Hypovolaemic, cardiogenic, obstructive and distributive
Mnemonic
Four types, separated at the bedside by the periphery and the filling pressure:
| Type | Peripheries | JVP or preload | Cardiac output |
|---|---|---|---|
| Hypovolaemic | Cold | Low | Low |
| Cardiogenic | Cold | High | Low |
| Obstructive | Cold | High | Low |
| Distributive | Warm | Low | High |
“Cold and empty is hypovolaemic; cold and full is a pump or an obstruction; warm is distributive.”
Obstructive shock is separated from cardiogenic by the specific signs of the cause: tension pneumothorax (tracheal deviation, absent breath sounds), tamponade (Beck’s triad), massive pulmonary embolism (right heart strain).
Neurogenic shock is the exception to the tachycardia rule: hypotension with bradycardia and warm peripheries after a high cord injury, because the sympathetic outflow is lost.
Expansion
| Type | Mechanism | Output | Resistance | Filling pressure |
|---|---|---|---|---|
| Hypovolaemic | Loss of volume | Low | High | Low |
| Cardiogenic | Pump failure | Low | High | High |
| Obstructive | Mechanical obstruction to filling or ejection | Low | High | High |
| Distributive | Loss of vascular tone | High or normal | Low | Low |
Examples: haemorrhage and dehydration; myocardial infarction and arrhythmia; tension pneumothorax, cardiac tamponade and massive pulmonary embolism; sepsis, anaphylaxis and neurogenic shock.
The most useful bedside discriminator is peripheral perfusion. Cold, clammy and mottled peripheries indicate compensatory vasoconstriction and therefore a low output state. Warm, flushed peripheries with a bounding pulse indicate vasodilatation and point to a distributive cause.
Filling pressure then separates hypovolaemic (low) from cardiogenic and obstructive (high).