Regional anesthetic techniques for the thoracic limb and thorax in small animals: A review of the literature and technique description

Successful management of a suspected air embolism during anaesthesia in a dog undergoing thoracic limb amputation

An 11-year-old, male, castrated, Springer Spaniel dog presented for right thoracic limb amputation due to chronic lameness. The dog was otherwise healthy. During brachial plexus dissection, end-tidal carbon dioxide dropped from 6.3 kPa to 1.3 kPa (47-10 mmHg) over 30 seconds, heart rate and spontaneous respiratory rate increased, and peripheral arterial haemoglobin oxygen saturation decreased from 98% to 78%. Initial patient assessment excluded equipment malfunction and cardiopulmonary arrest, prompting interdisciplinary conversation and targeted diagnostics. Arterial blood gas analysis, combined with the surgeons locating an entrainment point for air in the axillary vein, substantiated a diagnosis of vascular air embolism. Coordinated multidisciplinary interventions restored cardiorespiratory parameters within 40 minutes. The surgery was completed and the dog was successfully discharged. This report highlights the risk of venous air embolism during limb amputation and the importance of early recognition.

Feasibility of an electric current stimulator device to assess the sensory response after transversus abdominis plane block in Guinea pigs (Cavia porcellus)

OBJECTIVE

To assess the feasibility of using an adjustable intensity nerve stimulator for evaluating the sensory response after a transversus abdominis plane (TAP) block in guinea pigs (Cavia porcellus).

STUDY DESIGN

Prospective, randomized, blinded, experimental crossover study.

ANIMALS

A total of six adult guinea pigs (Cavia porcellus).

METHODS

Trial A involved a unilateral TAP block with 0.5% bupivacaine (1 mL kg-1), and trial B involved a unilateral sham block with an equivalent volume of 0.9% saline. In both trials, the noninjected side served as the control. An electrical stimulus was bilaterally applied at 10, 20, 30, 60, 90 and 120 minutes post-injection. Stimulus intensity was gradually increased and the current intensity (mA) at which a response (body movements and/or voluntary limb withdrawal and/or vocalization) occurred on each side was registered. Measurements over time (Friedman test) and between sides at each time point (Wilcoxon test) were compared.

RESULTS

In trial B, nonsignificant differences were observed between sides at each time point. In trial A, when comparing responses at each time point, nonsignificant differences were observed at 60 (p = 0.104), 90 (p = 0.598) and 120 minutes (p = 0.891); however, at 10 (p = 0.043), 20 (p = 0.027) and 30 minutes (p = 0.026), significant differences were observed. The stimulus intensity necessary to evoke a response in the bupivacaine-injected side was at least 23.8% higher than the current intensity required to elicit a response in the control side.

CONCLUSIONS AND CLINICAL RELEVANCE

The electrical stimulus method appears effective in distinguishing the presence or absence of sensory block in guinea pigs that were administered a TAP block. This approach may also serve to assess the onset time and duration of the block.

Anaesthetic mortality in cats: A worldwide analysis and risk assessment

BACKGROUND

Patient safety is essential in small animal anaesthesia. This study aimed to assess anaesthesia-related deaths in cats worldwide, identify risk and protective factors and provide insights for clinical practice.

METHODS

A prospective multicentre cohort study of 14,962 cats from 198 veterinary centres across different countries was conducted. Data on anaesthesia-related deaths, from premedication up to 48 hours postextubation, were collected. Logistic regression was used to analyse patient demographics, American Society of Anesthesiologists (ASA) classification, procedure type and anaesthetic drugs.

RESULTS

The anaesthesia-related mortality was 0.63%, with 74.5% of deaths occurring postoperatively. Cats with cachexia, a higher ASA status or who underwent abdominal, orthopaedic/neurosurgical or thoracic procedures exhibited elevated mortality. Mechanical ventilation use was associated with increased mortality. Mortality odds were reduced by the use of alpha2-agonist sedatives, pure opioids in premedication and locoregional techniques.

