Assessment of a point-of-care instrument for identification of primary hemostatic disorders in dogs

Adverse effects of trazodone in dogs on primary hemostasis and electrocardiogram: A single-blinded placebo-controlled crossover study

BACKGROUND

Trazodone is a serotonin antagonist/reuptake inhibitor medication commonly used for anxiety in dogs. Therapy with selective serotonin reuptake inhibitors in humans is associated with bleeding disorders and increased arrhythmogenesis.

HYPOTHESIS/OBJECTIVES

To evaluate markers of primary hemostasis and corrected QT (cQT) interval in dogs before and after oral administration of standard dosages of trazodone or placebo.

ANIMALS

Fifteen apparently healthy, client-owned dogs.

METHODS

A single-blinded, randomized placebo-controlled crossover study was performed. Dogs were administered trazodone (5 to 7.5 mg/kg PO Q12h) or placebo. [Correction added after first online publication on 14 October 2023. In the abstract (methods) section (57.5 mg/kg PO Q12h) changed as (5 to 7.5 mg/kg PO Q12h).] Buccal mucosal bleeding time (BMBT), platelet count, platelet aggregation via Plateletworks, PFA-100 closure time and cQT interval were measured. A Shapiro-Wilk test was performed followed by either a paired t test or a Wilcoxon signed-rank test.

RESULTS

No significant difference was detected in the BMBT, PFA-100 closure times, platelet counts, and cQT interval between trazodone or placebo. However, using Plateletworks, there was a significant decrease in platelet aggregation after administration of trazodone (95%; 81-97 vs 62%; 39-89, P = .002) and not placebo (95%; 81-97 vs 91%; 81-96, P = .21).

CONCLUSIONS

It is unknown if this represents a clinically relevant change or if dogs with preexisting impairment in primary hemostasis or receiving higher dosages or longer durations of trazodone could have a more substantial change in hemostatic variables.

Clinical Assessment of Primary Hemostasis: A Review

Primary hemostatic disorders such as thrombocytopenia and thrombocytopathia are commonly encountered in small animal practice. The key stages of primary hemostasis include platelet adhesion, activation, and aggregation. Understanding the interaction between tissues, platelets, and signaling molecules not only helps clinicians comprehend clot formation but also better recognize thrombocytopathias. Although congenital thrombocytopathia is rare, commercially available platelet function tests allow veterinarians to narrow differentials in many clinical settings. Thrombocytopenia can be easily diagnosed in any clinical setting. In this paper, we review the current understanding of primary hemostasis in veterinary medicine, including the clinical presentation and available diagnostics to identify platelet abnormalities.

Platelet function in dogs with chronic liver disease

OBJECTIVES

To assess platelet function, buccal mucosal bleeding time and plasma von Willebrand factor concentration in dogs with chronic inflammatory and/or fibrotic liver disease and to compare results with those obtained in healthy dogs.

MATERIALS AND METHODS

Preliminary study including 18 dogs with chronic inflammatory and/or fibrotic liver disease undergoing liver biopsy and 18 healthy age-matched control dogs. Platelet function was assessed by measuring closure time with the PFA-100® analyser using adenosine diphosphate (ADP) as an agonist. Buccal mucosal bleeding time, closure time and plasma von Willebrand factor antigen were measured in dogs in both groups. After undergoing ultrasound-guided needle biopsy, dogs were monitored for haemorrhage to determine if there was an association of any measurement with post-biopsy bleeding.

RESULTS

The closure time was not different between the liver disease group (median 76.3; range 53 to 118.5 seconds) and control group (72.8; 57 to 89.5 seconds). The buccal mucosal bleeding time was longer in the liver disease group (median 138; range 95 to 229 seconds) than the control group (103; 63 to 200 seconds). The plasma von Willebrand factor antigen concentration was not different between the liver disease group (median 203; range 109 to 351%) and control group (165.5; 63 to 246%).

CLINICAL SIGNIFICANCE

In this study, dogs with chronic necroinflammatory and/or fibrotic liver disease did not have overt, clinically relevant derangements in platelet function as assessed by buccal mucosal bleeding time, closure time and von Willebrand factor analysis. In addition, none of the dogs undergoing percutaneous ultrasound-guided biopsy in the study exhibited bleeding complications post-biopsy procedure.

A prospective randomized open-label trial on the comparative effects of 6% hydroxyethyl starch 130/0.4 versus polyionic isotonic crystalloids on coagulation parameters in dogs with spontaneous hemoperitoneum

OBJECTIVE

To evaluate the effects of 6% hydroxyethyl starch 130/0.4 (HES) and a polyionic isotonic crystalloid (CRYS) on standard coagulation tests and rotational thromboelastometry (ROTEM) in dogs with spontaneous hemoperitoneum (SHP).

DESIGN

Prospective randomized open-label clinical study.

SETTING

University teaching hospital.

ANIMALS

Forty-two client-owned dogs presented with SHP.

INTERVENTIONS

Dogs diagnosed with SHP and hypovolemic shock were randomly allocated to receive HES (10 mL/kg, n = 22) or CRYS (30 mL/kg, n = 20) intravenously over 20 minutes for hemodynamic stabilization.

MEASUREMENTS AND MAIN RESULTS

Parameters measured before (T₀ ) and after (T₁ ) treatment were HCT, platelet counts, prothrombin time, activated partial thromboplastin time, fibrinogen concentrations, and extrinsic activated (EXTEM), intrinsic activated (INTEM), and extrinsic activated with platelet inhibition ROTEM assays. Data were analyzed as absolute values and as the percentage change from T₀ to T₁ . No significant differences between groups were detected in any variable at T₀ , and for HCT, platelet counts, prothrombin time, activated thromboplastin time, and fibrinogen concentrations at T₁ . Clot formation time in EXTEM was significantly prolonged (P = 0.037), and maximum clot firmness was significantly decreased (P = 0.038) in the HES group compared to the CRYS group at T₁ . The percentage change in EXTEM clotting time (P = 0.012) and INTEM clot formation time (P = 0.031) was greater after HES than CRYS. Lysis indices remained at 100% for all ROTEM assays in both groups.

