Duration of action of mepivacaine and lidocaine in equine palmar digital perineural blocks in an experimental lameness model

Computed tomographic evaluation of the proximity of needles placed for perineural anesthesia of the palmar digital nerves to synovial structures in the foot: an ex vivo study

Background

Potential synovial penetration following palmar digital nerve blocks has not been investigated.

Objectives

To evaluate the proximity of needles placed for palmar digital nerve blocks to nearby synovial structures using computed tomography (CT).

Study design

Descriptive observational study.

Methods

In 18 cadaver forelimbs, sequential injection of the navicular bursa (NB), distal interphalangeal joint (DIPJ) and digital flexor tendon sheath (DFTS) was performed using 3, 5 and 10 mL diluted radiodense contrast medium, respectively. After each synovial injection, 25 gage needles were placed over the palmar digital nerves at the proximal aspect of the ungular cartilages (distal injections) and 1 cm further proximally (proximal injections), and CT examination was performed. Subsequently, needles were removed, and the synovial structures further distended with the same volume as for the first injection. Perineural needle placement and image acquisition were repeated. The distance between the needle tip and adjacent synovial structures was measured (mm) in reconstructed images. Results were analyzed in separate general linear mixed models, to determine the effect of needle position and synovial distension on the distance from the tip of the needle to the NB, DFTS and DIPJ.

Results

Synovial penetration was confirmed following 12/420 (3%) needle placements (NB n = 5, 1 after proximal and 4 after distal injections; DIPJ n = 2, DFTS n = 2, NB or DIPJ n = 3, all after distal injections). The mean distance from the needle tip to the NB and DIPJ was significantly smaller after the second distension (NB: p = 0.025; DIPJ: p < 0.001) and with the distal needle placements (NB: p < 0.001; DIPJ: p < 0.001). For the DFTS, the distance from the needle tip was significantly smaller with the proximal needle placements (p = 0.001).

Main limitations

Ex-vivo study.

Conclusion

There is a small risk of synovial penetration when performing palmar digital nerve blocks, especially when distension of adjacent synovial structures is present.

Transient Horner's syndrome in horses following cervical plexus local anesthesia

OBJECTIVE

To report the development of transient Horner's syndrome in horses following local anesthesia of the cervical plexus.

ANIMALS

A total of 37 horses.

STUDY DESIGN

Observational retrospective short case series.

METHODS

Medical records of cases undergoing ultrasound-guided cervical plexus anesthesia for standing prosthetic laryngoplasty at a single referral institution were evaluated (2019-2020).

RESULTS

Five of 37 horses (14%) developed transient signs of Horner's syndrome postoperatively. Obvious clinical signs began 2 to 5 h following local anesthesia and persisted for two to 4 h. Profuse unilateral sweating of the head and upper neck was the most apparent clinical sign.

CONCLUSION

Transient clinical signs of Horner's syndrome were seen following unilateral local anesthesia of the cervical plexus. Long-term adverse sequelae were not observed.

Evaluation of frontal and infratrochlear nerve blocks for standing sedated frontonasal sinusotomy in horses

OBJECTIVE

To determine if targeted blocking of frontal and infratrochlear nerves provided anesthesia for the approach to a frontonasal sinusotomy.

STUDY DESIGN

Two part study: Part 1 randomized crossover design; Part 2 proof of concept.

ANIMALS

N = 12; six each in Parts 1 and 2.

METHODS

Part 1: Each horse had either frontal and infratrochlear nerve blocks or a line block performed with 2% mepivacaine hydrochloride. Mechanical nociceptive thresholds (MNT) were obtained at five sites along a proposed frontonasal sinusotomy prior to injection, and at 10, 60, and 120 min after blocking. After a 4 day washout period, the opposite procedure was performed. Order of procedure and side of face were randomized. MNTs were analyzed using mixed-model ANOVA with p < .05. Part 2: Frontal and infratrochlear nerve blocks were performed followed by creation of a skin/periosteal incision, which was closed at 2 h. Ability to create and suture the incision, and the size of the incision were recorded.

RESULTS

For part 1, both line and targeted blocks resulted in at least two times an increase in median MNT values at each of the five sites, as compared to baseline MNT values (p < .0025). In Part 2, incisions could be completed in five of six horses, with median incision size of 6.5 × 5 cm.

CONCLUSION

Following frontal and infratrochlear nerve blocks, MNTs were increased along a proposed frontonasal sinusotomy, and skin incisions could be created in the majority of horses.

CLINICAL SIGNIFICANCE

Frontal and infratrochlear nerve blocks provide an alternative technique to create a frontonasal sinusotomy.

Topical ropivacaine hydrochloride 0.5% and lidocaine hydrochloride 2% significantly reduce corneal sensitivity without short-term negative side effects in horses

OBJECTIVE

To evaluate corneal sensitivity and acute side effects following application of ropivacaine hydrochloride 0.5% and lidocaine hydrochloride 2% on the healthy equine cornea.

ANIMALS STUDIED

Eight healthy adult horses.

