The effects of heparin and extracorporeal circulation on platelet counts and platelet microaggregation during cardiopulmonary bypass

Bleeding Following Deep Hypothermia and Circulatory Arrest in Children

Deep hypothermic circulatory arrest (DHCA) is a technique of extracorporeal circulation commonly used in children with complex congenital heart defects undergoing surgical repairs. The use of profound cooling (20°C) and complete cessation of circulation allow adequate exposure and correction of these complex lesions, with enhanced cerebral protection. However, the profound physiologic state of DHCA results in significant derangement of the coagulation system and a high incidence of postoperative bleeding. This review examines the impact of DHCA on bleeding and transfusion requirements in children and the pathophysiology of DHCA-induced platelet dysfunction. It also focuses on possible pharmacologic interventions to decrease bleeding following DHCA in children.

The effect of oxygenator membranes on blood: a comparison of two oxygenators in open-heart surgery

Open-heart surgery (OHS) requires cardiopulmonary bypass (CPB) in most patients. Membrane oxygenators are a critical component of the CPB system. Despite advancements in CPB technology, injury to blood components during CPB still occurs and may result in complications after surgery. The purpose of the present study was to evaluate the performance of the Medtronic Affinity NT® with Trillium coating and the Cobe Optima XP® oxygenators and compare their influence on blood components.

Two hundred and fifty-six male and female patients scheduled for urgent or elective cardiac surgery with CPB were randomly assigned to either the Affinity NT or the Optima XP oxygenators. Outcomes included platelets, hemoglobin, leukocyte counts, and O2 transfer, measured preoperatively and at 15, 45 and 75 min of CPB time. Blood loss was measured at six and 12 hours postoperatively. A modified intention-to-treat analysis was conducted.

The two groups were similar for age, sex, height, weight, body surface area, and blood components at baseline. There were no differences between the Affinity NT and Optima XP for any outcome measure, although a significant change with time was seen in platelets, hemoglobin, hematocrit and leukocytes, as well as O2transfer for both groups ( p <0.001). The Affinity NT oxygenator had a significantly lower difference in pressure across the membrane ( p <0.001) compared with the Optima XP.

In conclusion, the two oxygenators performed similarly with respect to their impact on blood components, O2transfer, and blood loss postoperatively during OHS with CPB. The Affinity NT had the smaller transmembrane pressure drop of the two.

Factor VII for excessive bleeding following congenital heart disease surgery

Recombinant activated factor VII may be effective in patients with severe bleeding following congenital heart disease surgery requiring cardiopulmonary bypass. From August 2009 through June 2011, 13 patients (median age, 5 months) were given recombinant activated factor VII for severe bleeding after open heart surgery, preventing sternal closure 2 h after completion of cardiopulmonary bypass, or chest tube drainage >10 mLċ kg−1ċh−1 for 2 h. The median dose was 75 µgċ kg−1. The response was positive if postoperative bleeding decreased, permitting sternal closure in the operating room, or if there was > 50% decrease in chest tube drainage. The 3 patients who received factor VIIa in the operating room had successful sternal closure within 1 h. Of the 10 patients who received factor VIIa in the intensive care unit, drainage decreased to < 50% in 1 h in 6 cases, and a second dose was required in 4. None required surgical reexploration. There were 4 deaths, none was related to bleeding. Nine patients were discharged (median hospital stay, 29 days) and were doing well after 3 months. There were no thrombotic complications. Recombinant activated factor VII may be an effective rescue therapy for severe postoperative hemorrhage.

Hypercoagulable state after off-pump coronary artery bypass grafting: evidence, mechanisms and implications

During the past decade, there has been a dramatic resurgence in the adoption of off-pump technology in coronary artery bypass surgery. This has inspired remarkable advances in the techniques of localized tissue stabilization and a greater understanding of the physiology of beating-heart mobilization and exposure. An avalanche of reports in the literature has demonstrated the early safety and efficacy of the procedure. However, despite abundant evidence validating the safety and efficacy of off-pump coronary artery bypass surgery, considerable controversy still persists regarding the long-term outcomes of this approach to myocardial revascularization. One area of concern, and even greater uncertainty, surrounds the issue of the existence of a hypercoagulable state after off-pump coronary artery bypass surgery. This article evaluates the current best evidence available from randomized controlled trials to assess the impact of off-pump coronary artery bypass surgery on coagulation, fibrinolysis and platelet activation, discusses the issue of hypercoagulability with emphasis on the mechanisms responsible for this actual or potential hypercoagulability, and explores the implications of this issue for clinical practice.