CONCLUSION

Compared to a 3-fold volume of CRYS, administration of HES was associated with impairment in ROTEM parameters in dogs with SHP, but no evidence of hyperfibrinolysis was detected.

Effects of clopidogrel and prednisone on platelet function in healthy dogs

Background

Glucocorticoids cause hypercoagulability, but it is unknown if they counteract clopidogrel's antiplatelet effects.

Hypothesis/Objectives

Determine the effects of clopidogrel and prednisone on platelet function.

Animals

Twenty‐four healthy dogs.

Methods

Double‐blinded, placebo‐controlled randomized trial. Platelet function was evaluated using a platelet function analyzer and impedance aggregometry (days 0, 14, and 28) for dogs treated with placebo, clopidogrel (2‐3 mg/kg/d), prednisone (2 mg/kg/d), or prednisone with clopidogrel PO for 28 days. Results were categorized as nonresponder versus responder (platelet function analyzer), and inadequate, ideal, or excessive response (aggregometry). Results were compared using mixed model, split‐plot repeated measures analysis of variance and generalized estimating equation proportional odds models. P < .05 was considered significant.

Results

Closure times differed by treatment (F [3, 20] = 10.5; P < .001), time (F [2, 40] = 14.3; P < .001), and treatment‐by‐time (F [6, 40] = 3.4; P = .01). Area under the curve (AUC) differed by treatment (F [3, 20] = 19.6; P < .001), time (F [2, 40] = 35.4; P < .001), and treatment‐by‐time (F [6, 40] = 13.5; P < .001). Based on closure times, 5/6 dogs each in the clopidogrel and prednisone/clopidogrel groups were responders. All dogs in the prednisone/clopidogrel group were overcontrolled based on AUC (days 14 and 28), whereas 5/6 (day 14) and 2/6 (day 28) dogs treated with clopidogrel were overcontrolled. Compared to clopidogrel, dogs receiving prednisone/clopidogrel were 11 times (P = .03) more likely to have an excessive response.

Conclusions and Clinical Importance

Administration of clopidogrel/prednisone increases platelet dysfunction in healthy dogs.

Effects of immunosuppressive agents on the hemostatic system in normal dogs

Background

In dogs, the effects of immunosuppressive medications on hemostasis are not well known.

Hypothesis/Objectives

The objective was to determine the effects of immunosuppressive medications on primary and secondary hemostasis. Our hypothesis was that cyclosporine and prednisone would increase markers of hypercoagulability and thromboxane synthesis, while azathioprine, mycophenolate mofetil, and leflunomide would have minimal effects on hemostasis.

Animals

Eight healthy dogs.

Methods

A randomized, cross‐over study used aggregometry, the PFA‐100 platelet function analyzer, viscoelastometry, platelet count, and prothrombin and activated partial thromboplastin times to evaluate hemostasis during the administration of prednisone, azathioprine, cyclosporine, mycophenolate mofetil, and leflunomide for 1 week each at standard oral doses. Urine 11‐dehydro‐thromboxane‐B₂ (11‐dTXB₂) and 6‐keto‐prostaglandin‐F_1α (6‐keto‐PGF_1α) concentrations, normalized to urine creatinine concentration, were measured.

Results

The aggregometry amplitude decreased from 51 ± 21 to 27 ± 14 (P = .002) during leflunomide treatment (ADP activation), but there were no differences in amplitude (P = .240) for any medications when platelets were activated with collagen. For all medications, there were no significant differences in viscoelastometry indices (ACT, P = .666; ClotRate, P = .340; and platelet function, P = .411) and platelet count (P = .552). Compared with pretreatment values, urinary 11‐dTXB₂‐to‐creatinine ratio increased (P = .001) after drug administration (from 3.7 ± 0.6 to 5.6 ± 1.1). Cyclosporine was associated with an increase (P < .001) in the 6‐keto‐PGF_1α‐to‐creatinine ratio (from 10.3 ± 4.6 to 22.1 ± 5.3).

Conclusions and Clinical Importance

Most immunosuppressive drugs do not enhance platelet function or coagulation in healthy dogs, suggesting that these medications might not predispose hypercoagulable dogs to thromboembolism. The results of our study need to be correlated with the clinical outcomes of hypercoagulable dogs.

Comparison of Multiplate, Platelet Function Analyzer-200, and Plateletworks in Healthy Dogs Treated with Aspirin and Clopidogrel

BACKGROUND

Platelet function testing may be warranted to assess response to aspirin and clopidogrel.

HYPOTHESIS/OBJECTIVES

To evaluate the effects of aspirin, clopidogrel, or combination therapy using 3 platelet function tests: Multiplate Analyzer (MP), Platelet Function Analyzer-200 (PFA), and Plateletworks (PW).

ANIMALS

Six healthy laboratory Beagles.

METHODS

Randomized double-blind placebo-controlled study (crossover design). Dogs were given aspirin 1 mg/kg, clopidogrel 2 mg/kg, or combination therapy for 1 week each, with a washout period of 2 weeks. Platelet function was assessed on days 0 and 7 of each phase using MP (adenosine diphosphate [ADP], arachidonic acid [AA], collagen [COL] agonists), PFA (P2Y, COL-ADP [CADP], COL-Epinephrine [CEPI] cartridges), and PW (ADP, AA, COL agonists). Platelet counts were obtained with impedance and optical counters.

RESULTS

For MP, mean aggregation was decreased for COL and AA with combination therapy and for ADP with all treatments. For PFA, mean CT was increased for the CEPI cartridge with aspirin; and for the P2Y and CADP cartridges with clopidogrel or combination therapy. More dogs receiving clopidogrel showed an increase in PFA CT using the P2Y than the CADP cartridge. For PW, mean aggregation was decreased for AA with all treatments; for ADP with clopidogrel or combination therapy; and for COL with clopidogrel. The PW results with the 2 hematology counters showed almost perfect agreement.

CONCLUSION AND CLINICAL IMPORTANCE

All platelet function tests detected treatment effects in some dogs and may have utility for monitoring therapy.