PROCEDURE

A randomized, masked, crossover study design was utilized. Baseline Semiquantitative Preclinical Ocular Toxicology (SPOT) scores and corneal touch thresholds (CTT) using a Cochet-Bonnet esthesiometer were recorded and measured, respectively, for eight healthy adult horses before medication application. Commercially available eyewash was used as a negative control. Ropivacaine hydrochloride 0.5% or lidocaine hydrochloride 2% solution was sprayed on a randomly selected eye, and the contralateral eye received eyewash. CTT was measured in both eyes at 1, 5, 15, 25, 35, 45, 55, 65, and 75 min post-application. Post-application SPOT scores were recorded immediately following the trial. Linear mixed model statistical analyses (mean ± standard error) were performed (p < .05).

RESULTS

Mean eyewash CTT (3.41 cm ± 0.464) was significantly different from ropivacaine-treated (1.44 cm ± 0.562) (p = .008) and lidocaine-treated eyes (1.75 cm ± 0.562) (p = .024); CTT was not significantly different between drug groups (p = .88). Time to maximum anesthesia was not significantly different between ropivacaine (13.25 min ± 3.353) and lidocaine (16.25 min ± 3.353) (p = .40). No side effects were appreciated as confirmed by SPOT.

CONCLUSIONS

Ropivacaine and lidocaine similarly decreased corneal sensitivity when applied topically without clinically evident short-term ocular side effects. Lidocaine may be preferable in clinical settings due to its large, multi-use vials and similar effects to ropivacaine.

Evaluation of Thermal Changes of the Sole Surface in Horses with Palmar Foot Pain: A Pilot Study

Background: Horses with palmar foot pain do not show a typical increase in temperature in the palmar aspect of the hoof and heel due to low blood flow. The objectives of the current study were to determine the changes and differences in the thermographic pattern of the sole surface in horses with unilateral palmar foot pain and non-lame horses before and after training. We hypothesized that the thermal pattern and the local temperature of the frog area and toe area would be similar, with an increased local temperature after training in both lame and non-lame horses. A pilot study was conducted to investigate the accuracy of thermography used to detect changes in local temperature and to compare the thermal patterns observed on the sole surface after training. Methods: The study group included eight horses with unilateral forelimb palmar foot pain (n = 8) and healthy contralateral limbs (n = 8). Four additional non-lame horses served as controls. The horses were selected for the study based on the following criteria: forelimb with unilateral chronic progressive lameness and positive reactions when performing the hoof test and frog wedge test, degenerative findings of the navicular bone, and improvement in lameness after perineural analgesia of the medial and lateral palmar digital nerve. The local temperatures of the frog and toe areas were measured before and after training in the affected and contralateral limbs in the study group and both forelimbs in the control group using an FLIR E50 thermal camera. Receiver operating characteristic (ROC) curve analysis was applied to check the sensitivity and specificity of the results for the studied groups. Results: The thermal patterns of the hoof presented differences between the three groups of horse limbs. After training, the temperature of the sole surface increased, and its area increased in the limbs affected with palmar foot pain compared with the non-lame limbs in the study group and the limbs in the control group. The temperature of the frog area did not increase after training in the limbs affected with palmar foot pain compared with the same area in the other groups. The ROC curve analysis demonstrated the medical applicability of this tool and showed that thermography is a reliable diagnostic test to correctly discriminate between non-lame horses and those with palmar foot pain. Conclusions: We recommend thermographic scanning of the toe and frog area to detect changes in the local temperature of the sole surface after training to discriminate the horses with palmar foot pain from non-lame ones. Further investigation is required to clarify whether the observed thermographic imaging features of the sole surface are characteristic for horses with palmar foot pain.

MicroRNA-27a Suppresses the Toxic Action of Mepivacaine on Breast Cancer Cells via Inositol-Requiring Enzyme 1-TNF Receptor-Associated Factor 2

Objective

To investigate the toxic effects of microRNA-27a on breast cancer cells through inositol-acquiring enzyme 1-TNF receptor-associated factor 2 inhibition by mepivacaine.

Methods

The elevation of miR-27a in MCF-7 of BCC lines was measured, and groups were set up as control, mepivacaine, and elevated groups. Cells from each group were examined for inflammatory progression.

Results

Elevated miR-27a in MCF-7 cells was able to distinctly augment the cell advancement (P < 0.01) and decline cell progression (P < 0.01). Meanwhile, miR-27a reduced the content of intracellular inflammatory factors IL-1β (P < 0.01) and IL-6 (P < 0.01), elevated the content of IL-10 (P < 0.01), suppressed levels of cleaved-caspase-3 and p-signal transducer and activator of transcription-3 (STAT3) (P < 0.01), and increased Bcl-2/Bax (P < 0.01).

Conclusion

Elevated miR-27a in MCF-7 of BCC lineage was effective in reducing the toxic effects of mepivacaine on cells and enhancing cell progression. This mechanism is thought to be related to the activation of the IRE1-TRAF2 signaling pathway in BCC. The findings may provide a theoretical basis for targeted treatment of BC in clinical practice.