LIMITATIONS

Limitations include non-randomised sampling, potential biases, unquantified response rates, subjective death cause classification and limited variable analysis.

CONCLUSIONS

Anaesthetic mortality in cats is significant, predominantly postoperative. Risk factors include cachexia, higher ASA status, specific procedures and mechanical ventilation. Protective factors include alpha2-agonist sedatives, pure opioids and locoregional techniques. These findings can help improve anaesthesia safety and outcomes. However, further research is required to improve protocols, enhance data quality and minimise risks.

Evaluating the Efficacy of a Peripheral Nerve Simulator-Guided Brachial Plexus Block in Rabbits Undergoing Orthopaedic Surgery Compared to Systemic Analgesia

Locoregional anaesthetic techniques are invaluable for providing multimodal analgesia for painful surgical procedures. This prospective, randomised study describes a nerve stimulator-guided brachial plexus blockade (BPB) in rabbits undergoing orthopaedic surgery in comparison to systemic lidocaine. Premedication was provided with intramuscular (IM) medetomidine, fentanyl, and midazolam. Anaesthesia was induced (propofol IV) and maintained with isoflurane. Nine rabbits received a lidocaine BPB (2%; 0.3 mL kg-1), and eight received a lidocaine constant rate infusion (CRI) (2 mg kg-1 IV, followed by 100 µg kg-1 min-1). Rescue analgesia was provided with fentanyl IV. Carprofen was administered at the end of the surgery. Postoperative pain was determined using the Rabbit Grimace Scale (RGS) and a composite pain scale. Buprenorphine was administered according to the pain score for two hours after extubation. Rabbits were filmed during the first two hours to measure distance travelled and behaviours. Food intake and faeces output were compared. Every rabbit in CRI required intraoperative rescue analgesia compared to none in BPB. However, rabbits in both groups had similar pain scores, and there was no difference in the administration of postoperative analgesia. There were no significant differences in food intake or faeces production over 18 h, and no significant differences in distance travelled or behaviours examined during the first two hours. BPB seems superior for intraoperative analgesia. Postoperatively, both groups were comparable.

Open Approach to the Transversus Abdominis Plane in Horses: A Cadaver Feasibility Study

The study's objective was to evaluate the feasibility and dispersion of an open approach to the transversus abdominis plane (TAP) block in eight adult equine cadavers. A ventral midline incision was made, starting 2 cm cranial to the umbilicus and extending 25 cm cranially. In total, 0.5 mL/kg of new methylene blue (NMB) was injected per horse, divided into six injections. Using an 18 g, 8 cm Tuohy needle, three injections were made per side. The needle was guided blindly into the TAP using palpation. A 60 mL syringe was attached directly to the needle, depositing ~0.08 mL/kg at each site. The time to complete the injections was recorded for each cadaver. Following injection, the ventral body wall was dissected to determine if the dye was present within the TAP space as well as to measure the extent of the dispersion of the dye, the cranial to caudal extent, and the width of the dye's spread. Complete deposition of NMB into the TAP (six of six sites) was achieved in 5/8 horses. The median time needed to perform all the injections was 263 s. Increased adiposity (retroperitoneal fat) was associated with unsuccessful injections. This approach to the TAP was easily and quickly performed, though less successful in horses with increased retroperitoneal fat and increased BCS.

Comparison of Ultrasound-Guided Versus Anatomical Landmark-Guided Thoracolumbar Retrolaminar Techniques in Canine Cadavers