Engineering a simple lateral flow device for animal blood coagulation monitoring

Increasing numbers of animals are diagnosed with thromboembolism, requiring anticoagulation treatment to prevent thrombotic events. Frequent and periodic coagulation monitoring is critical to ensure treatment effectiveness and patient safety by limiting blood coagulation ability within the desired therapeutic range. Point-of-care diagnostics is an ideal candidate for frequent coagulation monitoring due to rapid test results and no need for laboratory setting. This article reports the first utilization of no-reaction lateral flow assay (nrLFA) device for simple and low-cost animal blood coagulation monitoring in resource-limited setting. The nrLFA device consists of sample pad, analytical membrane and wicking pad, without conjugate pad, reagent printing or membrane drying. Citrated and heparinized animal blood were utilized to mimic different blood coagulation abilities in vitro by adding reversal agents CaCl2 and protamine sulfate. The travel distance of red blood cells (RBCs) on the nrLFA after a pre-determined test time serves as endpoint marker. Upon adding 500 mM CaCl2 solution to citrated bovine, canine, rabbit and equine blood, the average travel distance decreases from 10.9 to 9.4 mm, 8.8 to 5.7 mm, 12.6 to 9 mm, and 15.3 to 11.3 mm, respectively. For heparinized bovine and rabbit blood, the average distance decreases from 14.5 to 11.4 mm and from 9.8 to 7.2 mm, respectively, when adding 300 mg/l protamine sulfate solution. The effect of hematocrit on RBC travel distance in the nrLFA was also investigated. The nrLFA device will potentially improve treatment efficiency, patient safety, quality of life, and satisfaction for both animal patients and their owners.

Comparison of the effects of 7.2% hypertonic saline and 20% mannitol on whole blood coagulation and platelet function in dogs with suspected intracranial hypertension - a pilot study

BACKGROUND

Hyperosmolar therapy with either mannitol or hypertonic saline (HTS) is commonly used in the treatment of intracranial hypertension (ICH). In vitro data indicate that both mannitol and HTS affect coagulation and platelet function in dogs. The aim of this study was to compare the effects of 20% mannitol and 7.2% HTS on whole blood coagulation using rotational thromboelastometry (ROTEM®) and platelet function using a platelet function analyzer (PFA®) in dogs with suspected ICH. Thirty client-owned dogs with suspected ICH needing osmotherapy were randomized to receive either 20% mannitol (5 ml/kg IV over 15 min) or 7.2% HTS (4 ml/kg IV over 5 min). ROTEM® (EXTEM® and FIBTEM® assays) and PFA® analyses (collagen/ADP cartridges) were performed before (T0), as well as 5 (T5), 60 (T60) and 120 (T120) minutes after administration of HTS or mannitol. Data at T5, T60 and T120 were analyzed as a percentage of values at T0 for comparison between groups, and as absolute values for comparison between time points, respectively.

RESULTS

No significant difference was found between the groups for the percentage change of any parameter at any time point except for FIBTEM® clotting time. Within each group, no significant difference was found between time points for any parameter except for FIBTEM® clotting time in the HTS group, and EXTEM® and FIBTEM® maximum clot firmness in the mannitol group. Median ROTEM® values lay within institutional reference intervals in both groups at all time points, whereas median PFA® values were above the reference intervals at T5 (both groups) and T60 (HTS group).

CONCLUSIONS

Using currently recommended doses, mannitol and HTS do not differ in their effects on whole blood coagulation and platelet function in dogs with suspected ICH. Moreover, no relevant impairment of whole blood coagulation was found following treatment with either solution, whereas a short-lived impairment of platelet function was found after both solutions.

Comparison of the effects of a balanced crystalloid-based and a saline-based tetrastarch solution on canine whole blood coagulation and platelet function

OBJECTIVE

To evaluate the effects of a 6% hydroxyethyl starch (130/0.42) solution in either a buffered, electrolyte-balanced (HES-BAL), or a saline (HES-SAL) carrier solution on canine platelet function and whole blood coagulation.

DESIGN

Prospective, randomized study.

SETTING

University teaching hospital.

ANIMALS

Thirty-seven client-owned dogs undergoing general anesthesia for arthroscopy or imaging studies.

INTERVENTIONS

Dogs received a 15 mL/kg intravenous bolus of HES-SAL (n = 13), HES-BAL (n = 14), or a modified Ringer's solution (n = 10) over 30-40 minutes. Coagulation was analyzed using a Platelet Function Analyzer-100 (closure time [Ct_PFA ]), and whole blood thromboelastometry (ROTEM) with extrinsically (ex-tem and fib-tem) and intrinsically (in-tem) activated assays, which assessed clotting time (CT), clot formation time (CFT), maximal clot firmness (MCF), and lysis index (LI). Coagulation samples were assayed prior to fluid administration (T0), and 5 minutes (T1), and 3 hours (T2) following fluid bolus administration, respectively.

RESULTS

Both HES solutions resulted in impaired platelet function as indicated by a significant prolongation of Ct_PFA at T1 as compared to T0, but which resolved by T2. An IV bolus of Ringer's solution did not alter platelet function. In both HES groups, whole blood coagulation was significantly impaired at T1 as indicated by a significant increase in in-tem CFT, and a significant decrease in ex-tem, in-tem, and fib-tem MCF compared to T0. Furthermore, a significant increase in ex-tem CFT at T1 compared to T0 was found in the HES-SAL group. With the exception of in-tem MCF after HES-BAL, these effects were not present at T2. No significant differences were found in Ct_PFA or any ROTEM variable at any time point between HES-SAL and HES-BAL.

CONCLUSION

Administration of a single bolus of 15 mL/kg 6% HES 130/0.42 results in significant but short-lived impairment of canine platelet function and whole blood coagulation, regardless of carrier solution.

An in vitro comparison of the effects of voluven (6% hydroxyethyl starch 130/0.4) and hespan (6% hydroxyethyl starch 670/0.75) on measures of blood coagulation in canine blood

OBJECTIVE

To assess primary and secondary hemostasis following in vitro dilution of canine whole blood (WB) with hydroxyethyl starch (HES) 130/0.4 and HES 670/0.75.

DESIGN

In vitro experimental study.

SETTING

Private practice, teaching hospital.

