Classification and Core Pathophysiology of Shock

Categories of Shock

Four major shock categories are defined by underlying pathophysiology: hypovolemic, cardiogenic, obstructive, and distributive shock (Intensive Care Medicine guidelines) 1.
Hypovolemic shock results from intravascular volume loss, producing decreased cardiac output and compensatory vasoconstriction (Intensive Care Medicine guidelines) 1.
Cardiogenic shock arises from primary cardiac dysfunction that leads to inadequate cardiac output; the primary mechanism is poor myocardial contractility (Intensive Care Medicine guidelines) 2.
Obstructive shock is caused by mechanical obstruction of circulation, leading to low cardiac output and compensatory vasoconstriction, similar to hypovolemic and cardiogenic patterns (Intensive Care Medicine guidelines) 1.
Distributive shock is characterized by a hyperkinetic state and vascular system dysfunction (vasoplegia, shunting, reduced oxygen extraction); it may present with low, normal, or high cardiac output (Intensive Care Medicine guidelines) [1][2].

Decreased tissue perfusion underlies all shock types, causing inadequate oxygen delivery or utilization to meet cellular metabolic demands (Intensive Care Medicine guidelines) [1][3].
Cellular dysoxia is reflected by elevated blood lactate levels (typically > 2 mmol/L) across shock categories (Intensive Care Medicine guidelines) 1.
Organ dysfunction associated with shock correlates with increased mortality (Intensive Care Medicine guidelines) 3.

Shock may involve mixed mechanisms; for example, septic (distributive) shock frequently includes myocardial depression, creating a combined picture (Intensive Care Medicine guidelines) 2.
Typical clinical features across all shock types include hypotension, tachycardia, and signs of hypoperfusion such as abnormal skin perfusion, reduced urine output, and altered mental status; however, hypotension is not mandatory for the definition of shock (Intensive Care Medicine guidelines) 1.
Recognition of shock relies on rapid assessment of three readily accessible organ systems: skin (cutaneous perfusion), kidneys (urine output), and brain (mental status) (Intensive Care Medicine guidelines) 1.