Sensory nerve conduction and nociception in the equine lower forelimb during perineural bupivacaine infusion along the palmar nerves

The purpose of this investigation was to study lateral palmar nerve (LPN) and medial palmar nerve (MPN) morphology and determine nociception and sensory nerve conduction velocity (SNCV) following placement of continuous peripheral nerve block (CPNB) catheters along LPN and MPN with subsequent bupivacaine (BUP) infusion. Myelinated nerve fiber distribution in LPN and MPN was examined after harvesting nerve specimens in 3 anesthetized horses and processing them for morphometric analysis. In 5 sedated horses, CPNB catheters were placed along each PN in both forelimbs. Horses then received in one forelimb 3 mL 0.125% BUP containing epinephrine 1:200 000 and 0.04% NaHCO(3) per catheter site followed by 2 mL/h infusion over a 6-day period, while in the other forelimb equal amounts of saline (SAL) solution were administered. The hoof withdrawal response (HWR) threshold during pressure loading of the area above the dorsal coronary band was determined daily in both forelimbs. On day 6 SNCV was measured under general anesthesia of horses in each limb's LPN and MPN to detect nerve injury, followed by CPNB catheter removal. The SNCV was also recorded in 2 anesthetized non-instrumented horses (sham controls). In both LPN and MPN myelinated fiber distributions were bimodal. The fraction of large fibers (>7 μm) was greater in the MPN than LPN (P < 0.05). Presence of CPNB catheters and SAL administration did neither affect measured HWR thresholds nor SNCVs, whereas BUP infusion suppressed HWRs. In conclusion, CPNB with 0.125% BUP provides pronounced analgesia by inhibiting sensory nerve conduction in the distal equine forelimb.

Mepivacaine local anaesthetic duration in equine palmar digital nerve blocks

REASONS FOR PERFORMING STUDY

Perineural analgesics are used for lameness diagnosis but the duration of effect, knowledge of which would provide valuable information when performing subsequent blocks, is unknown.

OBJECTIVE

To evaluate the duration of a palmar digital nerve block using force plate measurements.

METHODS

Ten horses diagnosed with unilateral navicular syndrome were trotted at range of 3 +/- 0.15 m/sec over a force plate to record ground reaction forces for 5 trials of each forelimb. Data were recorded before nerve block, and then at 15 mins, 1, 2 and 24 h post nerve block.

RESULTS

Before nerve block, peak vertical force (mean +/- s.e.) was significantly higher in the contralateral forelimb (CL = 5345 +/- 188 N) than in the lame forelimb (L = 4256 +/- 204 N; P<0.05). At 15 mins post nerve block there was no significant difference between the 2 forelimbs (CL = 5140 +/- 184 N; L = 5126 +/- 129 N), and this remained the case for 1 h. By 2 h, the mean score for the lame leg had decreased (L = 4642 +/- 182 N) but was still greater than preblock. By 24 h, vertical forces had returned to preblock values.

CONCLUSIONS

The palmar digital nerve block was fully effective between 15 mins and 1 h. The analgesic effect began to subside between 1 and 2 h but sufficient analgesia persisted to affect gait characteristics beyond 2 h.

POTENTIAL RELEVANCE

When using a palmar digital nerve block, it is important to perform lameness evaluations between 15 mins and 1 h to be sure of effective nerve blockade.

Arthrogenic lameness of the fetlock: synovial fluid markers of inflammation and cartilage turnover in relation to clinical joint pain

REASONS FOR PERFORMING THE STUDY

Joint pain is one of the most common causes of lameness in the horse but its pathogenesis is poorly understood.

OBJECTIVES

To investigate which synovial fluid markers may be related to the presence of clinically detectable joint pain in the horse.

METHODS

Concentrations of structural (CPII, C2C, GAG) and inflammatory markers (PGE2, LTB4, CysLTs, bradykinin and substance P) were measured in fetlock joint fluid from 22 horses in which lameness was localised to the fetlock region by perineural anaesthesia. Levels of these markers were then compared in horses that responded (n = 15) to those that did not (n = 7) to subsequent intra-articular anaesthesia (IAA).

RESULTS

Of all markers analysed, only substance P levels were significantly higher (P = 0.0358) in synovial fluid of horses that showed a positive response to IAA compared to those with a negative response to IAA. Notably, while PGE2 levels were found to be elevated in all 22 lame horses compared to sound controls (P = 0.0025), they were not related to the response to IAA.

CONCLUSIONS

While levels of PGE2 are elevated in synovial fluid of lame horses that respond to perineural anaesthesia, only substance P is related to joint pain as detected by the response to intra-articular anaesthesia.