The Effect of Chiropractic Treatment on Limb Lameness and Concurrent Axial Skeleton Pain and Dysfunction in Horses

Chiropractic care is a common treatment modality used in equine practice to manage back pain and stiffness but has limited evidence for treating lameness. The objective of this blinded, controlled clinical trial was to evaluate the effect of chiropractic treatment on chronic lameness and concurrent axial skeleton pain and dysfunction. Two groups of horses with multiple limb lameness (polo) or isolated hind limb lameness (Quarter Horses) were enrolled. Outcome measures included subjective and objective measures of lameness, spinal pain and stiffness, epaxial muscle hypertonicity, and mechanical nociceptive thresholds collected on days 0, 14, and 28. Chiropractic treatment was applied on days 0, 7, 14, and 21. No treatment was applied to control horses. Data was analyzed by a mixed model fit separately for each response variable (p < 0.05) and was examined within each group of horses individually. Significant treatment effects were noted in subjective measures of hind limb and whole-body lameness scores and vertebral stiffness. Limited or inconsistent therapeutic effects were noted in objective lameness scores and other measures of axial skeleton pain and dysfunction. The lack of pathoanatomical diagnoses, multilimb lameness, and lack of validated outcome measures likely had negative impacts on the results.

Mechanical nociceptive assessment of the equine hoof after navicular bursa anesthetic infiltration validated by bursography

The analgesic specificity of navicular bursa (NB) anesthetic infiltration is still questionable. The study aimed to determine the mechanical nociceptive threshold of non-specific analgesia in the dorsal lamellar stratum, as well as in the sole, coronary band, and heel bulbs of the hoof, after navicular bursa anesthetic infiltration. Six healthy horses with no clinical or radiographic changes of the digits and no communication between the NB and the distal interphalangeal joint, were used. After random selection, the NB of one of the forelimbs was infiltrated with 2% lidocaine and the contralateral one with lactated ringer’s solution. Contrast was added to confirm radiographic infiltration. The mechanical nociceptive threshold was determined using a portable pressure dynamometer, before and at various times after the infiltration, in 10 points of the hoof. The effects of time and treatment were verified by ANOVA (P<0.05). There was no statistical difference in the values of the mechanical nociceptive threshold (P>0.05) in all regions evaluated. However, in one of the six hooves that receives lidocaine, complete absence of response to the painful stimulus (maximum force of 6 Kg over an area of 38.46 mm², for a maximum of 4 seconds) was observed in the dorsal lamellae between 30 and 60 min after infiltration. In conclusion, lidocaine infiltration of NB did not promote significant increases in the nociceptive threshold of the sole, coronary band, bulbs of the heel and dorsal lamellae clinically healthy horses. However, the occurrence of analgesia in one of the six hooves subjected to NB anesthesia indicates that the technique may not be fully specific in few horses.

Pharmacokinetics and clinical efficacy of Acetaminophen (Paracetamol) in adult horses with mechanically induced lameness

BACKGROUND

Acetaminophen has been used clinically in horses alone or combined with traditional NSAIDs for treatment of musculoskeletal pain in horses.

OBJECTIVES

To determine the pharmacokinetics and efficacy of acetaminophen at two doses in horses with mechanically induced lameness compared to phenylbutazone or placebo control.

STUDY DESIGN

In vivo experiment.

METHODS

Nine healthy mares with mechanical lameness induced via a reversible sole pressure horseshoe model were treated with acetaminophen (20 mg/kg PO; A20), acetaminophen (30 mg/kg PO; A30), phenylbutazone (2.2 mg/kg, PO; PB) and oral placebo (C) in a randomised 4-way Latin square model. Plasma concentrations for A20 and A30 were analysed via LC-MS/MS and noncompartmental pharmacokinetic analysis. Heart rate and heart rate variability were measured using a portable telemetry. Lameness was scored by three blinded boarded equine surgeons using the AAEP and 10-point scales.

RESULTS

Mean maximum plasma concentration (C_max ) for A20 was 20.01 ug/mL within 0.66h (T_max ) after administration; The mean C_max for A30 was 30.02 ug/mL with a T_max of 0.43 h. Post-treatment heart rate for A30 was significantly lower than A20 at 1 and 7 h; lower than PB at 2, 3, 4.5, and 7 h; lower than C at 2, 3.5, 4.5, 6, 7, and 8 h. 10-point Lameness scores were significantly improved for A30 than C at 2 and 4 h post-treatment; PB was significantly improved than C at 8 h post treatment. There were no significant differences in lameness between A20, A30, and PB.

MAIN LIMITATIONS

Small sample size, lack of objective lameness measurement.

CONCLUSIONS

Acetaminophen at 30 mg/kg produced a more rapid improvement in lameness scores and heart rate compared to other treatments in this model. Further evaluation of the pharmacokinetics and safety of repeated oral dosing of acetaminophen at 30 mg/kg is needed to determine clinical utility.

Liposomal bupivacaine provides longer duration analgesia than bupivacaine hydrochloride in an adjustable sole-pressure model of equine lameness

OBJECTIVE

To compare the efficacy and duration of action for perineural analgesia with liposomal bupivacaine (LB) versus bupivacaine hydrochloride (BHCl) in a sole-pressure induced model of forelimb lameness in horses.

ANIMALS

6 healthy adult research horses.

PROCEDURES

In 1 randomly assigned forelimb, grade 3/5 lameness was induced by use of a sole-pressure lameness model. Objective lameness (vector sum [VS]) was determined with an inertial sensor system at 0, 1, 6, and 24 hours after lameness induction to evaluate the model. Mechanical nociceptive thresholds (MNTs) and objective lameness (VS and force platform kinetics) were recorded prior to and at 1, 6, 24, 48, and 72 hours after perineural anesthesia of the palmar nerves at the level of the proximal sesamoid bones with LB or BHCl in random order, with a 1-week washout period between crossover treatments. Data analysis was performed with mixed-model ANOVA.