ANIMALS

Twenty-five healthy dogs.

INTERVENTIONS

Each dog underwent venipuncture and 18 mL of venous blood was sampled once.

MEASUREMENTS AND MAIN RESULTS

Collected blood was separated in 4 aliquots. Aliquot A served as baseline sample. The remaining tubes of WB were diluted with 0.9% saline, HES 670/0.75 and HES 130/0.4 at a ratio of 1:5.5. Dilutional effects were evaluated using prothrombin time (PT), activated partial thromboplastin time (aPTT), packed cell volume (PCV), thromboelastography (TEG), and platelet closure time (Ct), which was measured using a platelet function analyzer (PFA). Clot strength (ie, G value) was calculated from measured TEG values. Significant increases in PT (P < 0.05) and aPTT (P < 0.05) were documented following WB dilution with saline. Dilution of WB with HES 670/0.75 and HES 130/0.4 resulted in significant hypocoagulable changes in K, MA and G (P < 0.05) compared to baseline and saline. When comparing saline to HES 670/0.75, both R and K values were significantly increased (P < 0.05). K value was significantly increased (P < 0.05) when comparing baseline to HES 130/0.4 and HES 670/0.75. Ct (P < 0.05) was significantly prolonged after WB dilution with HES solutions but not after saline.

CONCLUSIONS

Dilution of WB with HES 670/0.75 and HES 130/0.4 resulted in changes in primary and secondary hemostasis. Although there were small differences between saline and HES 670/0.75, no differences between HES solutions were evident in this small study. This may suggest there would be minimal increases in bleeding risk when either solution is administered to dogs at low doses. Clinical relevance of our findings requires further investigation.

Influence of a low dosage of clopidogrel on platelet function in cats as measured by the platelet function analyser PFA-100 and the multiplate analyser

The antiplatelet drug clopidogrel is widely used for prophylaxis of arterial thromboses in cats in a standard dosage of 18.75mg per cat once daily. The aim of the study was to verify if a reduced daily dose of 10mg clopidogrel per cat has a similar antiplatelet effect as the standard dosage. Platelet function was measured with the platelet function analyser PFA-100^® and a novel impedance aggregometer. Suitability of the platelet function analyser was tested in citrated blood samples of 59 healthy cats and reference ranges were established. In addition, agonist concentrations for impedance aggregometry were optimised. In the main experiment two groups of 6 healthy cats received clopidogrel either in a dosage of 10 or 18.75mg per cat over a period of seven days. Analyses were performed on days 1, 2, 3, 5, and 7. In comparison to baseline both clopidogrel dosages showed an inhibitory effect on results of the platelet function analyser and velocity of ADP-induced platelet aggregation. Values at all times were different from baseline, with the exception of day 1 in cats receiving 10mg clopidogrel where the closure time of the platelet function analysis and part of ADP-induced aggregation did not show a significant difference. Significant differences were not found between the two doses. In conclusion, our study indicates that 10mg clopidogrel per day may be as effective as 18.75mg although the latter may be advantageous as an initial loading dosage to achieve effective levels more rapidly.

The effects of clopidogrel and omeprazole on platelet function in normal dogs

Omeprazole is used concurrently with clopidogrel to reduce gastrointestinal adverse effects. In humans, the concurrent use of these two drugs can reduce the antiplatelet efficacy of clopidogrel. Our objective was to determine the effects of omeprazole and clopidogrel on platelet function in healthy dogs. A crossover study utilized turbidimetric aggregometry (ADP and collagen) and the PFA-100^® with the collagen/ADP cartridge to evaluate platelet function in eight healthy dogs during the administration of clopidogrel (1 mg/kg/24 h p.o.), omeprazole (1 mg/kg/24 h p.o.), and a combination of clopidogrel and omeprazole. Drug metabolite concentrations were also measured. Compared to pretreatment, on Days 3 and 5, with ADP as the agonist, there was a significant decrease in maximum amplitude on aggregometry for both clopidogrel and clopidogrel/omeprazole groups. The following revealed no significant differences between clopidogrel and clopidogrel/omeprazole groups when compared on Days 3 and 5: maximum amplitude on aggregometry with ADP or collagen agonists, and PFA-100^® closure times. When compared to the clopidogrel group, clopidogrel metabolite concentrations in the clopidogrel/omeprazole group were significantly higher on Days 3 and 5. The concurrent administration of omeprazole and clopidogrel in healthy dogs was associated with an increase in the plasma concentration of an inactive metabolite of clopidogrel, but does not significantly alter the antiplatelet effects of clopidogrel.

Point of Care Assessment of Coagulation

Disorders of hemostasis can be difficult to fully elucidate but can severely affect patient outcome. The optimal therapy for coagulopathies is also not always clear. Point of care (POC) testing in veterinary medicine can assist in the diagnosis of hemostatic disorders and also direct treatment. Advantages of POC testing include rapid turnaround times, ease of use, and proximity to the patient. Disadvantages include differences in analytic performance compared with reference laboratory devices, the potential for operator error, and limited test options per device. Conventional coagulation tests such as prothrombin time, activated partial thromboplastin time, and activated clotting time can be measured by POC devices and can accurately diagnose hypocoagulability, but they cannot detect hypercoagulability or disorders of fibrinolysis. Viscoelastic POC coagulation testing more accurately evaluates in vivo coagulation, and can detect hypocoagulability, hypercoagulability, and alterations in fibrinolysis. POC platelet function testing methodologies can detect platelet adhesion abnormalities including von Willebrand disease, and can be used to monitor the efficacy of antiplatelet drugs. It is unlikely that a single test would be ideal for assessing the complete coagulation status of all patients; therefore, the ideal combination of tests for a specific patient needs to be determined based on an understanding of the underlying disease, and protocols must be standardized to minimize interoperator and interinstitutional variability.

The Effects of Cyclosporine and Aspirin on Platelet Function in Normal Dogs

Background

Cyclosporine increases thromboxane synthesis in dogs, potentially increasing the thrombogenic properties of platelets.

Hypothesis/Objectives

Our hypothesis was that the concurrent administration of low‐dose aspirin and cyclosporine would inhibit cyclosporine‐associated thromboxane synthesis without altering the antiplatelet effects of aspirin. The objective was to determine the effects of cyclosporine and aspirin on primary hemostasis.

