Which values indicate obstructive shock?

A cardiac index below 2.2 L/min/m² with a CVP above 15 mmHg and an elevated systemic vascular resistance. The combination of low flow and high right atrial pressure is the key finding.

How do you distinguish tamponade from pulmonary embolism?

By the relationship of the diastolic pressures. In tamponade CVP, PCWP and diastolic PA pressure equalise; in pulmonary embolism PCWP remains normal or low while PA pressures rise and PAPI falls.

The mechanical obstacle dams blood upstream of the affected segment. Whether the obstruction restricts filling of the heart from outside or occludes the pulmonary circulation, right atrial pressure rises in both cases.

Obstructive shock – hemodynamic profile

In obstructive shock a mechanical obstacle impedes filling of the heart or its outflow, while the myocardium itself is initially intact. Hemodynamically this produces a low cardiac index with a markedly raised central venous pressure and a compensatorily increased systemic vascular resistance. The decisive additional information comes from the relationship between CVP and PCWP: in pericardial tamponade all diastolic pressures equalise, whereas in pulmonary embolism CVP rises while PCWP stays normal or low.

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
ZVD	↑	> 15 mmHg	2-6
PCWP	→	Tamponade: ≈ CVP; pulmonary embolism: normal to low	6-15
PAPI	↓	< 0.9 in pulmonary embolism	> 0.9

Differentiation

Differentiate from	Discriminating parameter	Explanation
Cardiogenic shock	PCWP	In cardiogenic shock PCWP is distinctly higher than CVP. In tamponade the diastolic pressures equalise; in pulmonary embolism PCWP stays normal or low despite a high CVP.
Right heart failure	PAPI	Both show a high CVP with a low cardiac index. PAPI and the clinical course help: obstructive shock involves an acute mechanical obstacle, right heart failure a contractility problem of the right ventricle.

Causes

Pulmonary embolism
Pericardial tamponade
Tension pneumothorax
Constrictive pericarditis
Severe dynamic outflow tract obstruction
Vena cava compression syndrome

Clinical context

Distended neck veins together with a low cardiac output are the clinical hallmark and separate the picture immediately from hypovolemic shock. Tamponade shows pulsus paradoxus and equalisation of CVP, PCWP and diastolic PA pressure. Pulmonary embolism instead produces acute right heart strain with elevated PA pressures, a low PAPI and a normal PCWP — the right ventricle fails against a suddenly increased afterload it is not adapted to. Distinguishing between obstructive causes is often easier hemodynamically than separating the group from other forms of shock.

Frequently asked questions

Which values indicate obstructive shock?: A cardiac index below 2.2 L/min/m² with a CVP above 15 mmHg and an elevated systemic vascular resistance. The combination of low flow and high right atrial pressure is the key finding.
How do you distinguish tamponade from pulmonary embolism?: By the relationship of the diastolic pressures. In tamponade CVP, PCWP and diastolic PA pressure equalise; in pulmonary embolism PCWP remains normal or low while PA pressures rise and PAPI falls.
Why is CVP elevated?: The mechanical obstacle dams blood upstream of the affected segment. Whether the obstruction restricts filling of the heart from outside or occludes the pulmonary circulation, right atrial pressure rises in both cases.

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