Ultrasound‐guided nerve blocks of the pelvic limb in dogs

Saphenous and Sciatic Nerve Blockade with and without Obturator Nerve Block for Tibial Plateau Levelling Osteotomy Surgery in Dogs: A Randomized Controlled Trial

The objective of our study was to compare the efficacy of sciatic and saphenous ultrasound nerve blocks with and without US-guided obturator nerve block in dogs undergoing tibial-plateau-levelling-osteotomy (TPLO) surgery. This study was developed in two phases: identification of an ultrasound window in the inguinal region for obturator nerve block and utilization of it in dogs undergoing TPLO. Dogs were assigned randomly to one of two groups: one received the three blocks with 0.5% ropivacaine (ON group) and the second one (NoON group) with NaCl instead of ropivacaine for the obturator block. In phase 1, the obturator nerve was visible between the pectineus and the abductor muscles and was approached using an in-plane technique. It was possible to use the ultrasound window for phase two. The number of dogs that received at least one bolus of intraoperative rescue analgesia in the NoON group (12/15 dogs) was significantly higher (p = 0.003) in comparison with the ON group (4/15). An ultrasound window to block the obturator nerve in the inguinal compartment with an in-plane technique was found. The use of this approach could produce adequate analgesia with less motor function impairment in dogs for TPLO surgery.

Effects of two different topographic approaches for combined sciatic and femoral nerve block in calves, guided by ultrasound and neurostimulation

To evaluate the sensory and motor effects promoted by a combined sciatic and femoral nerve block in calves using two approaches. Six calves were used, in a crossover study. Ultrasound combined with neurostimulation, was used to perform the following block combinations: the proximal approach (PA), which consisted of the association of the parasacral approach (sciatic nerve block) and ventral to the ilium approach (femoral nerve block); distal approach (DA) consisted of the association of a lateral approach to the pelvic limb approach (sciatic nerve block), and an inguinal approach, underneath the femoral trigone (femoral nerve block). Pressure algometry and motor function of the limb where evaluated. Mechanical nociceptive threshold (MNT) increase, and ataxia duration means were 9.5 ± 0.7 kg and 10.4 ± 3.9 hr for PA and 10.4 ± 3.9 kg and 12.7 ± 1.9 hr for DA, respectively with no significant difference. There was no significant difference between MNT elevation time and the duration of ataxia using the same approach. The DA treatment showed significant MNT elevation in 72% of the tested regions, while the PA treatment showed an elevation in 100% regions tested. Topographic approaches closer to where the spinal nerves emerge produced a larger desensitised area.

A non-inferiority study comparing the ultrasound-guided parasacral with a novel greater ischiatic notch plane approach in canine cadavers

OBJECTIVE

To describe the gross and ultrasound anatomy of the parasacral region and an ultrasound-guided greater ischiatic notch (GIN) plane approach aimed at staining the lumbosacral trunk (LST) in canine cadavers. To evaluate if the ultrasound-guided GIN plane approach is non-inferior to the previously described ultrasound-guided parasacral approach at staining the LST.

STUDY DESIGN

Prospective, randomized, non-inferiority experimental anatomic study.

ANIMALS

A total of 17 (23.9 ± 5.2 kg) mesocephalic canine cadavers.

METHODS

Anatomic and echographic landmarks, and the feasibility of performing a GIN plane technique were evaluated using two canine cadavers. The remaining 15 cadavers had each hemipelvis randomly assigned to be administered either parasacral or GIN plane injection of 0.15 mL kg-1 dye solution. The parasacral region was dissected after injections to assess the staining of LST, cranial gluteal nerve, pararectal fossa and pelvic cavity. The stained LST were removed and processed for histological evaluation of intraneural injections. A one-sided z-test for non-inferiority (non-inferiority margin -14%) was used to statistically evaluate the success of the GIN plane versus the parasacral approach. Data were considered statistically significant when p < 0.05.

RESULTS

The GIN plane and parasacral approach stained the LST in 100% and 93.3% of the injections, respectively. The success rate difference between treatments was 6.7% [95% confidence interval, -0.6 to 19.0%; p < 0.001 for non-inferiority]. The GIN plane and parasacral injections stained the LST for 32.7 ± 16.8 mm and 43.1 ± 24.3 mm, respectively (p = 0.18). No evidence of intraneural injection was found.

CONCLUSIONS AND CLINICAL RELEVANCE

The ultrasound-guided GIN plane technique resulted in nerve staining that was non-inferior to the parasacral technique and may be considered an alternative to the parasacral approach to block the LST in dogs.

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

OBJECTIVE

To describe an ultrasound-guided lateral pre-iliac (LPI) and parasacral (PS) approach in feline cadavers (phase I) and compare the perioperative analgesic use and complications in cats administered LPI and PS blocks (group PNB) or epidural anesthesia (group EPI) for pelvic limb surgery (phase II).

STUDY DESIGN

Experimental uncontrolled, anatomic and retrospective cohort study.

ANIMALS

A group of eight feline cadavers and 52 medical records.

