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How can blood clots be prevented in hospitalised patients?

Leading expert in thrombosis and acquired bleeding disorders Professor Beverley Hunt OBE explains what healthcare professionals can do to combat the risk of blood clots in hospitalised patients and improve outcomes.  

Hospital patients are at a significant risk of suffering from blood clotting. In fact, being admitted to hospital with an illness carries a 15% chance of developing detectable Deep Vein Thrombosis (DVT) if there are no preventative measures taken after 14 days.1

Indeed, without these preventive measures, there would be around 25,000 deaths a year in the UK due to hospital acquired blood clots.2 Patients who have recently been discharged from hospital are also at increased risk, with up to 60% of all venous thromboembolism (VTE) cases occurring during or within 90 days of hospitalisation.3

In this article, we speak to a leading expert on thrombosis, Professor Beverley Hunt OBE, to find out what healthcare professionals can do to combat this risk of blood clots and improve patient outcomes.

What is the difference between Pulmonary Embolism (PE) and Deep Vein Thrombosis (DVT)?

Blood clotting is an important process that prevents excessive bleeding when a blood vessel is injured.4 However, sometimes clots form in places they shouldn’t.
When a blood clot forms in a vein or artery, it can stop the blood from flowing through the body. This can be extremely dangerous for the patient.

Deep Vein Thrombosis (DVT) occurs when a blood clot develops in a major vein, often in the leg. If the clot then breaks off and travels through the body, it can block a pulmonary artery, cutting off the blood supply to the lungs; this is called a pulmonary embolism (PE).4

Venous thromboembolism (VTE) is the umbrella term referring to all blood clots in the vein, and includes DVT and PE.

What are the signs and symptoms of a blood clot that healthcare professionals should look out for?

A clot can give you different symptoms based on where it is located, but “unexplained pain in the leg is the usual one for deep vein thrombosis,” Professor Hunt explains.

“For a pulmonary embolism, healthcare professionals should look out for shortness of breath and pleuritic chest pain, or really, any respiratory symptom that is unexplained. Coughing up blood is also a symptom, but it’s pretty rare,” she adds.

Professor Hunt warns that pulmonary emboli are a great “clinical mimic” that can imitate all sorts of different types of respiratory disease, such as a chest infection.

While blood clots are not always life-threatening, PE is a medical emergency that can cause permanent damage to the lungs or other organs due to lack of oxygen.

“It’s a serious condition,” Prof. Hunt states, “and it’s one of the major preventable causes of death due to hospital admission”.

What causes blood clots in hospital patients?

“Around 55 to 60% of blood clots are caused by hospital stays, with most of them occurring in the first 90 days following discharge,” Professor Hunt says. “We call this hospital associated thrombosis or ‘HAT’.

There are three risk factors for VTE, all of which commonly occur in hospital patients. These are: sticky blood, immobility, and damage to the vessel wall.

“If you have an operation or you’re acutely ill with pneumonia or some other form of infection, your blood gets sticky,” Prof. Hunt explains.

When blood is thicker or stickier than usual, it will clot more easily. Patients with sticky blood will often be given small doses of anticoagulant medicines to prevent clots occurring.

Immobility is also a major risk-factor for DVT. “When you sit in a chair for 90 minutes and don’t move, the blood flow through the veins drops by about 50%,” Professor Hunt says.

Slow-flowing blood is much more likely to clot than normal-flowing blood. Patients who have had a surgical operation and gone under general anaesthetic and those with an illness or injury that causes immobility (such as a fracture) are therefore much more likely to get a blood clot.

“We’re absolutely dependent on the muscles in the calf squeezing the veins and pushing the blood up the legs,” she says.

When there’s no movement, the blood flow through the veins drops off, which can predispose to a clot. Damage to the vessel wall, which often occurs during surgical procedures, can also lead to an increased risk of blood clots.

Healthcare practitioners should therefore be acutely aware of the risk of blood clots in patients who have recently undergone an operation, are immobile due to an illness or injury, as well as those who are at increased risk of sticky blood.

Are certain groups of people at greater risk of blood clots?

As well as the above risk factors, there are other reasons why certain groups of people may be at increased risk from a blood clot.

Research suggests that Black people have 30% to 60% higher rates of DVT than White people. If you are a smoker, obese, pregnant, or over the age of 60, you are also at increased risk.5

“One of the issues for older people is that, as you age, your blood naturally gets stickier. So, if you’re in your 80s and you take yourself off to bed for a couple of days with the flu, you have quite a high risk of DVT,” says Prof. Hunt.

