Point-of-care assessment of antiplatelet agents in the perioperative period: a review

Extended sample storage for platelet function testing in healthy dogs

BACKGROUND

Platelet function testing is important for monitoring the effects of antiplatelet therapy but is not readily used due to time constraints for testing and the need for specialized equipment.

OBJECTIVES

This study evaluated the effects of various storage methods on selected platelet function tests to determine if delayed platelet function testing is feasible in canine blood samples. Our hypotheses were that platelet function would not decline during storage and, thus, no differences in test results would be found over time.

METHODS

Thirteen healthy dogs were studied. Citrated blood samples were tested with a Platelet Function Analyzer-200 (PFA), which mimics high-shear conditions, using P2Y and CADP cartridges, after being held at room temperature for 2 h and refrigerated for 24 and 48 h. Plateletworks (PW), which measures aggregation based on platelet counting, was performed on an optical hematology analyzer using 10-min-old native samples, citrated samples held at room temperature for 3-4 h and refrigerated for 24 and 48 h, and samples stored in the preservative solution, AGGFix, up to 7 days.

RESULTS

PFA closure times increased with storage, especially with the P2Y cartridge. Median aggregation with fresh PW was 94%, and this was maintained at all time points (range of median values 88%-94%). Most samples showed decreased, yet still robust (>70%), aggregation with longer storage. Spontaneous aggregation in citrate was noted in most dogs. AGGFix stabilized platelet aggregates to allow for delayed testing.

CONCLUSIONS

Delayed platelet function testing is feasible, but ranges of expected values may differ from tests using fresh samples.

Monitoring of Antiplatelet Therapy

In the late 1990s, the antithrombotic antiplatelet agent, clopidogrel, a P2Y12 inhibitor, was introduced. Around the same time, there was an increase in a number of new methods to measure platelet function (e.g., PFA-100 in 1995), and this has continued. It became evident that not all patients responded to clopidogrel in the same way and that some patients had a relative "resistance" to therapy, termed "high on-treatment platelet reactivity." This then led to some publications to advocate platelet function testing being used for patients on antiplatelet therapy. Platelet function testing was also suggested for use in patients awaiting cardiac surgery after stopping their antiplatelet therapy as a way of balancing thrombotic risk pre-surgery and bleeding risk perioperatively. This chapter will discuss some of the commonly used platelet function tests used in these settings, particularly those that are sometimes referred to as point-of-care tests or that require minimal laboratory sample manipulation. The latest guidance and recommendations for platelet function testing will be discussed following several clinical trials looking at the usefulness of platelet function testing in these clinical settings.

Effect of packed red blood cell transfusion on thromboelastographic tracings in dogs with naturally occurring anemia

OBJECTIVE

To assess the effect of packed RBC (pRBC) transfusion on thromboelastographic (TEG) tracings in dogs with naturally occurring anemia.

ANIMALS

22 clinically anemic dogs that received a pRBC transfusion.

PROCEDURES

For each dog, a blood sample was collected before and within 3 hours after completion of the pRBC transfusion for a CBC, nonactivated TEG analysis, and measurement of blood viscosity. Wilcoxon signed rank tests were used to compare CBC, viscosity, and TEG variables between pretransfusion and posttransfusion blood samples. Multivariable linear regression was used to assess the effects of pretransfusion-posttransfusion changes in Hct, WBC count, and platelet count on changes in TEG variables.

RESULTS

Median posttransfusion Hct (21%; range, 13% to 34%) was significantly greater than the median pretransfusion Hct (12.5%; range, 7% to 29%). Packed RBC transfusion was associated with a median increase in Hct of 6.2% (range, 1.2% to 13%). Maximum amplitude significantly decreased from 74.9 to 73.8 mm and clot strength significantly decreased from 14,906 to 14,119 dynes/s after pRBC transfusion. Blood viscosity significantly increased, whereas platelet and WBC counts significantly decreased after transfusion. Multivariable linear regression revealed that pretransfusion-posttransfusion changes in Hct, WBC count, and platelet count were not associated with changes in TEG variables.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that pRBC transfusion had only small effects on the TEG tracings of hemodynamically stable dogs. Therefore, large changes in TEG tracings following pRBC transfusion are unlikely to be the result of the transfusion and should be investigated further.

