How astronauts deal with medical emergencies in space — and how scientists are working to prevent them

Astronaut health has been a concern since the very beginning of the space program. Effects such as motion sickness, disorientation, muscle atrophy and bone loss have affected every astronaut who’s left Earth. 

Over the years, NASA has figured out how to treat many of these conditions with medication and vigorous exercise while in orbit. But more serious health issues could potentially become show stoppers for longer missions to the moon and Mars, so scientists are working hard to understand more about what long distance astronauts may face, and how to deal with them if they come up.

Fortunately, serious health problems in space are rare. In January 2026, we saw the very first medical evacuation in the International Space Station’s 25 year history when astronaut Mike Finke developed a non-life threatening issue that needed to be fully diagnosed and treated on the ground. 

NASA has not released the cause of the medical emergency for privacy reasons, but Finke has reported that he is recovering and feeling fine.

Even though they’re rare, the close calls we’ve had are being closely examined to increase our understanding of how microgravity can affect human health.

For a recent episode of Quirks & Quarks, I spoke with a scientist from Simon Fraser University studying how blood clots form in microgravity after a blood clot was discovered in the neck of an unnamed female astronaut on space station in 2019.

Fortunately, teams on the ground and in space moved quickly to develop a treatment plan so the clot didn’t pose an immediate problem

In their initial study that focused only on women and was published in the journal Acta Astronautica, those scientists discovered how blood clots formed in microgravity become stronger and tougher to break down than the clots that form on the ground. 

The research team followed up that study on females by looking at the same issue in males to see if there are any sex differences with blood clotting in a microgravity environment.

Both Fincke and the unnamed female astronaut were diagnosed using a portable ultrasound device, which astronauts regularly use on the space station for routine health checks while experiencing weightlessness. It is one of several medical instruments carried on board the station at all times. But there is a limit to how much equipment can be carried to orbit, so there’s only so much that the astronauts can do once they find a problem.

Weightlessness can lead to blood clots, vision changes

In a weightless environment, fluids shift to the upper body, giving astronauts a condition referred to as “puffy faces and bird legs.” This means if blood clots do form, they are closer to the brain and pose a greater threat of becoming dislodged there.

Fortunately for the female astronaut, the blood clot in her jugular vein was discovered by ultrasound when she was gathering data for a research project.

Changes in the body’s fluid distribution can lead to other changes as well.

One condition that affected Canadian astronaut Bob Thirsk during his long duration flight in 2009 was the deterioration of his vision while in orbit. He found it more difficult to read instruments and manuals. Later they found it to be the result of pressure on the optic nerve at the point where it attaches to the eyeball and flattens it. 

This condition now has a name. Continuing NASA’s love of acronyms, it is now officially called Space-Associated Neuro-Ocular Syndrome (SANS) and is an ongoing concern. 

The cause of SANS is suspected to be related to changes in blood flow and pressure in the brain that affects the eyes. A 2020 study found that up to 70 per cent of astronauts can experience SANS during long term stints in space.

Injuries are also common in space.

A 2009 NASA study documented a total of 219 inflight musculoskeletal injuries, mostly on the astronaut’s hands. And another NASA study, done in 2017, found that exercise — meant to protect astronauts from harm — was the leading cause of injury on the space station.

Space surgery is not an option

The International Space Station is equipped with a well-stocked pharmacy, portable ultrasound, biomonitors and other instruments typically found in a hospital emergency department. In addition, every crew includes a flight surgeon, to monitor health and work with a team on the ground to handle medical issues. 

But some conditions cannot be treated in space, especially those that require open surgery. Appendicitis, for example, must be treated immediately, but involves an invasive procedure where the body has to be opened up. In a weightlessness environment, blood would spurt in every direction at the first cut and be totally unmanageable. So anything requiring surgery would mean a return to Earth as quickly as possible.

Currently, anyone who develops a serious health issue on the space station can be returned to Earth fairly quickly, but future explorers on the moon and Mars won’t have it so easy. Getting home from the moon takes three days, and returning from Mars can take up to a year waiting for the planets to align. And lengthy communication delays mean Earth-based medical teams may not be available to talk anyone through an emergency.

NASA is currently developing a plan for how to overhaul their approaches to medical care in space for these distant missions. The strategy, called Earth-Independent Medical Operations (EIMO), calls for the development of a medical system that will allow astronauts to deal with any health issues autonomously, without support from ground control if necessary. 

Even more emphasis will have to be made to catch and prevent potential health issues before leaving our planet. The farther humans journey and the longer time they spend away from Earth means they will have to be healthy from the start and able to take care of themselves once underway. 

But even so, there is still a chance that someone could succumb to a sudden medical episode or some type of fatal injury. If such a tragedy does occur, NASA already has a detailed plan in case an astronaut dies in space. A space suit will be used as a body bag until they can be returned home. 

Let’s hope we never have to see that happen.