Mechanisms of Shock

What are the types (or mechanisms) of shock? 

There are multiple mechanisms for shock:

  • • Hypovolemic shock: Hypovolemia, such as might occur with blood loss, vomiting, and diarrhea, decreases perfusion to the tissues and leads to shock.
  • • Distributive or vasodilatory shock: This type of shock is the final common pathway of a variety of conditions that result in vasodilation. Neurogenic distributive shock is caused by a spinal cord injury that eliminates sympathetic innervation to the blood vessels, causing profound vasodilation and bradycardia. Accidental ingestion of vasodilating medications can also result in distributive shock. Anaphylaxis results in vasodilation, and although anaphylaxis has many other components, shock is a part of the clinical picture. Septic shock is largely distributive in nature but is a complex process (see later discussion).
  • • Cardiogenic shock: Pump failure is the primary mechanism for cardiogenic shock. Decreased myocardial contractility makes adequate delivery of oxygen and nutrients impossible. Because children are very dependent on a normal heart rate to produce an adequate cardiac output, drugs and other conditions that cause bradycardia can lead to shock. The patient will have evidence of congestive heart failure, such as rales on pulmonary auscultation, hepatomegaly, and peripheral edema. Viral myocarditis, hypertrophic cardiomyopathy, and certain myocardial depressant drugs can cause cardiogenic shock.
  • • Septic shock: Many consider septic shock to be another form of distributive shock. In septic shock, a stimulus causes the formation of inflammatory mediators that result in profound vasodilation and shock. However, some of these mediators also directly depress myocardial activity; thus, septic shock can have features of both distributive and cardiogenic shock.


Jones AE, Craddock PA, Tayal VS, Kline JA: Diagnostic accuracy of left ventricular function for identifying sepsis among emergency department patients with nontraumatic, symptomatic, undifferentiated hypotension. Shock 2005;24:513-517.


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