The connection between venous thrombosis and immobility is clear. In fact, stasis is part of Wirchow’s triad. We also know that many people who are acutely ill should receive prophylactic anticoagulation. But what about people who are chronically immobile? This represents a huge number of people. Examples include people who are wheelchair dependent and people in long-term care facilities. Should they receive prophylactic anticoagulation? Of course, the obvious benefit would be preventing blood clots. But the flip side will be excess bleeding over time.
The Data on Venous Thrombosis and Immobility
Immobility is common. One study reported that nearly 1 in 5 hospitalized patients age 70 or greater were bedridden and were unable to stand without assistance. In on study, 18% of chronically bed-ridden patients developed a deep vein thrombosis. Not all were symptomatic. But we know that about 30% of deep vein thrombosis are asymptomatic. So the incidence goes up if you look for clots.
Another small study looked at the risk of recurrent clots in immobile patients. Researchers concluded that immobility was a risk-factor to consider when deciding about treatment duration.
Many stroke patients develop deep vein thrombosis as well. A study shed light on the timeline of clots. Researchers examined data on over 30,000 stroke patients over 15.7 years. During this time, 722 patients developed clots. When the researchers examined the timeline for clots to develop, they noticed that the highest risk was during the first month (HR or 19.7). After 3 months the risk declined rapidly. A study like this might imply that we need to prevent clots mostly during the acute phase of immobility. Or, perhaps, many patients do not remain immobile after 3 months.
Immobile Patients who had a Venous Thrombosis
In 2023 we published a paper in the Journal of General Internal Medicine describing the outcomes of chronically immobile patients who have already had a venous thrombosis. Our analysis included patients who had a deep vein thrombosis, pulmonary embolism, or both.
We were able to show that while treatment for 3 months was important, deciding how long to anticoagulate beyond that was harder. Patients tended to have more bleeds and deciding what to do was not simple. This was especially true in patients greater than 75 years of age. In these patients, we need to consider bleeding much more seriously.
The bottom line is that guidelines to not really help us here. Most guidelines suggest to tailor treatment duration according to risk of recurrence but also bleeding risk. But the guidelines we use the most such as those by the American College of Chest Physicians or the American Society of Hematology do not address immobile patients at all.
Some Chronically Immobile Patients are Protected from Clots
Most chronically immobile patients do not develop blood clots. The reason for this may be tied to a molecule called HSP47. It seems like a lack of this molecule is protective against venous thrombosis. Also, it seems like chronic immobility triggers down-regulation of this molecule. An interesting fact is that this modulation seems to occur in many mammals. For instance, bears downregulate this molecule during hibernation. Then, when they awake and are active again, the molecule levels rise. Experimental data suggest that humans also downregulate this molecule if they are subjected to long-term immobility.