Fibrinogen heterogeneity in horses.

BACKGROUND: Fibrinogen heterogeneity has been observed in humans and can influence fibrinogen measurements when using the modified Clauss assay. We hypothesized that fibrinogen heterogeneity also exists in horses. OBJECTIVES: To determine whether fibrinogen heterogeneity exists in horses. ANIMALS: Five clinically healthy horses from the university equine teaching herd. METHODS: Presumed fibrinogen was purified from pooled citrated plasma and electrophoresis performed. The purified protein was subjected to Western blotting using sheep antiserum against human fibrinogen, and liquid chromatography-tandem mass spectrometry (LC-MS/MS). RESULTS: Gel electrophoresis of nonreduced equine purified protein yielded 2 protein bands (approximately 377 and 318 kDa) that corresponded with the molecular weights of human high molecular weight fibrinogen and low molecular weight fibrinogen fractions, respectively. Electrophoretograms of reduced purified protein, Western blots, and LC-MS/MS supported that the purified nonreduced protein bands were fibrinogen. CONCLUSION: Fibrinogen heterogeneity exists in horses.

In vitro effects of lactated Ringer's solution, hypertonic saline, hydroxyethyl starch, hypertonic saline/hydroxyethyl starch, and mannitol on thromboelastographic variables of canine whole blood.

OBJECTIVE: To assess the in vitro effects of crystalloid and colloid IV fluids on the thromboelastographic (TEG) variables of canine whole blood. DESIGN: In vitro experimental study. SETTING: Veterinary teaching hospital. ANIMALS: Twenty-two healthy dogs. INTERVENTION: Citrated whole blood samples collected from healthy dogs were diluted with 3.4% hypertonic saline (HTS 3.4), 7% hypertonic saline (HTS 7), and 20% mannitol at 8% and 16% dilutions; hydroxyethyl starch 130/0.4 (HES 130/0.4) at 16% dilution; lactated Ringer's solution (LRS) at 16%, 33%, and 66% dilutions; and HTS 7-HES 130/0.4 at 25% and 50% dilutions. Kaolin-activated TEG analysis was concurrently performed on diluted and control (undiluted) samples. MEASUREMENTS AND MAIN RESULTS: Dilution of canine whole blood with LRS compared to control reduced α angle and MA at both 33% (P = 0.009 and P = 0.011, respectively) and 66% dilution (P < 0.001 and P < 0.001, respectively), and prolonged K time at 66% dilution (P = 0.003). At 16% dilution, HTS 3.4, prolonged R time (P = 0.007), while mannitol, a fluid iso osmolar to HTS 3.4, prolonged K time (P = 0.006), reduced α angle (P < 0.001), MA (P = 0.046), and LY60 (P = 0.015). At 8% dilution, HTS 7, a fluid of high osmolarity and tonicity, prolonged R time (P = 0.009) and reduced MA (P = 0.015), while all measured TEG variables were altered at the 16% dilution (P < 0.01 for all variables). HES 130/0.4 reduced α angle (P = 0.031) and MA (P = 0.001) and increased LY60 (P < 0.001) at 16% dilution. Comparing different fluid types, HES 130/0.4 and HTS 3.4 had no to minor, mannitol intermediate, and HTS 7 profound effects on TEG variables (P < 0.05) when compared to LRS at the same dilution. CONCLUSIONS: In vitro dilution of canine whole blood with commonly used IV fluids leads to thromboelastographic changes consistent with hypocoagulability in a dose dependent manner for all fluid types tested. Viscoelastic changes are also influenced by fluid characteristics, specifically tonicity and osmolarity.

Anti-inflammatory effects of a p38 MAP kinase inhibitor, doramapimod, against bacterial cell wall toxins in equine whole blood.

