Diane M. Rhodes

Clinical and biochemical abnormalities in endurance horses eliminated from competition for medical complications and requiring emergency medical treatment: 30 cases (2005–2006)

OBJECTIVE To describe the clinical and clinicopathologic abnormalities in endurance horses eliminated from competition and requiring emergency medical treatment. DESIGN Retrospective study over a 2-year period (2005-2006). Ten horses that successfully completed the ride in 2006 were included for comparison. SETTING Temporary equine emergency field hospital. ANIMALS All horses (n=30) that were removed from endurance competition and treated for a metabolic abnormality were studied. INTERVENTIONS Horses were treated with IV fluids and analgesics. Monitoring included lab work (PCV, total protein, and electrolytes) and serial physical examinations. Statistical analysis included descriptive statistics and parametric and nonparametric comparisons (ANOVA, Friedmans test, and Kruskal-Wallis) where appropriate. MEASUREMENTS AND MAIN RESULTS The clinical diagnoses identified included colic, esophageal obstruction, poor cardiovascular recovery, myopathy, and synchronous diaphragmatic flutter. As a group, these sick horses had lower plasma chloride and potassium and higher total plasma protein concentrations as compared with 10 healthy horses that successfully completed the ride (P<0.05, <0.01, and <0.05 for chloride, potassium, and total protein, respectively). Horses with colic had a lower PCV as compared with horses with poor recovery and those with synchronous diaphragmatic flutter (P<0.05). All horses, including colics, were treated medically and discharged to owners. CONCLUSIONS Based on the results of this study, the prognosis for horses requiring emergency veterinary treatment after being removed from endurance competition (for metabolic reasons) appears to be good if horses are withdrawn from competition under the same criteria outlined in this study. Biochemical abnormalities tend to be mild and do not necessarily aid in delineating sick horses from successfully completing horses. None of the horses with gastrointestinal disease required abdominal surgery.

Application of the sodium dilution principle to calculate extracellular fluid volume changes in horses during dehydration and rehydration

OBJECTIVE To apply the principle of sodium dilution to calculate the changes in the extracellular fluid (ECF) volume (ECFV) and intracellular fluid volume (ICFV) that occur during dehydration and rehydration in horses. ANIMALS 8 healthy horses of various breeds. PROCEDURES Horses were dehydrated over 4 hours by withholding water and administering furosemide. Saline (0.9% NaCl) solution was administered IV during the next 2 hours (20 mL/kg/h; total 40 mL/kg). Horses were monitored for an additional hour following IV fluid administration. Initial ECFV was determined by use of multifrequency bioelectrical impedance analysis, and serum sodium concentration was used to calculate total ECF sodium content. Sodium and fluid volume losses were monitored and calculated throughout the study and used to estimate changes in ECFV and ICFV during fluid balance alterations. RESULTS Changes during dehydration and rehydration primarily occurred in the ECFV. The sodium dilution principle estimated an overexpansion of the ECFV beyond the volume of fluid administered, indicating a small contraction of the ICFV in response to fluid administration. Serum and urinary electrolyte changes were recorded and were consistent with those of previous reports. CONCLUSIONS AND CLINICAL RELEVANCE The sodium dilution principle provided a simple method that can be used to estimate the changes in ECFV and ICFV that occur during fluid administration. Results suggested an overexpansion of the ECFV in response to IV saline solution administration. The sodium dilution principle requires further validation in healthy and clinically ill horses, which could provide clinical applications similar to those in other species.

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

Estimation of acute fluid shifts using bioelectrical impedance analysis in horses.

BACKGROUND Multi-frequency bioelectrical impedance analysis (MF-BIA) has been used to evaluate extracellular fluid volume (ECFV), but not fluid fluxes associated with fluid or furosemide administration in horses. If able to detect acute changes in ECFV, MF-BIA would be useful in monitoring fluid therapy in horses. HYPOTHESIS The purpose of this study was to evaluate the ability of MF-BIA to detect acute fluid compartment changes in horses. We hypothesized that MF-BIA would detect clinically relevant (10-20%) changes in ECFV. ANIMALS Six healthy mares were used in the study. METHODS This is an original experimental study. Mares were studied in 3 experiments: (1) crystalloid expansion of normally hydrated subjects, (2) furosemide-induced dehydration followed by crystalloid administration, and (3) acute blood loss followed by readministration of lost blood. MF-BIA measurements were made before, during, and after each fluid shift and compared to known changes in volume calculated based on the intravenous fluids that were administered in addition to urinary fluid losses. Mean errors between MF-BIA estimated change and known volume change were compared using nonparametric analysis of variance. Estimated ECFV pre- and post-fluid administration similarly were compared. The level of statistical significance was set at P < .05. RESULTS Results of the study revealed a statistically significant change in ECFV and total body water during crystalloid expansion and dehydration. Statistically significant changes were not observed during blood loss and administration. Mean errors between MF-BIA results and measured net changes were small. CONCLUSIONS AND CLINICAL IMPORTANCE MF-BIA represents a practical and accurate means of assessing acute fluid changes during dehydration and expansion of ECFV using isotonic crystalloids with potential clinical applications in equine critical care.

Evaluation of potential predictor variables for PCR assay diagnosis of Anaplasma phagocytophilum infection in equids in Northern California

OBJECTIVE To identify clinical or clinicopathologic variables that can be used to predict a positive PCR assay result for Anaplasma phagocytophilum infection in equids. ANIMALS 162 equids. PROCEDURES Medical records were reviewed to identify equids that underwent testing for evidence of A phagocytophilum infection by PCR assay between June 1, 2007, and December 31, 2015. For each equid that tested positive (case equid), 2 time-matched equids that tested negative for the organism (control equids) were identified. Data collected included age, sex, breed, geographic location (residence at the time of testing), physical examination findings, and CBC and plasma biochemical analysis results. Potential predictor variables were analyzed by stepwise logistic regression followed by classification and regression tree analysis. Generalized additive models were used to evaluate identified predictors of a positive test result for A phagocytophilum. RESULTS Total lymphocyte count, plasma total bilirubin concentration, plasma sodium concentration, and geographic latitude were linear predictors of a positive PCR assay result for A phagocytophilum. Plasma creatine kinase activity was a nonlinear predictor of a positive result. CONCLUSIONS AND CLINICAL RELEVANCE Assessment of predictors identified in this study may help veterinarians identify equids that could benefit from early treatment for anaplasmosis while definitive test results are pending. This information may also help to prevent unnecessary administration of oxytetracycline to equids that are unlikely to test positive for the disease.