Animals

Seven healthy dogs.

Methods

A randomized, crossover study utilized turbidimetric aggregometry and a platelet function analyzer to evaluate platelet function during the administration of low‐dose aspirin (1 mg/kg PO q24h), high‐dose aspirin (10 mg/kg PO q12h), cyclosporine (10 mg/kg PO q12h), and combined low‐dose aspirin and cyclosporine. The urine 11‐dehydro‐thromboxane‐B₂ (11‐dTXB₂)‐to‐creatinine ratio also was determined.

Results

On days 3 and 7 of administration, there was no difference in the aggregometry amplitude or the platelet function analyzer closure time between the low‐dose aspirin group and the combined low‐dose aspirin and cyclosporine group. On day 7, there was a significant difference in amplitude and closure time between the cyclosporine group and the combined low‐dose aspirin and cyclosporine group. High‐dose aspirin consistently inhibited platelet function. On both days, there was a significant difference in the urinary 11‐dTXB₂‐to‐creatinine ratio between the cyclosporine group and the combined low‐dose aspirin and cyclosporine group. There was no difference in the urinary 11‐dTXB₂‐to‐creatinine ratio among the low‐dose aspirin, high‐dose aspirin, and combined low‐dose aspirin and cyclosporine groups.

Conclusions and Clinical Importance

Low‐dose aspirin inhibits cyclosporine‐induced thromboxane synthesis, and concurrent use of these medications does not alter the antiplatelet effects of aspirin.

Platelet closure time in anesthetized Greyhounds with hemorrhagic shock treated with hydroxyethyl starch 130/0.4 or 0.9% sodium chloride infusions

OBJECTIVE

To measure platelet closure time (PCT) in dogs during controlled hemorrhagic shock and after fluid resuscitation with hydroxyethyl starch (HES) 130/0.4 or 0.9% sodium chloride.

DESIGN

Experimental interventional study.

SETTING

University veterinary teaching hospital.

ANIMALS

Eleven healthy Greyhounds.

INTERVENTIONS

Dogs were anesthetized and had 48 mL/kg of blood removed to induce hemorrhagic shock. Dogs received 20 mL/kg of HES 130/0.4 (n = 6) or 80 mL/kg of 0.9% sodium chloride (NaCl; n = 5) intravenously over 20 minutes. PCT was measured using the Platelet Function Analyzer-100 with collagen and adenosine-diphosphate cartridges at: T0 = 60 minutes after induction of anesthesia prior to hemorrhage, T1 = during hemorrhagic shock, and T2 = 40 minutes after completion of fluid bolus. Packed cell volume and platelet count were concurrently measured.

MEASUREMENT AND MAIN RESULTS

Hemorrhagic shock did not significantly change PCT, with no difference between T0 and T1. Both the HES 130/0.4 and 0.9% NaCl group had a significantly increased mean PCT at T2 of 91.4 seconds (95% CI 69.3-113.4) and 95.5 seconds (95% CI 78.2-112.8), respectively, compared to T1. The magnitude of change was significantly greater for the 0.9% NaCl group than the HES 130/0.4 group. There was no difference in the magnitude of change in PCV and platelet count between the 2 groups. The PCV and platelet count were >25% and >100,000/μL, respectively, in all dogs, except for dogs in the HES 130/0.4 group at T2 where platelet counts were <100,000/μL.

CONCLUSION

Controlled hemorrhagic shock in Greyhounds under anesthesia did not cause a significant change in PCT. Both HES 130/0.4 and 0.9% NaCl administration after induction of shock increased PCT. These results do not support that HES 130/0.4 causes relevant platelet dysfunction beyond hemodilution.

In vitro effects of 3% hypertonic saline and 20% mannitol on canine whole blood coagulation and platelet function

Background

Hyperosmolar therapy, using either mannitol or hypertonic saline (HTS), is considered the treatment of choice for intracranial hypertension. However, hyperosmolar agents may impair coagulation and platelet function, limiting their use in patients at risk for hemorrhage. Despite this, studies evaluating the effects of mannitol compared to other hyperosmolar agents in dogs are largely lacking. The aim of this study was to compare the in vitro effects on global hemostasis and platelet function of 20 % mannitol and 3 % HTS on canine blood.

Methods

Citrated whole blood from 15 healthy dogs was diluted with 0.9 % saline, 20 % mannitol and 3 % HTS in ratios of 1:16 and 1:8. Rotational thromboelastometry (ROTEM) was used to assess clotting time (CT), clot formation time (CFT) and maximal clot firmness (MCF) following extrinsic activation (Ex-tem) and after platelet inhibition (Fib-tem). A platelet function analyzer (PFA-100) was used to assess closure time (Ct_PFA).

Results

No significant differences were observed between untreated whole blood and samples diluted with saline. Samples diluted with both mannitol and HTS were hypocoagulable compared to untreated whole blood samples. At a dilution of 1:16, no significant differences were found between any measured parameter in samples diluted with saline compared to mannitol or HTS. At a 1:8 dilution, Ct_PFA was prolonged in samples diluted with mannitol and HTS compared to saline, and Ct_PFA was prolonged more with mannitol than HTS. Ex-tem CT was increased at a 1:8 dilution with mannitol compared to HTS. Ex-tem CFT was prolonged at a 1:8 dilution with both agents compared to saline, and was prolonged more with mannitol than HTS. Ex-tem MCF was reduced at a 1:8 dilution with both agents compared to saline.

Discussion and Conclusions

Data in this study indicate that both mannitol and HTS affect canine platelet function and whole blood coagulation in vitro in a dose-dependent fashion. The most pronounced effects were observed after high dilutions with mannitol, which impaired platelet aggregation, clot formation time, clot strength, and fibrin formation significantly more than HTS. Further in vivo studies are necessary before recommendations can be made.