Doramapimod (BIRB-796-BS), is an anti-inflammatory compound, acting through p38 MAPK inhibition, but its anti-inflammatory effects have not previously been studied in the horse. Whole blood aliquots from healthy horses diluted 1:1 with cell culture medium were incubated for 21 h with 1 µg/ml of lipopolysaccharide (LPS), lipoteichoic acid (LTA) or peptidoglycan (PGN) in the presence of increasing concentrations of doramapimod (3 × 10-8 M to 10-5 M). Cell bioassays were used to measure TNF-α and IL-1ß activity. Doramapimod significantly and potently inhibited TNF-α and IL-1ß activity induced by all three bacterial toxins. There was no significant difference in IC50 or maximum inhibition of TNF-α or IL-1ß production between any of the toxins. Maximum inhibition of IL-1ß was higher than that of TNF-α for all toxins, and this difference was significant for LPS (P = 0.04). Doramapimod was a potent inhibitor of TNF-α and IL-1ß for inflammation induced by LPS, LTA and PGN, with potency much greater than that of other drugs previously tested using similar methods.

Clinical use of plasma lactate concentration. Part 1: Physiology, pathophysiology, and measurement.

OBJECTIVE: To review the current literature with respect to the physiology, pathophysiology, and measurement of lactate. DATA SOURCES: Data were sourced from veterinary and human clinical trials, retrospective studies, experimental studies, and review articles. Articles were retrieved without date restrictions and were sourced primarily via PubMed, Scopus, and CAB Abstracts as well as by manual selection. HUMAN AND VETERINARY DATA SYNTHESIS: Lactate is an important energy storage molecule, the production of which preserves cellular energy production and mitigates the acidosis from ATP hydrolysis. Although the most common cause of hyperlactatemia is inadequate tissue oxygen delivery, hyperlactatemia can, and does occur in the face of apparently adequate oxygen supply. At a cellular level, the pathogenesis of hyperlactatemia varies widely depending on the underlying cause. Microcirculatory dysfunction, mitochondrial dysfunction, and epinephrine-mediated stimulation of Na+ -K+ -ATPase pumps are likely important contributors to hyperlactatemia in critically ill patients. Ultimately, hyperlactatemia is a marker of altered cellular bioenergetics. CONCLUSION: The etiology of hyperlactatemia is complex and multifactorial. Understanding the relevant pathophysiology is helpful when characterizing hyperlactatemia in clinical patients.

Clinical use of plasma lactate concentration. Part 2: Prognostic and diagnostic utility and the clinical management of hyperlactatemia.

OBJECTIVE: To review the current literature pertaining to the use of lactate as a prognostic indicator and therapeutic guide, the utility of measuring lactate concentrations in body fluids other than blood or plasma, and the clinical management of hyperlactatemia in dogs, cats, and horses. DATA SOURCES: Articles were retrieved without date restrictions primarily via PubMed, Scopus, and CAB Abstracts as well as by manual selection. HUMAN AND VETERINARY DATA SYNTHESIS: Increased plasma lactate concentrations are associated with increased morbidity and mortality. In populations with high mortality, hyperlactatemia is moderately predictive in identifying nonsurvivors. Importantly, eulactatemia predicts survival better than hyperlactatemia predicts death. Consecutive lactate measurements and calculated relative measures appear to outperform single measurements. The use of lactate as a therapeutic guide has shown promising results in people but is relatively uninvestigated in veterinary species. Increased lactate concentrations in body fluids other than blood should raise the index of suspicion for septic or malignant processes. Management of hyperlactatemia should target the underlying cause. CONCLUSION: Lactate is a valuable triage and risk stratification tool that can be used to separate patients into higher and lower risk categories. The utility of lactate concentration as a therapeutic target and the measurement of lactate in body fluids shows promise but requires further research.

Treatment of supraventricular tachycardia in a horse.

