This Medical Monday series is about risk factors for venous thromboembolism, VTE (pulmonary embolism and DVT). The post ‘Are you on the red or blue team?‘ outlines the difference between arterial and venous clots.
We are going to cover
Strong risk factors; being in hospital, having surgery and immobility
Moderate risk factors; age (60+), a previous blood clot, family history of blood clots, thrombophilia, cancer, contraceptive pill and hormone replacement therapy
Other risk factors; obesity, pregnancy, smoking and alcohol
Immobility
How high is the risk?
Immobility is often quoted as a major risk factor for venous thrombosis, but it is hard to identify how much it contributes to the problem as it is often associated with other factors; for example after surgery it is hard to know how much of the risk is due to the surgery itself and how much is due to being stuck immobile in bed. In recent years the link between immobility and thrombosis has become more apparent since the link between long distance air travel and thrombosis has been identified. However even this link is not very strong. It has been estimated that 1 person out of 4600 on a long-haul flight will develop a blood clot and many of these are small clots that resolve spontaneously. The risk is highest for flights of more than 8 hours.
Air-raid shelter death
The first time anybody made a link between prolonged immobility and blood clots was during the second World War. An interesting case was reported in 1940.
“A woman of 60 years took a deckchair into a public air-raid shelter and sat in it continuously for 10 hours. When she got up she complained he legs were numb and cramped and she found that her ankles were swollen. Some 8 to 10 mins after leaving the shelter to walk home she collapsed in the street, dead” (Simpson K, Lancet 1940).
A post mortem confirmed that she had died from a Pulmonary embolus. She was over weight and the theory was that the bar on the seat of the deckchair had blocked the blood flow from her legs and allowed the clot to form.
Hospitals, plaster casts and TV
Since then the relationship between immobility and thrombosis has become more established and in some situations is quite high. A study in 2014 of people over the age of 70 showed there was a 15 fold increase in the risk of a blood clot within the first 2 weeks of leaving hospital. Wearing a plaster cast can increase the risk about 6 fold and even being immobile at home with a short illness can increase the risk up to 5 times more than the incidence in the general population. As we have shown in a previous post even watching TV carries a risk
What does this mean for me?
The most important thing is to be aware there is a risk. Get active and where possible get up and move around particularly after a hospital stay or illness. If you have other risk factors for blood clots then you may need anticoagulant prophylaxis for a prolonged period of immobility. This is frequently given after surgery, but not used so frequently for people in a plaster cast or those immobile for medical conditions. There is a major push in many hospitals to make patients aware of the risk. Your local hospital may have a leaflet reminding you to talk to your doctor about the risk.
If you have previously had a blood clot you are at particularly high risk of another clot, so make sure you tell your doctor about your medical history.
We have previously covered what to do when flying; do some exercise, maintain good hydration and walk around the plane.
Interested in Murder?
For those interested, the air raid shelter paper was written by Keith Simpson as a junior doctor. He went on to become the Professor of forensic pathology at Guys Hospital, London and was involved with some of the most notorious murders in the UK. His book 40 years of murder is a good read.
Leave a Reply