Antiplatelet Effect of Ketorolac in Children After Congenital Cardiac Surgery

Background:

Ketorolac is used for pediatric analgesia after surgery despite its known platelet inhibition via the arachidonic acid (AA) pathway. The degree of platelet inhibitory effect after cardiac surgery is not well characterized. Thromboelastography with platelet mapping (TEG-PM) is emerging as a frequently used test to evaluate platelet inhibition via the AA pathway.

Methods:

Post hoc analysis of a data set collected in a prospective observational cohort study evaluating platelet inhibition in children after congenital heart surgery with cardiopulmonary bypass (CPB). Categorization into two groups: (1) received ketorolac and (2) did not receive ketorolac for analgesia after surgery. The TEG-PM was evaluated at two time points (prior to surgery and 12-48 hours after CPB).

Results:

Fifty-three children were studied; mean age was 6.6 (range: 0.07-16.7) years and 45% (n = 24) were female. Participants were distributed into two groups by ketorolac use, 41 within the ketorolac group and 12 in the no ketorolac group. All 41 participants who received ketorolac had platelet inhibition and 11 (91.7%) of 12 participants who did not receive ketorolac had normal platelet function after surgery ( P < .0001). There was no difference in patient characteristics or clinical data between the two groups.

Conclusions:

Ketorolac use in a cohort of children after congenital cardiac surgery was associated with platelet inhibition via the AA pathway when evaluated by TEG-PM.

Effects of a targeted blood management programme on allogeneic blood transfusion in abdominal aortic aneurysm surgery

OBJECTIVES

To investigate the impact of a dedicated cell salvage practitioner team on blood loss and allogeneic transfusion in abdominal aortic aneurysm (AAA) surgery.

BACKGROUND

Cell salvage reduces allogeneic transfusion in AAA surgery, but is commonly performed by the anaesthetic nurse. At our hospital, a dedicated patient blood management practitioner is present for all elective open AAA repairs.

METHODS/MATERIALS

Data were collected on 171 AAA patients operated on at the John Radcliffe Hospital, Oxford over a 3-year period, looking at the Patient Blood Management processes, including: blood loss, cell salvage, near-patient testing (thrombelastography) and transfusion rates of allogeneic blood products.

RESULTS

Blood loss ranged from 3-108% of estimated blood volume (EBV) (median 25% = 1500 mL). In seven patients who lost 70-110% of their EBV, none reached the thrombelastography intervention threshold for R time (11 min) or MA (48 mm) despite such massive blood loss. Overall, only 7/171 (4%) patients received intra-operative allogeneic blood, all of whom had a mean baseline haemoglobin concentration < 106 g L^-1 (median 98, range 95-105 g L^-1 ). In terms of other blood products, only 4/171 (2·3%) received one unit of platelets each intra-operatively. None received FFP or cryoprecipitate.

CONCLUSIONS

Such low levels of allogeneic transfusion have not been reported previously. We hypothesise that this is due to the additional blood management contributions of the specialised cell salvage practitioners and collaboration with the rest of the vascular surgical team. These results support the development of pre-operative anaemia clinics. Overall the service runs at a profit to the trust.

Essential Thrombocytosis and Labor Epidural Placement While on Aspirin: Assessing Hemorrhagic Risks: A Case Report

Essential thrombocytosis (ET) is a rare disease with known thrombotic and bleeding complications. We encountered a patient with a diagnosis of longstanding Janus kinase-2 gene-negative ET on aspirin therapy presenting for labor epidural. Evaluation of platelet function with point-of-care analysis using Plateletworks in a community hospital setting allowed confirmation of adequate numbers of functional platelets to support safe epidural placement. The relevant issues of ET for anesthesia management with labor epidurals are discussed. Unique, relevant, and unexpected findings from the platelet function testing are presented.

