A. Guedes

Use of a soluble epoxide hydrolase inhibitor as an adjunctive analgesic in a horse with laminitis

HISTORY A 4-year old, 500 kg Thoroughbred female horse diagnosed with bilateral forelimb laminitis and cellulitis on the left forelimb became severely painful and refractory to non-steroidal anti-inflammatory therapy (flunixin meglumine on days 1, 2, 3 and 4; and phenylbutazone on days 5, 6 and 7) alone or in combination with gabapentin (days 6 and 7). PHYSICAL EXAMINATION Pain scores assessed independently by three individuals with a visual analog scale (VAS; 0 = no pain and 10 = worst possible pain) were 8.5 on day 6, and it increased to 9.5 on day 7. Non-invasive blood pressure monitoring revealed severe hypertension. MANAGEMENT As euthanasia was being considered for humane reasons, a decision was made to add an experimental new drug, trans-4-{4-[3-(4-Trifluoromethoxy-phenyl)-ureido]-cyclohexyloxy}-benzoic acid (t-TUCB), which is a soluble epoxide hydrolase (sEH) inhibitor, to the treatment protocol. Dose and frequency of administration were selected based on the drug potency against equine sEH to produce plasma concentrations within the range of 30 nmol L(-1) and 2.5 μmol L(-1) . Pain scores decreased sharply and remarkably following t-TUCB administration and blood pressure progressively decreased to physiologic normal values. Plasma concentrations of t-TUCB, measured daily, were within the expected range, whereas phenylbutazone and gabapentin plasma levels were below the suggested efficacious concentrations. FOLLOW UP No adverse effects were detected on clinical and laboratory examinations during and after t-TUCB administration. No new episodes of laminitis have been noted up to the time of writing (120 days following treatment). CONCLUSIONS Inhibition of sEH with t-TUCB was associated with a significant improvement in pain scores in one horse with laminitis whose pain was refractory to the standard of care therapy. No adverse effects were noticed. Future studies evaluating the analgesic and protective effects of these compounds in painful inflammatory diseases in animals are warranted.

Sensory evoked potentials of the trigeminal nerve for the diagnosis of idiopathic headshaking in a horse

A 400-kg 5-year-old Arabian gelding was presented for a 2to 3-year history of progressive uncontrollable violent headshaking that precluded any type of physical activity and compromised quality of life. Although there were no triggering events for the observed behavior, headshaking was exacerbated when a bridle was placed on the horse’s head. One year before presentation, the horse underwent an extensive evaluation at another institution that included hematology and blood chemistry, testing for equine protozoal myelitis, skull radiographs, upper airway endoscopy (including guttural pouches), and magnetic resonance imaging of the head. Subtle asymmetry of the stylohyoid bone at its articulation was noted (left slightly thicker) on endoscopy. The rest of the diagnostic evaluation was within normal limits. Treatment with nonsteroidal anti-inflammatory drugs, gabapentin, and diet modification failed to control the episodes. Additional laboratory testing, as well as oral and ophthalmologic examinations, was performed by the referring veterinarian and found normal. The horse was referred for further evaluation. At presentation, the horse displayed violent continuous episodes of headshaking, which made the horse difficult to handle. Physical and neurologic examinations were normal except for the headshaking. These episodes were seen repeatedly while the horse was hospitalized, independent of time of day, light exposure, exercise, excitement, or confinement. The horse would frequently rub the right side of its face and eye. However, there were no obvious skin or ocular lesions. The horse would eat, but with interruptions attributable to headshaking. Some episodes associated with eating were triggered by hay touching the horse’s muzzle. Therefore, soaked hay and pellets were offered. Laboratory testing showed mild neutrophilia (7,117/ lL; reference range 2,600–6,800/lL) and 245 bands/lL with moderate toxicity, and normal plasma fibrinogen concentration; serum chemistry and blood gases analysis were within normal limits. Skull radiographs and upper airway endoscopy were not performed because computed tomography (CT) of the entire head was part of the diagnostic plan. A CT examination was done under general anesthesia and showed no abnormalities. Complete ophthalmologic and otoscopic examinations also were normal. Collection and evaluation of a spinal fluid sample were offered, but the owner declined. Somatosensory evoked potentials of the trigeminal complex using the infraorbital nerve (branch of the maxillary nerve) were studied in this horse using an evoked potential system (Nicolet Viking IV) as described by Aleman et al. In brief, with the horse in left lateral recumbency, a surface stimulus was applied to the dorsal gingival mucosa at the level of the right maxillary canine tooth. Three pairs of recording electrodes (Disposable EasyGrip monopolar electrode) were placed along the sensory pathway of the trigeminal complex. Recording site 1 (R1: infraorbital nerve) was at the level of the infraorbital foramen; site 2 (R2: maxillary nerve) was at the level of the maxillary foramen; and site 3 (R3: spinal tract of trigeminal complex) was at the level of the spinal cord segment 1. A 4th recording site (R4: cortical somatosensory) utilized subdermal electrodes placed at the level of the frontoparietal cerebral cortex (Fig 1A). A ground electrode was placed between the stimulus site and first recording site. A surface temperature probe was positioned dorsal to the facial crest to monitor regional temperature while recording (local temperature was maintained at 35°C). The stimulus rate was set at 3 Hz with a stimulus duration of 0.2 ms. The sweep speed was set at 5 ms per division. Each recording was the average of 1,000 responses. Acquisition sensitivities were variable with settings at 200, 100, 10, and 10 lV/divsion for recording sites 1, 2, 3, and 4, respectively. Band widths for R1–R3 were 20 Hz to 3 KHz, and 20–250 Hz for R4. Recordings were made at each of the following stimulus intensities (SI 0.1 mA): 2.5, 5, 10, 15, and 20 mA. Two sets of recordings were performed at each SI to test the reproducibility of the data. As a negative control, the study was also done with the SI From the Department of Medicine and Epidemiology, (Aleman, Madigan); the William R. Pritchard Veterinary Medical Teaching Hospital (Rhodes, Williams); and the Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA (Guedes). Corresponding author: M. Aleman, Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95691; e-mail: mraleman@ucdavis.edu. Submitted August 10, 2013; Revised August 29, 2013; Accepted September 19, 2013. Copyright

