Think twice: A cognitive perspective of an antibiotic timeout intervention to improve antibiotic use

ObjectivesTo understand clinicians' impressions of and decision-making processes regarding an informatics-supported antibiotic timeout program to re-evaluate the appropriateness of continuing vancomycin and piperacillin/tazobactam.MethodsWe implemented a multi-pronged informatics intervention, based on Dual Process Theory, to prompt discontinuation of unwarranted vancomycin and piperacillin/tazobactam on or after day three in a large Veterans Affairs Medical Center. Two workflow changes were introduced to facilitate cognitive deliberation about continuing antibiotics at day three: (1) teams completed an electronic template note, and (2) a paper summary of clinical and antibiotic-related information was provided to clinical teams. Shortly after starting the intervention, six focus groups were conducted with users or potential users. Interviews were recorded and transcribed. Iterative thematic analysis identified recurrent themes from feedback.ResultsThemes that emerged are represented by the following quotations: (1) captures and controls attention ("it reminds us to think about it"), (2) enhances informed and deliberative reasoning ("it makes you think twice"), (3) redirects decision direction ("…because [there was no indication] I just [discontinued] it without even trying"), (4) fosters autonomy and improves team empowerment ("the template… forces the team to really discuss it"), and (5) limits use of emotion-based heuristics ("my clinical concern is high enough I think they need more aggressive therapy…").ConclusionsRequiring template completion to continue antibiotics nudged clinicians to re-assess the appropriateness of specified antibiotics. Antibiotic timeouts can encourage deliberation on overprescribed antibiotics without substantially curtailing autonomy. An effective nudge should take into account clinician's time, workflow, and thought processes

Circulating monocyte-platelet aggregates are a more sensitive marker of in vivo platelet activation than platelet surface P-selectin: studies in baboons, human coronary intervention, and human acute myocardial infarction

BACKGROUND: Platelet surface P-selectin is considered the gold standard marker of platelet activation. Degranulated, P-selectin-positive platelets, however, aggregate with leukocytes in vitro and rapidly lose surface P-selectin in vivo. METHODS AND RESULTS: Flow cytometric tracking of autologous, biotinylated platelets in baboons enabled us to directly demonstrate for the first time in vivo that (1) infused degranulated platelets very rapidly form circulating aggregates with monocytes and neutrophils, and (2) 30 minutes after infusion of the degranulated platelets, the percentage of circulating monocytes aggregated with infused platelets persist at high levels, whereas the percentage of circulating neutrophils aggregated with infused platelets and the platelet surface P-selectin of nonaggregated infused platelets return to baseline. We therefore performed 2 clinical studies in patients with acute coronary syndromes. First, after percutaneous coronary intervention (n=10), there was an increased number of circulating monocyte-platelet (and to a lesser extent, neutrophil-platelet) aggregates but not P-selectin-positive platelets. Second, of 93 patients presenting to an Emergency Department with chest pain, patients with acute myocardial infarction (AMI) (n=9) had more circulating monocyte-platelet aggregates (34.2+/-10.3% [mean+/-SEM]) than patients with no AMI (n=84, 19.3+/-1.4%,

Evaluation of platelet function by flow cytometry

Platelet function in whole blood can be comprehensively evaluated by flow cytometry. Flow cytometry can be used to measure platelet reactivity, circulating activated platelets, platelet-platelet aggregates, leukocyte-platelet aggregates, procoagulant platelet-derived microparticles, and calcium flux. Clinical applications of whole blood flow cytometric assays of platelet function in disease states (e.g., acute coronary syndromes, angioplasty, and stroke) may include identification of patients who would benefit from additional antiplatelet therapy and prediction of ischemic events. Circulating monocyte-platelet aggregates appear to be a more sensitive marker of in vivo platelet activation than circulating P-selectin-positive platelets. Flow cytometry can also be used in the following clinical settings: monitoring of GPIIb-IIIa antagonist therapy, diagnosis of inherited deficiencies of platelet surface glycoproteins, diagnosis of storage pool disease, diagnosis of heparin-induced thrombocytopenia, and measurement of the rate of thrombopoiesis

Dissociation of glycoprotein IIb/IIIa antagonists from platelets does not result in fibrinogen binding or platelet aggregation