The retrolaminar block was developed in humans as an easier and safer alternative to the thoracic paravertebral block. This study aims to describe an ultrasound-guided thoracolumbar retrolaminar injection in canine cadavers and compare the injectate distribution between a landmark-guided and an ultrasound-guided thoracolumbar retrolaminar technique using computed tomography. Ten canine cadavers were randomised to receive two injections each of 0.6 mL/kg of iodinated contrast at the level of the twelfth thoracic vertebra (T12): a landmark-guided retrolaminar injection was performed on one hemithorax (group B, n = 10) and an ultrasound-guided on the other hemithorax (group U, n = 10). Groups were compared using the Mann-Whitney U test. The median (range) spread of the contrast in the paravertebral space was 0 (0-3) and 1 (0-5) vertebrae in groups B and U, respectively (p = 0.038). The median (range) extent of the spread surrounding the interverbal foramina was 4 (0-5) in group B and 4 (3-5) in group U. The median (range) spread along the retrolaminar space cranial and caudal to T12 was 3 (0-6) retrolaminar segments in group B and 3 (3-4) in group U. The potential of the ultrasound-guided retrolaminar injection to provide analgesia for dogs suffering from thoracolumbar pain should be further investigated.

Fentanyl sparing effect of ultrasound-guided proximal radial, ulnar, median, and musculocutaneous nerve (RUMM) block for radial and ulnar fracture repair in dogs: a retrospective case-control study

This study retrospectively evaluated the fentanyl-sparing effect of ultrasound-guided proximal radial, ulnar, median, and musculocutaneous nerve (RUMM) block for radial and ulnar fracture repair in dogs. Fentanyl was prepared for intraoperative analgesia in dogs, although proximal RUMM block was performed using 0.5% or 0.25% bupivacaine before surgery in the block group. Dogs without a nerve block were assigned to the control group. The fentanyl dose in the block group [0.8 (0-1.9) μg/kg/hr] [median (interquartile range)] was significantly lower than in the control group [8.4 (7.2-10) μg/kg/hr]. Surgery was performed without fentanyl in >50% of the dogs (5/7), using 0.5% bupivacaine. Ultrasound-guided proximal RUMM block can be useful as an intraoperative analgesic for radial and ulnar fracture repair in dogs.

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.

2022 ISFM Consensus Guidelines on the Management of Acute Pain in Cats

PRACTICAL RELEVANCE

Increases in cat ownership worldwide mean more cats are requiring veterinary care. Illness, trauma and surgery can result in acute pain, and effective management of pain is required for optimal feline welfare (ie, physical health and mental wellbeing). Validated pain assessment tools are available and pain management plans for the individual patient should incorporate pharmacological and non-pharmacological therapy. Preventive and multimodal analgesia, including local anaesthesia, are important principles of pain management, and the choice of analgesic drugs should take into account the type, severity and duration of pain, presence of comorbidities and avoidance of adverse effects. Nursing care, environmental modifications and cat friendly handling are likewise pivotal to the pain management plan, as is a team approach, involving the cat carer.

CLINICAL CHALLENGES

Pain has traditionally been under-recognised in cats. Pain assessment tools are not widely implemented, and signs of pain in this species may be subtle. The unique challenges of feline metabolism and comorbidities may lead to undertreatment of pain and the development of peripheral and central sensitisation. Lack of availability or experience with various analgesic drugs may compromise effective pain management.

EVIDENCE BASE

These Guidelines have been created by a panel of experts and the International Society of Feline Medicine (ISFM) based on the available literature and the authors' experience. They are aimed at general practitioners to assist in the assessment, prevention and management of acute pain in feline patients, and to provide a practical guide to selection and dosing of effective analgesic agents.

Axillary ultrasound-guided approach for the brachial plexus in pig cadavers: A descriptive study

Effective multimodal analgesia techniques are required when pigs are used as models in orthopedic human research. Regional anesthesia is a widely used technique to provide perioperative analgesia in animals undergoing orthopedic surgery. The brachial plexus (BP) block is indicated to desensitize the forelimb in many species but has not been yet described in pigs. The main aims of this study were to develop an ultrasound-guided axillary approach for the BP and to evaluate injectate spread and nerve staining in pig cadavers. Eight fresh F1 cross breed German Large White and German Landrace male pig cadavers were enrolled. Two cadavers were used for anatomical dissection of the axillary space and to determine the disposition of the BP. Six cadavers were used to perform a bilateral axillary ultrasound-guided approach for the BP, and after injecting 0.3 ml/kg of a solution of 2% lidocaine and new methylene blue (L-NMB), these were dissected to determine injectate spread and nerve staining. Upon dissection, the BP was observed in all the cases surrounded by the axillary sheath and in close proximity to the axillary artery. Ultrasonographic scanning and guidance for the approach to the BP was feasible in all cadavers and upon dissection, all the nerves forming the BP were stained in all their quadrants and in all the cases. In conclusion, the injection of 0.3 ml/kg of L-NMB through an ultrasound-guided axillary approach to the BP was feasible and adequate to entirely stain the BP in all pig cadavers. Further clinical studies are required to evaluate the effectiveness of this technique in live animals.