Platelet-mapping assay for monitoring antiplatelet therapy during mechanical circulatory support in children: A retrospective observational study

INTRODUCTION

The complex hemostatic changes associated with Berlin Heart (BH) implantation in children require a challenging antithrombotic treatment. The aim of this retrospective analysis was to evaluate the thromboelastography (TEG)-platelet mapping (PM) assay to monitor antiplatelet therapy in children implanted with a BH.

METHODS

TEG-PM was performed in 4 BH-implanted patients receiving dipyridamole and aspirin, and 9 healthy volunteers. Patients' antiplatelet therapy was adjusted to TEG-PM results. Light transmission aggregometry (LTA) was also available for 2 of these patients.

RESULTS

Between 2009 and 2014, 4 BH-implanted patients received a dual antiplatelet therapy monitored by TEG-PM. In 2 patients, 18 of 34 tracings were atypical, because the maximum amplitude due to fibrin never stabilized, which made difficult antiplatelet therapy adjustment as recommended by BH's guidelines. To overcome this difficulty, TEG-PM and LTA were next performed in parallel. However, both methods led to different decisions to adjust antiplatelet therapy in 57% of the cases. In order to better understand this atypical tracing, TEG-PM was also performed in 9 volunteers and surprisingly 3 of them had the same atypical tracing. This atypical tracing was corrected by adding apyrase, suggesting that adenosine diphosphate (ADP) participates to spontaneous platelet activation in heparinized samples. In addition, we evidenced a high variability in the responses of TEG-PM with ADP in volunteers.

CONCLUSIONS

Antiplatelet therapy monitoring in BH-implanted children remains challenging, as TEG-PM is sensitive to several preanalytical and analytical conditions.

Applying the Cell-Based Coagulation Model in the Management of Critical Bleeding

The cell-based coagulation model was proposed 15 years ago, yet has not been applied commonly in the management of critical bleeding. Nevertheless, this alternative model may better explain the physiological basis of current coagulation management during critical bleeding. In this article we describe the limitations of the traditional coagulation protein cascade and standard coagulation tests, and explain the potential advantages of applying the cell-based model in current coagulation management strategies. The cell-based coagulation model builds on the traditional coagulation model and explains many recent clinical observations and research findings related to critical bleeding unexplained by the traditional model, including the encouraging results of using empirical 1:1:1 fresh frozen plasma:platelets:red blood cells transfusion strategy, and the use of viscoelastic and platelet function tests in patients with critical bleeding. From a practical perspective, applying the cell-based coagulation model also explains why new direct oral anticoagulants are effective systemic anticoagulants even without affecting activated partial thromboplastin time or the International Normalized Ratio in a dose-related fashion. The cell-based coagulation model represents the most cohesive scientific framework on which we can understand and manage coagulation during critical bleeding.

Management of a Patient with a Thoracic Epidural After Accidental Clopidogrel Administration

We report a case of accidental clopidogrel administration in a patient receiving ongoing epidural analgesia postoperatively. The epidural catheter was removed 7 hours after the clopidogrel dose without incident. The onset of inhibition of adenosine diphosphate-induced platelet aggregation in healthy individuals has been reported at 12 to 24 hours after administration of a single 75-mg dose of clopidogrel. This case demonstrates the importance of understanding clopidogrel's pharmacology to avoid ordering unnecessary tests, which may delay catheter removal. Consideration of appropriate testing and limitations in the context of unintentional antiplatelet administration with indwelling neuraxial catheters is discussed.