OBJECTIVE: To describe the treatment of persistent supraventricular tachycardia (SVT) in a young horse in endurance training. CASE SUMMARY: A 6-year-old Arab gelding in endurance training presented for a dysrhythmia and decreased performance. SVT was diagnosed and conversion to a normal sinus rhythm was achieved following administration of a constant rate infusion of amiodarone. However, reversion to SVT occurred shortly after initiation of ridden exercise. A second attempt to convert the dysrhythmia with amiodarone failed, but normal sinus rhythm was achieved with transvenous electrical cardioversion (TVEC). Postmortem examination of the heart revealed extensive fibrous replacement of most of the left atrial myocardium; these changes likely provided the structural substrate for the dysrhythmia. The underlying cause of the fibrosis was not identified. NEW OR UNIQUE INFORMATION PROVIDED: SVT is a form of supraventricular tachyarrhythmia rarely diagnosed in the horse. A recent report has described sudden death of a horse following attempted conversion of SVT with oral flecainide acetate. In the present report, we describe short-term conversion of SVT in a horse using intravenous amiodarone with no significant adverse effects. When the dysrhythmia recurred, the animal was donated for teaching purposes and conversion was achieved with TVEC. Normal sinus rhythm persisted for 2 weeks until the horse was euthanized for postmortem evaluation of the heart. Intravenous amiodarone or TVEC could be considered as treatments for supraventricular tachyarrhyhmias other than atrial fibrillation in the horse.

The Equine Neonatal Central Nervous System: Development and Diseases.

Neonatal encephalopathy is the most common neurologic condition affecting newborn foals and shares similarities with perinatal asphyxia syndrome of human infants. In many cases of neonatal encephalopathy there is no obvious episode of acute or chronic hypoxia and other mechanisms likely play a role in the pathogenesis. Increased concentrations of neuroactive progestagens are found in affected foals; whether these molecules are protective, as has been suggested, or play a role in the pathogenesis is unknown. Neurologic diseases other than neonatal encephalopathy affect foals occasionally and should be considered when evaluating sick foals with clinical signs of neurologic dysfunction.

Use of viscoelastic coagulation testing to monitor low molecular weight heparin administration to healthy horses.

OBJECTIVES: To evaluate the utility of thromboelastography (TEG) and Sonoclot analyses to monitor the effects of low molecular weight heparin (LMWH) administration to healthy horses. DESIGN: Randomized crossover study. SETTING: Large animal veterinary teaching hospital. ANIMALS: Six adult mixed breed healthy mares. INTERVENTIONS: LMWH (dalteparin) was administered (50 U/kg subcutaneously) either every 12 or 24 h for 3 consecutive days. Blood samples were collected before LMWH administration and then at selected time points for analysis. Thromboelastography derived R-time (R), K-time (K), angle (ANG), and maximum amplitude (MA), and Sonoclot activated clot time (ACT), clot rate (CR), and platelet function (PF) were measured in whole blood 30 min after sample collection. Change (Δ) and percentage change (%Δ) from baseline of each TEG and Sonoclot variable were subsequently calculated. Anti-factor Xa activity and activated partial thromboplastin time (aPTT) were assayed in harvested plasma. The association between anti-factor Xa activity and TEG and Sonoclot (measured and calculated) variables was assessed by calculating correlation coefficients and multiple regression analysis. The ability of measured and calculated TEG and Sonoclot variables to predict when anti-factor Xa activity fell below suggested thromboprophylactic levels was assessed using receiver operating characteristic curve analysis. MEASUREMENTS AND MAIN RESULTS: The correlation between aPTT and anti-factor Xa activity was weak (r = 0.343). Changes in TEG and Sonoclot variables following LMWH administration were consistent with hypocoagulation. All measured and calculated TEG variables were significantly correlated with anti-factor Xa activity. Sonoclot ACT, ΔACT, CR, ΔCR, and %ΔCR were also significantly correlated with anti-factor Xa activity. TEG ΔR and %ΔR best predicted anti-factor Xa activity below the suggested thromboprophylactic level. CONCLUSIONS: Although correlations were modest, serial measurement of TEG variables may be used to monitor LMWH therapy in horses; however, further research is required in sick horses.

Pharmacodynamics of multi-dose low molecular weight heparin in healthy horses.

