Shock can result from the following mechanisms. Click on each one to find out more.

Hypovolaemic shock

Inadequate ventricular filling.

The most common cause of this type of shock is any cause of fluid loss: haemorrhage; salt and water loss; sepsis and burns.

A poor venous return to the heart will decrease the stroke volume and cardiac output as shown in the Frank-Starling Curve.

The patient will attempt to compensate by tachycardia and increased systemic vascular resistance (SVR). They become cold peripherally and shut down.

Cardiogenic shock

Cardiogenic shock is caused by pump failure.

The patient will have a poor cardiac output and will therefore attempt to maintain a blood pressure by increasing SVR. Blood pressure can be low, normal or high, but organ perfusion is compromised, peripheries are cold and the patient is prone to pulmonary oedema.

Early echocardiography is important to assess contractility, valve function and exclude significant pericardial effusion.

Distributive shock

Peripheral vasodilatation and subsequent maldistribution of blood flow. This leads to a relative hypovolaemia as there is more space in which to put the same volume of fluid.

Common examples of this type being septic, anaphylactic and neurogenic shock.

Obstructive shock

Obstructive shock is caused by extra-cardiac obstruction to blood flow. For example, in pulmonary embolism, aortic stenosis, pericardial effusion and tension pneumothorax.

As a result of the low cardiac output the patient will be tachycardic and have an increase in SVR. The patient becomes cold and shuts down. They may demonstrate raised JVP and venous congestion of the face and body due to the obstruction.