Management of Hemostasis and Coagulopathies for Surgical and Critically Ill Patients

An Evidence-Based Approach

Andy D. Nguyen,Amitava Dasgupta,Amer Wahed

• Verlag: Elsevier
• Jahr: 2016
• ISBN:
  9780128035696
• Thema: Medicine
• Thema: Biotechnology in Medicine

Management of Hemostasis and Coagulopathies for Surgical and Critically Ill Patients: An Evidence-Based Approach offers a concise guide to a sub-specialty of transfusion medicine from the clinical laboratory perspective. It focuses on the clinical tests that may be done during preoperative assessment, intraoperative, and postoperative assessment and management of surgical or critically ill patients. Management of hemostasis and coagulopathies is approached from an evidence-based perspective—the coagulation status of a patient according to the laboratory test results. Algorithms and decision-support software, designed by the authors, guide clinicians with an additional tool to base transfusion dosage on specific laboratory results, including the use of an artificial neural network for predicting more accurate blood use.

Chapters reflect the experience of all three authors who have successfully applied the algorithm for better patient management as well as decreased wastage of expensive blood products, from both the clinical laboratory/pathology and clinical medicine perspective. This book will appeal to a broad section of clinical laboratory and medical practitioners from hematopathology, to internal medicine, surgery, and anesthesiology. For hematopathologists and pathologists who are involved in laboratory medicine and transfusion medicine, this book will help them understand the proper utilization of blood products and how to avoid unnecessary waste and costs for the hospital. For general surgery practitioners, this book will provide practical guidelines on how to use blood products rationally for best medical practice. Internists will also gain insight from this book, learning which patients are at higher risk of bleeding during surgery so that they can alert their clinical colleagues.

• Focuses on the clinical tests that may be done during preoperative assessment, intraoperative, and postoperative assessment and management
• Explains new decision-support software developed by the authors as a tool for the management of bleeding patients
• Reviews common coagulation based tests (indication and interpretation) that are used to assist in the management of bleeding patients
• Provides an overview of various blood products, pharmacotherapeutic agents, antiplatelets, and anticoagulants, their usage strategy, indications, and therapy goals

Chapter 1

Coagulation-Based Tests and Their Interpretation

Abstract

This chapter covers all aspects of coagulation-based tests that are used to assist in the management of bleeding patients. Indications and interpretation of these tests are also discussed. The tests discussed include prothrombin time, partial thromboplastin time, mixing study, disseminated intravascular coagulation screen, thromboelastography, lupus antibody testing and testing for heparin-induced thrombocytopenia. Various platelet function tests are discussed, including platelet aggregation, VerifyNow, PFA and Plateletworks.

Keywords

Coagulation test; prothrombin time; partial thromboplastin time; mixing study; VerifyNow

Contents

1.1 Introduction 1

1.2 Complete Blood Count 2

1.3 Tests for Platelet Function 2

1.3.1 PFA-100 3

1.3.2 VerifyNow 3

1.3.3 Plateletworks 4

1.3.4 Platelet Aggregation 4

1.4 Prothrombin Time 6

1.5 Partial Thromboplastin Time 8

1.6 Thrombin Time 9

1.7 Fibrinogen Level 9

1.7.1 D-Dimer 9

1.7.2 Antithrombin III Level 10

1.7.3 Mixing Study 10

1.8 Thromboelastography 10

1.8.1 Platelet Mapping 13

1.8.2 Anti-Xa Assay 14

1.8.3 Plasma-Diluted Thrombin Time 14

1.9 Heparin-Induced Thrombocytopenia 14

1.9.1 Bleeding Patient With Normal Coagulation Tests 16

1.10 Conclusions 16

References 16

1.1 Introduction

Blood clotting (coagulation) is initiated within seconds after vascular injury to counteract bleeding. The main purpose of coagulation is to seal an injured vessel, which is accomplished by aggregation of platelets at the site of injury. Antimicrobial peptides are released from platelets when coagulation is activated. In addition, an intact platelet–fibrinogen plug can provide an active surface that allows the recruitment, attachment and activation of phagocytosing cells. Various tests are performed prior to surgery to assess risk of bleeding and during the perioperative and postoperative period to guide transfusion using appropriate blood components.