Assessment of platelet function in healthy sedated cats using three whole blood platelet function tests

The objectives of this study were to establish feline references intervals for 3 commercial whole blood platelet function test analyzer systems: Multiplate analyzer (MP; Roche Diagnostics International Ltd., Rotkreuz, Switzerland), Platelet Function Analyzer-100 (PF: Siemens Canada, Mississauga, Ontario, Canada), and Plateletworks Combo-25 kit (PW; Helena Laboratories, Beaumont, TX). Venipuncture was performed on 55 healthy sedated cats, and platelet aggregation in response to adenosine diphosphate (ADP), collagen (COL), and arachidonic acid (AA; MP only) was assessed using citrated blood. For the MP analyzer, median (95% confidence intervals [CIs]) area under curve (Units) for ADP, COL, and AA agonists were 87 (11-176), 81 (32-129), and 91 (59-129), respectively. For the PF analyzer, median (95% CIs) closure time, using COL-ADP cartridges, was 69 (46-89) sec. For the PW assay, median (95% CIs) percent aggregations for ADP and COL agonists were 71 (18-92) and 49 (9-96), respectively, using impedance hematology analyzer platelet counts, and 94 (25-98) and 68 (14-119), respectively, using flow cytometry hematology analyzer platelet counts. There were low correlations between the PF analyzer (COL-ADP cartridge) and MP analyzer (COL agonist; ρ = 0.11), and between the PF analyzer (COL-ADP cartridge) and PW assay (COL agonist using impedance platelet counts; ρ = 0.14). The PW assay percent aggregations using impedance and flow cytometric platelet counts were correlated for both ADP (ρ = 0.64) and COL (ρ = 0.64) agonists. Platelet function testing using these tests are feasible in cats, but 95% CIs are wide, so single results may be difficult to interpret. Platelet counting by impedance or flow cytometry may be used for the PW assay but are not interchangeable.

A medicinal herb-based natural health product improves the condition of a canine natural osteoarthritis model: a randomized placebo-controlled trial

An oral herb-based natural health product (NHP) was evaluated in the canine natural osteoarthritis model. At baseline, the peak vertical force (PVF, primary endpoint) and case-specific outcome measure of disability (CSOM) were recorded in privately-owned dogs. Dogs (16/group) were randomized to receive NHP formulations or a negative control. The PVF was measured at week (W) 4 and W8. Daily locomotor activity was recorded using accelerometer. The CSOMs were assessed bi-weekly by the owner. The NHP-treated dogs (n = 13) had higher PVF at W4 (p = 0.020) and W8 (p <0.001) when compared to baseline. The changes at W8 were higher than control dogs (n = 14, p <0.027) and consistent with Cohen's d effect size of 0.7 (95% confidence interval: 0.0-1.5). The NHP-treated dogs had higher locomotor activity at W8 (p = 0.025) when compared to baseline. No significant change was observed for the CSOM. The NHP improved the clinical signs of osteoarthritis in this model.

The effect of hetastarch 670/0.75 administered in vivo as a constant rate infusion on platelet closure time in the dog

OBJECTIVE

To evaluate the effects of hetastarch 670/0.75 on canine platelet function and clinical bleeding following its administration as a constant rate infusion (CRI) at 1 mL/kg/h and 2 mL/kg/h for 24 hours.

DESIGN

In vivo, prospective, open-label, crossover study.

SETTING

Research laboratory at a university veterinary facility.

ANIMALS

Eight healthy, adult male research dogs.

INTERVENTIONS

Each dog received 1 mL/kg/h hetastarch for 24 hours then 2 mL/kg/h with a washout period of 10 weeks between each experiment. Platelet closure time (CT) was measured using a platelet function analyzer with collagen adenosine diphosphate (ADP) cartridges. CT measurements were performed at baseline and 6, 12, and 24 hours following initiation of hetastarch infusion.

MEASUREMENTS AND MAIN RESULTS

At 1 mL/kg/h, mean CT was significantly increased at the 12- and 24-hour time point relative to the baseline value, although mean CT never rose to a value above the reference interval during the 24-hour infusion. At 2 mL/kg/h, median CT was also significantly increased at the 12- and 24-hour time point relative to the baseline value. Administration of 2 mL/kg/h did progressively prolong the median CT value though only exceeded the reference interval at the 24-hour time point. Despite the prolongation of median CT, there was no clinical evidence of spontaneous bleeding in any dog during the 24-hour infusion at either CRI rate.

CONCLUSIONS

Hetastarch 670/0.75 when used as a 24-hour CRI at 1 and 2 mL/kg/h prolongs CT in healthy dogs at 6, 12, and 24 hours. Median CT only exceeded the reference interval at 24 hours at 2 mL/kg/h.

Current diagnostic trends in coagulation disorders among dogs and cats

The diagnostic workup to differentiate hemorrhage caused by vascular injury from a systemic hemostatic imbalance typically involves a combination of broad screening tests and specific assays. The characterization of 3 overlapping phases of primary hemostasis, secondary hemostasis, and fibrinolysis provides a simple diagnostic framework for evaluating patients with clinical signs of hemorrhage. New techniques such as flow cytometry, thrombin-generation assays, thrombelastography, and anticoagulant drug monitoring are under investigation for veterinary patients; however, their ability to improve diagnosis or treatment requires further study in clinical trials.

Infection-associated platelet dysfunction of canine platelets detected in a flow chamber model

BACKGROUND

In the present study, the influence of bacterial infection, lipopolysacharides (LPS) and hydroxyethyl starch (HES) on platelet function in a parallel plate flow chamber were measured. Experiments were performed with non-activated and protease-activating-receptor (PAR) 4 agonist activated platelets. Comparative measurements were in vivo capillary bleeding time, platelet function analyzer and impedance aggregometry.

RESULTS

PAR 4 agonist did not increase platelet adhesion of platelets from dogs with bacterial inflammation in the flow chamber in contrast to platelets of healthy dogs. Except from impedance aggregometry with lower sensitivity and specificity, PFA did not detect platelet dysfunctions in dogs with infection. In vitro addition of LPS or HES significantly reduced platelet covered area after PAR-activation.

