methadone (0.1 mg kg^-1) was administered. Data were analyzed with the Friedman or the analysis of variance (anova) test, and p < 0.05 was considered statistically significant.

RESULTS

Only two cats in the CTR group were administered one dose of fentanyl during surgery. At 2, 6, 8, 12, 16, 20 and 24 hours after surgery, the pain score was higher in the CTR group. A mean dose of 0.5 ± 0.2 mg kg^-1 methadone was administered to all cats in the CTR groups within 24 hours. Methadone was not administered to the TAP group (pain score < 3).

CONCLUSIONS AND CLINICAL RELEVANCE

Ultrasound-guided TAP block can be a reliable adjunctive technique, providing analgesia for up to 24 hours in cats undergoing ovariectomy.

Comparison of the spread of two different volumes of contrast medium when performing ultrasound-guided transversus abdominis plane injection in dog cadavers

OBJECTIVES

To compare, via CT imaging, the spread of different volumes of diluted iodinated contrast medium in the transversus abdominis muscle plane of dog cadavers.

METHODS

Prospective, randomised study. An electro stimulation or a SonoTAP needle was inserted in plane with the ultrasound beam in the fascia between the internal oblique and transversus abdominis muscles. A test dose of 1 ml of diluted contrast (30 mg/mL iohexol) was injected to confirm positioning, followed by 0 · 5 mL/kg (n=14) or 1 mL/kg (n=12) and the distribution of the fluid compared.

RESULTS

Contrast medium was identified exclusively in the transversus abdominis plane in 19 of 26 dogs. In one dog, the contrast lay between the external and internal oblique muscles and partially in three dogs. Intraperitoneal contrast was detected in 6 of 26 dogs (23%). No significant differences were found in the dorso-ventral or cranio-caudal spread or area of distribution but a significant difference was found in the transverse spread. There was an association between poor ultrasound visualisation of the tip of the needle and intraperitoneal injection.

CLINICAL SIGNIFICANCE

Injection of 1 mL/kg of diluted contrast did not result in wider cranio-caudal spread in the transversus abdominis muscle plane of dog cadavers when compared with 0 · 5 mL/kg. Intraperitoneal injection is a risk and might be reduced with good needle visualisation.