METHODS

Bilateral LPI and PS approaches with 0.1 mL kg^-1 of dye to stain the femoral and obturator nerves and the lumbosacral trunk, respectively, were performed on each cadaver. Nerve staining effect was evaluated upon dissections (phase I). Perioperative analgesics use, and complication rates were retrospectively compared between groups PNB and EPI (phase II). Continuous data were compared using the Mann-Whitney U test and the prevalence of events with Fisher's exact test. Differences were considered significant when p < 0.05.

RESULTS

Dissections revealed that the LPI approach stained 94% and 75% of the femoral and obturator nerves, respectively. The PS approach stained 100% of the lumbosacral trunks. Cats enrolled in group PNB (n = 23) were administered lower doses of intraoperative opioids than those in group EPI (n = 25) (p = 0.006). Intraoperative rescue analgesia was required in 60% and 17.4% of cats enrolled in groups EPI and PNB, respectively (p = 0.003). Group PNB required more intraoperative anticholinergics than group EPI (p = 0.02). There were no differences in postoperative pain scores, analgesic use and complication rates.

CONCLUSIONS AND CLINICAL RELEVANCE

The ultrasound-guided LPI and PS approach stained the femoral/obturator nerves and the lumbosacral trunk, respectively, in feline cadavers. Furthermore, PNB was associated with lower intraoperative opioid use and similar postoperative pain and analgesic use compared with epidural anesthesia in a cohort of cats undergoing surgery of the pelvic limb.

Effect of temperature-responsive hydrogel on femoral and sciatic nerve blocks using bupivacaine in Beagle dogs

OBJECTIVES

To compare the duration of regional anesthesia of the pelvic limb using bupivacaine with and without a temperature-responsive hydrogel (TRH) in dogs.

METHODS

Under anesthesia using medetomidine (10 μg·kg^-1 ), alfaxalone (2 mg·kg^-1 ), and isoflurane, seven healthy male Beagles received four injections of 0.5% bupivacaine (1 mg·kg^-1 with 5 μg·ml^-1 epinephrine) to block the femoral and sciatic nerves bilaterally via ultrasound with nerve stimulation guidance. Bupivacaine was used on one pelvic limb (Bup treatment), and bupivacaine with TRH was used on the contralateral limb (Bup-TRH treatment). The nerve block was considered successful upon the absence of responses to pinching the digital pads and mid-tibial skin of both pelvic limbs with mosquito forceps; the pinch, proprioception, and locomotion tests were performed before (baseline) and at each hour after the nerve block until sensory and motor functions returned to baseline. The effect of TRH on nerve blocks was analyzed using a linear mixed model.

RESULTS

The duration of the sensory nerve block at the digital pads and mid-tibial skin was longer with Bup-TRH (8.0 ± 1.6 h and 10.9 ± 1.6 h, respectively) than with Bup treatment (3.7 ± 2.0 h and 8.0 ± 1.6 h, respectively). Motor block times of proprioception and locomotion were longer with Bup-TRH (9.3 ± 1.6 and 12.7 ± 1.5 h, respectively) than with Bup treatment (4.6 ± 1.9 and 9.6 ± 1.5 h, respectively). No complications were observed.

CLINICAL SIGNIFICANCE

TRH extended the duration of regional anesthesia of the pelvic limb using bupivacaine.

Comparison of two volumes for sciatic perineural injection using 1% methylene blue in rabbit cadavers

ABSTRACT The purpose of this study was to assess the efficacy of a blind technique for sciatic and femoral nerve block in rabbit cadavers by evaluating the spread of 1% methylene blue at two different volumes. Nine recently euthanized rabbits weighing 2.5(0.3kg were used. The sciatic (SN) and femoral (FN) nerves of each limb were randomly assigned for injection with 1% methylene blue at 0.2mL/kg (G0.2) or 0.3mL/kg (G0.3). Nerves were dissected and measured for depth and extension of staining (cm). Mean comparisons were performed using paired t test. The relation between volume and nerve staining ( 2cm was assessed using chi-square test. The mean depth of SN was 1.9±0.2 and 1.6±0.3cm and staining 1.9±1.4 and 2.0±1.2cm, respectively in G0.2 and G0.3. No relation was found between depth and dye spread and there was no association between nerve staining ( 2.0cm and volume of solution. The FN failed to be stained in all subjects. In conclusion, SN injection can be successfully performed without guidance in rabbits. The lower volume (0.2mL/kg) is recommended to avoid systemic toxicity.

Retrospective comparison of three locoregional techniques for pelvic limb surgery in dogs

OBJECTIVE

To retrospectively compare the efficacy and duration of effect of three commonly used locoregional blocks in dogs undergoing pelvic limb orthopaedic surgery.

STUDY DESIGN

Retrospective clinical study.

ANIMALS

A total of 236 dogs that underwent pelvic limb surgery and were administered a locoregional technique.