RESULTS

When evaluating the lameness model, there was a decrease in lameness at 24 hours in at least 1 limb of each horse (7/12 limbs); thus, screw length was increased by 1 to 2 mm at each 24-hour interval to maintain lameness. Compared with results at baseline, horses treated with BHCl had significant improvements in median MNT and VS identified at only 1 hour after injection, whereas treatment with LB yielded significantly improved median MNT, VS score, and peak vertical force for up to 24 hours.

DISCUSSION

In this experimental model of forelimb lameness, LB provided longer analgesia when compared with BHCl and should be further investigated for treatment of pain in horses.

Dexmedetomidine prolongs the duration of action of mepivacaine on anesthesia of the palmar digital nerves of horses

OBJECTIVE

To determine whether palmar digital nerve (PDN) blockade in horses with a combination of dexmedetomidine and mepivacaine would block the response to mechanical force applied to the digit longer than would anesthetizing these nerves with mepivacaine alone or dexmedetomidine alone.

ANIMALS

8 mares with no signs of lameness.

PROCEDURES

In a randomized, crossover, blinded, experimental study, both PDNs of the same forelimb of each horse were anesthetized by perineural injection with either 30 mg mepivacaine alone, 250 µg of dexmedetomidine alone, or 30 mg mepivacaine combined with 250 µg of dexmedetomidine. Each horse received each treatment, and treatments were administered ≥ 2 weeks apart. The mechanical nociceptive threshold was measured at a region between the heel bulbs with the use of a digital force gauge before (baseline) and at 15-minute intervals after treatment.

RESULTS

The mean duration of sensory blockade of the digit was 2-fold longer when a combination of mepivacaine and dexmedetomidine was administered (371 minutes), compared with when mepivacaine alone was administered (186 minutes). Treatment with dexmedetomidine alone did not change the mechanical nociceptive threshold substantially from baseline and resulted in no clinical signs of sedation.

CLINICAL RELEVANCE

Results indicated that relief from digital pain provided by perineural treatment with mepivacaine for PDN blockade can be extended by adding dexmedetomidine to the injectate.

Comparison of 2% mepivacaine and a solution of 2% lidocaine/epinephrine administered for median and ulnar nerve blocks in horses with naturally occurring forelimb lameness

OBJECTIVE

To compare a 2% lidocaine solution containing 5 μg/ml (1:200 000) epinephrine with 2% mepivacaine for reducing lameness in horses after use in proximal nerve blocks.

STUDY DESIGN

Experimental randomized crossover.

ANIMALS

Six adult horses with naturally occurring forelimb lameness.

METHODS

Horses were evaluated using an inertial gait sensor system. Lameness was measured as a vector sum (VS). Following baseline lameness examination, median and ulnar nerve blocks were performed with lidocaine/epinephrine (0.5 mg epinephrine added to 50 ml of 2% lidocaine immediately prior to administration) or an equal volume of 2% mepivacaine. Horses were trotted at 5 min and then at 30 min intervals for 150 min. After 24 h, nerve blocks were repeated using the other local anesthetic. Data were evaluated using linear models.

RESULTS

The reduction in the VS did not differ after nerve blocks with lidocaine/epinephrine or mepivacaine (P = .791). Mean time to VS <8.5 mm (n = 5) was 5 and 9.6 min for lidocaine/epinephrine and mepivacaine, respectively. For one horse, VS was not reduced to <8.5 mm with either treatment (this horse had the highest VS before treatments were administered). The decrease in VS to <8.5 mm lasted for 150 min in both treatment groups.

CONCLUSION

The outcomes of the median and ulnar nerve blocks performed with 2% lidocaine with epinephrine did not differ from blocks performed with 2% mepivacaine.

CLINICAL RELEVANCE

Two percent lidocaine with epinephrine may serve as an adequate replacement for proximal nerve blocks when mepivacaine is unavailable.

Duration of skin desensitisation following palmar digital nerve blocks with lidocaine, bupivacaine, mepivacaine and prilocaine

Objective comparative evidence of the time to onset and duration of effect provided by local anaesthetic (LA) agents for perineural blocks in the horse is lacking. Clear knowledge of these properties is required to guide clinically appropriate agent selection and aid interpretation of response to diagnostic blocks for lameness examinations. An interventional study, with complete, randomised crossover design was used to compare time to onset and duration of skin desensitisation provided by four LA agents applied to palmar digital nerve blocks in 12 horses. Effect at each time point was determined using a pressure gauge to measure the mechanical nociceptive threshold (MNT) over the heel bulbs. Complete desensitisation was defined when MNT was greater than four times the pre-block baseline. Onset and duration of complete desensitisation were recorded and compared across agents using a mixed linear model. When significant (P ≤ 0.05), post-hoc paired comparisons between agents were performed against a Tukey's corrected P ≤ 0.05. Onset of complete skin desensitisation for each agent was <5 min. Duration for lidocaine (mean 25 min; 95% confidence interval [CI] 9-42) was shorter than bupivacaine (53 min; 95% CI 39-65), which was shorter than both prilocaine (102 min; 95% CI 81-123) and mepivacaine (107 min; 95% CI 92-121), which were not different. Although onset of complete skin desensitisation was not different for the LA agents tested, duration varied from 25 min to nearly 2 h. Prilocaine and mepivacaine provided the most prolonged duration of effect, both exceeding bupivacaine.

