Learning outcomes Part 1 of 16

  • Definitions
  • Types of embolism
  • Consequences of embolism

Definitions - embolism Part 2 of 16

  • An embolus is a detached intravascular solid, liquid or gaseous mass that is carried by the blood to a site distant from its point of origin
  • The vast majority of emboli arise from thrombi
  • Other sources of emboli include air, nitrogen, fat, amniotic fluid, foreign bodies, tumour cells

Types of embolism Part 3 of 16

  • Pulmonary embolism – very important!
  • Systemic embolism
  • Air embolism
  • Fat embolism
  • Amniotic fluid embolism

Pulmonary embolism Part 4 of 16

The vast majority are caused by venous thromboembolism (VTE) arising from the deep veins of the lower limbs.

Clinical signs/symptoms vary depending on the size of the embolus.

The most common symptoms & signs are:

  • Pleuritic chest pain (sharp & stabbing pain, well localised, exacerbated by deep inspiration)
  • Breathlessness
  • Haemoptysis
  • Collapse
  • Tachycardia
  • Hypotension

Large emboli - macroscopic appearance Part 5 of 16

These are examples of very large pulmonary embolisms. They obstruct the pulmonary circulation. They most likely will present with severe chest pain and hypotension, collapse or even sudden death.

Microscopic appearance – large emboli Part 6 of 16

Microscopically the emboli have a similar appearance to thrombi

Intermediate emboli - macroscopic appearance Part 7 of 16

The flashcard below is a cross-section through a piece of lung. Note the red/darker areas of tissue marked by an arrow (a).

In this picture, an intermediate- sized thrombus has occluded a peripheral pulmonary artery leading to ischaemia and necrosis. These infarcts can present with haemoptysis and pleuritic chest pain.

Physiology aside - dual blood supply of the lungs Part 8 of 16

An embolus in the pulmonary artery branches does not always lead to pulmonary infarction. This is because the lungs have a dual blood supply.

They receive blood from the pulmonary artery (bringing venous blood from the right ventricle) as well as the bronchial arteries (which bring arterial blood from the aorta).

If an occlusion occurs in the pulmonary artery, the bronchial arteries can carry enough oxygenated blood to keep the lung parenchyma alive.

If there is any impairment of the systemic circulation (e.g. left ventricular dysfunction or atherosclerosis of the bronchial arteries) then the lung wouldn’t receive enough oxygenated blood if there is also a pulmonary embolus.

This results in an infarct of the lung. Often there’s enough blood to keep the tissue alive, but still make the infarct haemorrhagic. This is why in an infarcted pulmonary embolism the patient often presents with haemoptysis.

Complications of venous thrombo-embolism Part 9 of 16

Prevention of DVT & PE Part 10 of 16

Prevention of DVTs and PEs form a crucial part in any hospital admission. There are many methods which are used to discourage the formation of a DVT.

Systemic embolism Part 11 of 16

Definition – emboli which travel through the systemic arterial circulatory system.

The vast majority of these arise within the heart secondary to atrial fibrillation (altered flow) or thrombus formation over an area of myocardial infarction (altered wall).


Destination of systemic emboli Part 12 of 16

Fat embolism Part 13 of 16

A fat embolism is a rare form of embolism that often results from multiple fractures or a fracture of the femur.

Fat droplets enter the vein from bone marrow or surrounding adipose tissue.

Most of these cases have little clinical significance, with 1% showing clinical signs.

Air embolism Part 14 of 16

This occurs when air travels through the vascular system.

It can occur in decompression sickness (the bends) when divers ascend too quickly.

It can also (very rarely) occur if air enters the arterial or venous system through surgery or during a clinical procedure (e.g. cannulation).

Amniotic fluid embolism Part 15 of 16

During labour, if the placental membranes tear at the same time the uterine veins rupture, then amniotic fluid can get into the bloodstream and travels to the lungs.

Conclusion Part 16 of 16

Venous thromboembolism is an extremely common clinical scenario.

It is important that you –

  • Understand the risk factors for the development of a DVT/PE
  • Recognise the clinical signs and symptoms
  • Appreciate the complications of a PE
  • Can identify ways of preventing DVT formation