Review of the biology of bleeding and clotting in the surgical patient.

To effectively balance bleeding and clotting in surgical patients, the surgeon needs a fundamental knowledge of coagulation biology. The endothelium and activated platelets play crucial roles in coagulation. Activated platelets and damaged endothelial cells provide a platform of negatively charged phospholipids that not only bind coagulation factors and their complexes but also accelerate the conversion of inactive zymogens to active serine proteases. Endothelial shear stress also plays a pivotal role in coagulation and thrombosis by stimulating release of nitric oxide (NO) at the vascular interface, upregulating endothelial nitric oxide synthase (eNOS), and further mediating eNOS activation through direct phosphorylation. The effects of low shear stress result in a prothrombotic state and have been implicated in the etiopathology of atherosclerosis. Correctly diagnosing and appropriately treating perioperative bleeding in surgical patients require a basic understanding of the most common bleeding and clotting disorders. This article provides an overview of the characteristic features of common coagulopathic conditions and their treatment options. Given the challenge of balancing bleeding and clotting in surgical patients, hemostatic management must be tailored to each patient and should take into account the patient's genetic and acquired risk factors and the acute disturbances in bleeding and clotting caused by surgical intervention.