Case Report: Ultrasound Sciatic and Saphenous Nerve Blocks for Tibial Malunion Surgical Correction in a Pediatric African Leopard (Panthera pardus)

Little information is available regarding ultrasound-guided locoregional anesthesia in non-domestic species. Locoregional techniques have been shown to reduce intraoperative anesthetic requirements and provide postoperative pain relief. Decreasing dosage of general anesthetics allows more stable cardiopulmonary function during anesthesia and reduces the probability of side effects. An 11-week-old African leopard (Panthera pardus) was referred for treatment of a malunion angular limb deformity secondary to a tibial and fibular fracture. The animal was scheduled to undergo angular correction of the tibia via closing wedge osteotomy and fixation with a locking plate system. Following preanesthetic medication and induction of general anesthesia, a saphenous nerve block (ropivacaine 0.5%; 0.15 ml/kg) was performed under ultrasound guidance and a sciatic nerve block (ropivacaine 0.5%; 0.15 ml/kg) was performed using ultrasound and a peripheral nerve stimulator. Intraoperative anesthetic plane was considered light, yet no abrupt cardiocirculatory changes were seen, nor was rescue analgesia required. This case report suggests that sciatic and saphenous blockade could therefore be recommended as part of a multimodal plan of analgesia for orthopedic surgeries in pediatric exotic felids.

Clinical techniques in veterinary dermatology: regional anaesthesia of the canine and feline distal limb

BACKGROUND

Local anaesthesia for procedures involving the distal limb are a useful component of balanced protocols to achieve effective procedural analgesia for patients. A ring block is an effective and straightforward technique.

HYPOTHESIS/OBJECTIVE

To review and describe the ring block technique for local anaesthesia of the canine and feline distal limb.

ANIMALS

Images of hospitalized patients were used. These photographs were obtained with owner permission.

RESULTS

The clinical technique for the ring block of the canine or feline distal limb is described.

CONCLUSIONS AND CLINICAL IMPORTANCE

The ring block can be implemented simply and successfully for a variety of procedures involving the distal limb to provide effective analgesia.

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

OBJECTIVE

To describe the gross and microscopic anatomy of the sciatic nerve paraneural sheath and to report an ultrasound (US)-guided subparaneural approach to the sciatic nerve in dogs, comparing two different volumes of injectate.

STUDY DESIGN

Prospective, randomized, anatomical study.

ANIMALS

A group of nine middle-sized adult Mongrel canine cadavers (18 limbs).

METHODS

The sciatic nerves of three pelvic limbs of two canine cadavers were identified, exposed and isolated between the greater trochanter and the popliteal fossa for gross anatomical and microscopic examination. An additional three pelvic limbs were surgically dissected on the lateral surface of the limb; the sciatic nerves were isolated, and a 26 gauge over-the-needle catheter was inserted through the paraneural sheath under direct visualization. A methylene blue solution was then slowly injected into the subparaneural compartment through the catheter under US visualization using an 8-13 MHz linear-array transducer. Subsequently, 12 pelvic limbs (six cadavers) were randomly allocated to one of two groups; using US-guided percutaneous subparaneural approach, either 0.1 or 0.05 mL kg^-1of a 1:1 solution of methylene blue and 0.5% bupivacaine was injected. The spread of the dye solution and the amount of nerve staining were macroscopically scored. The stained sciatic nerves with their sheaths were then harvested for microscopic examination.

