What Causes Shock?

Shock can be the result of numerous different pathophysiological processes that can be broadly accommodated within four somewhat artificial categories: hypovolaemic, distributive, obstructive and cardiogenic [8] (Table 1).

Irrespective of the cause the inadequate delivery of oxygen to tissues results in a failure of aerobic metabolism leading to end organ dysfunction.

The situation becomes more confusing if examples of dysoxia are considered to be types of shock. Cyanide poisoning is a classic example wherein mitochondria are prevented from using oxygen. Such disease states are outside the remit of this module as the primary problem is not one of circulatory compromise.

Table 1: Categories of shock

(inadequate circulating  volume secondary to
fluid loss)


(inadequate perfusion secondary to


  • Haemorrhagic (e.g. trauma, GI  bleeding, obstetric  haemorrhage, ruptured  AAA)
  • Diarrhoea and vomiting
  • Diabetic ketoacidosis
  • Burns

  •  Sepsis
  •  Neurogenic shock
  •  Anaphylactic


(inadequate cardiac output as  a result of  mechanical  obstruction) 


(inadequate cardiac output as a result of  cardiac failure) 

  • Pulmonary embolism
  • Tension pneumothorax
  • Cardiac tamponade
  • Acute IVC or SVC obstruction
  • Myocardial infarction
  • Myocardial contusion
  • Myocarditis
  • Late sepsis
  • Overdose (e.g. beta  blockers)
  • Complete heart block

Learning bite

Shock describes a pathophysiological state with many different causes, NOT a specific diagnosis.

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