What are DVT and PE?
· Blood should flow in the circulation and only clot outside the circulation at the site of an injury. If blood clots within the circulation it is called thrombosis.
· Blood flows back to the heart in the veins. When thrombosis occurs in veins it is known as Deep Vein Thrombosis (DVT).
· The most common site for a DVT is in the deep veins in the legs.
· When a DVT forms pieces of the clot can break off and travel through the circulation to the heart and into the main artery to the lungs. This is called a pulmonary embolus (PE).

When do DVT and PE occur?
· DVT and PE are more likely to occur at certain times and being in hospital is one of the biggest times of risk. When DVT or PE occurs in hospital, or soon after discharge, it is called Hospital-Acquired-Thrombosis (HAT).
· HAT occurs because changes in blood clotting, due to illness, combined with reduced blood flow, due to immobility, increase the risk of thrombosis.
· There is a risk of DVT and PE when you travel but the risk is very much less than the risk when you are in hospital. Travel alone is rarely enough to cause a DVT or a PE. There is usually another risk factor, such as a recent operation or treatment for cancer.

Can risk of DVT and PE be measured in hospital?
· Much research has been done to determine risk factors for HAT. It is now common practice for doctors or nurses to ask patients questions when they are admitted to hospital to determine if they are at risk of HAT. ClotStop uses these questions to give you an idea before you go into hospital if you might be considered at risk. The aim of ClotStop is to inform you and empower you to ask if you have been risk assessed if you are admitted to hospital.
· The importance of risk assessment is that treatment can be given to patients considered to be at risk in order to reduce the likelihood of them developing HAT.

What can be done to stop DVT and PE in hospital?
· Treatment to reduce the risk of HAT can be divided into mechanical methods such as compression socks and drugs such as heparins.
· Stockings can be difficult to apply and they often become loose. There is also less evidence that they work, compared to heparin drugs.
· Heparin drugs are more reliable than compression stockings and are the most effective proven method for reducing DVT and PE.
· Sometimes heparin or stockings are used alone. Sometimes heparin and stockings are used to together. The choice made by a doctor depends on their assessment of thrombosis and bleeding risk and the other treatments that a patient will receive.

Should all patients be given heparin to reduce the risk of DVT and PE?
· Definitely not. There is a balance of benefit and risk when prescribing heparin drugs as these are anticoagulants. An anticoagulant may reduce the risk of thrombosis but it also increases the risk of bleeding.
· A common lay perspective is that 'any risk' of DVT or PE should be an indication for prescribing heparin. However, 'any risk' is definitely not a reason. Heparin is only indicated when the risk of DVT or PE is high enough to justify the risk of bleeding that the drug may cause. The risk of bleeding is small but if it does occur it can be dangerous. Doctors are trained to weigh up the balance of benefit and risk so they can decide what the best option for you is.

Are DVT and PE different to blood clots that occur in arteries?
· Yes. Blood flows in arteries from the heart to all parts of the body. The arteries are a high pressure high flow system. Thrombosis in arteries is usually due to degeneration of the wall of the artery; this is called atherosclerosis. Risk factors for arterial thrombosis include smoking, ageing, high blood pressure, high lipid levels, and diabetes.
· In most instances there is no link between thrombosis in veins (DVT and PE) and thrombosis in degenerate arteries (causing heart attack and stroke).
· HAT (Hospital-Acquired-Thrombosis) only includes DVT and PE.