CONCLUSIONS

The flow chamber detects platelet dysfunctions in dogs with inflammatory diseases. In vitro addition of LPS highlights the inhibiting effect of bacterial wall components on platelet function. Platelet dysfunction induced by infection could possibly also be diagnosed after treatment of sepsis with colloids has commenced. The flow chamber could be a useful tool to detect sepsis associated platelet dysfunction given that larger prospective trials confirm these findings from a proof of concept study.

In vitro effect of hydroxyethyl starch 130/0.42 on canine platelet function

OBJECTIVE

To evaluate the effect of 6% hydroxyethyl starch (HES) solution, with a molecular weight of 130 kDa and a degree of substitution of 0.42, on canine platelet function in vitro.

SAMPLES

Blood samples from 31 healthy adult dogs.

PROCEDURES

Citrated blood was diluted with saline (0.9% NaCl) solution or HES 130/0.42 in ratios of 1:9 (ie, 1 part saline solution or HES 130/0.42 and 9 parts blood) and 1:3. Platelet plug formation time (closure time [Ct]) was measured with a platelet function analyzer and cartridges coated with collagen and ADP.

RESULTS

Median baseline Ct with citrated blood was 84.0 seconds (interquartile range, 74.5 to 99.5 seconds). Results obtained with 1:9 dilutions with saline solution and HES 130/0.42 were not significantly different from baseline results. The 1:3 dilutions with saline solution and HES 130/0.42 resulted in median Cts of 96.0 seconds (interquartile range, 85.5 to 110.8 seconds) and 112.0 seconds (92.0 to 126.0 seconds), respectively. Results obtained with both 1:3 dilutions were significantly different from baseline results. The Ct obtained with the HES dilution was also significantly different from that of the 1:3 dilution with saline solution.

CONCLUSIONS AND CLINICAL RELEVANCE

Saline solution and HES 130/0.42 in a 1:3 dilution affected canine platelet function by prolonging Cts. The HES 130/0.42 had a significantly greater effect on canine platelets than did saline solution.

Cyclooxygenase expression and platelet function in healthy dogs receiving low-dose aspirin

BACKGROUND

Low-dose aspirin is used to prevent thromboembolic complications in dogs, but some animals are nonresponsive to the antiplatelet effects of aspirin ("aspirin resistance").

HYPOTHESIS/OBJECTIVES

That low-dose aspirin would inhibit platelet function, decrease thromboxane synthesis, and alter platelet cyclooxygenase (COX) expression.

ANIMALS

Twenty-four healthy dogs.

METHODS

A repeated measures study. Platelet function (PFA-100 closure time, collagen/epinephrine), platelet COX-1 and COX-2 expression, and urine 11-dehydro-thromboxane B(2) (11-dTXB(2)) were evaluated before and during aspirin administration (1 mg/kg Q24 hours PO, 10 days). Based on prolongation of closure times after aspirin administration, dogs were divided into categories according to aspirin responsiveness: responders, nonresponders, and inconsistent responders.

RESULTS

Low-dose aspirin increased closure times significantly (62% by Day 10, P < .001), with an equal distribution among aspirin responsiveness categories, 8 dogs per group. Platelet COX-1 mean fluorescent intensity (MFI) increased significantly during treatment, 13% on Day 3 (range, -29.7-136.1%) (P = .047) and 72% on Day 10 (range, -0.37-210%) (P < .001). Platelet COX-2 MFI increased significantly by 34% (range, -29.2-270%) on Day 3 (P = .003) and 74% (range, -19.7-226%) on Day 10 (P < .001). Urinary 11-dTXB(2) concentrations significantly (P = .005, P < .001) decreased at both time points. There was no difference between aspirin responsiveness and either platelet COX expression or thromboxane production.

CONCLUSIONS AND CLINICAL IMPORTANCE

Low-dose aspirin consistently inhibits platelet function in approximately one-third of healthy dogs, despite decreased thromboxane synthesis and increased platelet COX expression in most dogs. COX isoform expression before treatment did not predict aspirin resistance.

Defects in coagulation encountered in small animal critical care

Critically ill small animals are at risk for developing coagulation abnormalities. The processes of inflammation and coagulation are intertwined, and severe inflammation can lead to disturbances of coagulation. Severe coagulation dysfunction is associated with increased morbidity and mortality. Pathophysiology, diagnosis, and treatment of coagulation dysfunction are discussed. Defects in coagulation in small animal patients are complex and a consensus on diagnosis and treatment has yet to be reached.

The effect of Hetastarch (670/0.75) in vivo on platelet closure time in the dog

OBJECTIVE

To evaluate the effect of 6% hydroxyethyl starch (HES) solution in vivo, with an average molecular weight of 670 kDa and degree of substitution of 0.75, on canine platelet function.

DESIGN

Prospective, controlled-experimental study.

SETTING

University of California, Davis, Veterinary Medical Teaching Hospital.

ANIMALS

Seven healthy employee-owned dogs.

INTERVENTIONS

Seven dogs were included in the treatment group. Four of these dogs also served as the control group. Platelet closure time (CT) was measured using a platelet function analyzer and collagen/ADP cartridges. Dogs were given 20 mL/kg of either sodium chloride 0.9% (control group, n=4) or HES (treatment group, n=7) IV over 1 hour. CT was measured before the infusion, and at 1, 3, 5, and 24 hours after the start of the infusion.

MEASUREMENTS AND MAIN RESULTS

There was a significant change over time from 0 to 24 hours (P<0.001), a significant difference between groups across time (P<0.001), and a significant group-by-time interaction (P=0.007). At 3 hours, mean CT for the treatment group was 122.3+/-18.1 seconds, which was significantly different (P<0.001) from the control group (71.0+/-3.5 s). At 5 hours, mean CT for the treatment group was 142.7+/-33.9 seconds, which was significantly different (P=0.001) from the control group (75.0+/-8.6 s). Mean CT at 24 hours was within the reference interval for both the control and treatment group (66.0+/-2.9 and 81.8+/-11.9 s, respectively); however, CT in 3 individual dogs in the treatment group at this time point remained prolonged.

CONCLUSIONS

A clinically relevant dose of HES 670/0.75 prolongs CT in dogs for up to 24 hours. This may be due to platelet dysfunction in addition to the effects of hemodilution, and therefore, may increase the risk of bleeding.