METHODS

A total of 236 hospital records were reviewed and 230 included in statistical analysis. Dogs were grouped as following: electrostimulation-guided pre-iliac femoral and sciatic nerve block (group PFS, n = 70); ultrasound-guided saphenous and sciatic nerve block (group SS, n = 76); or lumbosacral epidural (group EPI, n = 84). In group EPI, bupivacaine 0.5% or ropivacaine 0.75% was used with morphine. Dogs were pain scored (short form of the Glasgow Composite Measure Pain Scale) hourly following recovery from anaesthesia. Analysed data included: time to first postoperative dose of methadone, pain score at that time, intraoperative rescue analgesia, intraoperative hypotension and ability to walk and urinate overnight. Separate analyses were performed including all pelvic limb surgeries and including only elective stifle surgeries. Kruskal-Wallis and Mann-Whitney tests were performed. A p value < 0.05 was considered significant. The median (range) is reported.

RESULTS

For all pelvic limb surgeries, the time to first postoperative methadone was 530 (110-1337), 440 (140-1030) and 466 (135-1094) minutes in groups EPI, PFS and SS, respectively, and was not significantly different. Postoperatively, 10/84, 15/70 and 12/76 dogs in groups EPI, PFS and SS, respectively, did not require methadone (nonsignificant). Significantly fewer dogs in group EPI (18%) required intraoperative rescue analgesia compared with group SS (38%), but not compared with PFS (30%). Significantly more dogs in group EPI had hypotension intraoperatively (30%) and urinary retention postoperatively (62%).

CONCLUSIONS AND CLINICAL RELEVANCE

Intraoperative analgesia may be superior with EPI than SS for some surgeries of the pelvic limb, but not for stifle surgeries. All three techniques provided similar requirement for postoperative analgesia, but EPI caused higher incidence of intraoperative hypotension and postopertive urinary retention.

Opioid requirements after locoregional anaesthesia in dogs undergoing tibial plateau levelling osteotomy: a pilot study

OBJECTIVE

To determine the intraoperative and early postoperative opioid requirement after ultrasound-guided sciatic and/or femoral nerve block or epidural anaesthesia in dogs undergoing tibial plateau levelling osteotomy (TPLO).

STUDY DESIGN

Prospective, masked, pilot, randomized, clinical trial.

ANIMALS

A total of 40 client-owned dogs undergoing TPLO.

METHODS

Each dog was randomly assigned to group SF (combined sciatic and femoral nerve block), group S (sciatic nerve block), group F (femoral nerve block) or group E (epidural anaesthesia). A total of 0.3 mL kg^-1 of ropivacaine 0.5% was administered to each nerve or in the epidural space. Intraoperatively, fentanyl (2 μg kg^-1) was administered intravenously when heart rate, mean arterial pressure or respiratory rate increased by >30% compared with baseline values. Postoperatively, a visual analogue scale (VAS) and a modified German version of the French pain scale (4AVet) were used to assess pain every 30 minutes for 150 minutes and again once the morning after surgery. Methadone (0.1 mg kg^-1) was administered intravenously if the VAS was ≥ 4 cm [maximal value 10 cm; median (interquartile range)] or the composite pain score was ≥5 [maximal value 15; median (interquartile range)]. Significance was defined as p ≤ 0.05.

RESULTS

Groups SF and E required less total intraoperative and early postoperative opioid doses compared with groups S and F (p = 0.031). No dogs in group SF had a block failure or required postoperative methadone. A reduced methadone requirement was found in group SF compared with all the other groups up to 150 minutes after recovery (p = 0.041).

CONCLUSIONS AND CLINICAL RELEVANCE

Combined sciatic and femoral nerve block and epidural anaesthesia lead to less cumulative consumption of perioperative opioids than single nerve blockade. Sciatic or femoral nerve block alone might be insufficient to control nociception and early postoperative pain in dogs undergoing TPLO.

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.

A Survey-Based Study Into the Use of Peripheral Nerve Blocks for Pelvic Limb Surgery Among Veterinary Professionals With an Interest in Anesthesia

Peripheral nerve blocks are commonly recommended as perioperative analgesia for orthopedic procedures. We aimed to determine the prevalence of use of techniques and drugs among veterinary professionals with an interest in anesthesia. Veterinary professionals were contacted via an email (ACVA-list) and newsletter (Association of Veterinary Anesthetists) containing a link to an online survey. Surveys completed in full were used for analysis. Analysis found that peripheral nerve blocks (PNBs) and epidural analgesia techniques were the preferred techniques of 46% and 38% of individuals, respectively. Of those using PNBs, nerve stimulator techniques were most common, used by 72% of individuals. Bupivacaine was used by 71% of individuals. Adjuvants were used by 37% of respondents; most commonly an alpha-2 agonist. Severe adverse effects were reported by 11 respondents, while 49% of individuals had not witnessed any adverse effects. More experienced veterinary anesthetists (>100 blocks performed) were more likely to have seen adverse effects. In conclusion, PNBs are utilized by anesthetists for pelvic limb orthopedic surgery, with nerve stimulation being the most commonly used PNB technique. Bupivacaine was the most commonly used local anesthetic however, diversity in both the techniques and drugs used was evident among respondents.