Temperature effects on haemostasis in whole blood from ticagrelor- and aspirin-treated patients with acute coronary syndrome

BACKGROUND

Comatose survivors after cardiac arrest are treated with mild induced hypothermia and potent platelet- inhibiting drugs after coronary stenting. Previous studies have shown an increased incidence of stent thrombosis during clopidogrel and aspirin treatment in conjunction with induced hypothermia. The aim of this study was to investigate the in vitro effect of induced hypo- and hyperthermia on blood from patients undergoing ticagrelor- and aspirin-mediated platelet inhibition.

METHODS

Whole blood from 15 patients with acute coronary syndrome who were treated with ticagrelor and aspirin and from eight healthy volunteers was incubated for 1 hour at 28, 33, 37, and 39°C.

RESULTS

In blood from patients with acute coronary syndrome, the activated clotting time (Sonoclot) was prolonged in mild hypothermic (33°C) compared to normothermic (37°C) samples. Sonoclot, clotting rate and platelet function were decreased in hypothermic compared to normothermic samples. Platelet-induced activation and aggregation (Multiplate) was unchanged in mild hypothermic compared to normothermic samples. In contrast, mild hypothermia supported increased platelet activation as measured with flow cytometry with up-regulation of PAC-1 and P-selectin on the platelet surface.

CONCLUSION

In acute coronary syndrome patients treated with ticagrelor and aspirin, in vitro hypothermia to 33°C markedly increased platelet activity measured with flow cytometry, whereas viscoelastic coagulation test (Sonoclot) revealed a hypocoagulative response. Prospective clinical trials studying platelet inhibition at different temperatures and correlating changes in platelet function to bleeding or stent occlusion are needed.

Platelet aggregation and clot formation in comatose survivors of cardiac arrest treated with induced hypothermia and dual platelet inhibition with aspirin and ticagrelor; a prospective observational study

INTRODUCTION

We conducted a prospective observational study in cardiac arrest survivors treated with mild induced hypothermia, evaluating different platelet function tests at hypo- and normothermia. We also investigated the relation between gastric emptying and vasodilator stimulated phosphoprotein (VASP).

METHODS

Comatose survivors of out of hospital cardiac arrest were included and divided into two groups, depending on whether dual platelet inhibition with peroral ticagrelor and aspirin was given or not. The first blood samples (T1) were collected 12-24 hours after reaching target temperature (33°C) and were compared to blood samples collected 12-28 hours after reaching normothermia (37°C) (T2) within each group. All samples were analysed by Sonoclot viscoelasticity, flow cytometry based VASP and with multiple electrode aggregometry, Multiplate®; adenosine diphosphate (ADP), collagen (COL), thrombin receptor agonist peptide (TRAP) and arachidonic acid (ASPI). Sonoclot and Multiplate® instruments were set on in vivo temperatures. Gastric secretion from the nasogastric tube was measured to assess absorption of per orally administered antiplatelet drugs. Differences between T1 and T2 within each group were calculated using Wilcoxon matched pairs signed test. Significance levels were set at P <0.01.

RESULTS

In total, 23 patients were included. In patients with dual platelet inhibition (n =14) Multiplate®-analyses showed no changes in ADP stimulated platelets. COL, TRAP and ASPI aggregations were higher at T2 compared to T1. Sonoclot-analyses showed that activated clotting time (ACT) was unchanged but both clot rate (CR) and platelet function (PF) were higher at T2 compared to T1. VASP decreased from 53 ± 28(T1) to 24 ± 22(T2), (P <0.001). The average volume of gastric secretion aspirated before T1 correlated well with VASP (T1), r =0.81 (P <0.001). In patients with no platelet inhibition, (n =9) similar changes between T1 and T2 were seen as in patients with dual platelet inhibition while VASP was unchanged.

CONCLUSIONS

We have demonstrated increased platelet aggregation and strengthened clot formation over time in out of hospital cardiac arrest patients treated with hypothermia. In patients on oral dual platelet inhibition, the effect of ticagrelor was delayed, probably due to slow gastric emptying.