POTENTIAL RELEVANCE

Substance P is associated with clinically detectable joint pain in the horse. Elevated levels of PGE2 in fetlock-lame horses, regardless of their response to IAA, indicate that either this mediator does not reflect intra-articular pain or that IAA might have limitations in differentiating between intra- and peri-articular sources of pain. Either way, a negative response to IAA may not exclude intra-articular pathology.

Effects of stylopharyngeus muscle dysfunction on the nasopharynx in exercising horses

REASONS FOR PERFORMING STUDY

Nasopharyngeal collapse has been observed in horses as a potential cause of exercise intolerance and upper respiratory noise. No treatment is currently available and affected horses are often retired from performance.

OBJECTIVE

To determine the effect of bilateral glossopharyngeal nerve block and stylopharyngeus muscle dysfunction on nasopharyngeal function and airway pressures in exercising horses.

METHODS

Endoscopic examinations were performed on horses at rest and while running on a treadmill at speeds corresponding to HRmax50, HRmax75 and HRmax, with upper airway pressures measured with and without bilateral glossopharyngeal nerve block.

RESULTS

Bilateral glossopharyngeal nerve block caused stylopharyngeus muscle dysfunction and dorsal nasopharyngeal collapse in all horses. Peak inspiratory upper airway pressure was significantly (P = 0.0069) more negative at all speeds and respiratory frequency was lower (P = 0.017) in horses with bilateral glossopharyngeal nerve block and stylopharyngeus muscle dysfunction compared to control values.

CONCLUSIONS

Bilateral glossopharyngeal nerve anaesthesia produced stylopharyngeus muscle dysfunction, dorsal pharyngeal collapse and airway obstruction in all horses.

POTENTIAL RELEVANCE

The stylopharyngeus muscle is probably an important nasopharyngeal dilating muscle in horses and dysfunction of this muscle may be implicated in clinical cases of dorsal nasopharyngeal collapse. Before this information can be clinically useful, further research on the possible aetiology of stylopharyngeus dysfunction and dysfunction of other muscles that dilate the dorsal and lateral walls of the nasopharynx in horses is needed.

Anatomical and experimental studies of brachial plexus, sciatic, and femoral nerve-location using peripheral nerve stimulation in the dog

OBJECTIVE

To investigate the anatomy of the brachial plexus, sciatic, and femoral nerves for the use of a peripheral nerve-stimulator to perform nerve blocks in dogs.

STUDY DESIGN

Prospective experimental trial.

ANIMALS

Four canine cadavers and four healthy adult dogs weighing 23 +/- 2.5 kg.

METHODS

Phase I: in four canine cadavers, an anatomical study was conducted to evaluate accurate needle-insertion techniques. Phase II: the utility of these techniques, and the value of electrostimulation, were evaluated in four anesthetized dogs in lateral recumbency (medetomidine, 5 microg kg(-1)/ketamine 5 mg kg(-1)) using an electrical stimulator and shielded needles.

RESULTS

For the brachial plexus, the needle was inserted cranial to the acromion, medial to the subscapularis muscle, at an angle of approximately 20-30 degrees in relation to a plane vertical to the surface on which the animal was lying, oriented parallel to the long axis of the animal, in a ventro-caudal direction. For the sciatic nerve, the needle was inserted just cranial to the sacrotuberous ligament, through the gluteus superficialis muscle, at an angle of approximately 60 degrees in relation to the horizontal plane, in a ventro-cranial direction, and up to the level of the ischium. For the femoral nerve, the needle was inserted perpendicular to the skin, just cranial to the femoral artery, and directed a little caudally. Using a peripheral nerve-stimulator, all nerves were located, and muscle contractions were elicited at a current of 0.2-0.4 mA. No complications were observed during the procedures.

CONCLUSION

Electrostimulation of peripheral nerves is useful in locating the branches of the brachial plexus as well as the sciatic and femoral nerves in dogs.

CLINICAL RELEVANCE

Peripheral nerve stimulation increases the reliability of a nerve block when compared with blind needle-insertion.

The effects of medetomidine on radial nerve blockade with mepivacaine in dogs

OBJECTIVE

To compare the sensory and motor effects of adding medetomidine to mepivicaine, administered either perineurally or systemically, for radial nerve block in dogs.

STUDY DESIGN

Prospective randomized cross-over study.

ANIMALS

Six healthy Beagles, aged 18.7 +/- 6.3 months and weighing 10.4 +/- 1.3 kg.