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.

Ultrasound-guided psoas compartment and sciatic nerve blocks for pain management of hind limb procedures in the alpaca (Vicugna pacos)

Background:

Loco-regional anesthetic techniques are considered important in the multimodal approach to analgesia in both human and veterinary medicine. No such techniques are described in the alpaca, bar the use of epidural. This is in part due to the lack of anatomical description for this species. While this limitation exists, the use of ultrasound guidance makes peripheral nerve blocks a viable possibility in the alpaca.

Case description:

A 12-month-old alpaca was referred for the treatment of a septic left tarso-crural joint. Due to a poor prognosis, amputation of the limb under general anesthesia was performed. Sciatic and psoas compartment blocks were attempted with the ultrasound-guided injection of ropivacaine prior to the start of the procedure. While the femoral nerve was possible to visualize, no obturator nerve was identified. A 5-year old alpaca was also referred for a left hind lateral claw removal, due to a squamous cell carcinoma. The sciatic nerve block was performed prior to the claw amputation under general anesthesia. No changes in heart and respiratory rate, or blood pressure suggestive of nociception, were observed in either of these cases. At the end of both the procedures, the patients experienced uneventful recoveries characterized by the ability to maintain the standing position, interest in food, and normal behavior.

Conclusion:

This report identifies the ease of performance and the challenges encountered using the ultrasound-guided psoas compartment and sciatic nerve blocks in the alpaca. It is our hope that this report encourages the use of ultrasound-guided loco-regional techniques in this species.

Novel ultrasound-guided lateral approach for femoral nerve block in cats: a pilot study

OBJECTIVES

The aim of this study was to describe the technique for a novel lateral approach to femoral nerve block in cat cadavers.

METHODS

Five feline cadavers were used in our prospective cadaveric experimental study. Ultrasonography was used to identify the anatomy injection site. Both pelvic limbs were injected with a volume (0.1 ml/kg) of methylene blue in each cat. The cadavers were placed in lateral recumbency, with the limb to be blocked positioned uppermost. The transducer was held perpendicular to the most proximal area of the pelvic limb, ventral to the greater trochanter and slightly cranial to the femur. Methylene blue was injected after the localisation of the femoral nerve. Immediately after the injection, the cat was turned and the technique was repeated on the contralateral side. After performing the 'block' in both limbs, the area was dissected bilaterally and the success was evaluated. A positive femoral nerve staining was considered for a coverage of ⩾1 cm.

RESULTS

A total of 10 ultrasound-guided femoral nerve injections were performed. Ninety percent (n = 9/10) of the nerves were successfully dyed.

CONCLUSIONS AND RELEVANCE

The novel ultrasound-guided lateral approach may be suitable and reproducible for a successful femoral nerve blockade in cats. Further investigations about the clinical usefulness and safety of this femoral nerve block in live cats are required.

Locoregional Anesthesia for Hind Limbs

The field of locoregional anesthesia is showing good and promising results for intraoperative and postoperative analgesia, reducing opioid requirements and improving early postoperative recovery. Peripheral nerve blocks are being reinvigorated as a viable option to decrease the administration of opioids and some of the consequences of their use and yet provide high-quality analgesia. In this article, techniques to block the pelvic limb are discussed.

Ultrasonographic study of a modified axillary approach to block the major branches of the brachial plexus in dogs

OBJECTIVE

To provide ultrasonographic mapping of the axillary region of dogs to facilitate identification of the major branches of the brachial plexus in relation to the axillary artery.

STUDY DESIGN

Prospective study.

ANIMALS

A total of two dog cadavers and 50 client-owned, healthy dogs weighing >15 kg.

METHODS

In Phase 1, anatomical dissections were performed to identify the relation of the major brachial plexus nerves to the axillary artery. In Phase 2, with the dogs in dorsal recumbency with thoracic limbs flexed naturally, the axillary space was scanned using a linear array probe oriented on the parasagittal plane until the axis transverse to nerves was found. Then, the transducer was rotated to a slight lateral angle approximately 30° to midline. The examination aimed to identify the axillary artery and the musculocutaneous, radial, median and ulnar nerves in addition to determining their position and distribution in four predefined sectors.

RESULTS

The musculocutaneous nerve was observed in all animals cranial to the axillary artery. The radial, ulnar and median nerves were distributed around the axillary artery, with >90% on the caudal aspect of the axillary artery (sectors 1 and 2).

CONCLUSIONS AND CLINICAL RELEVANCE

Ultrasonography identified the location of the brachial plexus nerves near the studied sectors, providing useful guidance for performing a brachial plexus nerve block.

Effects of hyaluronidase on ropivacaine or bupivacaine regional anaesthesia of the canine pelvic limb

OBJECTIVE

To determine the effect of hyaluronidase on time to onset and offset of anaesthesia in ropivacaine or bupivacaine femoral-ischiatic nerve blocks.

STUDY DESIGN

Blinded randomized crossover trial.

ANIMALS

Eight dogs.

