Disseminated intravascular coagulation (DIC) is never a primary disease per se, but a serious and often life-threatening complication of a variety of diseases. DIC can be acute or chronic, and fatal or non-fatal, depending on: the underlying cause; the body’s ability to compensate for and control the process; and the intervention we are able to provide.

The key event in DIC is systemic activation of coagulation to an extent which cannot be contained by the body’s anticoagulant mechanisms. This leads to a sequence of events which result in the clinical and laboratory manifestations of DIC. The pathophysiology of DIC is similar regardless of the initiating cause:

• Activation of the coagulation cascade leads to fibrin (formed from fibrinogen by the action of thrombin) deposition in the microvasculature (thrombosis). Thrombus formation results in ischemia and end-organ damage (manifested clinically as increased liver enzymes, azotemia, cardiac arrhythmias, abdominal pain, respiratory alkalosis, and CNS signs).
  
• This activation of coagulation results in consumption and depletion of coagulation factors, including procoagulant factors (especially those that are non-enzymatic factors–fibrinogen, factor V, and factor VIII) and anticoagulant factors such as AT-III. This results in prolongation of clotting tests (ACT, APTT, PT), decreased concentrations of fibrinogen and AT-III, and signs of a bleeding disorder.
  
• Platelets are activated by the thrombin generated from coagulation, become trapped by fibrin deposited in the microvasculature, and participate in formation of intravascular thrombi. This leads to thrombocytopenia. Red cells are also damaged by fibrin in the microvasculature, leading to formation of schistocytes (this is sometimes referred to as microangiopathic hemolysis).
  
• Plasmin, the active enzyme of fibrinolysis, is generated by tissue plasminogen activator (which is released by endothelial cells in response to thrombin). Plasmin degrades fibrin clots as well as circulating fibrinogen (to form fibrin and fibrinogen degradation products, FDPs). Elevated concentrations of FDPs inhibit platelet function and fibrin polymerization, thereby exacerbating the bleeding diathesis.
  
• Hypotension and shock in patients with DIC is promoted by plasmin and various kinins, which lead to increased vascular permeability and vasodilation.
  
• Although clinical signs of bleeding predominate, it is important to remember that organ damage due to thrombosis and ischemia is occurring simultaneously. The clinical signs of bleeding can include petechiation, mucosal surface bleeding, bleeding from venipuncture sites or wounds, subcutaneous hematomas, and deep muscle bleeding. Thrombosis tends to be less clinically obvious, although acral cyanosis and gangrene can occur.