METHODS

Dogs were anesthetized briefly with sevoflurane on three separate occasions and received each treatment administered in random order: mepivacaine 5 mg kg(-1) perineurally around the radial nerve with saline 0.01 mL kg(-1) intramuscularly (CONTROL); mepivacaine 5 mg kg(-1) and medetomidine 0.01 mg kg(-1) combined, perineurally with saline 0.01 mL kg(-1) intramuscularly (MEDPN); mepivacaine 5 mg kg(-1) perineurally around the radial nerve with medetomidine 0.01 mg kg(-1) intramuscularly (MEDIM). All nerve blocks were performed with the aid of a nerve locator. Motor effects were evaluated based on the ability to bear weight. Sensory effects were evaluated by the response to a graded-electrical stimulus. These were evaluated at 5-minute intervals for the first hour, and at 10-minute intervals thereafter. Mean intervals were calculated as follows: time to motor block onset, duration of motor block, time to peak sensory block, duration of peak sensory block (i.e. period of no response to maximal stimulus intensity), and duration of residual sensory block (i.e. time to return to baseline sensory function). Treatment means were compared using a one-way analysis of variance for repeated measures and, where significant differences were noted, a Student-Newman-Keuls test was applied; p < 0.05 was considered significant.

RESULTS

Medetomidine, administered either systemically or perineurally, significantly prolonged duration of peak motor block, peak sensory block, and residual sensory block compared with CONTROL.

CONCLUSION

Medetomidine prolonged sensory and motor blockade after radial nerve block with mepivacaine in dogs.

CLINICAL RELEVANCE

Medetomidine may prove to be a useful adjunct to peripheral nerve blockade with local anesthetics.

Administering Dental Nerve Blocks

Dental nerve blocks provide excellent pain management for many oral procedures. They are easy and inexpensive to perform, provide a rapid onset of action, and work in concert with anesthetic and other analgesic modalities. This article explains how to administer various dental nerve blocks and discusses the indications and precautions associated with their use.

Electrical nerve stimulation to facilitate placement of an indwelling catheter for repeated brachial plexus block in a traumatized dog

A 10-year-old, 7 kg, male mixed breed dog was presented, following a dog fight, with open fractures of the radius and ulna and extensive skin and muscle lesions. Using electric nerve stimulation, an indwelling catheter was positioned in the axillary space and 2 mg kg(-1) bupivacaine was injected. Complete sensory and motor blocks were obtained allowing amputation distal to the non-traumatized tissue and debridement of the limb. The injection of bupivicaine was repeated 5 hours after the first bolus and a similar result was obtained in term of muscle relaxation and pain alleviation. Subsequent injections were not successful in providing the same effect, most likely as a result of catheter displacement and alternate means of analgesia were used.

Xylazine Premedication does not Modify the Onset and Duration of Cisatracurium Blockade in Anaesthetized Dogs

The purpose of this study was to evaluate the effect of xylazine as premedication on the onset time and duration of cisatracurium neuromuscular blockade in anaesthetized dogs. This study was carried out on 12 healthy dogs aged 0.5-6 years and weighing 9-26 kg undergoing various elective surgical procedures. The dogs were randomly divided into two groups of t (test) and c (control), with six dogs each. In group t, premedication was conducted using acepromazine maleate 0.3 mg kg(-1) and xylazine 0.3 mg kg(-1) and in group c only acepromazine (same dose) was injected intramuscularly 20 min before general anaesthesia. After induction with thiopental, anaesthesia was maintained with halothane in oxygen to deliver an end-tidal halothane concentration of 1.1%. Neuromuscular blockade was induced with cisatracurium 0.2 mg kg(-1) and monitored using the train-of-four (TOF) stimulation pattern applied at the ulnar nerve. The onset time of cisatracurium blockade was 195 +/- 85.44 s in test and 153.3 +/- 38.16 s in control group. The duration of neuromuscular blockade was 24.8 +/- 4.79 min in t and 28.3 +/- 5.46 min in the c group. Statistical analysis of the data showed no significant difference between groups in terms of onset and duration of neuromuscular blockade.

Paravertebral block for forelimb anesthesia in the dog--an anatomic study

OBJECTIVE

To determine the anatomic landmarks for performing paravertebral forelimb block in the dog.

STUDY DESIGN

Technique description.

ANIMALS

Nine canine cadavers.

METHODS

Each intervertebral foramen between the C5 and T2 vertebrae was targeted. With the dog in lateral recumbency, a 20 SWG 3'' spinal needle was placed at a 45 degree angle from a vertical transverse plane (with the dog standing this plane would be perpendicular to the ground) 2-3 cm lateral to the median plane for the three cranial intervertebral foramina and at a 90 degree angle with the same transverse plane 2-3 cm lateral to the median plane for the T1-T2 intervertebral foramina.

