Which values indicate hypovolemic shock?

A cardiac index below 2.2 L/min/m² together with low filling pressures: PCWP below 8 mmHg and CVP below 5 mmHg, with a compensatorily elevated systemic vascular resistance.

How do you distinguish hypovolemic from cardiogenic shock?

Solely by the filling pressures. Cardiac index and vascular resistance change in the same direction in both; only PCWP separates them reliably.

Why is vascular resistance elevated?

Sympathetic compensation constricts the resistance vessels to maintain mean arterial pressure as cardiac output falls. The raised SVR is therefore a consequence of the shock, not its cause.

Hypovolemic shock – hemodynamic profile

Hypovolemic shock results from loss of circulating volume, whether through haemorrhage, fluid loss or sequestration into the interstitium. Hemodynamically it presents as a low cardiac index with reduced filling pressures: PCWP below 8 mmHg and CVP below 5 mmHg. Systemic vascular resistance rises compensatorily to maintain mean arterial pressure. The underlying pattern is therefore empty both forward and backward — in contrast to cardiogenic shock, where filling pressures rise.

For educational use only. Not for clinical use.

Hemodynamic profile

Parameter	Direction	Typical	Normal range
CI	↓	< 2.2 L/min/m²	2.5-4.0
SVR	↑	> 1400 dyn·s·cm⁻⁵	800-1200
PCWP	↓	< 8 mmHg	6-15
ZVD	↓	< 5 mmHg	2-6
SvO2	↓	< 60 %	65-75

Differentiation

Differentiate from	Discriminating parameter	Explanation
Cardiogenic shock	PCWP	PCWP separates the two: low in hypovolemic shock (< 8 mmHg), elevated in cardiogenic shock (> 18 mmHg). Cardiac index and vascular resistance behave identically in both.
Obstructive shock	ZVD	CVP is low in hypovolemic shock and high in obstructive shock. Both show low cardiac output with high vascular resistance.

Causes

Acute haemorrhage, traumatic or gastrointestinal
Severe diarrhoea or vomiting
Polyuria, for example from osmotic diuresis
Burns with extensive plasma loss
Capillary leak syndrome with interstitial sequestration
Excessive diuretic therapy

Clinical context

The extremities are cool, capillary refill is prolonged and the neck veins are collapsed. Marked respiratory variation of the pressure tracings is characteristic, since an underfilled circulation responds particularly sensitively to intrathoracic pressure swings. The low CVP distinguishes the picture from obstructive shock, where CVP is high. Because cardiac index and vascular resistance behave exactly as they do in cardiogenic shock, measuring a filling pressure is indispensable — without PCWP or CVP the distinction remains hemodynamically open.

Frequently asked questions

Which values indicate hypovolemic shock?: A cardiac index below 2.2 L/min/m² together with low filling pressures: PCWP below 8 mmHg and CVP below 5 mmHg, with a compensatorily elevated systemic vascular resistance.
How do you distinguish hypovolemic from cardiogenic shock?: Solely by the filling pressures. Cardiac index and vascular resistance change in the same direction in both; only PCWP separates them reliably.
Why is vascular resistance elevated?: Sympathetic compensation constricts the resistance vessels to maintain mean arterial pressure as cardiac output falls. The raised SVR is therefore a consequence of the shock, not its cause.

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