RESULTS

The paraneural sciatic nerve sheath was easily identified distinct from the nerve trunk both macroscopically and with US visualization, and microscopically. Complete staining was achieved in five of six (83.3%) sciatic nerves in each group; no difference was found in the amount of staining between the two groups. Microscopically, no signs of sciatic nerve intraneural injection were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

The US-guided subparaneural injection of 0.05 mL kg^-1 of a dye injectate resulted in satisfactory nerve staining without evidence of sciatic nerve intraneural injection.

Development of a lateral ultrasound-guided approach for the proximal radial, ulnar, median and musculocutaneous (RUMM) nerve block in cats

OBJECTIVE

To describe a lateral ultrasound (US)-guided approach to the radial, ulnar, median and musculocutaneous (RUMM) nerves through a single proximal in-plane insertion in cats and to determine whether one or two injection points are required to successfully stain all the target nerves.

STUDY DESIGN

Prospective study.

ANIMALS

A total of eight client-owned healthy cats and 12 cat cadavers.

METHODS

In live cats, the US anatomy of the brachium, the landmarks and the site for needle accesses were determined. Then, 12 thawed feline cadavers were used to assess the spread of dye solution and nerve staining following the US-guided proximal-lateral-humeral RUMM injection using one and two injection points. Each cadaver was injected with 0.15 mL kg^-1 of a 0.25% new methylene blue solution in either a single injection aimed for the radial nerve of one limb (G1) or via two sites delivering 0.1 mL kg^-1 and 0.05 mL kg^-1 aimed for the radial and musculocutaneous nerves of the opposite limb, respectively (G2). Upon dissection, staining of the target nerves around their circumference for length of >1 cm was considered successful.

RESULTS

Sonoanatomy was consistent with anatomy upon dissection and target nerves were identified in all cadavers. Staining was 100% successful for the radial, median and ulnar nerves in both groups, and 41.7% and 100% for the musculocutaneous nerve in G1 and G2, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

This novel lateral US-guided approach for the proximal RUMM nerve block allowed a good identification of the nerves and related structures, and it provided a consistent muscular structure through which the needle could be easily guided. An injection performed in two aliquots (within the caudal and cranial compartments of the neurovascular sheath) appeared to be necessary to successfully stain all the target nerves.

Local and regional anaesthesia in dogs and cats: Descriptions of specific local and regional techniques (Part 2)

Pain management in veterinary patients is a crucial component of appropriate patient care. Local anaesthetic drugs used in local and regional blockade can completely block the transmission of nociceptive impulses, decreasing both intra‐operative nociception and postoperative pain, while decreasing the potential incidence of adverse effects that can be associated with systemic boluses of drugs. For efficacy and safety, this class of drugs is recommended as part of the analgesic protocol in the majority of surgical procedures and traumatic injuries. Numerous local and regional blocks are proven effective in dogs and cats, thus providing the clinician with ample opportunity to include these blocks in practice. This manuscript, Part 2 of a two‐part instalment, focuses on brief descriptions of select commonly used local/regional anaesthesia techniques for dogs and cats that cover a multitude of painful surgeries/injuries and that can be implemented in any practice. In Part 1 of this topic, detailed information on local anaesthetic drugs commonly used in small animal practice was reviewed (Grubb & Lobprise, 2020).

Ultrasound-guided erector spinae plane block in canine cadavers: relevant anatomy and injectate distribution

OBJECTIVE

To investigate the distribution and nerve staining of two volumes of lidocaine-dye solution after ultrasound-guided erector spinae plane (ESP) injections in canine cadavers.

STUDY DESIGN

Experimental cadaveric study.

ANIMALS

A total of nine canine cadavers.