Platelet mapping assay interference due to platelet activation in heparinized samples

OBJECTIVES

Thromboelastography Platelet Mapping (TEGPM) is an assay designed to detect platelet inhibition due to aspirin or clopidogrel-like drugs. The purpose of this study was to evaluate potential causes of error in the design or operation of the assay.

METHODS

We evaluated percent inhibition of platelets due to aspirin or clopidogrel using TEGPM, which measures clot viscoelastic maximum amplitude (MA) after activation with adenosine diphosphate (ADP) or arachidonic acid (AA) and subtraction of MA due to fibrin (MAFibrin).

RESULTS

MAFibrin measured in heparinized blood showed an unstable increasing pattern in 28% of samples (16 of 58). The platelet aggregation inhibitor eptifibatide corrected increasing MAFibrin in 14 of 16 cases, while the thrombin inhibitor argatroban corrected increasing MAFibrin in six of 16 cases, suggesting that unanticipated platelet activation/ aggregation was a more important cause of unstable rising MAFibrin than uninhibited thrombin. The unstable increased MAFibrin falsely increased percent ADP inhibition on average from 19% to 38% and percent AA inhibition from 29% to 58%. Heparinized samples showed platelet clumping and had procoagulant platelet microvesicle levels double those in citrate anticoagulant.

CONCLUSIONS

Unanticipated platelet activation/aggregation occurring in the heparinized TEGPM samples lead to erroneous percent inhibition results.

Brodde M. State of the art in platelet function testing

Platelets perform many functions in hemostasis but also in other areas of physiology and pathology. Therefore, it is obvious that many different function tests have been developed, each one conceived and standardized for a special purpose. This review will summarize the different fields in which platelet function testing is currently in use; diagnostics of patients with bleeding disorders, monitoring patients' response to anti-platelet therapy, monitoring in transfusion medicine (blood donors, platelet concentrates, and after transfusion), and monitoring in perioperative medicine to predict bleeding tendency. The second part of the review outlines different methods for platelet function testing, spanning bleeding time, and platelet counting as well as determining platelet adhesion, platelet secretion, platelet aggregation, platelet morphology, platelet signal transduction, platelet procoagulant activity, platelet apoptosis, platelet proteomics, and molecular biology.

Learning curve of Wingspan stenting for intracranial atherosclerosis: single-center experience of 95 consecutive patients

Background

Symptomatic brain hemorrhage was a significant cause of periprocedural stroke or death following stenting in the Stenting and Aggressive Medical Management for Preventing Recurrent Stroke in Intracranial Stenosis trial, which called into question the safety of Wingspan stenting for intracranial atherosclerosis. This study analyzed the role of a learning curve in the safety and outcome of Wingspan stenting from the experience of 95 consecutive patients at a single center.

Methods

In this prospective study the endpoints were major stroke or death (modified Rankin Scale score >3) within 30 days, other neurological complications, technical procedural problems, technical success in completion of angioplasty and stenting and recurrent ischemic stroke in the corresponding vascular territory after 30 days. Data splitting into quarters was used for learning curve analysis.

Results

The periprocedural major stroke or death rate was 4.2% (4/95), minor stroke rate was 5.3% (5/95), total 9.5% (9/95). The technical procedural problem rate was 11.6% (11/95) and the technical success rate was 93.7% (89/95). The 89 patients were followed for 38.9±22.7 months (median 40.8, range 0.2–72, 3463 patient-months) after stenting. The risk of recurrent ischemic stroke in the corresponding vascular territory was 0.7% per patient per year (2/3463 patient-months). Guidewire- or angioplasty-related hemorrhage was the major cause of periprocedural major stroke or death (3/4, 75%) and did not occur in the last quarter. Periprocedural intracerebral hemorrhage was uncommon and perforator stroke did not occur.

Conclusions

There may be a learning curve for mastering the safety precautions of Wingspan stenting for intracranial atherosclerosis.

P2Y12 Receptor Inhibitors in Acute Coronary Syndromes: What Is New on the Horizon?

