The Endothelial‐Independent Effect of Desmopressin, In Vitro, on Platelet Function

Thrombocytopenia in chronic liver disease: Lessons from transplanted patients

Assessment of platelet function utilizing viscoelastic testing.

Platelets play a critical role in the pathophysiology of atherothrombotic disease. A pivotal event contributing to the understanding of platelet-dependent clot formation was the development of the platelet aggregometer in 1962.1 An aggregometer specifically measures the ability of platelets to adhere via glycoprotein IIb/IIIa (integrin αIIbβ3), and thousands of articles using this technique have been published, characterizing platelet function; however, the usefulness of these measurements remains unclear. Whereas the aggregometer and related techniques that measure platelet aggregation or glycoprotein expression have led to large amounts of data characterizing platelet function in various settings, the clinical importance of measurable differences in platelet function is still debated.2 The use of platelet function testing is established in rarer platelet abnormalities, such as the autosomal recessive bleeding disorder Glanzmann thrombasthenia,3 but no clear consensus has been reached on its usefulness for highly prevalent diseases caused by platelet-dependent thrombosis, such as myocardial infarction. A major factor for this discrepancy is that many of the platelet function defects that lead to bleeding are known to be caused by a single defect, whereas thrombosis in the setting of cardiovascular disease is presumed to be multifactorial. Article p 2490 The evolution of platelet function studies in various clinical settings has led to the realization that wide interindividual variability exists in the platelet activation response.4,5 What accounts for this variability? Only a few studies have systematically examined this question. Platelet function has been established as markedly dependent on the type of agonist used, the agonist concentration, and the concomitant use of antiplatelet therapy.6 In addition, in the large population-based Framingham Heart Study, O’Donnell and colleagues7 have demonstrated that heritable factors play a major role in determining platelet aggregation, as opposed to measured covariates. Less clear from the current literature is the direct …

Low COAT platelets are frequent in patients with bleeding disorders of unknown cause (BDUC) and can be enhanced by DDAVP

In vitro evaluation of stored platelets: is there hope for predicting posttransfusion platelet survival and function?

Abnormal hemostasis is associated with many of the complications of trauma-associated morbidity and mortality. Platelets are integral in the maintenance of hemostasis. Samples were obtained from 100 trauma patients on arrival at the emergency room (initial time) and at 24, 48, and 72 hours later. Samples were also obtained from 10 healthy controls at the same time intervals. Using flow cytometry, three parameters were used to measure platelet activation: platelet microparticles, expression of P-selectin (CD62P), and expression of the activated conformation of glycoprotein IIb-IIIa (PAC-1 binding). Platelet function was measured using a platelet function analyzer (PFA-100, Dade International Inc., Miami, FL). One hundred trauma patients were enrolled. The average age was 40 years, 75% were men, and 84% had blunt injuries. The mean Injury Severity Score was 22.3 +/- 10.9 (mean +/- SD) and the average Glasgow Coma Scale score was 11 +/- 4. All three platelet activation parameters were increased in trauma patients versus controls for all time periods (p < 0.001). Trauma patients had a trend toward a shorter initial collagen/epinephrine closure time versus controls (p = 0.096). Compared with the 24-, 48-, and 72-hour time intervals, initial collagen/epinephrine closure times were shortened (p < 0.001, p < 0.001, and p < 0.001). Platelet function returned to normal reference ranges within 24 hours but platelet activation parameters remained elevated at least 72 hours after initial trauma. In contrast, when trauma patients with and without brain injury were compared, brain injury patients had increased platelet activation but decreased platelet function (increased collagen/epinephrine closure times). In addition, there was a significant prolongation in collagen/epinephrine closure times for the 24-, 48-, and 72-hour time points in nonsurviving patients versus survivors. There was no association between platelet activation and function and other adverse outcomes including pulmonary embolism, deep venous thrombosis, and disseminated intravascular coagulation. Severe injury usually results in increased platelet activation and function. However, the combination of increased platelet activation with decreased function was associated with increased mortality.