METHODS

Each dog underwent four treatments separated into two blocks - initially, the ropivacaine treatment block: RS (ropivacaine 0.5% plus saline 0.9%) and RH (ropivacaine 0.5% plus hyaluronidase 100 IU mL^-1), followed 3 weeks later by the bupivacaine treatment block: BS (bupivacaine 0.5% plus saline) and BH (bupivacaine 0.5% plus hyaluronidase). The local anaesthetics were administered at 0.1 mL kg^-1 per site. Hyaluronidase and saline were administered at 0.02 mL kg^-1 per site. Performance of femoral-ischiatic blocks was aided by a combined ultrasound-electrolocation technique. The mechanical nociceptive threshold was measured, until offset or 360 minutes, using an algometer to ascertain baseline, onset and offset of anaesthesia. Onset and offset of anaesthesia were defined as a 25% increase above and as a return to <25% above baseline nociceptive threshold readings, respectively.

RESULTS

The median (range) onset of anaesthesia for RS and RH was 21 (3-60) and 12 (3-21) minutes, respectively (p = 0.141), and offset was 270 (90-360) and 180 (30-300) minutes, respectively (p = 0.361). By contrast, the median (range) onset of anaesthesia for BS and BH was 24 (3-60) and 9 (3-27) minutes, respectively (p = 0.394), and offset was 360 (240-360) and 330 (210-360) minutes, respectively (p = 0.456).

CONCLUSION AND CLINICAL RELEVANCE

Hyaluronidase had no effect on the onset and offset times of ropivacaine and bupivacaine femoral-ischiatic nerve blocks in dogs compared with saline. The onset and offset times were highly variable in all treatments. Clinically, the high variability of the onset and offset times of the regional anaesthesia of these local anaesthetic drugs means that clinicians must monitor the animal's response and, if required, provide additional analgesic drugs.

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.

Evaluation of the potential efficacy of an ultrasound-guided adductor canal block technique in dog cadavers

OBJECTIVE

To evaluate an ultrasound-guided technique for adductor canal (AC) block by describing the distribution of methylene blue around the AC, popliteal fossa, saphenous, tibial and common fibular nerves in dog cadavers.

STUDY DESIGN

Prospective experimental trial.

ANIMALS

Ten mixed breed canine cadavers weighing 28.55 ± 3.94 kg.

METHODS

Ultrasound scans of the AC were performed bilaterally in 10 canine cadavers. A high-frequency linear transducer was placed on the long axis of the pectineus muscle and using an in-plane technique, an insulated needle was introduced at a proximal to distal direction into the AC. Methylene blue 0.1% (0.3 mL kg^-1) was administered followed by dissection. The presence of dye over the target nerves for ≥2 cm was considered successful distribution. Three of 10 cadavers were submitted to computed tomography (CT) and one of them to magnetic resonance (MR) evaluation.

RESULTS

Methylene blue reached the AC in 20 (100%) and the popliteal fossa in 17 (85%) pelvic limbs. Staining was successful in the saphenous nerve (4.0 ± 1.57 cm) in 11 (55%) limbs, tibial nerve (2.65 ± 0.8 cm) in six (30%) and common fibular nerve (2.7 ± 0.9 cm) in four (20%). There was no evidence of staining around the motor branches of the femoral nerve. No intraneural or intravascular dye spread was found during dissections. Contrast distribution to the popliteal fossa was observed in three limbs (50%) in CT and in one (50%) MR image.

CONCLUSIONS AND CLINICAL RELEVANCE

Although the tibial and common fibular nerves were not stained as often as the saphenous nerve, dye was encountered throughout the popliteal fossa near the nerves. The AC block may be useful for intra and postoperative analgesia in stifle surgery with minimal femoral motor dysfunction. However, further study is required to confirm its efficacy and safety in vivo.

Blood concentration of bupivacaine and duration of sensory and motor block following ultrasound-guided femoral and sciatic nerve blocks in dogs

Peripheral nerve blocks are becoming increasingly popular for perioperative use as anesthetics and analgesics in small animals. This prospective study was performed to investigate the duration of motor and sensory blockade following use of bupivacaine for ultrasound-guided femoral and sciatic nerve blocks in dogs and to measure the plasma concentrations of bupivacaine that result from these procedures. Six dogs were anesthetized twice using a randomized cross-over design. At the first anesthetic, dogs were assigned to receive either an ultrasound-guided femoral nerve block or sciatic nerve block with 0.15 mL kg^-1 of bupivacaine 0.5%. Two months later, the other nerve block was performed during a second anesthetic. At 5, 10, 15, 20, 30 and 60 minutes after injection, arterial blood samples were collected for laboratory measurement of bupivacaine. After 60 minutes, dogs were recovered from anesthesia. Starting at two hours post-injection, video-recordings of the dogs were made every two hours for 24 hours. The videos were randomized and the degree of motor and sensory blockade was evaluated using a three-point scoring system (0 = no effect, 1 = mild effect, 2 = complete blockade) by two blinded assessors. The median (range) times to full recovery from motor blockade were 11 (6–14) hours (femoral) and 12 (4–18) hours (sciatic), and 15 (10–18) hours (femoral) and 10 (4–12) hours (sciatic) for sensory blockade. There were no differences in the median times to functional recovery for the two techniques. Plasma concentrations of bupivacaine were no different following the blocks and were less than 0.78 μg mL^-1 at all times. These results suggest that these ultrasound-guided nerve blocks do not result in potentially toxic systemic levels of local anesthetic and that their duration of action is useful for providing anesthesia and analgesia for pelvic limb procedures.

