Amie Koenig

The effect of unfractionated heparin on thrombelastographic analysis in healthy dogs

OBJECTIVE To determine the effect of single and multiple doses of SQ heparin (200 U/kg) on the thrombelastogram of healthy dogs. DESIGN Prospective study. SETTING University research facility. ANIMALS Six random-source female dogs. INTERVENTIONS Baseline parameters, including a CBC with platelet count, prothrombin time, activated partial thromboplastin time (aPTT), and antithrombin were performed. Thrombelastography (TEG) and aPTT were performed hourly for 12 hours after unfractionated heparin dosing (200 U/kg, SQ). Anti-Xa activity was assayed at 0, 3, 6, and 8 hours. Heparin was then administered every 8 hours for 3 days. The sampling protocol on Day 4 was identical to Day 1. MEASUREMENTS AND MAIN RESULTS On Day 1, percentage change from baseline for TEG parameter R, as well as absolute values of K, angle, and maximum amplitude (MA) were evaluated. Statistically significant (P<0.01) prolongation of the R time and a decrease in angle and MA was seen in all dogs by hour 3. R and MA were unmeasurable for most dogs between 3 and 5 hours. All TEG tracings returned to baseline by 12 hours. Day 4 TEG tracings mimicked those on Day 1. Only 1 dog achieved aPTT values outside the reference interval on both days. Anti-Xa activity levels increased on Day 4 but not on Day 1. Based on post hoc in vitro analysis, prolongation of R time occurred at plasma heparin levels as low as 0.075 U/mL, well below the lower limit of detection of the anti-Xa activity level assay. CONCLUSIONS Administration of SQ heparin results in progressive changes in the TEG tracing, with maximal change occurring 3-5 hours after dosing. The extensive prolongation of the R time also indicates that TEG may be too sensitive and limits its utility as a monitoring tool for unfractionated heparin therapy.

The effects of cytochalasin D and abciximab on hemostasis in canine whole blood assessed by thromboelastography and the PFA-100® platelet function analyzer system.

The selective inhibition of platelet function in whole blood coagulation testing may allow insights into the nature of hypercoagulability in dogs with critical illness. To determine the effects of cytochalasin D and abciximab on hemostatic parameters in canine citrated whole blood, an in-vitro study was designed using thromboelastography (TEG) and a platelet function analyzer (PFA-100®). 8 clinically healthy mixed breed dogs donated blood that was anticoagulated with 3.2% sodium citrate in a 9:1 blood-to-citrate ratio. Addition of cytochalasin D to citrated whole blood from 6 dogs at concentrations ranging from 0 µg/ml to 10 µg/ml caused a maximal reduction of TEG maximum amplitude (MA) at a concentration of 7.5 µg/ml (52.7 ± 4.3 to 14.3 ± 7.8 mm). Addition of abciximab to canine citrated whole blood at concentrations of either 20 µg/ml or 40 µg/ml did not affect the TEG tracing; however, addition of abciximab to citrated canine whole blood at concentrations of 10 µg/ml and 20 µg/ml significantly prolonged PFA-100 closure times (72.5 ± 15 to 149.2 ± 91 sec and 275.6 ± 54 sec, respectively, P < 0.04). Inhibition of canine platelet function by cytochalasin D is demonstrated by TEG, but abciximab did not change TEG tracings. Abciximab does, however, inhibit platelet aggregation under shear stress as measured by the PFA-100. Inhibition of canine platelet function with cytochalasin D may allow further TEG studies in dogs with clinical disease.

Comparison of an implantable telemetry device and an oscillometric monitor for measurement of blood pressure in anaesthetized and unrestrained green iguanas (Iguana iguana).

OBJECTIVE The objective of this study was to compare an implanted direct blood pressure monitor and a non-invasive oscillometric unit for use in anesthetized and awake green iguanas. STUDY DESIGN Prospective experimental trial. ANIMALS Four male and four female adult green iguanas (Iguana iguana) weighing 1833 +/- 534 g. METHODS For each animal, the carotid artery was surgically exposed and the catheter tip of the pressure transducer was placed in the aortic arch. Non-invasive blood pressure was measured using a cuff over the left femoral region. Pulse rate, respiratory rate and arterial blood pressure (ABP) measurements were taken every 5 minutes. Direct ABP measurements consisted of recording numerical values and graphic output. Simultaneous direct and indirect measurements were repeated in awake animals. RESULTS The oscillometric device failed to provide a reading in over 80% of attempts, and failed to provide readings that correlated with direct measurements. The implanted direct transducer was capable of detecting blood pressures throughout all ABP ranges examined. CONCLUSIONS The implantable transducer was a reliable means of determining blood pressure in this study, while the oscillometric device was unreliable and often failed to provide any reading. CLINICAL RELEVANCE We do not recommend using the oscillometric device as described in a research or clinical setting for green iguanas. The advantages of an implantable device include the ability to monitor awake and anesthetized subjects remotely and continuously. These monitors are small, biocompatible and function across a wide range of ABP.