Efficacy and duration of effect for liposomal bupivacaine when administered perineurally to the palmar digital nerves of horses

OBJECTIVE

To determine the efficacy and duration of effect for liposomal bupivacaine following perineural administration to the medial and lateral palmar digital nerves of horses.

ANIMALS

9 nonlame mares.

PROCEDURES

For each horse, 2 mL of liposomal bupivacaine (13.3 mg/mL; total dose, 53.2 mg or approx 0.11 mg/kg) or sterile saline (0.9% NaCl) solution was injected adjacent to the medial and lateral palmar digital nerves at the level of the distal aspect of the proximal sesamoid bones of a randomly selected forelimb. Twenty-one days later, the opposite treatment was administered in the contralateral forelimb. A digital algometer was used to measure the mechanical nociceptive threshold (MNT) immediately before and at predetermined times for 48 hours after injection of each treatment. The mean MNT was compared between the 2 treatments at each measurement time.

RESULTS

The mean MNT for the liposomal bupivacaine-treated limbs was significantly greater (ie, the limb was less sensitive) than that for the saline-treated limbs between 30 minutes and 4 hours after treatment injection. Following liposomal bupivacaine administration, 1 horse developed mild swelling at the injection sites that resolved without treatment within 24 hours. No other adverse effects were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that liposomal bupivacaine is another option for perineural anesthesia in horses. Further research is necessary to determine the optimal dose and better elucidate the duration of effect for the drug when used for palmar digital nerve blocks in horses.

Comparison of speed of onset and analgesic effect of 2% mepivacaine hydrochloride deposited within or outside the neurovascular bundle at the level of the proximal sesamoid bones in horses with naturally occurring forefoot-related lameness

OBJECTIVE

To compare the speed of onset and analgesic effect of mepivacaine deposited within or immediately outside the neurovascular bundle at the base of the proximal sesamoid bones in horses.

ANIMALS

6 horses with naturally occurring forefoot-related lameness.

PROCEDURES

In a crossover study design, horses were randomly assigned to receive 1 of 2 treatments first, with the second treatment administered 3 to 7 days later. Trotting gait was analyzed with an inertial sensor-based motion analysis system immediately before treatment to determine degree of lameness. Afterward, ultrasound guidance was used to inject 2% mepivacaine hydrochloride around the palmar digital nerves of the affected forelimb at the level of the base of the proximal sesamoid bones either within the subcircumneural space or outside the circumneural sheath. After injection, gait was reevaluated at 5-minute intervals for 45 minutes.

RESULTS

Mepivacaine deposition outside the circumneural sheath did not resolve lameness in any horse; for 3 horses, the mean time to 70% reduction of initial vertical head movement was 13.3 minutes, and the remaining 3 horses had no such reduction at any point. Mepivacaine deposition within the subcircumneural space resulted in a mean time to 70% reduction of initial vertical head movement of 6.7 minutes and mean time to resolution of lameness of 21.7 minutes.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that when peripheral nerves of horses lie within a sheath, local anesthetic solution should be deposited within the sheath for an effective nerve block. If local anesthetic solution is deposited outside the sheath, the nerve block may yield erroneous results.

Comparison of analgesic and tissue effects of subcutaneous perineural injection of liposomal bupivacaine and bupivacaine hydrochloride in horses with forelimb lameness induced via circumferential clamp

OBJECTIVE

To evaluate the analgesic and tissue effects of liposomal bupivacaine administered SC as an abaxial sesamoid nerve block in horses with experimentally induced lameness.

ANIMALS

6 healthy mature light-breed horses.

PROCEDURES

In a randomized crossover study, a circumferential hoof clamp was applied to a forelimb to induce reversible lameness. An abaxial sesamoid nerve block of the lame forelimb was performed by SC perineural injection of 10 mg of liposomal bupivacaine or bupivacaine HCl/site. Quantitative gait data were objectively obtained with a body-mounted inertial sensor system before (baseline) and at 30-minute intervals after treatment. Time to return to 85% of baseline lameness was determined. After a minimum 4-day washout period, procedures were repeated with the alternate limb and treatment. Lastly, the palmar digital nerves and perineural tissues were collected and examined histologically.

RESULTS

SC perineural injection of liposomal bupivacaine ameliorated forelimb lameness in 5 of 6 horses. The median duration of analgesia was not significantly different between liposomal bupivacaine (4.5 hours) and bupivacaine HCl (3.0 hours). Histologically, mild inflammation was noted in 3 of 10 sites injected with liposomal bupivacaine and in none of the sites injected with bupivacaine HCl.

CONCLUSIONS AND CLINICAL RELEVANCE

SC perineural injection of 10 mg of liposomal bupivacaine/site ameliorated experimentally induced forelimb lameness in some horses. At milligram-equivalent doses, liposomal bupivacaine had a similar duration of analgesia to that of bupivacaine HCl. Further investigation is required before recommending clinical use of liposomal bupivacaine for nerve blocks in horses.

