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Definition, classification, etiology, and pathophysiology of shock in adults

David F Gaieski, MD
Mark E Mikkelsen, MD, MSCE
Section Editor
Polly E Parsons, MD
Deputy Editor
Geraldine Finlay, MD


Shock is a life-threatening condition of circulatory failure. The effects of shock are initially reversible, but rapidly become irreversible, resulting in multiorgan failure (MOF) and death. When a patient presents with undifferentiated shock, it is important that the clinician immediately initiate therapy while rapidly identifying the etiology so that definitive therapy can be administered to reverse shock and prevent MOF and death.

The definition, classification, etiology, and pathophysiology of shock are discussed in this review. The clinical presentation and diagnostic evaluation of undifferentiated shock and the evaluation of patients with specific forms of shock are discussed separately. (See "Evaluation of and initial approach to the adult patient with undifferentiated hypotension and shock" and "Evaluation and management of suspected sepsis and septic shock in adults" and "Clinical manifestations and diagnosis of cardiogenic shock in acute myocardial infarction" and "Etiology, clinical manifestations, and diagnosis of volume depletion in adults" and "Initial evaluation of shock in the adult trauma patient and management of NON-hemorrhagic shock" and "Clinical presentation, evaluation, and diagnosis of the nonpregnant adult with suspected acute pulmonary embolism".)


Shock is defined as a state of cellular and tissue hypoxia due to reduced oxygen delivery and/or increased oxygen consumption or inadequate oxygen utilization. This most commonly occurs when there is circulatory failure manifested as hypotension (ie, reduced tissue perfusion). Shock is initially reversible, but must be recognized and treated immediately to prevent progression to irreversible organ dysfunction. "Undifferentiated shock" refers to the situation where shock is recognized but the cause is unclear.


Four types of shock are recognized: distributive, cardiogenic, hypovolemic, and obstructive. However, these are not exclusive, and many patients with circulatory failure have a combination of more than one form of shock (multifactorial shock) (table 1). There are many etiologies within each class, all of which are discussed in detail in the sections below. (See 'Distributive' below and 'Cardiogenic' below and 'Hypovolemic' below and 'Obstructive' below and 'Combined' below.)

Septic shock, a form of distributive shock, is the most common form of shock among patients admitted to the intensive care unit, followed by cardiogenic and hypovolemic shock; obstructive shock is rare [1,2]. As an example, in a trial of 1600 patients with undifferentiated shock, septic shock occurred in 62 percent, cardiogenic shock in 16 percent, hypovolemic shock in 16 percent, other types of distributive shock in 4 percent (eg, neurogenic shock, anaphylaxis), and obstructive shock in 2 percent [2].

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Literature review current through: Nov 2017. | This topic last updated: May 25, 2016.
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