Evaluation of a point-of-care coagulation analyzer (Abaxis VSPro) for identification of coagulopathies in dogs.

Objective To evaluate the ability of the Abaxis VSPro, a point-of-care analyzer that measures prothrombin time (PT) and activated partial thromboplastin time (aPTT), to identify dogs with coagulopathies caused by administration of anticoagulants. Setting Veterinary teaching hospital. Animals Six healthy adult dogs that are part of a preexisting research colony. One dog was not included in the warfarin portion of the study. Measurements and Main Results Unfractionated heparin (UFH, 50 U/kg IV once then 300 U/kg SQ q 8 h) was administered to prolong aPTT. Citrated whole blood was used for PT and aPTT analyses with the VSPro and were run in duplicate. The VSPro results were compared to PT and aPTT measured in plasma with a standard benchtop coagulometer (AMAX Destiny). A washout period of at least 24 hours followed. Once dogs had normal PT and aPTT values, warfarin was administered (0.25–0.30 mg/kg PO) once then (0.15 mg/kg PO) as needed up to every 12 hours to prolong PT values. Seventy separate samples were evaluated for PT and 73 samples for aPTT. Pearson correlation coefficients (PCC) for replicate VSPro measures of PT and aPTT were 0.941 and 0.891, respectively (P < 0.001). The PCC between VSPro and AMAX was 0.578 for PT and of 0.865 for PTT (P < 0.001). Receiver operating characteristic (ROC) analysis indicated a maximum sensitivity and specificity for diagnosis of coagulopathy (by AMAX) at VSPro PT value of 21.6 seconds (sensitivity 72%, specificity 86%) and a maximum sensitivity and specificity at VSPro aPTT of 105.3 seconds (sensitivity 93%, specificity 89%). The positive predictive value for PT and aPTT were 84% and 89%, respectively. Conclusions The Abaxis VSPro showed acceptable correlation with clinical laboratory tests, and is a useful POC device for identification of animals with abnormalities in PT or aPTT.OBJECTIVE To evaluate the ability of the Abaxis VSPro, a point-of-care analyzer that measures prothrombin time (PT) and activated partial thromboplastin time (aPTT), to identify dogs with coagulopathies caused by administration of anticoagulants. SETTING Veterinary teaching hospital. ANIMALS Six healthy adult dogs that are part of a preexisting research colony. One dog was not included in the warfarin portion of the study. MEASUREMENTS AND MAIN RESULTS Unfractionated heparin (UFH, 50 U/kg i.v. once then 300 U/kg s.q. q 8 h) was administered to prolong aPTT. Citrated whole blood was used for PT and aPTT analyses with the VSPro and were run in duplicate. The VSPro results were compared to PT and aPTT measured in plasma with a standard benchtop coagulometer (AMAX Destiny). A washout period of at least 24 hours followed. Once dogs had normal PT and aPTT values, warfarin was administered (0.25-0.30 mg/kg p.o.) once then (0.15 mg/kg p.o.) as needed up to every 12 hours to prolong PT values. Seventy separate samples were evaluated for PT and 73 samples for aPTT. Pearson correlation coefficients (PCC) for replicate VSPro measures of PT and aPTT were 0.941 and 0.891, respectively (P < 0.001). The PCC between VSPro and AMAX was 0.578 for PT and of 0.865 for PTT (P < 0.001). Receiver operating characteristic (ROC) analysis indicated a maximum sensitivity and specificity for diagnosis of coagulopathy (by AMAX) at VSPro PT value of 21.6 seconds (sensitivity 72%, specificity 86%) and a maximum sensitivity and specificity at VSPro aPTT of 105.3 seconds (sensitivity 93%, specificity 89%). The positive predictive value for PT and aPTT were 84% and 89%, respectively. CONCLUSIONS The Abaxis VSPro showed acceptable correlation with clinical laboratory tests, and is a useful POC device for identification of animals with abnormalities in PT or aPTT.