No evidence for an intrinsic platelet defect in patients with liver cirrhosis--studies under flow conditions.

Splenectomy during liver transplant can affect platelet function. In this study, our primary aim was to assess the perioperative platelet function by rotational thromboelastometry and the effects of splenectomy on platelet function. We studied 40 consecutive liver transplant recipients with end-stage liver disease (50% as a result of hepatitis C). Patients with splenectomy were compared with patients without splenectomy (n = 20/group). Three platelet function parameters by rotational thromboelastometry were studied: platelet activation with arachidonic acid, platelet activation with adenosine diphosphate, and platelet activation with thrombin receptor-activating peptide 6. Patients were monitored perioperatively and until postoperative day 21. Heparin was infused for 2 days postoperatively (60-180 U/kg/day), followed by administration of subcutaneous low-molecular-weight heparin (40 mg/24 h) on postoperative days 2 and 3 and oral acetylsalicylic acid when platelet count was >50 × 103/μL. Liver disease contributed to low perioperative platelet count and function. Patients showed significant improvement by postoperative day 14 and day 21, particularly after splenectomy. Platelet count was significantly correlated with the 3 platelet function parameters by rotational thromboelastometry (P < .001). Acetyl salicylic acid was required earlier (postoperative day 3) for patients with splenectomy (8/20) but only affected the platelet function represented by platelet activation with arachidonic acid, whereas other platelet activation pathways were less affected. Patients received no transfusions of platelet units. End-stage liver disease significantly contributed to low platelet function and counts before transplant. Two weeks were required for recovery of patients posttransplant, with further enhancement by splenectomy. Some recipients showed recovery that exceeded the normal reference range, which warranted monitoring. Acetyl salicylic acid only affected 1 platelet activation receptor.

We describe a patient who experienced intraoperative bleeding after being treated with platelet receptor glycoprotein IIb/IIIa antagonist eptifibatide. We used Sonoclot and Thrombelastograph to monitor antiplatelet effects of eptifibatide.

SOD2 in platelets: with age comes responsibility

Current methods of assessing platelet function: relevance to transfusion medicine

Clotting, anticoagulation, platelet consumption, and poor platelet function are major factors in clinical extracorporeal circulation (ECC). We have shown that nitric oxide-releasing (NOReL) coatings prevent thrombosis in a rabbit model of ECC without systemic anticoagulation. Nitric oxide-releasing prevents platelet adhesion and activation, resulting in preserved platelet count and function. Previous work has shown that activated platelets form platelet-derived microparticles (PMPs). These experiments were designed to determine if PMPs can identify platelet function during ECC. The objective of this study is to investigate the effects of NOReL on platelet activation and PMP formation during ECC. Uncoated ECCs, including with and without systemic heparin, and NOReL-coated ECCs, including DBHD/N2O2 and argatroban (AG)/DBHD/N2O2-coated ECCs without systemic heparin, were tested in a 4-hour rabbit thrombogenicity model. Before and after ECC exposure, platelets were stimulated with collagen, and PMPs were measured using flow cytometry. The uncoated ECCs clotted within the first hour, while the NOReL-coated ECCs circulated for 4 hours. During pre-ECC blood exposure, platelets stimulated with collagen produced PMPs. With post-ECC exposure, platelets from uncoated circuits generated less PMPs than baseline (mean ± SDs: 23246 ± 3611 baseline vs. 1300 ± 523 uncoated post circuit, p = 0.018) when stimulated with collagen. However, platelets from the AG/DBHD/N2O2-coated ECCs generated a greater number of PMPs as baseline values (23246 ± 3611 baseline vs. 37040 ± 3263 AG/DBHD/N2O2 post 4 hours circuit, p = 0.023). Blood exposure during ECC results in platelet activation and clotting in uncoated ECCs. The remaining circulating platelets have lost function, as demonstrated by the low PMP formation in response to collagen. AG/DBHD/N2O2-coated ECCs prevented significant platelet activation and clotting, while DBHD/N2O2 trended towards prevention of platelet activation. In addition, function of the circulating platelets was preserved, as demonstrated by PMP formation in response to collagen. These results indicate that PMPs may be an important measure of platelet activation during ECC. Platelet-derived microparticles may provide a simplified way to measure platelet function during clinical ECC.