RESULTS

Three out of nine (33%) of the cadavers had successful staining of all four desired nerves and the remaining six (66%) cadavers had successful staining of three of the four nerves. The C6-C7 spinal nerve was successfully stained in all nine cadavers. The other three nerves were each successfully stained in seven out of nine (78%) cadavers.

CONCLUSIONS AND CLINICAL RELEVANCE

The landmarks allow reliable placement of a solution at the nerves comprising the brachial plexus, allowing anesthesia of the entire forelimb in the dog.

Development and verification of saphenous, tibial and common peroneal nerve block techniques for analgesia below the thigh in the nonchondrodystrophoid dog

OBJECTIVE

To document simple and reliable local, infiltrating nerve blocks for the saphenous, tibial and common peroneal nerves in the dog.

STUDY DESIGN

Laboratory technique development; in vivo blind, controlled, prospective study.

ANIMALS

Twenty canine cadavers and 18 clinically normal, client-owned dogs.

METHODS

A peripheral nerve blockade technique of the tibial, common peroneal, and saphenous nerves was perfected through anatomic dissection. Injections were planned in the caudal thigh for the tibial and common peroneal nerves, and in the medial thigh for the saphenous nerve. Cadaver limbs were injected with methylene blue dye and subsequently dissected to confirm successful dye placement. Clinically normal dogs undergoing general anesthesia for unrelated, elective procedures were randomly assigned to treatment (bupivacaine; n = 8) or control (saline; n = 8) nerve blocks of the nerves under study. Upon recovery from general anesthesia, skin sensation in selected dermatomes was evaluated for 24 hours.

RESULTS

Cadaver tibial, common peroneal, and saphenous perineural infiltrations were successful in nonchondrodystrophoid dogs (100, 100, and 97%, respectively.) Intraneural injection was rare (1%; 1/105; tibial nerve) in cadaver dogs. In the treatment group of normal dogs, duration of loss of cutaneous sensation in some dermatomes (saphenous, superficial and deep peroneal nerve) was significantly different than control dogs; the range of desensitization occurred for 1-20 hours. No clinical morbidity was detected.

CONCLUSIONS

This technique for local blockade of the tibial, common peroneal, and saphenous nerves just proximal to the stifle is easy to perform, requires minimal supplies and results in significant desensitization of the associated dermatomes in clinically normal, nonchondrodystrophoid dogs.

CLINICAL RELEVANCE

This technique may be an effective tool for post-operative analgesia to the femoro-tibial joint and distal pelvic limb. Other applications, using sustained-release drugs or methods, may include anesthesia/analgesia in high-risk patients or as a treatment for chronic pelvic limb pain or self-mutilation.

A comparison of four methods of analgesia in cats following ovariohysterectomy

OBJECTIVE

To evaluate the effectiveness of preoperative administration of oral carprofen, subcutaneous ketoprofen, and local nerve block with bupivacaine in preventing postoperative pain-associated behavior in cats after ovariohysterectomy.

ANIMALS

Fifty-two female intact cats. Materials and methods Cats received butorphanol (0.44 mg kg(-1) IM), carprofen (2.2 mg kg(-1) PO), ketoprofen (2.2 mg kg(-1) SQ), or bupivacaine infiltration block (1.1 mg kg(-1) SQ) before surgery. Cortisol and drug concentrations and visual analog scale (VAS) and interactive visual analog scale (IVAS) pain-associated behavior scores were measured 2 hours before and 0, 1, 2, 4, 8, 12, and 24 hours after ovariohysterectomy.

RESULTS

Cats receiving butorphanol had significantly increased IVAS scores 2 hours after surgery compared with baseline measurements. Cats receiving carprofen, ketoprofen, and bupivacaine had significant increases from baseline in VAS and IVAS scores 1 and 2 hours after surgery. VAS and IVAS scores for cats receiving bupivacaine were significantly greater 1 and 2 hours after surgery than for cats that received butorphanol. Cats receiving carprofen had significant increases in cortisol 1 hour after surgery and significant decreases 24 hours after surgery compared with baseline measurements.

CONCLUSIONS AND CLINICAL RELEVANCE

Preoperative carprofen and ketoprofen have effects on pain-associated behavior similar to butorphanol in cats undergoing ovariohysterectomy. Cats receiving bupivacaine blocks may require additional analgesics immediately after surgery.

Evidence of bias affecting the interpretation of the results of local anaesthetic nerve blocks when assessing lameness in horses

Eighteen observers were influenced to different extents in the grades of lameness they allocated to eight horses by whether they knew that a nerve block had been administered; on a scale from 0 to 10 the mean difference in grade allocated once the observer knew a horse had been nerve-blocked was increased by 0.4. The consistency of the assessments made by the individual observers was good, with a an average of 0.6 of a grade difference when grading the same horse on two occasions. The agreement between the assessments of four orthopaedic experts was reasonable (+/-1 grade), but significantly poorer for four non-experts and 10 final year veterinary students.