Evaluation and clinical use of an intraoral inferior alveolar nerve block in the horse

REASONS FOR PERFORMING STUDY Local anaesthesia is often required to facilitate invasive procedures in equine dental patients under standing sedation. OBJECTIVES To show that an intraoral approach can be used to desensitise the inferior alveolar nerve in horses and report complications seen with this technique. METHODS The distance of the mandibular foramen from the distal (caudal) edge of the mandibular third molar tooth, rostral edge of the mandibular ramus and ventral margin of the mandible were measured in 26 adult equine skulls of various ages and breeds. Computed tomography (CT) was used to verify the placement of the local anaesthetic with a custom-made device on 4 equine cadaver heads. The technique was applied in 43 clinical cases having procedures performed on the mandibular quadrants using the delivery device. RESULTS Computed tomography demonstrated that the intraoral approach provided deposition of the local anaesthetic at the mandibular foramen and anatomical localisation of mandibular foramen indicated that anaesthetic solution could be delivered with a 38 mm needle. Clinical patients to lerated invasive dental procedures following the inferior alveolar nerve block with a 5 ml dose of local anaesthetic, without evidence of self-inflicted lingual trauma. CONCLUSIONS The inferior alveolar nerve was successfully desensitised with the intraoral approach with minimal complications. The reduced volume of local anaesthetic and ability to deposit the local anaesthetic in close proximity to the nerve compared with an extraoral technique may decrease the complication of self-inflicted lingual trauma.

Soluble epoxide hydrolase activity and pharmacologic inhibition in horses with chronic severe laminitis.

BACKGROUND The roles of soluble epoxide hydrolase and lipid mediators in inflammatory and neuropathic pain could be relevant in laminitis pain management. OBJECTIVES To determine soluble epoxide hydrolase (sEH) activity in the digital laminae, sEH inhibitor potency in vitro, and efficacy of a sEH inhibitor as an adjunct analgesic therapy in chronic laminitic horses. STUDY DESIGN In vitro experiments and clinical case series. METHODS sEH activity was measured in digital laminae from euthanised healthy and laminitic horses (n = 5-6/group). Potency of 7 synthetic sEH inhibitors was determined in vitro using equine liver cytosol. One of them (t-TUCB; 0.1 mg/kg bwt i.v. every 24 h) was selected based on potency and stability, and used as adjunct therapy in 10 horses with severe chronic laminitis (Obel grades 2, one horse; 3-4, nine horses). Daily assessments of forelimb lifts, pain scores, physiologic and laboratory examinations were performed before (baseline) and during t-TUCB treatment. Data are presented as mean ± s.d. and 95% confidence intervals (CI). RESULTS sEH activity in the digital laminae from laminitic horses (0.9±0.6 nmol/min/mg; 95% CI 0.16-1.55 nmol/min/mg) was significantly greater (P = 0.01) than in healthy horses (0.17±0.09 nmol/min/mg; CI 0.07-0.26 nmol/min/mg). t-TUCB as an adjunct analgesic up to 10 days (4.3±3 days) in laminitic horses was associated with significant reduction in forelimb lifts (36±22%; 95% CI 9-64%) and in pain scores (18±23%; 95% CI 2-35%) compared with baseline (P = 0.04). One horse developed gas colic and another corneal vascularisation in a blind eye during treatment. No other significant changes were observed. MAIN LIMITATIONS Absence of control group and evaluator blinding in case series. CONCLUSIONS sEH activity is significantly higher in the digital laminae of actively laminitic compared with healthy horses, and use of a potent inhibitor of equine sEH as adjunct analgesic therapy appears to decrease signs of pathologic pain in laminitic horses.