Dual antiplatelet therapy with aspirin and a P2Y₁₂ receptor inhibitor represents the cornerstone therapy for patients with acute coronary syndromes or undergoing percutaneous interventions, leading to a reduction of subsequent ischemic events. Variable response to clopidogrel has received close attention, and pharmacokinetic, pharmacodynamic, and pharmacogenomic factors have been identified as culprits. This led to the introduction of newer, potentially safer, and more effective antiplatelet agents (prasugrel and ticagrelor). Additionally, several point-of-care assays of platelet function have been developed in recent years to rapidly screen individuals on antiplatelet therapy. While the routine use of platelet function testing is uncertain and not currently recommended, it may be useful in instances when the degree of platelet inhibition may be uncertain such as high-risk patients undergoing percutaneous coronary intervention or when there may be a suspected pharmacodynamic interaction with other drugs. The current paper focuses on the P2Y₁₂ receptor inhibitors and their pharmacogenetics and indications in patients with acute coronary syndromes or receiving percutaneous coronary interventions as well as the applicability of platelet function testing in this clinical context.

Hypocoagulability, Hypercoagulability and the Interpretation of ‘Normal’ Kaolin-Activated Thrombelastographs in the Perioperative Period

Kaolin-activated whole blood thrombelastography (TEG) is an appealing test of coagulation in the perioperative period, because it assesses many aspects of coagulation and can be performed at the point of care. In this issue, Weinberg et al report the use of kaolin-activated TEG as a global assessment of coagulation as part of their investigation of coagulation activation after hepatic resection for cancer1. However, while kaolin-activated TEG assesses many aspects of coagulation, it does not assess all aspects of coagulation, so ‘normal’ findings should be interpreted with caution.

Prevention of the renarrowing of coronary arteries using drug-eluting stents in the perioperative period: an update

The management of patients scheduled for surgery with a coronary stent, and receiving 1 or more antiplatelet drugs, has many controversies. The premature discontinuation of antiplatelet drugs substantially increases the risk of stent thrombosis (ST), myocardial infarction, and cardiac death, and surgery under an altered platelet function could also lead to an increased risk of bleeding in the perioperative period. Because of the conflict in the recommendations, this article reviews the current antiplatelet protocols after positioning a coronary stent, the evidence of increased risk of ST associated with the withdrawal of antiplatelet drugs and increased bleeding risk associated with its maintenance, the different perioperative antiplatelet protocols when patients are scheduled for surgery or need an urgent operation, and the therapeutic options if excessive bleeding occurs.

Management of perioperative stent thrombosis in patients undergoing surgery

Surgery often requires the interruption of standard dual antiplatelet therapy using aspirin and clopidogrel. Here, we present three patients who underwent surgery and suffered from a perioperative stent thrombosis associated with premature discontinuation of dual antiplatelet therapy. Although there are missing evidence-based data and key guidelines, we suggest that patients who undergo surgery after coronary stenting may benefit from an individualized perioperative antiplatelet management strategy. After premature dual antiplatelet therapy discontinuation, when the bridging of the preoperative time interval with the use of a short acting intravenous glycoprotein (GP) IIb-IIIa inhibitor including a platelet function testing has been missed and a coronary stent thrombosis has occurred, the patients should be administered a GPIIb-IIIa inhibitor for 12&#x2013;24 hours, followed by aspirin for one day and a dual antiplatelet treatment after 24&#x2013;48 hours. Our patients benefited from this individualized practical approach.

Thromboelastography during Adult Donor Care

Thromboelastography is a test of blood coagulation used to evaluate all components of clot formation and possible abnormal clot dissolution. It supplements traditional laboratory testing by demonstrating the integration of coagulation factors, platelets (number and function), and other factors during coagulation. Analysis of abnormalities demonstrated by thromboelastography can guide organ procurement coordinators in titrating appropriate quantities of fresh frozen plasma, cryoprecipitate, or platelet transfusions during treatment of coagulation in adult donors.