USE OF A NERVE LOCATOR TO FACILITATE ADMINISTRATION OF MANDIBULAR NERVE BLOCKS IN CROCODILIANS

As part of a clinical workup of dental problems in a large crocodilian collection, mandibular nerve blocks were performed in the animals. A nerve locator was used to facilitate placement of the nerve blocks in American alligators (Alligator mississippiensis), Yacare caiman (Caiman yacare), and a dwarf crocodile (Osteolaemus tetraspis). Provision of analgesia is a frequently underused aspect of patient care in reptiles. Use of a nerve stimulator provides an objective measurement of nerve conduction blockade and may be useful in exotic species in which anatomic landmarks for nerve block placement are not well established.

Development of a retrobulbar injection technique for ocular surgery and analgesia in dogs

OBJECTIVE

To develop and compare 3 techniques for retrobulbar injection of local anesthetic agents for ocular surgery and analgesia in dogs.

DESIGN

Prospective study.

ANIMALS

17 dogs (including 9 cadavers).

PROCEDURES

Inferior-temporal palpebral (ITP), perimandibular, and combined superior-inferior peribulbar injection techniques were compared by assessing the distribution of latex after injection into the orbits of 5 canine cadavers; magnetic resonance imaging (MRI) evaluation of the distribution of contrast agent after injection in the retrobulbar space of 4 canine cadavers; and assessment of the efficacy and MRI evaluation of the anatomic distribution of injections of a lidocainecontrast agent mixture in 4 anesthetized, nonrecovery dogs. By use of the preferred technique (ITP), the ocular effects of lidocaine anesthesia were evaluated in 4 dogs; during a 2-week period after treatment, dogs underwent ophthalmic examination, Schirmer tear testing (STT), intraocular pressure (IOP) measurement, and Cochet-Bonnet esthesiometry.

RESULTS

Of the 3 techniques, the ITP technique was the preferred method for retrobulbar administration of anesthetic agent in dogs because it was efficacious (pupil dilation and central rotation of the globe achieved in all eyes), easiest to perform, and provided thorough coverage of the intraconal retrobulbar space without complication. During the 2-week follow-up period, the ITP injection did not significantly affect STT, IOP, or Cochet-Bonnet esthesiometry values in dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

In dogs, retrobulbar administration of anesthetic agents via the ITP technique is a potential alternative to systemic administration of neuromuscular blocking agents for ophthalmic surgery and provides the additional benefit of local ocular analgesia.

[Disorders of the origin of the suspensory ligament in the horse: a diagnostic challenge]

Lameness in horses due to pain originating from the proximal metacarpal/metatarsal region remains a diagnostic challenge. In cases of obvious lameness the pain can be localised to this region by diagnostic anaesthesia. Because a variety of disorders can cause lameness in this region different imaging modalities including radiography, ultrasonography and scintigraphy should be used to arrive at an accurate diagnosis. Even though a precise anatomic-pathologic diagnosis can still be an enigma, because not only bone and joints, but also soft tissue structures including the proximal suspensory ligament, its origin at the proximal metacarpus/ metatarsus, its fascia, the superficial fascia, as well as the intermetacarpal/metatarsal ligaments, the accessory ligament of the deep digital flexor tendon and both digital flexor tendons may be involved. Magnet resonance tomography (MRT) shows a high diagnostic sensitivity in imaging soft tissue structures and bone. In horses MRT is still at the beginning. The MRT appearance of the proximal metacarpal/metatarsal region has not yet been evaluated in detail and there are only few anatomic studies of the origin of the suspensory ligament in horses. The first experiences showed, that more gross and histologic examinations are necessary to fully interpret MRT-images and to differentiate pathologic alterations from clinically not relevant variations.

Controlled, clinical trial assessing saphenous, tibial and common peroneal nerve blocks for the control of perioperative pain following femoro-tibial joint surgery in the nonchondrodystrophoid dog

OBJECTIVE

To determine whether bupivacaine peripheral nerve block of the saphenous, tibial and common peroneal nerves proximal to the femoro-tibial joint reduces peri-operative pain following extracapsular surgical stabilization of cranial cruciate ligament rupture in the nonchondrodystrophoid dog.

ANIMALS

Forty-one dogs with naturally acquired femoro-tibial joint instability. Study design Randomized, controlled, clinical trial.