Equivalence between invasive and oscillometric blood pressures at different anatomic locations in healthy normotensive anaesthetised horses

REASONS FOR PERFORMING STUDY Accurate blood pressure measurement is essential for effective clinical assessment and appropriate interventions in anaesthetised horses. Information on the accuracy of oscillometry for blood pressure measurement on the appendages of mature horses is limited. OBJECTIVES To assess equivalence between invasive and oscillometric blood pressures at different anatomic locations in horses. STUDY DESIGN Prospective experimental study using 6 healthy mature horses. METHODS Blood pressure was measured invasively in the right transverse facial artery and noninvasively by oscillometry in nondependent limbs and tail of laterally recumbent sevoflurane- or desflurane-anaesthetised horses. Cuff widths of 5-12 cm were tested on the tail, metatarsus, metacarpus and distal radius/ulna. Equivalence between mean arterial pressure (MAP) oscillometric and MAP invasive was assessed using a linear mixed effects model with a significance level of P≤0.05. RESULTS Twenty paired measurements were obtained for each cuff size in each of the locations, totalling 340 measurements. There was only one location (tail) and one cuff width (6 cm; cuff width-to-tail circumference ratio of 0.25) that resulted in equivalence between MAP measured with the oscillometric and the invasive methods (P = 0.8). All other locations (metacarpus, radius/ulna, metatarsus) and cuff widths were not equivalent (P≤0.01). CONCLUSIONS A cuff width-to-tail circumference ratio of 0.25 is recommended for accurate oscillometric blood pressure measurement in mature, laterally recumbent anaesthetised normotensive horses. Studies with variable haemodynamics are warranted. Oscillometric measurements at other extremities and/or with other cuff sizes cannot be recommended for clinical use.

Desflurane and sevoflurane elimination kinetics and recovery quality in horses

OBJECTIVE To evaluate pharmacokinetics, recovery times, and recovery quality in horses anesthetized with 1.2 times the minimum alveolar concentration of sevoflurane or desflurane. ANIMALS 6 healthy adult horses. PROCEDURES Anesthesia was maintained with sevoflurane or desflurane for 2 hours at 1.2 times the minimum alveolar concentration. Horses recovered without assistance. During recovery, end-tidal gas samples were collected until horses spontaneously moved. Anesthetic concentrations were measured by use of gas chromatography. After a 1-week washout period, horses were anesthetized with the other inhalation agent. Video recordings of anesthetic recovery were evaluated for recovery quality on the basis of a visual analogue scale by investigators who were unaware of the anesthetic administered. Anesthetic washout curves were fit to a 2-compartment kinetic model with multivariate nonlinear regression. Normally distributed interval data were analyzed by means of paired Student t tests; ordinal or nonnormally distributed data were analyzed by means of Wilcoxon signed rank tests. RESULTS Horses recovered from both anesthetics without major injuries. Results for subjective recovery evaluations did not differ between anesthetics. Area under the elimination curve was significantly smaller and time to standing recovery was significantly less for desflurane than for sevoflurane, although distribution and elimination constants did not differ significantly between anesthetics. CONCLUSIONS AND CLINICAL RELEVANCE Differences in area under elimination the curve between anesthetics indicated more rapid clearance for desflurane than for sevoflurane in horses, as predicted by anesthetic blood solubility differences in this species. More rapid elimination kinetics was associated with faster recovery times, but no association with improved subjective recovery quality was detected.

Airway responsiveness in CD38-deficient mice in allergic airway disease: studies with bone marrow chimeras