METHODS

ESP injections were performed between the longissimus thoracis muscle and the dorsolateral edge of the ninth thoracic transverse process. Two cadavers were transversally cryosectioned after unilateral ESP injections [0.6 mL kg^-1; high volume (HV)]. In seven cadavers, bilateral ESP injections with HV or low volume (0.3 mL kg^-1; LV) were performed. Gadodiamide was added to the injectate for two cadavers and magnetic resonance imaging (MRI) was performed pre- and post-injection. Injectate distribution and nerve staining of the branches of the spinal nerves were recorded after gross anatomical dissection. The thoracic paravertebral and epidural spaces were examined for dye solution.

RESULTS

Cryosections, MRI and gross dissections showed that the injectate spread dorsally to the transverse processes, over the ventromedial aspect of the longissimus thoracis muscle where the medial and lateral branches of the dorsal branches of the spinal nerves are located. LV and HV stained a median (range) of 4 (2-7) and 4 (3-8) medial branches, respectively (p = 0.52). LV and HV stained 4 (2-5) and 5 (4-7) lateral branches (p = 0.26), respectively. Ventral branches were not stained, and dye was not identified in the epidural or paravertebral spaces.

CONCLUSIONS

and clinical relevance Medial and lateral branches were consistently stained over several spinal segments. The number of nerves stained was not different with HV or LV, and the ventral branches of the spinal nerves were not stained in any cadaver. ESP block may find a clinical application to desensitize structures innervated by the medial and lateral branches of the dorsal branches of the thoracic spinal nerves.

Locoregional Anesthesia of the Thoracic Limbs and Thorax in Small Animals

The incorporation of nerve stimulation and ultrasound guidance to veterinary regional anesthesia allows accurate performance of techniques to block the thoracic limb and the thorax. When performed correctly, regional anesthesia can either constitute an alternative to the use of opioids and other systemic analgesics, or have a significant opioid-sparing effect. This article provides an overview of some techniques described using objective methods of nerve location, which can be used to provide perioperative locoregional anesthesia and analgesia to the thoracic limb and thorax. The approaches described may be used to decrease the perioperative use of opioids in small animals.

Ultrasound-guided superficial serratus plane block in dog cadavers: an anatomical evaluation and volume dispersion study

OBJECTIVE

To evaluate the anatomy of the serratus plane in dogs to establish the optimal landmarks for a superficial serratus plane (SSP) block and evaluate ropivacaine-methylene blue solution dispersion with three volumes of injection.

STUDY DESIGN

Prospective experimental cadaveric study.

ANIMALS

A formaldehyde solution-preserved dog cadaver and 15 frozen/thawed adult dog cadavers.

METHODS

The thoracic wall of the formaldehyde-preserved cadaver was dissected. An SSP injection was performed on each hemithorax of the cadavers, with the ultrasound transducer placed over the fourth and fifth ribs, at the level of the shoulder joint. A needle was inserted in-plane in a caudocranial direction until it could be visualized between the serratus ventralis thoracis and latissimus dorsi muscles. Dog cadavers were injected with a ropivacaine-methylene blue solution at 0.3, 0.6 and 1.0 mL kg^-1 and were dissected to determine the spread of the dye.

RESULTS

The thoracic wall muscles identified in the formalinized cadaver were the cutaneous trunci, latissimus dorsi, external abdominal oblique, serratus ventralis thoracis, scalenus, serratus dorsalis cranialis and external intercostal. The nerves identified in the SSP included the lateral cutaneous branches of intercostal nerves, intercostobrachial nerves and long thoracic nerve. The solution was successfully injected at the SSP in 26 of 29 (89.7%) attempts. Dermatomal dye spread, median (range), was 4 (3-6), 4 (2-5) and 5 (4-8) for 0.3, 0.6 and 1.0 mL kg^-1, respectively, with no significant difference among them.

CONCLUSIONS AND CLINICAL RELEVANCE

Injections for an SSP block were easily performed under ultrasound guidance, using the fourth and fifth ribs at the level of the shoulder joint as reference landmarks. An injected volume of 0.3 mL kg^-1 may be sufficient for hemithorax analgesia in dogs. Further studies in dogs are required to determine the utility of this technique.