The clot that kills you usually starts in your leg

A pulmonary embolism is a sudden blockage in a lung artery. It usually
happens when a blood clot breaks loose and travels through the bloodstream to
the lungs.

It is serious, and can cause permanent lung damage, low blood oxygen,
and damage to other organs starved of oxygen. **It can be life-threatening,
especially if a clot is large or there are many.**

Where the clot comes from

The clot is usually a deep vein thrombosis — a clot in the leg. Rarely, the
blockage is something else entirely: air bubbles, clumps of fat, or parts of a
tumour.

Everything sensible about prevention follows from that first sentence. The
lung is where the damage happens; the leg is where the problem is made.

What raises the risk

• Surgery, especially joint replacement
• Medical conditions — cancers, heart diseases, lung diseases
• A broken hip or leg bone, or other trauma
• Hormone-based medicines — birth control pills, menopause hormone therapy
• Pregnancy and childbirth — the risk is **highest for about six weeks
  after childbirth**
• Not moving for long periods — bed rest, a cast, a long flight
• Age, rising especially after 40
• Family history and genetics
• Obesity

Symptoms

Shortness of breath · rapid breathing · **chest pain or discomfort that gets
worse when you cough or breathe deeply** · increased heart rate · coughing up
blood · very low blood pressure, lightheadedness or fainting.

Sometimes there are no symptoms at all until a serious complication such as
pulmonary hypertension — high blood pressure in the lung arteries.

PE can be difficult to diagnose. A provider takes a medical history including
symptoms and risk factors, does a physical exam, and orders imaging and blood
tests.

Treatment is immediate

If you have a PE you need medical treatment right away. The goal is to
break up clots and stop new ones forming.

Medicines

Procedures

• Catheter-assisted thrombus removal — a flexible tube reaches the clot in
  the lung, and a tool inserted through it breaks the clot up or delivers
  medicine. Usually done under anaesthetic.
• A vena cava filter, for people who cannot take blood thinners. Placed
  inside the vena cava, it catches clots before they reach the lungs. **It does
  not stop new clots forming** — it only stops them arriving.

Prevention, which is mostly about legs

• Keep taking blood thinners, with regular checkups so the dose
  prevents clots without causing bleeding
• Heart-healthy lifestyle changes — eating, exercise, quitting smoking
• Compression stockings, to prevent deep vein thrombosis
• Move your legs when sitting for long periods, such as on long journeys
• Move around as soon as possible after surgery or after being confined to
  bed

Source: National Heart, Lung, and Blood Institute, via MedlinePlus.