What are the different types of shock?

Types of Shock

There are four major categories of shock: hypovolemic, distributive, cardiogenic, and obstructive—each primarily related to dysfunction of a specific organ system (blood/fluid compartment, vascular system, heart, or circulatory blockage, respectively). 1

The Four Primary Categories

1. Hypovolemic Shock

• Results from intravascular volume loss due to hemorrhage, severe dehydration, or fluid sequestration 1
• Hemodynamic profile: Decreased cardiac index (<2.2 L/min/m²), decreased pulmonary capillary wedge pressure (PCWP), decreased central venous pressure (CVP), and elevated systemic vascular resistance (SVR) as a compensatory mechanism 2
• Treatment priority: Aggressive fluid resuscitation with balanced crystalloids is the definitive therapy—vasopressors are NOT the primary treatment and should only be used transiently in life-threatening hypotension while achieving volume restoration 3

2. Distributive Shock

• Characterized by pathological vasodilation leading to relative hypovolemia despite normal absolute intravascular volume 1
• Hemodynamic profile: Normal or increased cardiac index, markedly decreased SVR, normal or decreased PCWP, and normal or decreased CVP 2
• Clinical presentation: Hypotension with warm extremities, elevated lactate, and signs of hypoperfusion despite adequate volume 2
• Subtypes include: Septic shock (most common form of distributive shock), anaphylactic shock, and neurogenic shock 4
• Treatment approach: Combination of vasoconstrictors (norepinephrine first-line) and fluid replacement after adequate crystalloid resuscitation 3, 1

3. Cardiogenic Shock

• Arises from primary cardiac dysfunction with inadequate cardiac output due to impaired myocardial contractility 1
• Hemodynamic profile: Decreased cardiac index (<2.2 L/min/m²), elevated PCWP (>15 mmHg), elevated CVP (>15 mmHg), and elevated SVR as compensatory vasoconstriction 2
• Most common cause: Acute myocardial infarction, occurring in 7-10% of AMI cases, typically associated with >40% loss of left ventricular myocardium 5, 2
• Clinical presentation: Hypotension, signs of hypoperfusion, pulmonary congestion, and cool extremities 2
• SCAI staging system: Provides standardized classification from Stage A (at risk) to Stage E (extremis with cardiac arrest requiring CPR/ECMO), with mortality increasing stepwise through stages 2
• Treatment depends on hemodynamics: Norepinephrine for persistent hypotension with tachycardia; inotropes (dobutamine/milrinone) for low cardiac output with adequate preload; phenylephrine or vasopressin for afterload-dependent states 3

4. Obstructive Shock

• Results from mechanical blockage of circulation causing elevated resistance and impaired cardiac filling or outflow 1
• Hemodynamic profile: Elevated CVP, variable cardiac index depending on the specific obstruction, and elevated SVR 2
• Common causes: Massive pulmonary embolism, tension pneumothorax, cardiac tamponade, and constrictive pericarditis 6
• Treatment priority: Immediate life-saving intervention to remove the obstruction (needle decompression, pericardiocentesis, thrombolysis/embolectomy) 1

Hemodynamic Differentiation Framework

The American College of Cardiology recommends using three key parameters to differentiate shock types 2:

• Cardiac Index (normal: 2.2-4.0 L/min/m²): Reduced in cardiogenic and hypovolemic shock; normal or elevated in distributive shock 2
• Systemic Vascular Resistance: Elevated in cardiogenic shock; decreased in distributive shock; elevated in hypovolemic and obstructive shock 2
• Pulmonary Capillary Wedge Pressure: Elevated in cardiogenic shock (>15 mmHg); decreased in hypovolemic shock; normal or decreased in distributive shock 2

Critical Clinical Pitfalls

• Dynamic hemodynamic changes occur rapidly as shock progresses or responds to treatment, requiring continuous reassessment rather than single-point measurements 2
• Late-stage septic shock can develop myocardial depression and may be confused with cardiogenic shock, but the primary hemodynamic pattern remains distributive with decreased SVR 2
• One shock state may convert to another during the clinical course—for example, prolonged hypovolemic shock can lead to distributive shock from systemic inflammatory response 4
• Mixed shock states are common in critically ill patients, particularly combining cardiogenic and distributive components in severe sepsis with myocardial depression 4