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Objective: To determine the effect of xylazine on intracranial pressure (ICP) in standing compared to isoflurane-anesthetized horses., Design: Prospective, crossover study design., Setting: University Teaching Hospital., Animals: Six adult horses donated to the University. Horses were determined to be healthy via physical examination, complete blood count, and neurological evaluation., Interventions: Horses were anesthetized, maintained on isoflurane in oxygen in left lateral recumbency, and ventilated to normocapnia. Horses were instrumented for intraparenchymal measurement of ICP, invasive blood pressure, pulse oximetry, and end tidal gas analyzer. Xylazine 1 mg/kg was administered IV and ICP, systolic arterial pressure, mean arterial pressure (MAP), diastolic arterial pressure, and heart rate were recorded and cerebral perfusion pressure (CPP) was calculated for the following 15 minutes. Twenty-four to 36 hours following anesthetic recovery, xylazine 1 mg/kg was administered IV and ICP, heart rate, and Doppler blood pressure (BPdop) on the tail were monitored for 15 minutes., Measurements and Main Results: There was a decrease in ICP following administration of xylazine in anesthetized horses (P < 0.003) but not standing horses (P = 0.227). There was an increase in systolic arterial pressure, MAP, diastolic arterial pressure (P < 0.001), and BPdop (P = 0.001) following administration of xylazine. As a result, CPP increased in anesthetized horses (P < 0.03). There was a negative association between ICP and MAP in anesthetized horses (P = 0.007) but not ICP and BPdop conscious horses (P = 0.379)., Conclusions: Administration of xylazine to anesthetized horses resulted in an increased CPP due to decreased ICP with concurrent increased MAP. Administration of xylazine to standing horses did not result in a change in ICP. However, with the increase in BPdop found in awake horses, it is likely that CPP would also increase in awake horses following xylazine administration., (© Veterinary Emergency and Critical Care Society 2021.)

Objective: To determine whether an association exists between direct intracranial pressure (ICP) measurement and ultrasonographic measurement of optic nerve sheath diameter (ONSD) in anesthetized and standing horses., Design: Cross-sectional study performed on a convenience sample of healthy adult horses., Setting: University teaching hospital., Animals: Eight adult horses donated to the University. Enrolled horses were free of abnormalities on physical examination, CBC, neurological evaluation, and ophthalmological examination., Measurements and Main Results: Horses were anesthetized in lateral recumbency for placement of an ICP transducer. Three head positions (neutral, elevated, and lowered) were used to alter ICP. ICP and ONSD in 2 directions (D1 and D2) were recorded at 5 and 10 minutes after position change to elevated and lowered. ICP and ONSD measurements were repeated in standing sedated horses 24-36 hours after recovery from anesthesia. Linear regressions were performed with ICP as the dependent variable and ONSD as the independent variable by head position and times. Linear regressions were also performed for change from neutral under anesthesia, with ONSD as the independent variable and ICP as the dependent variable, by head position and times. Significance was set at P < 0.05. There was a moderate association between ICP and ONSD in horses with head lowered at 5 and 10 minutes (R 2 values = 63%-78%) and weak association in head elevated at 10 minutes (R 2 values = 56%-63%). There was a weak association between change from neutral ICP and change from neutral ONSD in the elevated anesthetized position at 10 minutes for summed D1 + D2 (R 2  = 33%)., Conclusions: Consistent associations between direct ICP and ONSD in anesthetized or standing horses were not observed. This inconsistency limits the clinically utility of transpalpebral ultrasonographic ONSD measurement for ICP monitoring in horses., (© Veterinary Emergency and Critical Care Society 2021.)