Sonoclot® Evaluation of Single‐ and Multiple‐Dose Subcutaneous Unfractionated Heparin Therapy in Healthy Adult Dogs

BACKGROUND Heparin therapy is difficult to monitor due to variation in animal response. While laboratory measurements of activated partial thromboplasin time (aPTT) and Anti-Xa activity (AXA) accurately describe heparin effect, their availability is limited. HYPOTHESIS Sonoclot analysis would be as sensitive as AXA and aPTT to monitor effects of unfractionated heparin (UFH) in healthy adult dogs. ANIMALS Six adult mixed-breed dogs. METHODS A prospective study design was employed. On day 1, baseline samples were collected (CBC, PT, aPTT, and Sonoclot), and UFH (300 U/kg SC) was administered to 6 dogs following an IV loading dose of 50 U/kg. Sonoclot and aPTT were performed hourly for 12 hours. AXA was assayed at hours 3, 6, 9, and 12. UFH (300 U/kg q8 h SC) was administered at 12 hours, and subsequently (q8 h) for 2 additional days. On day 4, a final dose of UFH was administered, and a sampling protocol identical to day 1 was performed. RESULTS Sonoclot activated clotting time (ACT) and clot rate (CR) correlated with AXA (R = 0.69, R = 0.65, respectively, P < .001), although to a lesser degree than aPTT (R = 0.75, P < .001). Linear regression using ACT and CR as covariates indicated a stronger correlation with AXA (R = 0.73, P < .001). ACT values strongly correlated with aPTT (R = 0.87, P < .001). CONCLUSIONS AND CLINICAL IMPORTANCE Administration of UFH to healthy dogs results in progressive changes in Sonoclot values. AXA was correlated with a combination of ACT and CR and with aPTT. Sonoclot may play a role in monitoring UFH therapy; however, prospective studies evaluating its utility in clinical cases are warranted.

Effects of rest temperature, contact activation, and sample technique on canine thrombelastography

Objective To determine the effects of rest temperature, contact activation (CA), and sample collection technique on thrombelastography (TEG) using canine whole blood. Design Prospective, experimental study. Setting University-based research facility. Animals Twelve healthy, adult, mixed-breed dogs. Interventions Blood was collected by jugular venipuncture. Tubes containing 3.2% sodium citrate, with and without 75 μg/mL corn trypsin inhibitor (CTI), were filled by vacuum. Samples rested for 30 minutes at 3 temperatures: 37°C, room temperature (RT, 20–22°C), or warmed to 37°C 5 minutes prior to analysis (prewarmed). Samples were analyzed at 37°C. CTI-treated samples were analyzed with and without 1:50,000 tissue factor (TF) as activator. Six dogs were also tested similarly using a needle/syringe collection technique. Measurement and Main Results Prewarmed samples exhibited greater MA compared to RT (55.5 ± 7.2 mm vs. 53.5 ± 6.0, P< 0.05), while 37°C samples exhibited a steeper angle (56.7 ± 10.4°C vs. 52.4 ± 8.6°C) and greater MA (55.9 ± 7.5 mm vs. 53.5 ± 6.0 mm) than RT samples (both P< 0.05). CTI-treated samples were hypocoagulable (R time 45 min [7.5–56.8 min], angle 8.2°C [5.1–42.5°C], MA 29.2 ± 9.7 mm, P< 0.001), with TF activation returning all but the angle (42.5 ± 7.6°C) to values similar to citrated samples (angle = 56.7 ± 10.4°C, P = 0.017). Collection using a syringe/needle method revealed a shorter R time for prewarmed samples only (R time 4.7 ± 0.7 min, vs. 5.6 ± 0.8 min for vacuum-collected samples, P = 0.008). Conclusions Even in the absence of exogenous activators, CA has an impact on canine TEG results. The effects of rest temperatures and sample collection technique on TEG appear to be minimal.OBJECTIVE To determine the effects of rest temperature, contact activation (CA), and sample collection technique on thrombelastography (TEG) using canine whole blood. DESIGN Prospective, experimental study. SETTING University-based research facility. ANIMALS Twelve healthy, adult, mixed-breed dogs. INTERVENTIONS Blood was collected by jugular venipuncture. Tubes containing 3.2% sodium citrate, with and without 75 μg/mL corn trypsin inhibitor (CTI), were filled by vacuum. Samples rested for 30 minutes at 3 temperatures: 37°C, room temperature (RT, 20-22°C), or warmed to 37°C 5 minutes prior to analysis (prewarmed). Samples were analyzed at 37°C. CTI-treated samples were analyzed with and without 1:50,000 tissue factor (TF) as activator. Six dogs were also tested similarly using a needle/syringe collection technique. MEASUREMENT AND MAIN RESULTS Prewarmed samples exhibited greater MA compared to RT (55.5 ± 7.2 mm vs. 53.5 ± 6.0, P< 0.05), while 37°C samples exhibited a steeper angle (56.7 ± 10.4°C vs. 52.4 ± 8.6°C) and greater MA (55.9 ± 7.5 mm vs. 53.5 ± 6.0 mm) than RT samples (both P< 0.05). CTI-treated samples were hypocoagulable (R time 45 min [7.5-56.8 min], angle 8.2°C [5.1-42.5°C], MA 29.2 ± 9.7 mm, P< 0.001), with TF activation returning all but the angle (42.5 ± 7.6°C) to values similar to citrated samples (angle = 56.7 ± 10.4°C, P = 0.017). Collection using a syringe/needle method revealed a shorter R time for prewarmed samples only (R time 4.7 ± 0.7 min, vs. 5.6 ± 0.8 min for vacuum-collected samples, P = 0.008). CONCLUSIONS Even in the absence of exogenous activators, CA has an impact on canine TEG results. The effects of rest temperatures and sample collection technique on TEG appear to be minimal.