Desensitisation of the distal forelimb following intrathecal anaesthesia of the carpal sheath in horses

BACKGROUND

The effect of intrathecal anaesthesia of the carpal sheath on distal forelimb sensitivity in horses remains unknown.

OBJECTIVES

To assess the effect of carpal sheath anaesthesia on skin sensitivity of the distal forelimb and to determine potential locations for desensitisation of palmar nerves.

STUDY DESIGN

In vivo experimental and descriptive anatomical studies.

METHODS

Mepivacaine hydrochloride 2% (0.6 mg/kg) was injected unilaterally in the carpal sheath of 8 horses. Mechanical nociception of the distal forelimb was measured with a dynamometer and compared with the control limb at t_0, t_15, t_30, t_60, t_90, t₁₂₀ and t_180 minutes . Additionally, the carpal sheath of 10 pairs of cadaveric limbs was injected with latex and potential locations for anaesthetic diffusion to the neighbouring nerves were identified during longitudinal dissection (one limb) and in 3-cm-thick transverse cuts (opposite limb).

RESULTS

Six of 8 horses (75%) were completely desensitised at the level of both heel bulbs. Anaesthetic injection was not smooth in the 2 horses without desensitisation. Desensitisation started between 30 and 60 minutes in 67% of desensitised heel bulbs (8/12), and 50% (6/12) of them were still completely desensitised at 180 minutes. Cadaveric specimens revealed close proximity between the sheath and the medial palmar nerve as it travels inside the mesotenon of the digital flexor tendons in the carpal region and with both palmar nerves at the proximal metacarpal region.

MAIN LIMITATIONS

Skin mechanical nociception does not necessarily correlate with deep pain but remains the main clinical tool used by practitioners to assess distal limb anaesthesia.

CONCLUSIONS

Intrathecal anaesthesia of the carpal sheath led to distal limb skin desensitisation through diffusion to the palmar nerves at 2 possible locations. Carpal sheath anaesthesia should be interpreted within 15 minutes following injection and anaesthetic blocks distal to the carpus should be delayed for more than 3 hours following carpal sheath anaesthesia.

Intratesticular mepivacaine versus lidocaine in anaesthetised horses undergoing Henderson castration

BACKGROUND

In horses undergoing castration, direct comparison of intratesticular lidocaine vs mepivacaine as analgesic adjuncts has not yet been analysed.

OBJECTIVE

To compare the effects of intratesticular lidocaine and mepivacaine during equine castration using the Henderson drill under total intravenous anesthesia.

STUDY DESIGN

Randomised, double-blinded clinical study.

METHODS

Thirty-four stallions were anaesthetised using xylazine-ketamine and randomly selected to receive 10 mL either lidocaine or mepivacaine injected into each testicle. Both surgeon and anaesthetist were blinded to the selected treatment. A total of 5 minutes were required to pass between injection and first incision. Routine castration using a Henderson drill was performed. Heart rate, respiratory rate and SpO₂ were serially recorded. Total surgical time, time prior to clamping of each testicle and time to second incision were recorded. Cremaster muscle relaxation, surgical quality scores, number of additional ketamine boluses, recovery time and recovery quality were assessed between groups.

RESULTS

Cremaster relaxation scores were significantly better for the mepivacaine group over the lidocaine group on a 1-3 scoring system (1 being most relaxed, 3 being least). The average cremaster relaxation score on both testicles treated with mepivacaine was 1 compared to the lidocaine treatment averaging 2 [P = .03 first testicle; P = .04 second testicle]. The lidocaine group had an increased number of horses requiring additional ketamine (25% of horses) compared to the mepivacaine group (16% of horses). No other significant differences were observed between the groups.

MAIN LIMITATIONS

The use of only one injection method and lack of post-operative pain scoring limit the conclusions that can be drawn from these results.

CONCLUSION

Intratesticular mepivacaine when compared with intratesticular lidocaine results in improved cremaster muscle relaxation when only waiting five min prior to the start of the procedure.

Systemic and local effects of lidocaine or mepivacaine when used for intravenous regional anaesthesia of the distal limb in standing sedated horses

BACKGROUND

Local anaesthetics are being combined clinically with amikacin in intravenous regional limb perfusion (IVRLP), with limited knowledge on the analgesia provided and its onset and duration of action after tourniquet application and release.

OBJECTIVE

To evaluate the systemic clinical effect, limb withdrawal to nociceptive stimulation, and plasma and synovial fluid concentrations after IVRLP with lidocaine or mepivacaine in standing sedated horses.

STUDY DESIGN

Prospective, controlled, randomised, cross-over study.

METHODS

Six healthy adult horses were sedated and received IVRLP with lidocaine, mepivacaine or saline (negative control), or perineural anaesthesia of the medial and lateral palmar and palmar metacarpal nerves (positive control) in one forelimb with a 3-week washout period between trials. Electrical and mechanical stimuli were used to test nociceptive threshold of the limb before and after IVRLP/perineural anaesthesia. For lidocaine and mepivacaine trials, blood was collected from the jugular vein and synovial fluid from the radiocarpal joint before, during and out to 24 hours after IVRLP. Drug concentrations were measured using high-performance liquid chromatography.