Older people are also at heightened risk of falls, fractures and arthritis, all of which can lead to immobility and increase the risk of VTE.

What does the NHS do to prevent blood clots in hospitalised patients?

Professor Hunt says the NHS is “amazing” at preventing hospital associated thrombosis, thanks to ‘The National VTE Prevention Programme’.

“The charity Thrombosis UK spent eight years fighting for the programme which was implemented in 2010,” she explains. “Now, every patient who goes to an English or Welsh hospital has a VTE risk assessment. As part of the risk assessment, healthcare practitioners have to tick off the risk factors for having clots and compare them with the bleeding risks. If the risk of thrombosis outweighs the bleeding risks, then the patient will usually be recommended small doses of blood thinners.”

“This has been going on alongside NICE guidance for the past 12 years, and it has meant that the number of deaths in hospitals and in the first 90 days after discharge have fallen by about 15%. Other countries now look to us because we have this very effective system,” Prof. Hunt says.

What about on a more global scale?

“I’m currently working with the World Health Organization (WHO) so that we can prioritise and make people aware of the risks of hospital associated thrombosis,” says Prof. Hunt.

“The dream is that one day, if you go into hospital anywhere in the world, you will have VTE risk assessment and get the appropriate prevention if you’re at risk. This isn’t happening at the moment, so we’ve still got a lot of work to do.”

What advice would you give to healthcare professionals working in secondary care?

Professor Hunt advises other healthcare professionals to “follow NICE guidance and carry out a VTE risk assessment when the patient is admitted.”

She warns, however, that clinicians should be aware that the guidance is a bit outdated when it comes to stockings.

“Some British trials have shown that anti-embolic stockings don’t have any effect on surgical patients. In fact, some trials have shown they can actually cause harm, including breaks in the skin and that type of thing. So, there’s a big swing against using anti-embolic stockings at the moment, and NICE guidance hasn’t caught up with the current evidence yet.

“As a result, many hospitals are removing stockings from their thromboprophylaxis protocols and are instead using intermittent pneumatic compression (IPC) devices. IPC devices use cuffs around the legs that fill with air like a balloon. The device then squeezes the leg, acting like a muscle would, which helps to keep the blood flowing. They are very effective and are just as good as having small doses of blood thinners,” Prof. Hunt explains.

What can patients who are discharged from hospital do to lower their risk of VTE?

“Patients who have been recently discharged from hospital need to make sure they keep mobile, and ensure they are not sitting in front of the television for very long periods.

“If you’re going to sit for a long period of time, you need to do exercises with your legs to keep the blood flowing, such as tweaking your ankles and moving your foot up and down.

“If you suspect you have a blood clot, it is important that you contact your healthcare professionals as soon as possible,” Prof. Hunt advises.

Is there anything that GPs should be aware of when it comes to at-risk patients presenting in primary care?

“GPs should look out for the usual signs of VTE in patients who have recently been discharged from hospital, such as leg pain or respiratory symptoms. When people have respiratory symptoms post discharge, they often get considered for chest infection, but in fact, a PE can present in exactly the same way as a chest infection.

“Primary care practitioners should also be aware of the risk of blood clots in Covid patients. Covid-19 is a major risk factor for having clots and we have seen many patients with DVT and PE during the pandemic, particularly among those with co-occurring conditions such as COPD and pneumonia,” Prof. Hunt warns.

But Professor Hunt has one take home point for all healthcare practitioners, and that is to be aware that DVT often presents silently. She said: “If you look in the old surgical textbooks, you’ll often see a picture of an enormously swollen, red leg that’s labelled deep vein thrombosis.”

“However, we know from modern studies that about 80% of deep vein thrombosis are clinically silent in that they don’t have any swelling and they don’t have any change in colour. So, if someone presents with unexpected pain in the leg, and there’s no obvious explanation, one needs to think about deep vein thrombosis.”

Professor Beverley Hunt, OBE, is the chair for the World Thrombosis Day Scientific Steering Committee and professor of thrombosis and haemostasis at King’s College London where she cares for those with clots. In England, she sat on the NICE guidelines’ development group and clinical standards committee for the prevention of venous thromboembolism in hospitalised patients. 



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