CD38 is a cell-surface protein involved in calcium signaling and contractility of airway smooth muscle. It has a role in normal airway responsiveness and in airway hyperresponsiveness (AHR) developed following airway exposure to IL-13 and TNF-α but appears not to be critical to airway inflammation in response to the cytokines. CD38 is also involved in T cell-mediated immune response to protein antigens. In this study, we assessed the contribution of CD38 to AHR and inflammation to two distinct allergens, ovalbumin and the epidemiologically relevant environmental fungus Alternaria. We also generated bone marrow chimeras to assess whether Cd38(+/+) inflammatory cells would restore AHR in the CD38-deficient (Cd38(-/-)) hosts following ovalbumin challenge. Results show that wild-type (WT) mice develop greater AHR to inhaled methacholine than Cd38(-/-) mice following challenge with either allergen, with comparable airway inflammation. Reciprocal bone marrow transfers did not change the native airway phenotypic differences between WT and Cd38(-/-) mice, indicating that the lower airway reactivity of Cd38(-/-) mice stems from Cd38(-/-) lung parenchymal cells. Following bone marrow transfer from either source and ovalbumin challenge, the phenotype of Cd38(-/-) hosts was partially reversed, whereas the airway phenotype of the WT hosts was preserved. Airway inflammation was similar in Cd38(-/-) and WT chimeras. These results indicate that loss of CD38 on hematopoietic cells is not sufficient to prevent AHR and that the magnitude of airway inflammation is not the predominant underlying determinant of AHR in mice.

Electrophysiologic Study of a Method of Euthanasia Using Intrathecal Lidocaine Hydrochloride Administered during Intravenous Anesthesia in Horses

Background An intravenous (IV) overdose of pentobarbital sodium is the most commonly used method of euthanasia in veterinary medicine. However, this compound is not available in many countries or rural areas resulting in usage of alternative methods such as intrathecal lidocaine administration after IV anesthesia. Its safety and efficacy as a method of euthanasia have not been investigated in the horse. Hypothesis/Objectives To investigate changes in mean arterial blood pressure and electrical activity of the cerebral cortex, brainstem, and heart during intrathecal administration of lidocaine. Our hypothesis was that intrathecal lidocaine affects the cerebral cortex and brainstem before affecting cardiovascular function. Animals Eleven horses requiring euthanasia for medical reasons. Methods Prospective observational study. Horses were anesthetized with xylazine, midazolam, and ketamine; and instrumented for recording of electroencephalogram (EEG), electrooculogram (EOG), brainstem auditory evoked response (BAER), and electrocardiogram (ECG). Physical and neurological (brainstem reflexes) variables were monitored. Mean arterial blood pressure was recorded throughout the study. Results Loss of cerebro‐cortical electrical activity occurred up to 226 seconds after the end of the infusion of lidocaine solution. Cessation of brainstem function as evidenced by a lack of brainstem reflexes and disappearance of BAER occurred subsequently. Undetectable heart sounds, nonpalpable arterial pulse, and extremely low mean arterial blood pressure supported cardiac death; a recordable ECG was the last variable to disappear after the infusion (300–1,279 seconds). Conclusions and Clinical Importance Intrathecal administration of lidocaine is an effective alternative method of euthanasia in anesthetized horses, during which brain death occurs before cardiac death.

Cerebral and brainstem electrophysiologic activity during euthanasia with pentobarbital sodium in horses.

Background An overdose of pentobarbital sodium administered IV is the most commonly used method of euthanasia in veterinary medicine. Determining death after the infusion relies on the observation of physical variables. However, it is unknown when cortical electrical activity and brainstem function are lost in a sequence of events before death. Hypothesis/Objectives To examine changes in the electrical activity of the cerebral cortex and brainstem during an overdose of pentobarbital sodium solution for euthanasia. Our testing hypothesis is that isoelectric pattern of the brain in support of brain death occurs before absence of electrocardiogram (ECG) activity. Animals Fifteen horses requiring euthanasia. Methods Prospective observational study. Horses with neurologic, orthopedic, and cardiac illnesses were selected and instrumented for recording of electroencephalogram, electrooculogram, brainstem auditory evoked response (BAER), and ECG. Physical and neurologic (brainstem reflexes) variables were monitored. Results Loss of cortical electrical activity occurred during or within 52 seconds after the infusion of euthanasia solution. Cessation of brainstem function as evidenced by a lack of brainstem reflexes and disappearance of the BAER happened subsequently. Despite undetectable heart sounds, palpable arterial pulse, and mean arterial pressure, recordable ECG was the last variable to be lost after the infusion (5.5–16 minutes after end of the infusion). Conclusions and Clinical Importance Overdose of pentobarbital sodium solution administered IV is an effective, fast, and humane method of euthanasia. Brain death occurs within 73–261 seconds of the infusion. Although absence of ECG activity takes longer to occur, brain death has already occurred.

Pain Management in Horses

There has been great progress in the understanding of basic neurobiologic mechanisms of pain, but this body of knowledge has not yet translated into new and improved analgesics. Progress has been made regarding pain assessment in horses, but more work is needed until sensitive and accurate pain assessment tools are available for use in clinical practice. This review summarizes and updates the knowledge concerning the cornerstones of pain medicine (understand, assess, prevent, and treat). It highlights the importance of understanding pain mechanisms and expressions to enable a rational approach to pain assessment, prevention, and management in the equine patient.