METHODS

Dogs diagnosed with suspected cranial cruciate ligament injury based on physical and radiographic evidence were randomly assigned to treatment (bupivacaine) or control (saline) nerve blocks before femoro-tibial joint surgery. Pain scores, skin sensation, pain threshold to incisional pressure, time to first systemic 'rescue' opioid analgesic and total analgesic dose were evaluated for 24 hours. p < 0.05 was considered significant.

RESULTS

Treatment dogs had a significantly longer period of cutaneous desensitization than control dogs. There were no significant differences between treatment and control groups for pain score, pain threshold to incisional pressure, or time to first-rescue analgesic. The treatment group received significantly more supplemental analgesics than the control group.

CONCLUSIONS

These peripheral nerve blocks were easy to perform and resulted in significant desensitization of the associated nerve autonomous zones, but did not improve post-operative analgesia.

CLINICAL RELEVANCE

Clinical benefit was not detected when using this technique for peri-operative pain management following extracapsular cranial cruciate ligament surgical stabilization.

Evaluation of skin sensitivity after shock wave treatment in horses

OBJECTIVE

To evaluate the effects of shock wave treatment on cutaneous nerve function, compared with the effects of local nerve block and sedation.

ANIMALS

18 clinically sound Swiss Warmbloods.

PROCEDURE

Horses were randomly allocated to 3 groups and received different amounts and types of shock waves (extracorporeal shock wave treatment [ESWT] or radial pressure wave treatment [RPWT]). Horses were sedated with xylazine and levomethadone. Shock waves were applied to the lateral palmar digital nerve at the level of the proximal sesamoid bones on 1 forelimb. Skin sensitivity was evaluated by means of an electrical stimulus at the coronary band before and 5 minutes after sedation and at 4, 24, and 48 hours after application of ESWT or RPWT. On the contralateral forelimb, skin sensitivity was tested before and 10 minutes after an abaxial sesamoid nerve block.

RESULTS

No significant changes in skin sensitivity were detected, regardless of the shock wave protocol applied. Mean reaction thresholds after sedation were more than twice the baseline thresholds. After the abaxial sesamoid block, no reaction was recorded in any of the horses.

CONCLUSIONS AND CLINICAL RELEVANCE

Application of ESWT or RPWT to the palmar digital nerve had no effect on cutaneous sensation distal to the treated region for at least 2 days after application. The analgesic effect of sedation on reaction to electrical stimuli was distinct but varied among horses.

A New Approach for Perineural Injection of the Lateral Palmar Nerve in the Horse

OBJECTIVE

To evaluate the accuracy of a new technique for perineural injection of the lateral palmar nerve and to determine frequency of inadvertent injection into the carpal synovial sheath with this technique.

STUDY DESIGN

Prospective experimental study.

ANIMALS

Thirty equine cadaver forelimbs.

METHODS

Each of 3 clinicians injected 0.5 mL of a 1% aqueous solution of new methylene blue as a marker at the medial aspect of the accessory carpal bone of 10 limbs. Immediately after each injection, the lateral palmar nerve was identified by dissection of and inspected for proximity of dye, and the carpal synovial sheath was inspected for the presence of dye.

RESULTS

New methylene blue solution was observed to surround the nerve (29 limbs) or to lie within 2 mm of it (1 limb). Dye was not found in the carpal synovial sheath of any specimen.

CONCLUSIONS

Using this technique, perineural injection of the lateral palmar nerve can be consistently achieved, and the carpal synovial sheath is unlikely to be penetrated by the needle during the procedure.

CLINICAL RELEVANCE

The technique described provides an accurate and simple method for perineural injection of the lateral palmar nerve proximal to the origin of its deep branch. This technique can be used to anesthetize the lateral palmar nerve for diagnosis of pain originating in the palmaroproximal aspect of the metacarpus without risk of inadvertently desensitizing structures within the carpal synovial sheath.

Calf response to caustic paste and hot-iron dehorning using sedation with and without local anesthetic

Dairy producers require effective methods of reducing the pain associated with dehorning. Previous work has shown that analgesics can reduce pain associated with hot-iron dehorning, but these interventions may not be practical for some producers. Some producers favor the use of caustic paste (to cause a chemical burn as opposed to thermal burn), but little is known about how to treat pain caused by caustic burns. In 2 experiments, head shaking and head rubbing behaviors were used to evaluate pain following dehorning using caustic paste. In experiment 1, sedated calves were dehorned using a caustic paste, with or without a lidocaine local block. Calves treated with lidocaine showed no evidence of reduced pain response in the hours after the caustic paste was applied. In experiment 2, response to caustic paste dehorning with a sedative only was compared with hot-iron dehorning using a sedative and local anesthetic. In the first 4 h after dehorning, calves dehorned with a hot iron showed more head shaking than calves dehorned with caustic paste. These results indicate that dehorning with caustic paste combined with a sedative results in less pain to calves than dehorning with a hot iron combined with a sedative and a local anesthetic.