Development of an ultrasound-guided technique for retrobulbar nerve block in dromedary camels: a cadaveric study

OBJECTIVE

Description of an ultrasound (US)-guided technique for retrobulbar nerve blockade in dromedary (Camelus dromedarius) cadavers.

STUDY DESIGN

Prospective experimental cadaveric study that was carried out in three phases: phase I: anatomical dissection and development of US-guided technique; phase II: methylene blue (MB) injection; phase III: contrast medium (CM), US-guided injections with computed tomography (CT) control.

ANIMALS

A total of 36 orbits from 18 heads were obtained from 18 dromedary cadavers.

METHODS

Phase I: anatomical dissections were carried out bilaterally, using two heads to determine needle site placement. Phase II: a US-guided, lateral, in-plane approach using one of three volumes of MB (3, 6, or 9 mL) was evaluated in six heads (four orbits per volume tested) to establish the ideal injection volume. Injections of MB that strongly stained all retrobulbar nerves were considered successful, whereas insufficient MB volumes resulted in weak or no nerve staining. Phase III: US-guided retrobulbar injection with CM was carried out using 20 orbits. Computed tomography was performed after each injection trial to determine the accuracy of needle placement and CM dispersal. An injection was judged to be successful when the CT images revealed that the needle was located within the retractor bulbi muscle cone and the CM reached the target nerves at the orbitorotundum and the optic foramina.

RESULTS

Only injection of 9 mL of MB stained the target nerves sufficiently, whereas there was no or only weak staining with 3 and 6 mL, respectively. Therefore, 9 mL of CM was used for the US-guided injections in phase III. Subsequent CT scans revealed satisfying CM distribution within the ocular muscle cone in 18 of 20 cases (90% success rate).

CONCLUSIONS AND CLINICAL RELEVANCE

US-guided retrobulbar injection in dromedary cadavers is feasible. Further research is required to assess its practicality and usefulness in vivo.

[Comparison of ultrasound guided femoral and sciatic nerve block versus epidural anaesthesia for orthopaedic surgery in dogs]

OBJECTIVE

Comparison of ultrasound-guided femoral and sciatic nerve block versus epidural anaesthesia with bupivacaine and morphine for orthopaedic surgery of the pelvic limb in dogs with respect to analgesic effectiveness, clinical utility and side effects.

MATERIAL AND METHODS

The study included 22 dogs (American Society of Anesthesiologists, ASA grades I and II) undergoing orthopaedic surgery distal to the mid-femoral bone. The study was designed as a randomized, prospective, blinded clinical trial. All dogs were randomly assigned to receive 0.5 mg/kg bupivacaine (0.5%) and 0.1 mg/kg morphine sulphate (1%) either as epidural anaesthesia (group EPI) or by ultrasound-guided femoral and sciatic nerve block (group LA). During surgery, the heart rate, respiratory rate, mean arterial pressure (MAP), end-tidal isoflurane concentrations and dose of rescue analgesia (fentanyl boluses of 5 µg/kg i. v.) were measured. Pain severity was scored (short form of the Glasgow Composite Measure Pain Scale, GCMPS) before surgery and postoperatively at 2, 4, 6, 12 and 24 hours after extubation. Post-operative rescue analgesia consisted of methadone (0.2 mg/kg i. v.), and was applied when the GCMPS > 6. For statistical analysis, the Chi-square, Fisher, and Wilcoxon tests and one- and two-way ANOVA were applied. Differences were considered statistically significant at p < 0.05.

RESULTS

Only the MAP was significantly different between the two treatment groups. Intra- and postoperative MAP of group LA (111.2 ± 11.2 mmHg and 119.3 ± 18.2 mmHg, respectively) was higher than in group EPI (86.6 ± 8.7 mmHg and 95.2 ± 13.1 mmHg, respectively). None of the dogs developed urinary retention or ambulatory deficits when completely recovered from anaesthesia. No other side effects were noted.

CLINICAL RELEVANCE

In conclusion, femoral and sciatic nerve blocks and epidural anaesthesia ensure comparable analgesic effects in canine patients undergoing orthopaedic surgery of the pelvic limb. The lower mean arterial blood pressure of group EPI was not of clinical relevance.

Comparison of lidocaine and lidocaine-epinephrine for the paravertebral brachial plexus block in dogs

OBJECTIVE

To compare the motor and sensory block efficacy and duration of a modified paravertebral brachial plexus block (PBPB) after administration of lidocaine alone (LI) or combined with epinephrine (LE).

STUDY DESIGN

Prospective, randomized, blinded, crossover study.