Commonly used coagulation tests for such purposes include the following:

• Complete blood count

• Tests for platelet function

• Disseminated intravascular coagulation (DIC) screen, which consists of prothrombin time (PT), partial thromboplastin time (PTT), thrombin time (TT), fibrinogen level and D-dimer

• Antithrombin III level

• Thromboelastograph (TEG)

• Special testing such as anti-Xa assay, diluted thrombin time and tests for heparin-induced thrombocytopenia

1.2 Complete Blood Count

A complete blood count (CBC) is one of the most common laboratory tests ordered by clinicians, and this test is also essential prior to surgery to evaluate a patient for bleeding risk. For CBC analysis, the specimen must be collected in an ethylenediaminetetraacetic acid (EDTA) tube (lavender or purple top).

CBC consists of white blood cell (WBC) count (or leukocyte count), WBC differential count, red blood cell count (or erythrocyte count), hematocrit, hemoglobin, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, red cell distribution width, platelet count and mean platelet volume. Some of these parameters are directly measured by the analyzer, whereas others are calculated from various measured parameters. In general, hemoglobin and hematocrit levels are used to determine the need for and extent of packed red blood cell (PRBC) transfusion. Platelet count is used as an important parameter to determine the necessity for platelet transfusion.

1.3 Tests for Platelet Function

Available analyzers for various tests for platelet function include PFA-100, Plateletworks and VerifyNow. In addition, the platelet aggregation test is also useful. These tests are used to determine platelet function and to decide if platelet transfusion may be needed.

1.3.1 PFA-100

The PFA-100 system is a platelet function analyzer that may be used to assess platelet-related primary hemostasis. The instrument utilizes two disposable cartridges that are coated with platelet agonists. Blood is collected in a citrate tube and is then transferred to a sample cup. Blood is aspirated from the sample cup and passes through an aperture in a membrane that is coated with platelet agonists. When platelet aggregation takes place, the aperture closes and the blood flow stops. The time taken for the aperture to close is the closure time. One membrane is coated with collagen/epinephrine (CEPI), and the other membrane is coated with collagen/adenosine diphosphate (CADP). If the CEPI closure time is prolonged but the CADP closure time is normal, this is most likely due to aspirin. If both CEPI and CADP closure times are prolonged or CEPI closure time is normal and CADP closure time is abnormal, this implies platelet dysfunction or von Willebrand disease. PFA-100 is insensitive to von Willebrand disease type 2N, clopidogrel, ticlopidine and storage pool disease. PFA-100 results are affected by thrombocytopenia and low hematocrits. They are not affected by heparin or deficiencies of clotting factors other than fibrinogen. Interpretation of PFA-100 results is summarized in Table 1.1.

Table 1.1

Interpretation of PFA-100

Result	CEPI closure time	CADP closure time
No platelet dysfunction	Normal	Normal
vWD 2N, clopidogrel, ticlopidine, storage pool disease	Normal	Normal
Aspirin effect	Prolonged	Normal
Platelet dysfunction or vWD	Normal or prolonged	Prolonged

vWD 2N: von Willebrand disease type 2N.

1.3.2 VerifyNow

VerifyNow is a rapid, turbidimetric whole blood assay capable of evaluating platelet aggregation. This assay is based on the ability of activated platelets to bind with fibrinogen. The VerifyNow IIb/IIIa assay utilizes fibrinogen-coated microparticles, whereas thrombin receptor-activating peptide is used as an agonist to maximally stimulate platelets in order to determine platelet function. If GpIIb/IIIa (glycoprotein IIB/IIIa) antagonists are present in patients’ blood, then platelet aggregation should be reduced. In the VerifyNow aspirin assay, arachidonic acid (AA) is used as the agonist in order to measure the antiplatelet effect of aspirin. Results are expressed in aspirin reactive units (ARU). The VerifyNow P2Y12 assay is similarly used to assess the antiplatelet effect of clopidogrel, and results are expressed in Plavix rea...