Specialists at Royal Brompton Hospital’s severe respiratory failure service have established a clear link between Covid-19 and blood clotting, by using hi-tech CT scans to take images of lung function in patients most seriously affected by the disease. All of those tested suffered a lack of blood flow, suggesting clotting within the small vessels in the lung. This, the clinical team told the Sunday Telegraph newspaper, partly explains why some patients are dying of lung failure through lack of oxygen in the blood.
Doctors believe that careful use of anticoagulants (known as blood-thinners) can eventually save lives, but testing will need to be extremely careful as the drugs can also have serious consequences, so a "blanket" use of anticoagulants would not be appropriate. Any treatment would also have to start very early to prevent clots forming.
Dr Brijesh Patel, senior intensivist and clinical senior lecturer at Royal Brompton and Imperial College, London, commented: "These are very unwell patients but I think the majority of patients will end up on significant therapeutic doses of blood-thinning agents as we learn more about this disease. If these interventions in the blood are implemented appropriately, they will save lives."
Other recent European studies found signs of blood clotting in a third of coronavirus patients, but Dr Patel explained "we have to be cautious" with how we proceed with blood thinning agents.
“You have to do it in the right way otherwise you can cause harm,” continued Dr Patel. “There are a variety of blood-thinning agents as well. Which you use depends on the patient so we have to have a more personalised medicine approach."
Professor Peter Openshaw, a specialist in experimental medicine at Imperial College, London and honorary physician at St Mary's hospital, expressed optimism over the discovery at the Royal Brompton. "It does sort of explain the rather extraordinary clinical picture that is being observed with people becoming very hypoxic, very low on oxygen and not really being particularly breathless," he said. "That would fit with it having a blood vessel origin."
Immunothrombosis experts at Hammersmith Hospital and Royal Brompton are also looking at the link between immune inflammation and blood clotting.
"It's an unprecedented amount of collaboration and development of a really quite extraordinary story about a virus that we hitherto knew nothing," said Prof Openshaw, a member of the Sage sub-group on clinical information. All the time we are discovering new twists and this intravascular clotting is a really nasty twist that we haven't seen before with many other viruses."
Dr Patel added: "We've seen over 150 patients that have come through the Royal Brompton and having had a look at many of them over the past couple of months we've learnt a lot about them. We have the sickest cohorts of those in intensive care because of our extracorporeal membrane oxygenation (ecmo) service, which effectively is an artificial lung service where we take blood out of patients and oxygenate them outside their body. All these patients have perfusion problems seen in the tiny vessels of the lungs. Blood flow is decreased in these patients and it's only visible from dual energy scans.
"When you have the flu, the immune system is activated but it's appropriately done so. In Covid, it seems to be hyper activated and dysregulated, which then prompts this storm. We are still conducting lots of research but one of the hypotheses that we think is happening is that the virus is often directly affecting the cells that line the vessels in the lungs. The vessels in the lung can be quite sensitive to infection or any trauma and they can activate an immune response which then goes on to activate the clotting system. It's inflammation and coagulation. We think that might be causing clots to be forming within the lungs itself.
"Multi-disciplinary and national collaboration with scientists like Prof Openshaw and specialist haematologists like Dr Deepa Arachchillage from Imperial College, is changing our understanding of this disease and how we can quickly but safely treat these patients in intensive care.”
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For media queries:
Please direct media enquiries to Clare Elliott, assistant director of communications and public affairs. Outside office hours a member of the team can be contacted via the hospitals' switchboards on 020 7352 8121 (Royal Brompton Hospital) or 01895 823 737 (Harefield Hospital).
For the Sunday Telegraph extended news piece (paywall access):