Sonoclot evaluation of whole blood coagulation in healthy adult dogs.

OBJECTIVE To establish a standard protocol for analysis of canine whole blood and generate reference intervals for healthy dogs using the Sonoclot analyzer, and to compare Sonoclot values to standard and viscoelastic coagulation tests. DESIGN Prospective study. SETTING Veterinary University research facility and teaching hospital. ANIMALS Twelve healthy random source dogs and 52 healthy dogs from the general veterinary school population. INTERVENTIONS Blood sampling for viscoelastic coagulation testing. MEASUREMENTS AND MAIN RESULTS Blood was collected from 12 healthy adult dogs by jugular venipuncture. After a rest period at room temperature of 30, 60, or 120 minutes, 340 μL of citrated blood was added to 20 μL of 0.2 M CaCl(2) in 1 of 2 cuvette types warmed to 37° C. Cuvettes contained a magnetic stir-bar with glass beads (gbACT+) or only a magnetic stir-bar (nonACT). Reference interval samples were collected from 52 healthy adult dogs and analyzed in duplicate. The ACT, CR, and PF were not affected by duration of rest period for either cuvette type. ACT variability was decreased when using gbACT+ cuvettes (P < 0.05). In normal dogs reference intervals (mean ± 2 SD) using gbACT+ cuvettes were: ACT 56.0-154.0 seconds, CR 14.85-46.0, and PF 2.1-4.05. ACT correlated to TEG R-time, K-time, and angle, while CR correlated with all TEG parameters. Fibrinogen correlated with ACT, CR, and PF. Sonoclot did not correlate with other common coagulation tests. CONCLUSIONS Sonoclot provides viscoelastic evaluation of canine whole blood coagulation and correlated to several TEG parameters and fibrinogen. A standard protocol and reference intervals were established.Objective To establish a standard protocol for analysis of canine whole blood and generate reference intervals for healthy dogs using the Sonoclot analyzer, and to compare Sonoclot values to standard and viscoelastic coagulation tests. Design Prospective study. Setting Veterinary University research facility and teaching hospital. Animals Twelve healthy random source dogs and 52 healthy dogs from the general veterinary school population. Interventions: Blood sampling for viscoelastic coagulation testing. Measurements and Main Results Blood was collected from 12 healthy adult dogs by jugular venipuncture. After a rest period at room temperature of 30, 60, or 120 minutes, 340 μL of citrated blood was added to 20 μL of 0.2 M CaCl2 in 1 of 2 cuvette types warmed to 37° C. Cuvettes contained a magnetic stir-bar with glass beads (gbACT+) or only a magnetic stir-bar (nonACT). Reference interval samples were collected from 52 healthy adult dogs and analyzed in duplicate. The ACT, CR, and PF were not affected by duration of rest period for either cuvette type. ACT variability was decreased when using gbACT+ cuvettes (P < 0.05). In normal dogs reference intervals (mean ± 2 SD) using gbACT+ cuvettes were: ACT 56.0–154.0 seconds, CR 14.85–46.0, and PF 2.1–4.05. ACT correlated to TEG R-time, K-time, and angle, while CR correlated with all TEG parameters. Fibrinogen correlated with ACT, CR, and PF. Sonoclot did not correlate with other common coagulation tests. Conclusions Sonoclot provides viscoelastic evaluation of canine whole blood coagulation and correlated to several TEG parameters and fibrinogen. A standard protocol and reference intervals were established.