ANIMALS

A total of eight healthy female Beagle dogs.

METHODS

Under general anesthesia, modified PBPB was performed on the left thoracic limb using neurostimulation and/or ultrasound guidance to administer lidocaine (2 mg kg^-1; 0.2 mL kg^-1) either alone (treatment LI, n = 10) or with epinephrine (1:100,000; treatment LE, n = 9). Sensory block was evaluated through reaction to a painful mechanical stimulus applied at five sites on the limb. Motor block effect was evaluated according to visual gait assessments and thoracic limb vertical force measurements under dynamic and static conditions. Data were analyzed using repeated-measures generalized estimating equations. All statistical tests were performed two-sided at the α = 0.05 significance threshold.

RESULTS

The duration of sensory block did not differ significantly between treatments. Visible gait impairment was more persistent in LE than in LI (118 ± 63 minutes for LI and 163 ± 23 minutes for LE; mean ± standard deviation) (p = 0.027). At nadir value, dynamic peak vertical force was lower in LE than in LI (p = 0.007). For both dynamic and static evaluations, the nadir and the return to baseline force were delayed in LE (return to normal at 180-200 minutes) when compared with LI (130-140 minutes) (p < 0.005).

CONCLUSIONS AND CLINICAL RELEVANCE

The addition of epinephrine to lidocaine prolonged the duration and increased the intensity of the regional block, as verified by visual gait assessment and kinetic analysis. No significant difference was noted between treatments regarding sensory blockade. Kinetic analysis could be useful to evaluate regional anesthetic effect in dogs.

Validation of the dorsal approach for the blockade of the femoral nerve using ultrasound and nerve electrolocation in cats

OBJECTIVES

This study was conducted to validate the dorsal approach for femoral nerve (FN) blockade in cats and to verify the efficacy of the sole use of peripheral nerve electrolocation (PNE) or ultrasound (US)-guided technique to achieve the block.

METHODS

This study was carried out in two phases. In phase 1, five adult experimental cats were used to validate the approach. In each cat, one FN was located by US and the accuracy of this location confirmed by PNE. Then, 2 mg/kg lidocaine 2% (diluted in saline to a final volume of 1 ml) was injected around the target nerve and the success of the blockade was evaluated. In phase 2, four adult experimental cats were included in two groups to verify the reliability of this approach to block eight FNs by the sole use of PNE (group 1) or US-guided technique (group 2). Evidence of motor blockade, time required to perform the blockade, onset time and duration of the blockades were determined.

RESULTS

The FN was successfully located by US in all cats enrolled in phase 1, as confirmed by PNE in all cases. The success rate was clinically higher in group 2 (87.5%) than in group 1 (75.0%). The US-guided technique required less time to perform and produced blocks of longer duration. Recovery was uneventful in all cases.

CONCLUSIONS AND RELEVANCE

The combined use of PNE and US-guided technique enabled validation of the dorsal approach for the FN blockade as it provided a successful FN blockade in all cases. The sole use of a US-guided technique may offer some advantages over the use of a sole PNE-guided technique to perform these blocks.

Ultrasound-guided anaesthetic blockade of the pelvic limb in calves

This study aimed to describe a suitable acoustic window to facilitate access to the sciatic and femoral nerves in calves and to study the effects of their blockade with local anaesthetics. The neuroanatomical and ultrasound (US) study was performed on the cadavers of 10 calves, and the effects of 2% lidocaine with epinephrine (0.2 mL/kg) were determined in five healthy calves. The sciatic nerve in the cadavers was easily visualised as a hyperechoic band distal to the femoral greater trochanter and caudal to the femoral shaft. The femoral nerve in the cadavers was not easily identified, and was visualised as a hyperechoic oval structure situated immediately medial to the psoas major muscle and lateral to the femoral artery. The sciatic nerve was stained by methylene blue, injected under US guidance, in 9/10 cases, and the femoral nerve was stained in 6/10 cases. Sciatic nerve blockade under US guidance produced adduction of the limb with metatarsophalangeal joint flexion, while the femoral nerve blockade produced reduced weight bearing. The sciatic nerve blockade produced a reduced response to the noxious stimulus, mainly in the phalanges, proximal and distal metatarsus, tarsus and tibia and, following the femoral nerve blockade, in the medial subarea of the femur. However, femoral nerve blockade produced a more variable degree of blockade. In conclusion, US -guided anaesthetic blockade of the sciatic nerve in calves may be considered for surgery in the distal pelvic limb, although further studies are necessary to determine its clinical application.