BACKGROUND: The primary mechanism of action of glycoprotein (GP) IIb/IIIa antagonists is inhibition of the final common pathway of platelet aggregation: fibrinogen binding to the GP IIb/IIIa complex. However, it has been reported that induction of fibrinogen binding and platelet aggregation is an intrinsic prothrombotic property of low-dose GP IIb/IIIa antagonists. These apparently paradoxical results have been extensively referenced in the cardiology literature. METHODS AND RESULTS: By platelet aggregation and flow cytometry, we demonstrate that (1) dissociation of GP IIb/IIIa antagonists (abciximab, tirofiban, eptifibatide, or xemilofiban) from platelets does not result in platelet aggregation; (2) tirofiban and eptifibatide can induce a fibrinogen-binding-competent conformation of the GP IIb/IIIa receptor, but stable fibrinogen binding does not occur without fixation; (3) the slow off-rate of abciximab exposes only a small proportion of unblocked GP IIb/IIIa receptors at any time, and these also fail to stably bind fibrinogen; and (4) the GP IIb/IIIa antagonist-induced fibrinogen binding in some previously reported experiments was probably the result of artifactual thrombin generation. CONCLUSIONS: Under physiological conditions, GP IIb/IIIa antagonists currently in clinical use do not have an intrinsic activating property that results in platelet aggregation or stable fibrinogen binding to GP IIb/IIIa

GPIIb-IIIa antagonist-induced reduction in platelet surface factor V/Va binding and phosphatidylserine expression in whole blood

In addition to inhibition of platelet aggregation, GPIIb-IIIa antagonists may reduce thrombotic events via other mechanisms. In a novel whole blood flow cytometric system, we investigated the effects of GPIIb-IIIa antagonists, in the presence or absence of thrombin inhibitors, on platelet surface-bound factor V/Va and platelet surface phospholipids. Diluted venous blood was incubated with either buffer or a GPIIb-IIIa antagonist (abciximab, tirofiban, or eptifibatide). Some samples were pre-incubated with clinically relevant concentrations of unfractionated heparin (UFH), a low molecular weight heparin, a direct thrombin inhibitor, or buffer only. Platelets were then activated and labeled with mAb V237 (factor V/Va-specific) or annexin V (binds phosphatidylserine), fixed, and analyzed by flow cytometry. In the absence of thrombin inhibitors, GPIIb-IIIa antagonists (especially abciximab) significantly reduced agonist-induced platelet procoagulant activity, as determined by reduced binding of V237 and annexin V. At high pharmacologic concentrations, unfractionated heparin and enoxaparin, but not hirudin, further reduced factor V/Va binding to the surface of activated platelets in the presence of GPIIb-IIa antagonists. Agonist-induced platelet procoagulant activity was reduced in a patient with Glanzmann\u27s thrombasthenia. We conclude that GPIIb-IIIa antagonists reduce platelet procoagulant activity in whole blood and heparin and enoxaparin augment this reduction. Fibrinogen binding to GPIIb-IIIa is important in the generation of platelet procoagulant activity

GPIIb-IIIa antagonists reduce thromboinflammatory processes in patients with acute coronary syndromes undergoing percutaneous coronary intervention

OBJECTIVE: To investigate the effects of abciximab, eptifibatide and no GPIIb-IIIa antagonist (control) on soluble CD40 ligand (sCD40L) and the formation of leukocyte-platelet aggregates (LPA) in 98 ACS patients undergoing percutaneus coronary intervention (PCI). BACKGROUND: sCD40L and LPA are increased in patients with ACS. METHODS: sCD40L was measured by enzyme-linked immunosorbent assay (ELISA) and LPA by whole blood flow cytometry. RESULTS: There were no baseline differences between the three groups in sCD40L and LPA. At the end of PCI, sCD40L was unchanged in the controls, decreased by 30% (P andlt; 0.001) in the abciximab group and by 11% (P andlt; 0.02) in the eptifibatide group. Eighteen to 24 h after PCI, sCD40L was unchanged in the controls, reduced 30% (P andlt; 0.001) in the abciximab-treated group and 9% (P andlt; 0.01) in the eptifibatide-treated group. At the end of PCI, circulating monocyte-platelet aggregates (MPA) were reduced by 12% (P = NS) in the abciximab-treated group, 13% in the eptifibatide-treated group (P = NS), but slightly increased in the controls (P = NS). Eighteen to 24 h after PCI, MPA were reduced by 41% (P andlt; 0.001) compared to baseline in the abciximab-treated group, by 23% (P = NS) in the eptifibatide-treated group, and 15% (P = NS) in the controls. In contrast to control patients presenting while on clopidogrel, control patients presenting not on clopidogrel demonstrated a reduction in sCD40L and LPA 18-24 h post-PCI (P = NS). At low receptor occupancy, GPIIb-IIIa antagonists did not augment the release of sCD40L or the number of circulating LPA. CONCLUSIONS: GPIIb-IIIa antagonists reduce circulating sCD40L and LPA formation in patients with ACS undergoing PCI. At low receptor occupancy, GPIIb-IIIa antagonists do not activate platelets