The effect of bilateral glossopharyngeal nerve anaesthesia on swallowing in horses

REASONS FOR PERFORMING STUDY

Dysfunction of the glossopharyngeal nerve has been implicated as a cause of dysphagia in horses. However, recent studies have indicated that this is not the case.

OBJECTIVES

To determine whether bilateral glossopharyngeal nerve anaesthesia would cause dysphagia in horses or result in measurable alterations in the timing, function, or sequence of swallowing.

METHODS

Swallowing was evaluated in 6 normal horses with and without bilateral glossopharyngeal nerve anaesthesia. Swallowing dynamics were assessed subjectively and objectively based on time from prehension of food until swallowing, number of tongue movements until initiation of swallowing, depth of bolus at the base of the tongue prior to initiation of swallow and evidence of tracheal aspiration using fluoroscopy and endoscopy.

RESULTS

There was no evidence of aspiration or dysphagia in horses before or after bilateral glossopharyngeal nerve block. No observed or measured differences in swallowing sequence or function could be detected in blocked compared to unblocked horses. However, there was a trend in blocked horses for the number of tongue pushes and the time to swallowing to be increased.

CONCLUSIONS

Glossopharyngeal nerve function may not be essential for normal swallowing function in otherwise healthy horses.

POTENTIAL RELEVANCE

Clinically, normal swallowing is not an appropriate test of glossopharyngeal nerve function and dysphagic horses should not be assumed to have glossopharyngeal nerve dysfunction.

Evaluation of the analgesic effect of lidocaine and bupivacaine used to provide a brachial plexus block for forelimb surgery in 10 dogs

Twenty adult dogs weighing between 1.4 and 53.5 kg and aged between six months and nine years were anaesthetised and the brachial plexus was localised with the aid of a nerve stimulator. In 10 of the dogs a brachial plexus block was induced with a mixture of lidocaine and bupivacaine and the other 10 each received 0.25 ml/kg saline as a control. The end-tidal isoflurane concentration was maintained between 1.3 and 1.4 per cent during surgery for carpal arthrodesis or a fracture of the radius or ulna. Acute heart rate or blood pressure increases of 20 per cent or more were treated with 1 microg/kg fentanyl intravenously. Postoperatively, signs of pain were scored by a single blinded observer at hourly intervals until eight hours after the block had been induced, on a scale from 0 to 18. Dogs with pain scores above 5 received 0.1 to 0.2 mg/kg methadone intravenously, repeated as necessary. During surgery the control dogs received significantly more fentanyl (median 0.05 microg/kg/minute, range 0.02 to 0.20 microg/kg/minute) than the group given local anaesthetic (median 0 microg/kg/minute, range 0 to 0.02 microg/kg/minute). Postoperatively, the control group required significantly more methadone (median 0.2 mg/kg, range 0.1 to 1 mg/kg) than the treated group (median 0 mg/kg, range 0 to 0.13 mg/kg).

Comparison of analgesic techniques for antler removal in halothane-anaesthetized red deer (Cervus elaphus): electroencephalographic responses

OBJECTIVE

To provide evidence for an analgesic effect of antler pedicle compression or lidocaine 'ring block' by comparing changes in median and spectral edge frequencies and total electroencephalographic (EEG) power during the application of each technique followed by antler removal.

ANIMALS

Twenty-nine 2-year-old red deer (Cervus elaphus) stags weighing 106-131 kg each were used in this study. Stags were carrying immature growing antler suitable for commercial harvest.

MATERIALS AND METHODS

Anaesthesia was induced using propofol (8.25 +/- 1.28 mg kg(-1)) and ketamine (2.18 +/- 0.15 mg kg(-1)) and maintained with halothane in oxygen. End-tidal halothane (Fe'HAL), expired CO(2) tension (Pe'CO(2)), SpO(2), EEG, ECG, and direct arterial blood pressures were recorded continuously. Respiratory rate and somatic responses were recorded at specific time points. After stabilization of anaesthesia (Fe'HAL was approximately 0.8%) baseline data were recorded. Stags were randomly allocated to one of three treatment groups; control, local anaesthesia, or compression band. One antler was removed 4 minutes after the application of treatment. Electroencephalographic responses to application of treatment and antler removal were analysed using area under the curve (AUC) analysis. Mean AUC was compared between groups using anova, and when significant differences were found, groups were compared post hoc with two-tailed t-tests. Significance levels were set at p </= 0.05.