OBJECTIVES: To compare the pharmacodynamics of once daily and twice daily administration of low molecular weight heparin (LMWH) administration in horses. STUDY DESIGN: Randomized cross over study. ANIMALS: Adult mixed breed healthy mares (n = 6). METHODS: LMWH (dalteparin) was administered (50 U/kg subcutaneously) either every 12 or 24 hours for 3 consecutive days. Anti-factor Xa activity was measured before and at select time points after LMWH administration. Packed cell volume (PCV), platelet count, partial thromboplastin time (PTT), and anti-thrombin (AT) activity were monitored throughout the study. RESULTS: No changes in PCV, platelet count, or AT activity were detected with either frequency of daily LMWH administration. Values for PTT increased throughout the study but never exceeded the normal reference interval. Anti-factor Xa activity was maintained within or above the suggested thromboprophylactic range (0.1-0.2 U/mL) when LMWH was administered twice daily, but fell below this range ≈ 16 hours after administration when given once daily. For both once and twice daily LMWH administration, the area under the curve was significantly greater after the last dose of LMWH when compared to the first dose. CONCLUSIONS: Administration of LMWH once or twice daily for 3 consecutive days appears to be safe in healthy adult horses. Anti-factor Xa activity was maintained within or above the suggested thromboprophylactic range for 24 hours with twice daily LMWH administration but not with once daily administration.

Liver lobe torsion in six horses.

CASE DESCRIPTION: 6 horses were determined to have torsion of a liver lobe at 4 referral institutions over a 21-year period. CLINICAL FINDINGS: Clinical findings were nonspecific but often included signs of marked inflammation. Two of the 6 horses were examined because of colic, and 2 were assessed because of peritonitis that failed to respond to treatment; the remaining 2 horses were examined because of nonspecific clinical signs that included inappetence, lethargy, and weight loss. The results of laboratory tests were widely variable, and values for liver enzyme activities were typically within reference limits or only mildly increased. Most affected horses had markedly increased peritoneal nucleated cell counts. TREATMENT AND OUTCOME: Exploratory laparotomy and resection of the affected liver lobe was performed in 5 horses. Three of those patients survived to discharge. CLINICAL RELEVANCE: Results suggested that diagnosis of liver lobe torsion in horses may be difficult because clinical signs and results of laboratory testing are nonspecific and variable. Most affected horses had markedly abnormal peritoneal fluid. The prognosis for hepatic lobe torsion can be good, and early surgical correction is expected to improve outcome.

Comparison of three point-of-care blood glucose meters for use in adult and juvenile alpacas.

OBJECTIVE: To compare the performance of 3 point-of-care glucose meters in adult and juvenile alpacas with that of a laboratory-based analyzer. DESIGN: Evaluation study. ANIMALS: 35 adult alpacas and 21 juvenile alpacas. PROCEDURES: Whole blood samples obtained via jugular venipuncture were tested with all 3 point-of-care glucose meters; plasma samples were also tested with 1 of those meters. Glucose concentrations determined by use of the point-of-care meters were compared with results from the laboratory-based analyzer. RESULTS: Plasma glucose concentrations determined by use of the laboratory-based analyzer ranged from 36 to 693 mg/dL. Over the entire range of glucose concentrations tested, the Lin concordance correlation coefficient (agreement) was significant and excellent for all comparisons. Concordance decreased for 1 glucometer when testing whole blood samples over a narrower range of glucose concentrations (50 to 200 mg/dL). Bias was typically small (< 10 mg/dL) for 3 of the 4 comparisons but considerable for 1 meter with the use of whole blood. The limits of agreement were wide for all comparisons over the entire range of glucose concentrations tested but decreased to within acceptable limits when the narrower glucose range (50 to 200 mg/dL) was analyzed for 3 of the comparisons. For samples with a PCV < 25%, bias and the limits of agreement were greater for one of the meters tested. CONCLUSIONS AND CLINICAL RELEVANCE: Discrepancies between point-of-care glucose meters and reference techniques can be considerable in alpacas, emphasizing the importance of assessing individual meter performance in a target population.