RESULTS

Nociceptive thresholds for lidocaine, mepivacaine and perineural anaesthesia trials were significantly increased compared with saline and baseline values at 10, 20 and 30 minutes, with no differences between anaesthetic trials. During this time, horses had lower heart rates than IVRLP with saline. After tourniquet release at 30 minutes, nociceptive thresholds for lidocaine and mepivacaine trials gradually returned to baselines, whereas perineural anaesthesia trial remained unchanged out to an hour. Plasma lidocaine and mepivacaine concentrations were ≤50 ng/mL while the tourniquet was in place, significantly increasing 10 minutes after tourniquet release. Maximal lidocaine and mepivacaine concentrations in synovial fluid were reached 25 minutes after IVRLP injection.

MAIN LIMITATIONS

Amikacin was not included in the perfusate.

CONCLUSION

Similar to perineural anaesthesia, IVRLP with lidocaine or mepivacaine provides anti-nociception to the distal limb in standing sedated horses while a tourniquet is applied with concentrations remaining below toxic levels in plasma and synovial fluid.

Effects of acepromazine and xylazine on subjective and objective assessments of forelimb lameness

BACKGROUND

To facilitate lameness evaluation, sedatives such as xylazine and acepromazine are regularly used in the clinical setting, despite concerns that they may confound lameness assessment.

OBJECTIVES

The objective of this study was to determine the effect of low doses of acepromazine and xylazine on subjective and objective lameness assessment.

STUDY DESIGN

Randomised, blinded, crossover study.

METHODS

Six horses with experimentally induced solar pain were evaluated over a 1-hour period after treatment with intravenous xylazine (0.1 or 0.2 mg/kg), intravenous acepromazine (0.02 or 0.04 mg/kg), intravenous saline (1 mL) or local analgesia (4 mL 2% mepivacaine administered subcutaneously). Lameness was assessed objectively with inertial sensors and subjectively on a scale from 0 to 5. Lameness assessments were compared with logistic regression analysis to account for the repeated measures and cross-over study design (P < .05).

RESULTS

Xylazine (0.1 and 0.2 mg/kg) or acepromazine (0.02 and 0.04 mg/kg) did not result in significant differences in objective lameness assessment (vector sum) or average subjective lameness grade. Local analgesia was associated with a decrease in subjective lameness grade (OR 0.32 [0.11-0.92], P = .03). Objective measures of lameness (vector sum) were significantly decreased 45 minutes (vector sum 41.8, P = .04) and 60 minutes (vector sum 47.3, P = .03) following local analgesia administration compared with baseline (vector sum 121.4).

MAIN LIMITATIONS

Extrapolation of the experimental model of moderate lameness used in this study to broad range of clinical lameness situations should be performed carefully.

CONCLUSIONS

These results support the use of low doses of xylazine or acepromazine to facilitate forelimb lameness evaluation up to 1 hour in duration.

Evaluation of the effects of commonly used α2-adrenergic receptor agonists alone and in combination with butorphanol tartrate on objective measurements of lameness in horses

OBJECTIVE

To determine the effects of 3 α₂-adrenergic receptor agonists (α₂-ARAs), alone or in combination with butorphanol tartrate, on objective measurements of lameness in horses.

ANIMALS

17 adult polo horses with naturally occurring forelimb or hind limb lameness (or both).

PROCEDURES

In a crossover design, each horse received each protocol (saline [0.09% NaCl] solution [2 mL, IV] or xylazine hydrochloride [0.33 mg/kg, IV], detomidine hydrochloride [0.007 mg/kg, IV], or romifidine hydrochloride [0.033 mg/kg, IV] alone or in combination with butorphanol [0.007 mg/kg, IV]) in random order, with a washout period (≥ 7 days) between protocols. Horses were assessed immediately prior to (baseline) and 10, 15, 20, 30, and 40 minutes after administration of each protocol for degree of sedation, mechanical nociceptive threshold (MNT), and objective lameness measurements.

RESULTS

Compared with baseline values, sedation scores and MNTs were significantly higher at all evaluated time points following administration of all sedation protocols except xylazine alone; following administration of xylazine alone, sedation scores and MNTs were significantly higher at ≤ 30 minutes and ≤ 20 minutes, respectively. Significant differences in objective forelimb lameness measurements were noted after administration of the 3 α₂-ARA-butorphanol combinations. Most significant differences in objective measurements of hind limb lameness were detected after administration of detomidine or romifidine, alone or in combination with butorphanol.

CONCLUSIONS AND CLINICAL RELEVANCE

In the study horses, xylazine alone had the least impact on objective lameness measurements. The administration of α₂-ARAs, particularly detomidine or romifidine, alone or in combination with butorphanol, resulted in small but significant effects on objective lameness measurements.

Intra-articular anaesthesia of the equine stifle improves foot lameness

BACKGROUND

Equine diagnostic anaesthesia can be a useful tool in challenging lameness examinations. However, anaesthetics diffuse over time leading to nonspecific desensitisation of periarticular structures. Nerves that convey sensation from the distal limb to the central nervous system pass in close proximity to the caudal stifle joint capsule. Therefore, diffusion of intra-articular (IA) anaesthetics could cause inadvertent desensitisation of the distal limb resulting in a false diagnosis of stifle lameness.

