Cardiogenic shock overview

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Cardiogenic shock is defined as an insufficient forward cardiac output to maintain adequate perfusion of vital organs to meet ongoing demands for oxygenation and metabolism. Cardiogenic shock is due to either inadequate left ventricular pump function (such as in congestive heart failure) or inadequate left ventricular filling (such as in cardiac tamponade or mitral stenosis with tachycardia). In so far as the course of treatment differs substantially, cardiogenic shock should be distinguished from other forms of shock such as septic shock, distributive shock, hypovolemic shock and neurogenic shock.

Definition

Cardiogenic shock is defined as sustained hypotension (>30 minutes) with evidence of tissue hypoperfusion despite adequate left ventricular filling pressure. Signs of tissue hypoperfusion include oliguria (<30 mL/h), cool extremities, cyanosis and altered mentation.

The pathophysiology of cardiogenic shock is complex and multifactorial. Furthermore, there are a variety of compensatory mechanisms in response to the pathophysiology that can mask the underlying hemodynamic derangements that may be present. As a result, the diagnostic criteria for cardiogenic shock are complex and have been debated.

Given that the condition is a form of "shock", many clinicians argue that by definition "shock" must therefore be present. However, some clinicians argue that hypotension alone should not be the key criteria in so far as compensatory tachycardia and vasoconstriction may compensate for the reduced cardiac output to yield only a mildly depressed systolic blood pressure. These clinicians advocate a hemodynamic definition with greater reliance placed on hemodynamic measures and interpretation of the cardiac output in the context of left ventricular filling pressure as often gauged by the pulmonary capillary wedge pressure. For instance, a patient who has a history of hypertension who now has a blood pressure of 100 mm Hg with a markedly elevated systemic vascular resistance (SVR) and pronounced tachycardia with a markedly reduced cardiac output, would be in cardiogenic shock in the judgement of some clinicians despite the absence of hypotension. Some definitions require a drop in systolic blood pressure of 30 mm Hg.

In clinical trials, cardiogenic shock has been defined as follows by the SHOCK investigators:

Clinical Criteria

1. Systolic blood pressure <90 mm Hg for at least 30 minutes
2. Evidence of hypoperfusion
3. Cool, clammy periphery
4. Decreased urine output
5. Decreased level of consciousness

Hemodynamic Criteria

1. Left ventricular end diastolic pressure or pulmonary capillary wedge pressure >15 mm Hg
2. Cardiac index <2.2 L/min/m2

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