Circulating monocyte-platelet aggregates are an early marker of acute myocardial infarction

OBJECTIVES: We investigated whether elevated levels of circulating monocyte-platelet aggregates (MPA) can be used to identify patients with acute myocardial infarction (AMI). BACKGROUND: Commonly used blood markers of AMI reflect myocardial cell death, but do not reflect the earlier pathophysiologic processes of plaque rupture, platelet activation and resultant thrombus formation. Circulating MPA form after platelet activation. METHODS: In a single center between October 1998 and November 1999, we measured circulating MPA in a blinded fashion by whole blood flow cytometry in 211 consecutive patients who presented to the emergency department (ED) with chest pain and were admitted to rule out AMI. Acute myocardial infarction was diagnosed by a CK-MB fraction greater than three times control. RESULTS: Patients with AMI (n = 61), as compared with those without AMI (n = 150), had significantly higher numbers of circulating MPA (11.6 +/- 11.4 vs. 6.4 +/- 3.6, mean +/- SD, p \u3c 0.0001). After controlling for age, the adjusted odds of developing AMI for patients in the 2nd, 3rd and 4th quartiles of MPA, in comparison with patients in the lowest quartile (odds ratio = 1.0), were 2.1 (95% confidence interval [CI]: 0.7, 6.8), 4.4 (95% CI: 1.5, 13.1) and 10.8 (95% CI: 3.6, 32.0), respectively. The number of circulating MPA in patients with AMI presenting within 4 h of symptom onset (14.4) was significantly greater than those presenting after 4 h (9.4) and after 8 h (7.0), (p \u3c 0.001). Of the 61 patients with AMI, 35 (57%) had a normal creatine kinase isoenzyme ratio at the time of presentation to the ED, but had high levels of circulating MPA (13.3). CONCLUSIONS: Circulating MPA are an early marker of AMI

The cleaved peptide of PAR1 is a more potent stimulant of platelet-endothelial cell adhesion than is thrombin

PURPOSE: Platelet-endothelial cell adhesion is an important pathologic response to vessel injury or inflammation. On binding to its endothelial or platelet G protein-linked seven-transmembrane domain receptor, protease-activated receptor-1 (PAR1), thrombin releases a 41-amino acid peptide (TR(1-41)). We examined the effect of TR(1-41) on platelet activation and on platelet-endothelial cell adhesion. METHODS: A monolayer of confluent human saphenous vein endothelial cells was incubated with washed human platelets. Platelets were stimulated with either TR(1-41), TR(21-41), scrambled TR(1-41), adenosine diphosphate (ADP)-epinephrine (EPI), thrombin, or thrombin receptor activating peptide (TRAP). Platelet activation was identified with flow cytometry. The magnitude of platelet-endothelial cell adhesion was determined with a laser scanning cytometer that scanned the monolayer of endothelial cells and identified fluorescently bound platelets. RESULTS: Maximal thrombin stimulation (0.1 U/mL) induced a threefold increase in platelets bound to endothelial cells compared with buffer alone. Stimulation with TR(1-41) (20 mmol/L) tripled the number of platelets bound to endothelial cells compared with thrombin. Scrambled sequence of TR(1-41) (20 mmol/L) and TR(21-41) (20 mmol/L), neither of which induces platelet activation, had minimal effect on platelet adhesion. Both TRAP (20 mmol/L) and ADP-EPI (20 mmol/L) induced less platelet-endothelial cell adhesion than did thrombin. TR(1-41)-induced platelet-endothelial cell adhesion was partially blocked by glycoprotein (GP)IIb-IIIa-specific monoclonal antibody, 10E5 (10 mg/mL). CONCLUSIONS: TR(1-41), the cleaved peptide of PAR1, is a more potent stimulant of platelet-endothelial cell adhesion than is thrombin, TRAP, or ADP-EPI, and this adhesion is at least in part mediated by the platelet GPIIb-IIIa receptor