The effect of physical exercise on the daily rhythm of platelet aggregation and body temperature in horses

The goal of this study was to investigate the influence of physical activity on the daily rhythm of platelet aggregation and body temperature in horses. Blood samples from 12 Thoroughbred horses, six sedentary animals and six athletes (studied both before and after a period of inactivity) were collected at 4h intervals for 48h via an intravenous cannula inserted into the jugular vein. Body temperature was recorded every 4h for 48h with a rectal probe. Platelet aggregation was measured with an aggregometer. Collagen was used to test the aggregation of the plasma samples. Statistical analysis of the data was performed by one-way repeated-measures analysis of variance (ANOVA) and by single cosinor method. Cosinor analysis identified the periodic parameters and their acrophases (expressed in hours) during the 2 days of monitoring. On each single day, there was a highly significant effect of time in all the horses, with P values <0.05. Temperature rhythms were unaffected by exercise. Platelet aggregation in exercising horses differed from the sedentary horses, and this difference disappeared after a 2-week period of rest. The results could be interpreted as indicating that physical exercise has an influence on the daily rhythm of platelet aggregation in horses.

Influencing factors of ADP-induced, epinephrine-induced and ristomycin-induced platelet aggregation in dogs

Functional defects of platelets are often studied by in-vitro aggregation tests with chemical compounds such as ADP, epinephrine and ristomycin (ristocetin). The aim of the present work was to investigate the effect of some diseases and that of nonsteroidal anti-inflammatory drug treatment on platelet aggregation in dogs. The examination had been carried out on 115 dogs by a Carat TX4 optical aggregometer (Entec GmbH, Ilmenau, Germany) first used in veterinary practice. The dogs were divided in three groups: healthy (control) dogs (n = 43), diseased dogs with normal haemostasis profile (n = 44), and dogs suffering from arthropathies with normal haemostasis profile treated with the nonsteroidal anti-inflammatory drugs ketoprofen or carprofen (n = 21). Following establishment of normal platelet aggregation curves in healthy dogs we found that some diseases such as diabetes mellitus, Cushing's disease, mastocytoma and lymphoma increased or decreased the aggregation maximum of platelets or caused changes in the feature of the aggregation curve. Carprofen treatment had no effect on platelet aggregation while ketoprofen decreased the aggregation maximum. These results showed that Carat TX4 aggregometer proved a useful instrument in studying platelet aggregation in platelet-rich plasma of dogs. For clinical pathologists it is important to know that the effects of some diseases and nonsteroidal anti-inflammatory drug treatments have to be taken into account when in-vitro platelet aggregation is evaluated. Based on our results and on those of other studies, we think standardization in aggregation methodology is highly recommended in veterinary laboratories.

Evaluation of a bench-top coagulation analyzer for measurement of prothrombin time, activated partial thromboplastin time, and fibrinogen concentrations in healthy dogs

OBJECTIVE

To evaluate a bench-top coagulation analyzer for determination of prothrombin time (PT), activated partial thromboplastin time (APTT), and fibrinogen concentration in healthy dogs.

ANIMALS

55 healthy adult dogs.

PROCEDURES

PT, APTT, and fibrinogen concentration were determined by use of the coagulation analyzer. Values were compared with results obtained independently by a conventional laboratory.

RESULTS

Correlations (with 95% confidence intervals) between the coagulation analyzer and conventional laboratory values were 0.760 (0.610 to 0.857), 0.700 (0.448 to 0.721), and 0.896 (0.878 to 0.918) for PT, APTT, and fibrinogen concentration, respectively. Using linear regression, comparison of data from the coagulation analyzer and the conventional laboratory provided equations relating the coagulation analyzer values with values from the conventional laboratory and suggested that APTT and fibrinogen values from the coagulation analyzer and conventional laboratory were approximately the same within expected random variation. Prothrombin time values for the coagulation analyzer were significantly offset from the PT values for the conventional laboratory but still were correlated reasonably well with the conventional laboratory values.

CONCLUSIONS AND CLINICAL RELEVANCE

By use of the mechanical method of analysis, fibrinogen concentrations obtained with a bench-top coagulation analyzer correlated well with results for a conventional laboratory, indicating that the coagulation analyzer is a reliable instrument for determination of this coagulation variable. Coagulation analyzer results for PT and APTT correlated less strongly with those for the conventional laboratory, but they would still be considered clinically reliable.

Platelet function in dogs: breed differences and effect of acetylsalicylic acid administration

BACKGROUND

Clinical studies investigating platelet function in dogs have had conflicting results that may be caused by normal physiologic variation in platelet response to agonists.

OBJECTIVES

The objective of this study was to investigate platelet function in clinically healthy dogs of 4 different breeds by whole-blood aggregometry and with a point-of-care platelet function analyzer (PFA-100), and to evaluate the effect of acetylsalicylic acid (ASA) administration on the results from both methods.

METHODS

Forty-five clinically healthy dogs (12 Cavalier King Charles Spaniels [CKCS], 12 Cairn Terriers, 10 Boxers, and 11 Labrador Retrievers) were included in the study. Platelet function was assessed by whole-blood aggregation with ADP (1, 5, 10, and 20 microM) as agonist and by PFA-100 using collagen and epinephrine (Col + Epi) and Col + ADP as agonists. Plasma thromboxane B(2) concentration was determined by an enzyme immunoassay. To investigate the effect of ASA, 10 dogs were dosed daily (75 or 250 mg ASA orally) for 4 consecutive days.

RESULTS

A higher platelet aggregation response was found in CKCS compared to the other breeds. Longer PFA-100 closure time (Col + Epi) was found in Cairn Terriers compared to Boxers. Plasma thromboxane B(2) concentration was not statistically different between groups. Administration of ASA prolonged the PFA-100 closure times, using Col + Epi (but not Col + ADP) as agonists. Furthermore, ASA resulted in a decrease in whole-blood platelet aggregation.

CONCLUSIONS

Platelet function is influenced by breed, depending upon the methodology applied. However, the importance of these breed differences remains to be investigated. The PFA-100 method with Col + Epi as agonists, and ADP-induced platelet aggregation appear to be sensitive to ASA in dogs.