Perioperative Coagulopathy, Bleeding, and Hemostasis During Cardiac Surgery

Cardiac surgery patients use 10%-25% of the blood products transfused annually in the United States. The transfusion of red blood cells or blood products has been the subject of intense scrutiny over the past 10 years. Bleeding after cardiac surgery can be surgical or nonsurgical and lead to hemodynamic compromise and surgical reexploration. Because hemorrhage and blood product transfusions are associated with multiple negative outcomes, including increased mortality, it is prudent to understand the mechanisms responsible for nonsurgical bleeding. This review focuses on the physiology of the normal coagulation and fibrinolysis, risk factors associated with patients presenting for cardiac surgery, impairments of normal hemostasis associated with cardiac surgery and cardiopulmonary bypass (CPB), and potential interventions to reduce perioperative blood loss and blood transfusion.

Comparison of early platelet activation in patients undergoing on-pump versus off-pump coronary artery bypass surgery

OBJECTIVE

Cardiopulmonary bypass has been shown to be associated with platelet dysfunction, which has a potential for increasing the risk of perioperative bleeding. Off-pump coronary artery bypass surgery is thought to avoid this deleterious effect of pump use on platelets. However, the influence of off-pump coronary artery bypass surgery on platelets has not been thoroughly studied.

METHODS

Accordingly, we evaluated 60 patients undergoing coronary artery bypass grafting prospectively using cardiopulmonary bypass and warm cardioplegic arrest (n = 30) or an off-pump technique (n = 30). Platelet function was evaluated before and 2 hours after coronary artery bypass grafting.

RESULTS

Among patients undergoing on-pump coronary artery bypass surgery, all studies of platelet function were significantly abnormal after surgical intervention compared with results before surgical intervention. Similarly, among patients undergoing off-pump coronary artery bypass surgery, evidence of platelet dysfunction after surgical intervention was noted, with a lower platelet count and a higher proportion of P-selectin- and Annexin V-positive platelets. However, compared with the preprocedural value, the postprocedural decrease in platelet count (78,200 x 10(3)/microL vs 103,000 x 10(3)/microL) and platelet aggregation (0.8% vs 10.9%) and increase in bleeding time (0 minutes vs +1.3 minutes), P-selectin-positive platelets (6.0% vs 9.1%), and Annexin V-positive platelets (1.7% vs 3.7%) were significantly lower in the off-pump coronary artery bypass surgery group compared with those in the on-pump coronary artery bypass surgery group, respectively.

CONCLUSIONS

Early postoperative decrease in platelet count and increase in platelet activation occurs to a much lesser extent and does not alter bleeding time or adenosine diphosphate-induced platelet aggregation in patients undergoing off-pump coronary artery bypass surgery. This lack of significant effects on platelets might in part account for the potential decreased risk in bleeding and for the preserved hemostasis seen in patients undergoing off-pump coronary artery bypass surgery compared with those undergoing on-pump coronary artery bypass grafting surgery.

Cell-derived microparticles and exosomes in neuroinflammatory disorders

All blood cells and the vascular endothelium shed microparticles (MP) from their plasma membranes when suitably stimulated, and assay of MP in patient blood has found increasing application to the monitoring of disease states. In addition, mounting evidence suggests that MP are not mere epiphenomena but play significant roles in the pathophysiology of thromboses, inflammation, and cancers. This chapter endeavors to summarize the limited number of studies thus far done on MP in neurological disorders such as multiple sclerosis (MS), transient ischemic attacks, and the neurological manifestations of antiphospholipid syndrome (APS). In addition, the chapter offers some plausible hypotheses on possible roles of MP in the pathophsyiology of these disorders, chiefly, the hypothesis that MP are indeed important participants in some neuropathologies, especially those which are ischemic in nature, but probably also inflammatory ones. The chapter also goes over the history and general principles of MP studies (e.g., assay methods and pitfalls), comparison with alternative methods (e.g., soluble markers of disease states), subclasses of MP (such as exosomes), and other topics aimed at helping readers to consider MP studies in their own clinical fields. Tables include a listing of bioactive agents known to be carried on MP, many of which were heretofore considered strictly soluble, and some of which can be transferred from cell to cell via MP vectors, for example certain cytokine receptors.

Autologous blood transfusion for cardiopulmonary bypass: effects of storage conditions on platelet function

OBJECTIVES

Cardiopulmonary bypass impairs formation of large stable platelet aggregates (macroaggregation), although formation of small aggregates (microaggregation) is preserved. A factor in the uncertain benefits of intraoperative autologous blood transfusion may be the effects of storage on platelet function. The effects of citrate preservative and heparinization before storage on platelet function was therefore assessed.

METHODS

Twenty-seven patients undergoing elective coronary artery bypass grafting were randomly allocated to have 450 to 1,000 mL of blood taken into CPDA anticoagulant bags either before (n = 14) or after heparinization (n = 13). Samples from the patients and stored blood were anticoagulated with rhirudin, 200 U/mL. The macroaggregatory response to submaximal collagen was measured by impedance aggregometry and microaggregation by single platelet counting.