Assessment of a point-of-care lactate monitor in emergency admissions of adult horses to a referral hospital.

BACKGROUND: Blood lactate concentration [LAC] is considered a useful indicator of disease severity in horses. Agreement of point-of-care (POC) lactate monitors with laboratory standards has not been established for clinically abnormal horses. HYPOTHESIS: It was hypothesized that results from a POC lactate monitor would be in agreement with a laboratory-based measurement of [LAC]. ANIMALS: The study included adult horses presented for emergency evaluation. METHODS: A prospective observational study was performed. [LAC] was measured with whole blood (AWB) and plasma (APL) by means of a POC monitor (Accutrend) and compared with results from whole blood measured by a laboratory blood gas analyzer (NOVA). RESULTS: Samples from 221 horses were used to compare the 2 lactate measurement techniques. Agreement (p +/- SE) was closest between APL and NOVA (0.97 +/- 0.01); an average observed difference of 0.15 +/- 0.89 (mean +/- SD) and 95% limits of agreement (LOA) -1.89, 1.59 also were found. Agreement was preserved and 95% LOA further decreased in horses with NOVA [LAC] of <5 mM and PCV <40%. Agreement was modest when testing whole blood samples on the POC monitor with increased 95% LOA. CONCLUSIONS AND CLINICAL IMPORTANCE: Results indicate close agreement between NOVA and the POC monitor when [LAC] was measured with plasma. Results were less consistent at higher [LAC] but sufficiently reliable to follow trends. Although whole blood may be used with the POC monitor to identify clinically important hyperlactatemia, results may be insufficiently reliable to monitor trends.

Trauma with neurologic sequelae.

Spinal cord injury (SCI) in horses may arise from rearing and falling backward, collisions, kicks, and slipping. The pathophysiology of SCI comprises a primary mechanical injury followed by a cascade of secondary events. These secondary events include microvascular ischemia, oxidative stress, excitotoxicity, ion dysregulation, and inflammation. It is often the severity of secondary injury that limits the restoration of neurologic function. Clinical signs after SCI depend on the location of the lesion and the relative amount of damage to the gray and white matter. Acute management of SCI should include optimization of oxygen delivery to the injured tissues. A brief discussion of some of the more promising medical therapies that have been investigated in human medicine and may be applicable to equine patients is included.

Severe acute rhabdomyolysis associated with Streptococcus equi infection in four horses.

Four Quarter Horses (9 months to 7 years of age) with submandibular lymphadenopathy and firm muscles (palpation of which elicited signs of pain) were evaluated; in general, the horses had a stiff gait, and 3 horses became recumbent. Streptococcus equi was cultured from aspirates of lymph nodes or samples of purulent material collected from the auditory tube diverticula. Once the horses were recumbent, their condition deteriorated rapidly despite aggressive antimicrobial and antiinflammatory treatment, necessitating euthanasia within 24 to 48 hours. One horse did not become recumbent and recovered completely. Among the 4 horses, common clinicopathologic findings included neutrophilia, hyperfibrinogenemia, and high serum activities of creatine kinase and aspartate aminotransferase. Necropsies of the 3 euthanatized horses revealed large, pale areas most prominent in the semimembranosus, semitendinosus, sublumbar, and gluteal muscles that were characterized histologically by severe acute myonecrosis and macrophage infiltration of necrotic myofibers. Streptococcus equi was identified in sections of affected muscle by use of immunofluorescent stains for Lancefield group C carbohydrate and S. equi M protein. In the 4 horses of this report, acute severe rhabdomyolysis without clinical evidence of muscle atrophy or infarction was associated with S. equi infection; rhabdomyolysis was attributed to either an inflammatory cascade resembling streptococcal toxic shock or potentially direct toxic effects of S. equi within muscle tissue.