OBJECTIVES

To determine if IA stifle anaesthesia can alleviate lameness originating in the distal limb.

STUDY DESIGN

Crossover experiment.

METHODS

Nine horses were fitted with a circumferential hoof clamp to induce a moderate unilateral hindlimb lameness. Intra-articular stifle anaesthesia was performed and gait was evaluated every 10 min during the 90-min trial using an inertial sensor system. Push-off and landing components of the lameness were assessed by measuring the mean inter-stride difference between the maximum and minimum heights of the pelvis respectively. Differences were compared using a Wilcoxon signed-rank test.

RESULTS

Overall, horses with hoof clamp-induced foot pain had a reduction in push-off lameness after IA stifle anaesthesia. The mean change in diffmax at 90 min was -4.3 mm (P = 0.005) for the experimental group vs. -2.3 mm (P = 0.2) for the control group. Lameness decreased over time, with an average improvement of 23% at 30 min, 33% at 60 min and 38% at 90 min. There was high inter-horse variability; 3/9 horses improved by ~50% within 30 min, while 2/9 improved by ~30% and 4/9 had minimal (<10%) or no improvement in lameness. Improvement after IA stifle anaesthesia was not related to the severity of baseline lameness (P = 0.3-0.7).

MAIN LIMITATIONS

Limited clinical applicability of our lameness induction model.

CONCLUSIONS

Intra-articular stifle anaesthesia reduces foot lameness in a third of horses by up to 50% within 30 min. Clinically, the results of IA stifle anaesthesia should be considered in the light of these findings before treatment recommendations are made, as additional diagnostics may be required to rule out pain originating in the distal limb.

Effect of the addition of epinephrine to a lidocaine solution on the efficacy and duration of palmar digital nerve blocks in horses with naturally occurring forefoot lameness

OBJECTIVE To determine whether addition of epinephrine to a lidocaine solution would prolong and potentiate the efficacy of a palmar digital nerve block (PDNB) in horses. ANIMALS 6 adult horses with naturally occurring forefoot lameness. PROCEDURES Initially, a PDNB with a 2% lidocaine solution was performed on the affected foot of each horse. Three days later, the PDNB was repeated with a 1% lidocaine solution or a 1% lidocaine solution containing epinephrine (dilution, 1:200,000). After another 3-day washout period, the PDNB was repeated with the treatment opposite that administered for the second PDNB. Gait was analyzed with a computerized lameness analysis system and heart rate and extent of skin sensation between the heel bulbs of the blocked foot were evaluated at predetermined times for 2 hours after each PDNB. RESULTS Efficacy and duration of the PDNB did not differ significantly between the 2% and 1% lidocaine treatments. The addition of epinephrine to the 1% lidocaine solution improved the efficacy and prolonged the duration of the PDNB. It also resulted in a positive correlation between skin desensitization and amelioration of lameness. Median heart rate remained unchanged throughout the observation period for all 3 treatments. No adverse effects associated with the PDNBs were observed. CONCLUSIONS AND CLINICAL RELEVANCE Addition of epinephrine (dilution, 1:200,000) to a 1% lidocaine solution improved the efficacy and prolonged the duration of a PDNB in horses with naturally occurring lameness and might be clinically useful for lameness evaluations and standing surgery of the forefoot of horses.

Unilateral cervical plexus block for prosthetic laryngoplasty in the standing horse

BACKGROUND

Locoregional anaesthetic techniques can facilitate certain surgeries being performed under standing procedural sedation. The second and third spinal cervical nerves (C2, C3) are part of the cervical plexus and provide sensory innervation to the peri-laryngeal structures in people; block of these nerves might permit laryngeal lateralisation surgery in horses.

OBJECTIVES

To describe the anatomical basis for an ultrasound-guided cervical plexus block in horses. To compare this block with conventional local anaesthetic tissue infiltration in horses undergoing standing prosthetic laryngoplasty.

STUDY DESIGN

Cadaveric study followed by a double-blinded prospective clinical trial.

METHODS

A fresh equine cadaver was dissected to characterise the distribution of C2 and C3 to the perilaryngeal structures on the left side. A second cadaver was utilised to correlate ultrasound images with the previously identified structures; a tissue marker was injected to confirm the feasibility of an ultrasound-guided approach to the cervical plexus. In the clinical study, horses were assigned to two groups, CP (n = 17; cervical plexus block) and INF (n = 17; conventional tissue infiltration). Data collection and analyses included time to completion of surgical procedure, sedation time, surgical field conditions and surgeon's perception of block quality.

RESULTS

We confirmed that C2 and C3 provided innervation to the perilaryngeal structures. The nerve root of C2 was identified ultrasonographically located between the longus capitis and the cleidomastoideus muscles, caudal to the parotid gland. The CP group was deemed to provide better (P<0.0002) surgical conditions with no differences in the other variables measured.

MAIN LIMITATIONS

Further studies with larger numbers of horses may be necessary to detect smaller differences in surgical procedure completion time based on the improved surgical filed conditions.

CONCLUSIONS

For standing unilateral laryngeal surgery, a cervical plexus block is a viable alternative to tissue infiltration and it improves the surgical field conditions.