In a journal report written by astronaut-doctor Serena M. Auñón-Chancellor, M.D. it was revealed that an ISS astronaut suffered a deep vein thrombosis (DVT) two months into a six-month stint aboard the ISS. The astronaut, with NASA and other doctors was treated via telemedicine and was able to successfully complete their mission aboard the ISS.

What is a DVT?

A DVT is a blood clot, or thrombus, which forms in one of the body’s larger veins. Typically when earthbound clinicians speak of a DVT, they are referring to blood clots which form in the lower bodies of people who are in long term medical care. The formation of such clots is dangerous as these clots can detach (becoming an embolus) and move through the vein to the heart, lungs, or brain. This can result in cardiopulmonary embolism or a stroke.

Prior to spaceflight, astronauts undergo a massive battery of medical tests. While there is no public list of which tests are performed, it should be noted that for long-term spaceflight, tests for antithrombin III deficiency, protein C deficiency, protein S deficiency, factor V Leiden mutation, prothrombin gene mutation, and antiphospholipid syndrome should be conducted on every astronaut, particularly female astronauts. This is because birth control medication, sometimes given during spaceflight, can have the effect of increasing clotting factors.

An Asymptomatic Finding

Typically DVTs would be found because of symptoms, such as swelling, redness, skin discoloration, or cramps. However, in spaceflight, swelling of the face and reddish discoloration are normal as blood volume shifts toward the head and upper body in low-gravity environments.

In this particular instance the DVT was asymptomatic (showing no signs or trouble) and was found during an experiment conducted on the ISS. This study was being conducted to evaluate the distribution of fluid in astronauts during micro- and zero-gravity exposure. The test was conducted using an ultrasound on the jugular vein. At the time of the test, the astronaut in question found a DVT, which is the first time a DVT had ever been discovered in an astronaut in flight.

NASA doctors were consulted, but there is no base of medical information about DVTs in space. They consulted with Dr. Stephan Moll, M.D., an expert on DVT from UNC School of Medicine. In an interview, Dr. Moll stated that his first inclination was to hop on a rocket and visit the patient. As this was not an option, they used telemedicine techniques to observe the astronaut and the DVT using ultrasound, and to develop a plan of treatment.

The astronaut was given a blood thinner, Enoxaparin (Lovenox®), of which there was a small supply on board the ISS. This was given as a daily intravenous shot for 43 days, at which time a resupply mission reached the ISS which brought Apixaban (Eliquis®) oral pills. The treatment plan continued until four days before returning to earth. This decision was made as the journey home can be strenuous on the body and the medical team did not want to exacerbate this through the use of blood thinners. After returning to earth, the astronaut did not continue to take the blood thinners and has received no further treatment.

While still on board the ISS, the astronaut conducted regular ultrasound screenings on themself, with direction given by radiology team on Earth. Dr. Moll also received phone calls and emails from the astronaut, which he and his wife found fascinating. Generally, the astronaut reached out and asked questions like any other patient.

This case of a first DVT in space, while not ideal, does give NASA medical staff a new base of information for how to treat DVTs in micro- and zero-gravity environments. This will prove to be useful in the future, especially for years-long missions, to Mars or Europa for instance.

Works Consulted:

• Buckey, Jay C. Jr. Space Physiology. Oxford U P, 2006
• Auñón-Chancellor, Serena M., et al. “Venous Thrombosis During Spaceflight,” N Engl J Med 2020; 382:89-90 DOI: 10.1056/NEJMc1905875