RESULTS

During macroaggregation, before cardiopulmonary bypass, the ex vivo median (interquartile range) response was 16.3 (12.4-18.7) Omega. This decreased 10 minutes after heparin to 8.9 (3.3-11.0) Omega (p < 0.0001). In the blood bags (in vitro), the initial response for nonheparinized blood was 4.8 (0.1-7.5) Omega (p < 0.002 v ex vivo) and at end-cardiopulmonary bypass was 2.4 (1.6-8.2) Omega. During microaggregation, in vivo heparinization decreased microaggregation both ex vivo and in vitro in CPDA blood; the in vitro response of nonheparinized blood at end-cardiopulmonary bypass was greater than that seen after in vivo heparinization (p < 0.007). No difference in bleeding or transfusion requirements was seen.

CONCLUSIONS

Collecting blood into CPDA anticoagulant caused a marked deterioration in platelet function. This was worse after in vivo heparinization and included depression of microaggregation.

Platelet Preservation With a Glycoprotein IIb/IIIa Inhibitor in a Porcine Cardiopulmonary Bypass Model

BACKGROUND

We tested whether administration of FK633, a short-acting glycoprotein IIb/IIIa inhibitor, before median sternotomy and cardiopulmonary bypass was able to interrupt the platelet activation loop and thereby preserve platelet number and function.

METHODS

This study investigated 16 pigs that underwent median sternotomy and 120 minutes of normothermic cardiopulmonary bypass (100 mL/kg) adding pericardial blood to the perfusate. FK633 was administered with heparin to one group (group F, n = 8), whereas only heparin was administered to the control group (group C, n = 8). Blood samples were obtained at several times, and complete blood count, platelet aggregation to adenosine diphosphate, thrombin-antithrombin complex, and bradykinin were evaluated. P-selectin expression and fibrinogen binding on platelet surfaces were measured by flow cytometry. Template bleeding times were measured before and after cardiopulmonary bypass. Chest tube drainage and hematocrit were determined at 2 and 6 hours after cardiopulmonary bypass.

RESULTS

In group F, platelet counts were preserved from 90 minutes of cardiopulmonary bypass. Platelet aggregation was inhibited at the beginning of cardiopulmonary bypass and showed no change at wound closure, and bleeding times were shortened at 2 hours after cardiopulmonary bypass. There were significant reductions in hematocrit of drainage. Flow cytometry showed no changes in P-selectin expression and fibrinogen binding in group F, whereas P-selectin expression and fibrinogen binding were elevated in group C.

CONCLUSIONS

Platelet inhibition with FK633 before invasive surgical procedure preserved platelet counts during and after cardiopulmonary bypass, and produced normal or near-normal bleeding times in the immediate postoperative period.

The state of platelets preserved in extracorporeal circulation with a glycoprotein IIb/IIIa inhibitor

INTRODUCTION

Temporary inhibition of platelet function during extracorporeal circulation (platelet anesthesia) can preserve platelet count. We hypothesized that platelet anesthesia with a glycoprotein IIb/IIIa inhibitor could preserve activated platelets.

MATERIALS AND METHODS

Fresh human blood from donors was recirculated for 120 min in a simulated extracorporeal circuit. Heparin and FK633, a short-acting platelet glycoprotein IIb/IIIa inhibitor, were added to recirculated blood in one group (group F, n=5) whereas only heparin was used in controls (group C, n=5). Blood samples were obtained from the donors, and at 0, 5, 15, 30, 60, and 120 min of recirculation. Platelet counts, beta-thromboglobulin, thrombin-antithrombin complex, and aggregation to adenosine diphosphate were measured. Flow cytometry was performed for measurement of fibrinogen binding, platelet surface expression of P-selectin, and microparticles.

RESULTS AND CONCLUSIONS

In the FK633 group, platelet counts were preserved and beta-thromboglobulin levels remained unchanged, whereas in group C, platelet counts decreased significantly and beta-thromboglobulin increased significantly from 30 and 60 min, respectively. FK633 inhibited platelet aggregation and fibrinogen binding to platelets throughout recirculation. A significant difference between groups with respect to microparticle parameters and thrombin-antithrombin complex levels was evident by 120 min. P-selectin expression increased at 0 min in both groups, and was preserved significantly at 5 min and reduced at 120 min in group F. Platelet counts were preserved by platelet anesthesia during recirculation without platelet activation. These results suggest that FK633 inhibits the amplification loop by reducing the binding of fibrinogen to glycoprotein IIb/IIIa and platelet aggregation.

Coronary artery bypass grafting in an immune thrombocytopenic purpura patient using off-pump techniques

We performed an off-pump coronary artery bypass grafting (OPCABG) procedure on a 60-year-old woman with idiopathic thrombocytopenic purpura (ITP) whose platelet count was 42 x 10(3) per microliter on admission. She was treated with immunoglobulin G (IgG) (0.5 g.kg(-1).d(-1)) for 4 days, resulting in a platelet count rise to 187 x 10(3) per microliter. She subsequently underwent an uneventful OPCABG procedure without requiring any blood transfusions. The combination of OPCABG and preoperative IgG therapy appears to be an ideal strategy for ITP patients requiring coronary revascularization.