NASA astronaut on board ISS develops blood clot in space, gets treated by doctors on Earth

This was the first time a blood clot had been found in an astronaut in space, so there was no established method of treatment in zero gravity; Blood clot expert Dr. Stephan Moll, professor of medicine in the UNC School of Medicine, consulted NASA on how to treat the US astronaut.

                            NASA astronaut on board ISS develops blood clot in space, gets treated by doctors on Earth
Dr. Stephan Moll at NASA (UNC School of Medicine)

The field of telemedicine advanced a notch further when a blood clot expert from the University of North Carolina (UNC) School of Medicine got an email from NASA and later a call from space. The reason: an astronaut onboard NASA's International Space Station (ISS) had a blood clot in the jugular vein of the neck.

Back on Earth, such a case can be quickly handled by doctors. But since this was the first time a blood clot had been found in an astronaut in space, there was no established method of treatment for it in zero gravity. There was no prior knowledge of what the risks or complications might be. All decisions were made with the knowledge from what doctors do on Earth, what might happen in space, and how are things different in zero gravity.

The research team writes in the New England Journal of Medicine that medical decisions, in this case, were implemented through “concerted efforts” across multiple space agencies to overcome the numerous logistic and operational challenges. 

Dr. Stephan Moll, UNC School of Medicine blood clot expert, was the only non-NASA physician the space agency consulted when it was discovered that the astronaut had a deep vein thrombosis (DVT) -- or blood clot -- in the jugular vein of the neck. 

“My first reaction when NASA reached out to me was to ask if I could visit the ISS to examine the patient myself. NASA told me they couldn't get me up to space quickly enough, so I proceeded with the evaluation and treatment process from here in Chapel Hill," says Dr. Moll, a member of the UNC Blood Research Center. He co-wrote the case study on the successful treatment.

"My first reaction when NASA reached out to me was to ask if I could visit the International Space Station (ISS) to examine the patient myself. NASA told me they couldn't get me up to space quickly enough, so I proceeded with the treatment process from here in Chapel Hill," says Dr. Stephan Moll.
(UNC School of Medicine)

Deep vein thrombosis occurs when a blood clot (thrombus) forms in one or more of the deep veins in the body, usually in the legs.

The astronaut’s blood clot was asymptomatic – which implies the person did not have any symptoms that would have otherwise made them aware of the clot. The DVT was discovered when the astronauts was taking ultrasounds of their neck for a research study on how body fluid is redistributed in zero gravity. 

Approximately two months into a six-month mission ISS mission, “obstructive left internal jugular venous thrombosis was suspected in an astronaut during an ultrasound examination. Follow-up ultrasound examination performed by the astronaut, guided in real-time and interpreted by two radiologists on Earth, confirmed the presence of venous thrombosis with subacute characteristics," says the report.

The team further writes, "Internal jugular venous thrombosis on Earth is typically associated with cancer, a central venous catheter, or ovarian hyperstimulation. Unprovoked isolated venous thrombosis of the internal jugular vein is uncommon."

For privacy reasons, the research team did not reveal the astronaut's identity in their report, including information such as when this event happened. 

According to Dr. Moll, normally, the protocol for treating a patient with DVT would be to start them on blood thinners for at least three months to prevent the clot from getting bigger and to lessen the harm it could cause if it moved to a different part of the body such as the lungs.

"There is some risk when taking blood thinners that if an injury occurs, it could cause internal bleeding that is difficult to stop. In either case, emergency medical attention could be needed. Knowing there are no emergency rooms in space, we had to weigh our options very carefully," says Dr. Moll.

The International Space Station as it appeared in 2018. (NASA)

The medical team, which also included NASA doctors, decided the astronaut should start taking a blood thinner to prevent the clot from growing. The team was limited in its pharmaceutical options as the ISS keeps a small supply of various medicines on board. There was also a limited supply of a blood thinner injection (Enoxaparin) available onboard the ISS. Moll advised NASA on what dosage of Enoxaparin would effectively treat the DVT while also lasting long enough until NASA could get a new shipment of drugs to the ISS.

The course of treatment with Enoxaparin - a drug delivered by an injection into the skin - lasted for around 40 days. On day 43 of the astronaut's treatment, a supply of Apixaban, a pill that is taken orally, was delivered to the ISS by a supply spacecraft.

The treatment process lasted for more than 90 days. During the treatment, the astronaut performed ultrasounds on their neck with guidance from a radiology team on Earth to monitor the blood clot. 

Moll also spoke to the astronaut during this period through email and phone calls. The astronaut wanted to talk about what to expect, what could be the side-effects, and the treatment. 

“When the astronaut called my home phone, my wife answered and then passed the phone to me with the comment, 'Stephan, a phone call for you from space.' That was pretty amazing. It was incredible to get a call from an astronaut in space. They just wanted to talk to me as if they were one of my other patients. And amazingly the call connection was better than when I call my family in Germany, even though the ISS zips around Earth at 17,000 miles per hour," says Moll.

Timeline of diagnosis and treatment. (Venous Thrombosis during Spaceflight/New England Journal of Medicine)

Four days before returning to Earth, the astronaut stopped taking blood thinners. This is because the process of re-entry can be physically demanding and potentially dangerous for astronauts. Hence, the medical team did not want an injury to be worsened by blood thinners. The astronaut landed safely on Earth and the blood clot did not need any more treatment. 

“On follow-up 6 months after the return to Earth, the astronaut continued to be asymptomatic,” the report says. 

With new NASA missions planned this year, Dr. Moll says more research is needed to figure out how blood and blood clots behave in space. 

“How do you minimize risk for DVT? Should there be more medications for it kept on the ISS? All of these questions need answering, especially with the plan that astronauts will embark on longer missions to the moon and Mars,” says Dr. Moll, who continues his work with NASA. 

This case in spaceflight, says the team, highlights unique complexities of space medicine. This includes the “need for non–evidence-based clinical decision making; the need for patient-performed, radiologist-guided telemedicine ultrasonography; and a limited pharmacy in which long-term anticoagulation is not supported, syringes are a limited commodity, and drawing liquids from vials is a significant challenge because of surface-tension effects.”

The researchers say “active astronaut surveillance and experimental models” are critical to the development of prevention and management strategies for blood clots in weightlessness, especially with future plans for prolonged space travel to the Moon and Mars.

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