Ultrasound-guided block of sciatic and femoral nerves: an anatomical study

The sheep is a popular animal model for human biomechanical research involving invasive surgery on the hind limb. These painful procedures can only be ethically justified with the application of adequate analgesia protocols. Regional anaesthesia as an adjunct to general anaesthesia may markedly improve well-being of these experimental animals during the postoperative period due to a higher analgesic efficacy when compared with systemic drugs, and may therefore reduce stress and consequently the severity of such studies. As a first step 14 sheep cadavers were used to establish a new technique for the peripheral blockade of the sciatic and the femoral nerves under sonographic guidance and to evaluate the success rate by determination of the colorization of both nerves after an injection of 0.5 mL of a 0.1% methylene blue solution. First, both nerves were visualized sonographically. Then, methylene blue solution was injected and subsequently the length of colorization was measured by gross anatomical dissection of the target nerves. Twenty-four sciatic nerves were identified sonographically in 12 out of 13 cadavers. In one animal, the nerve could not be ascertained unequivocally and, consequently, nerve colorization failed. Twenty femoral nerves were located by ultrasound in 10 out of 13 cadavers. In three cadavers, signs of autolysis impeded the scan. This study provides a detailed anatomical description of the localization of the sciatic and the femoral nerves and presents an effective and safe yet simple and rapid technique for performing peripheral nerve blocks with a high success rate.

Use of needle enhancing software to improve injection technique amongst inexperienced anaesthetists performing ultrasound-guided peripheral nerves blocks in dogs

OBJECTIVE

To determine if the use of needle enhancing software facilitate injection technique in ultrasound-guided peripheral nerve blocks.

STUDY DESIGN

Prospective, blinded, randomized controlled trial.

ANIMALS

Eight hind limbs from canine cadavers.

METHODS

The limbs were randomly allocated to two groups; software on (group I) and software off (group II). Eight anaesthetists with no previous experience of ultrasound-guided regional anaesthesia were recruited. Thirty-six procedures were carried out (18 per group). After sciatic nerve visualisation via ultrasonography, the anaesthetist introduced a needle guided by ultrasonography. When the tip of the needle was considered by the anaesthetist to be as close as possible to the nerve without touching it, 0.05 mL of methylene blue dye was injected. Parameters evaluated included: number of attempts to visualise the needle with ultrasonography, time spent to perform the technique, subjective evaluation of ease of needle visualisation, proximity of the tip of the needle to the nerve, and, at dissection of the leg, inoculation site of the dye in relation to the nerve.

RESULTS

Significant differences between groups were identified in relation to the number of attempts (group I: median 1, IQR: 1 - 1 attempts versus group II: median 1, IQR: 1 - 4 attempts, p = 0.019), and the relationship between the dye and the nerve during hind limb dissection (72.2% of the nerves were stained in group I versus 16.6% in group II, p = 0.003). No significant difference between groups was observed with respect to the time taken to perform the procedure (group I: median 25.5, IQR: 18.4 - 44.3 seconds versus group II: median 35.7, IQR: 18.6-78.72 seconds, p = 0.31), subjective evaluation of the needle visualization (p = 0.45) or distance between the tip of the needle and the nerve as measured from the ultrasound screen (p = 0.23).

CONCLUSIONS AND CLINICAL RELEVANCE

This study identified greater success rate in nerve staining when the needle enhancing software was used. The results suggest that the use of this technique could improve injection technique amongst inexperienced anaesthetists performing ultrasound-guided peripheral nerve blocks in dogs.

Ultrasound-guided dorsal approach for femoral nerve blockade in cats: an imaging study

This study was conducted to describe and validate a dorsal ultrasound-guided approach to block the femoral nerve (FN) in cats by means of anatomical and computed tomography (CT) studies. The anatomical study was carried out in four fresh feline cadavers to determine the anatomic landmarks to approach this nerve. Then, an ultrasonographic study of the FN was performed in another eight cadavers using a 13 MHz linear transducer. The accuracy of the neurolocation by ultrasonography (US) was determined in four cadavers by the injection of 1 ml blue ink around the FN. The staining of the nerve was evaluated in anatomical studies. The feasibility of this technique was also evaluated by CT after injecting 1 ml of an iodinated contrast medium (150 mgl/ml) around the FN in the other four cadavers. The landmarks to approach the FN were the cranial border of the iliac crest and the dorsal processes of L6 and L7. The FN was visualised as a round hypoechogenic structure surrounded by a hyperechogenic rim located within the iliopsoas muscle on transverse scans. The anatomical and CT studies confirmed the accuracy of the US location of the FN. The dorsal ultrasound-guided approach may allow feasible and accurate access to the FN in cats and it could be useful in producing successful blockade.

Ultrasound-guided block of the feline sciatic nerve

This study was conducted to validate an ultrasound-guided technique to block the sciatic nerve in cats. An anatomical study was first carried out in four feline cadavers to evaluate the feasibility of the glutea (cranial and caudal), femoris and poplitea ultrasonographical approaches for the sciatic nerve block. The results showed that the femoris approach was optimal because the region was free of vascular and bony structures, and the needle was easily visualised in-plane. Then, the efficacy of the femoris ultrasonographical approach to block the sciatic nerve was tested in six healthy adult experimental cats. A dose of 2 mg/kg lidocaine 2% diluted in saline to a final volume of 1 ml was administered in all cats. The blockade was successful in all cases and the cats recovered uneventfully. This study shows the usefulness of the femoris approach in performing an ultrasound-guided blockade of the sciatic nerve in cats.