Objective: Objectives of this study were to compare the ability of serial thromboelastography, Sonoclot, and traditional coagulation panels to detect coagulopathies associated with disease category, systemic inflammatory response syndrome (SIRS), complications, and nonsurvival in horses with gastrointestinal disease., Design: Prospective clinical evaluation., Setting: University referral hospital., Animals: One hundred twenty-one horses admitted as emergencies for gastrointestinal disease and 28 healthy adult horses., Intervention: Blood samples were collected ≤4 times from emergency horses (admission and if surviving and hospitalized on days 2-4) and once from healthy horses. Thromboelastography (with and without tissue factor activation), Sonoclot, and a traditional coagulation panel were performed on each sample., Measurements and Main Results: Emergency horses were grouped based on disease category (ie, nonstrangulating medical, nonstrangulating surgical, strangulating, and inflammatory), survival to discharge, SIRS at admission, requirement for exploratory celiotomy, ileus, diarrhea, fever, thrombophlebitis, and laminitis. Changes over time were evaluated individually and compared between disease groups. Horses with gastrointestinal disease had dynamic changes in coagulation and fibrinolysis during the first 4 days of hospitalization that were correlated with disease category, SIRS, complications, and fatality. The multivariate logistic regression model for nonsurvival included activated partial thromboplastin time on day 2 and LY30 on day 3 (overall model significance P < 0.0001). The odds of nonsurvival were 23.75 times higher if activated partial thromboplastin time was >85.6 s on day 2 and 9.38 times higher if LY30 was >1% on day 3., Conclusions: Horses with gastrointestinal disease have activation of coagulation and fibrinolysis. Magnitude of change in these parameters is small and predictive value moderate, making application of these tests to direct therapy in clinical patients difficult. Effect of specific treatments (eg, surgery) on these tests and coagulation has not been determined. Further studies are required to determine if these tests could be used to help monitor response to treatment in individual animals or specific disease states., (© Veterinary Emergency and Critical Care Society 2013.)

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., (© Veterinary Emergency and Critical Care Society 2013.)

Objectives: To develop a standardized technique for thrombelastography (TEG) analysis in healthy adult horses, with and without the ex vivo addition of tissue factor (TF) as an activator. To determine reference intervals for TEG parameters in the horse, and to determine if traditional coagulation tests correlate with TEG., Design: Prospective, observational., Setting: Veterinary teaching hospital., Animals: Twenty-six healthy adult horses., Interventions: None., Measurements and Main Results: Thrombelastography with (TF-TEG) and without (TEG) the addition of TF performed by 4 operators. Coagulation profiles (prothrombin time, activated partial thromboplastin time, platelet count, fibrinogen, antithrombin, and fibrinogen degradation products) were assessed in a subset of horses. Mean values (SD) for TEG parameters in healthy horses were: reaction time (R)=17.0 minutes (3.0 min), K time (K)=5.8 minutes (2.3 min), clotting rate (Ang)=42 degrees (14 degrees ), maximum clot strength (maximum amplitude [MA])=60.3 mm (5.7 mm), CL30=97.0% (2.0%), LY30=0.8% (0.6%), CL60=92% (5.9%), LY60=3.2% (2.5%). Mean values (SD) for TF-TEG parameters were: R-TF=6.6 minutes (1.4 min), K-TF=3.1 minutes (1.0 min), Ang-TF=50.9 degrees (9 degrees ), MA-TF=62.3 mm (5.1 mm), CL30-TF=97.8% (1.6%), LY30-TF=0.6% (0.5%), CL60-TF=90.8% (4.2%), and LY60-TF=3.6% (1.9%). The addition of TF decreased R and K and increased Ang. TF-TEG had a narrower SD for R, K, Ang, CL60 and LY60 compared with TEG. Interoperator differences were reduced by the addition of TF. Regression analysis indicated a positive relationship between MA and fibrinogen concentrations (P=0.02) and R-TF time and prothrombin time (P=0.03)., Conclusion: TF-TEG using the described protocol may minimize variability in data obtained across institutions or users. However, due to the variability associated with different operators, it is recommended that each laboratory set up individual reference intervals with the personnel who will perform the assay, and that the assay protocols and data obtained are compared on a regular basis.