Achieving haemostasis and, simultaneously, preventing venous thromboembolism (VTE) in the perioperative and critical care setting is challenging. Although the traditional coagulation parameters, including international normalised ratio (INR), activated partial thromboplastin time (aPTT) and platelet count, are important, evidence suggests that far more subtle aspects of platelet dysfunction may occur without antiplatelet therapy, and play a pivotal role both in critical bleeding and the pathogenesis of VTE. With advances in our ability to measure platelet activity and function beyond platelet count alone, we are making substantial progress in our understanding of how and when platelets interact and cross-talk with coagulation factors to achieve haemostasis and, conversely, contribute to the development of VTE after major surgery or trauma. With the ability to quantify the ability of platelets to aggregate, it is clear that platelet function tests have the potential to assist prediction of bleeding after cardiac surgery, especially for those who are treated with P 2 Y 12 -blockers. In addition, unregulated platelet activation or, conversely, platelet dysfunction in the absence of antiplatelet therapy, is increasingly being recognised as one of the key missing elements in the pathogenesis of VTE or critical bleeding, respectively. Our current understanding of the coagulation system—in particular the significance of platelet dysfunction and activation—may not be adaptive to benefit survival in all patients, especially after traumatic brain injury (TBI). Indeed, cardiolipin release from damaged neuronal mitochondria into the systemic circulation may explain why coagulopathy after TBI is associated with increased VTE instead of bleeding. Similarly, in patients with acquired coagulopathy due to liver disease, sepsis or trauma, excessive platelet activation has been observed explaining why these patients are not immune to developing VTE and, hence, VTE prophylaxis is still needed. While many drugs can inhibit platelet function through one of the three major platelet activation pathways—cyclooxygenase/thromboxane A 2 , P 2 Y 12 -ADP and thrombin—currently we do not have many interventions that can improve platelet function. Recent evidence suggested that an antioxidant polyphenol, resveratrol, may improve platelet function by reducing apoptosis and improving platelet mitochondrial function. We are now entering the exciting stage of precision-medicine in the area of coagulation in perioperative and critical care. Ultimately, we would be able use information beyond abnormal platelet count, INR and aPTT to guide platelet transfusion including withholding unnecessary platelet transfusion, and also avoid omission of VTE prophylaxis in the critically ill.

The pathophysiological background of chronic thromboembolic pulmonary hypertension (CTEPH) has not been fully elucidated. Evidence suggests that abnormal platelet function and ineffective fibrinolysis may play a key role in the development of the disease. The purpose of this study was to evaluate platelet and coagulation function in CTEPH, using non-conventional global coagulation assays, and platelet activation and endothelial dysfunction laboratory markers. A total of 40 newly-diagnosed CTEPH patients were studied, along with 35 healthy controls. Blood samples from CTEPH patients were taken directly from the pulmonary artery. All subjects were assessed with platelet function analyzer-100, light transmission aggregometry, thromboelastometry, endogenous thrombin potential. von Willebrand antigen and activity, p-selectin, thromboxane A2 and serotonin levels were also assessed. The results showed that CTEPH patients present diminished platelet aggregation, presence of disaggregation, decreased rate of fibrinolysis, defective thrombin generation and increased levels of thromboxane A2, p-selectin, von Willebrand antigen and activity. Serotonin levels did not present any differences between the two groups. The results of this study suggest that CTEPH patients present platelet function, fibrinolytic, thrombin generation and other clot formation abnormalities. Well-designed clinical studies are needed to further evaluate the complex hemostatic abnormalities in the CTEPH setting and assess their potential clinical applications.

DDAVP is not a panacea for children with bleeding disorders.