Outcome of positive‐pressure ventilation in dogs and cats with congestive heart failure: 16 cases (1992–2012)

OBJECTIVE To describe the indications, duration of ventilation, underlying cardiac diseases, and outcome of dogs and cats undergoing positive-pressure ventilation (PPV) for treatment of congestive heart failure (CHF). DESIGN Two-site retrospective study (1992-2012). SETTING Two university small animal teaching hospitals. ANIMALS Six cats and 10 dogs undergoing PPV for CHF. INTERVENTIONS None. MEASUREMENTS AND MAIN RESULTS Medical records were searched to identify patients requiring PPV for treatment of pulmonary edema secondary to CHF. Sixteen animals fulfilled these criteria. Patient signalment, duration of PPV, underlying cardiac disease, arterial or venous blood gas values, pharmacologic therapy before, during, and after PPV, anesthetic drugs, complications, and outcome were recorded. Overall survival to discharge was 62.5% (10/16). Mean (±SD) duration of PPV was 30.8 ± 21.3 hours and average time from presentation for CHF to initiation of PPV was 5.9 ± 6.4 hours. Azotemia at the time of initiation of ventilation, development of anuria or oliguria, and use of pentobarbital for anesthesia were negatively associated with survival (P = 0.011, P = 0.036, and P = 0.036, respectively). Survival-to-discharge rate was 77% (10/13) for patients treated after 2005 and those not receiving pentobarbital. There was no significant effect attributed to age, sex, weight, species, nature of heart disease, furosemide dose, length of ventilation, use of vasopressors, first-time CHF events, or plasma lactate concentration on survival to discharge. CONCLUSIONS Dogs and cats requiring PPV for CHF have a good overall prognosis for hospital discharge and require PPV for a relatively short duration. Azotemia, oliguria or anuria, and the use of pentobarbital are negatively associated with outcome.

Formulation and validation of a predictive model to correct blood glucose concentrations obtained with a veterinary point-of-care glucometer in hemodiluted and hemoconcentrated canine blood samples

OBJECTIVE To determine the effect of PCV on veterinary point-of-care (POC) glucometer measurements in canine blood samples and develop a formula to correct the glucose concentration as measured by a point-of-care glucometer (POCgluc) given a known PCV. DESIGN Experimental and prospective study. SAMPLES Blood samples from 6 healthy dogs and from 30 hospitalized dogs. PROCEDURES 60 mL of heparinized blood was obtained from each of 6 healthy dogs. Samples were processed into packed RBCs and plasma. Packed RBCs were resuspended with plasma to achieve a range of PCVs from 0% to 94%. Duplicate POCgluc and PCV measurements were obtained for each dilution; following POCgluc measurements, plasma samples were analyzed for glucose concentration by a clinical laboratory biochemical analyzer (LABgluc). A correction formula for POCgluc was developed. Measurements of POCgluc, PCV, and LABgluc were also determined from blood samples of 30 dogs admitted to the veterinary teaching hospital. RESULTS Values of LABgluc for each sample were similar at any PCV. As PCV decreased, POCgluc was falsely increased; as PCV increased, POCgluc was falsely decreased, compared with LABgluc. The absolute difference between POCgluc and LABgluc increased as the PCV changed from 50%. Compared with POCgluc, the corrected POCgluc had a significantly improved correlation with LABgluc, which was also reflected in improvements in Clarke and consensus error grid analyses. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that in dogs with hemodilution or hemoconcentration, POCgluc did not reflect actual patient glucose concentrations. Use of a correction formula reduced this error. Corrected POCgluc data had strong, significant correlations with LABgluc data.

Endocrine emergencies in dogs and cats.

Success in treatment of endocrine emergencies is contingent on early recognition and treatment. Many endocrine diseases presenting emergently have nonspecific signs and symptoms. In addition, these endocrine crises are often precipitated by concurrent disease, further making early identification difficult. This article concentrates on recognition and emergency management of the most common endocrine crises in dogs and cats.