Chapter 5: Surgical Hemostasis and Clotting Mechanisms

Introduction

The most important considerations for maintaining surgical hemostasis begin before the operation starts. This chapter provides practical tools to approach patients before, during, and after the surgical procedure. Below is a summary explanation of normal hemostasis, and how it can be conceptualized into four basic components. Explanations are provided to illustrate the uses and limitations of the routine coagulation tests. Common coagulation disorders are briefly discussed. Preoperative management of anticoagulants is discussed. The routine clinical application of these basic concepts of blood coagulation can enhance practice and benefit patients.

Basic Concepts of Hemostasis

Hemostasis is a term describing the complex processes that keep blood in its fluid state within the vasculature, yet allows it to clot to stop hemorrhage.

The Four Conceptual Components of Hemostasis

• The process of normal hemostasis can be divided conceptually into four basic components of the blood, listed as follows: (1) blood vessel, (2) platelets, (3) coagulation system, and (4) fibrinolytic system (Table 5-1).

• These four components undergo a series of regulated events that lead to clot formation.

Primary Hemostasis

Four steps leading to a platelet plug formation are as follows:

1. Blood vessel and platelet interactions

   • Initial reaction with the blood vessel itself triggering vasoconstriction, which decreases blood flow slowing bleeding and allows for platelet adhesion

2. Platelet adhesion

   • The initial contact interaction between platelets and any nonplatelet surface (the vessel wall)

   • Mediated by a platelet surface glycoprotein receptor termed GPIb complex and the plasma protein, von Willebrand factor (vWF)

3. Platelet aggregation

   • A platelet membrane surface receptor, “the aggregation receptor” which is not present on unstimulated platelets is expressed.

   • The platelet aggregation receptor is made up of two platelet surface proteins, termed GPIIb/GPIIIa.¹

   • GPIIb/GPIIIa binds fibrinogen on one end; another platelet expressing GPIIb/GPIIIa binds the other end of the fibrinogen, leading to platelet aggregation.

4. Platelet release

   • Platelets are activated by the adhesion and release of thromboxaine A2, serotonin, and ADP, which activates other platelets, and further slows blood flow.

   • This whole sequence from vasoconstriction to the formation of a platelet plug and, finally, a platelet aggregate and release constitutes the process of primary hemostasis.

   • This process is independent of blood coagulation and occurs even in patients with hemophilia.

   • This process is however insufficient to completely stop hemorrhage—you need adequate secondary hemostasis.

   • The most common inherited disorder of primary hemostasis is von Willebrand disease and acquired is thrombocytopenia.

   • Most common bleeding symptoms caused by defects in primary ...