RESULTS

Median frequency (F(50)) was increased during antler removal in the control group and during both application and antler removal in the compression group. In the lidocaine group, F(50) was decreased during both application and antler removal. Spectral edge frequency (F(95)) was increased during the antler removal period in the control group and during both application and antler removal in the compression group. In the lidocaine group, F(95) was decreased in the application time period. Total EEG power (P(tot)) was decreased in the removal period in the control group. In the compression group, P(tot) was decreased in the removal period. In the lidocaine group, P(tot) was decreased in the application period. There were no significant differences in EEG variables between antler removal in the control group and application of compression (p = 0.19-0.96).

CONCLUSIONS

These data suggest that lidocaine 'ring block' of the antler pedicle provides adequate analgesia for velvet antler removal. The use of antler pedicle compression bands represents a noxious stimulus in its own right and is not as protective as lidocaine 'ring block' against the noxious stimulus of surgical antler removal.

CLINICAL RELEVANCE

Compression of the antler pedicle has been recommended as an alternative to lidocaine 'ring block' for velvet antler removal. The results of this study suggest that antler pedicle compression is noxious. In addition, antler pedicle compression offers less effective analgesia than lidocaine 'ring block'.

Comparison of analgesic techniques for antler removal in halothane-anaesthetized red deer (Cervus elaphus): cardiovascular and somatic responses

OBJECTIVE

To compare changes in heart rate and arterial pressures resulting from compression of the antler pedicle or lidocaine 'ring block' and during subsequent antler removal during minimal halothane anaesthesia.

ANIMALS

Twenty-nine 2-year-old red deer (Cervus elaphus) stags, weighing 106-131 kg and carrying immature growing antler suitable for commercial harvest were studied.

MATERIALS AND METHODS

Anaesthesia was induced using intravenous propofol (median dose 8.0 mg kg(-1), range 5.2-11.0) and ketamine (median dose 2.2 mg kg(-1), range 1.9-2.4) and maintained using halothane in oxygen. End-tidal halothane concentration (Fe'HAL) end-tidal CO(2) tension (Pe'CO(2)), SpO(2), EEG, ECG, and direct systolic (SAP) mean (MAP) and diastolic (DAP) arterial pressures were recorded continuously. Respiratory rate and somatic responses were recorded. Baseline data were recorded once anaesthesia (Fe'HAL approximately 0.8%) was stable. Stags were randomly allocated to control, lidocaine 'ring block' or compression band treatment groups. One antler was removed 4 minutes after treatment. Cardiovascular responses to the application of analgesia and antler removal were analysed using a general estimates equation for repeated measures or area under the curve (AUC) analysis. Mean AUC was compared between groups using anova, and when significant differences were found, groups were compared post hoc with two-tailed t-tests. Somatic response data were compared with Fisher's exact chi-square test. A value of p < 0.05 was considered significant.

RESULTS

Heart rate fell during observations in all groups with no significant differences between groups. Arterial pressures in the control and lidocaine groups during treatment and removal were not different from baseline values or from each other. Compression group pressures were significantly higher than baseline during both treatment and removal. Compression group DAP and MAP were significantly higher after antler removal than during treatment. In control and lidocaine groups, the AUC for SAP, DAP, and MAP over the combined baseline, treatment, and removal period did not differ. The compression group AUC for DAP and MAP were significantly greater over the experimental period than both the lidocaine group and control groups. Somatic responses occurred in one animal at lidocaine injection and three at compression application. Somatic responses occurred in eight control animals and two in the compression group at antler removal. More animals responded to antler removal in the control group than in the compression (p = 0.015) or lidocaine (p < 0.001) groups.

CONCLUSIONS

Compression of the antler pedicle appears to be noxious. Pedicular compression is a less effective analgesic technique for antler removal compared to 'ring blocks' with lidocaine.

CLINICAL RELEVANCE

This study suggests that lidocaine 'ring blocks' are the current technique of choice for antler removal in deer.

Brachial plexus block using electrolocation for pancarpal arthrodesis in a dog

Conduction blockade was achieved at the brachial plexus of a dog undergoing surgery for pancarpal arthrodesis. The lidocaine/bupivacaine mixture used was the sole analgesic treatment applied during surgery and for 3 hours post-operatively. Location of the plexus brachialis was facilitated using a nerve stimulator. A low volume of lidocaine and bupivacaine (0.26 mL kg(-1)) resulted in successful blockade, which was evident from stable cardiorespiratory variables at low end-tidal (1.3-1.4%) isoflurane concentrations. Pain scoring and examination of motor and sensory function indicated adequate pain relief for 7 hours. While localization of the plexus brachialis can be performed 'blindly', electrolocation improves the success rate for less experienced anaesthetists.