Astronaut Alexander Gerst practices cardiopulmonary resuscitation (CPR) as cosmonaut Sergey Prokopev looks on during an emergency training session aboard the International Space Station. Credit: NASA Johnson
- Manual cardiopulmonary resuscitation (CPR) techniques, including the “handstand” method, are ineffective in microgravity due to the lack of a counter-force to compression, resulting in insufficient chest compression depth.
- Automatic Chest Compression Devices (ACCDs), particularly mechanical piston devices, demonstrate significantly improved efficacy in microgravity compared to manual methods, consistently achieving the necessary compression depth for blood flow to the brain.
- Traditional manual CPR is also less effective in the hypogravity of the Moon and Mars due to reduced body weight, necessitating more frequent rescuer changes and potentially alternative techniques like the Seated-Arm-Lock (SEAL) method.
- While ACCDs offer a promising solution for both microgravity and hypogravity environments, their weight and size present a logistical challenge for spacecraft, necessitating a cost-benefit analysis by space agencies regarding their inclusion in emergency medical kits.
French researchers simulating weightlessness on a modified jet have found that manual cardiopulmonary resuscitation (CPR) is ineffective in space. This conclusion could reshape emergency medical protocols for upcoming missions to the Moon and Mars.
Their experiment, designed to simulate the weightlessness of space, revealed a critical flaw in emergency medical procedures for astronauts: standard methods of CPR are severely less effective without gravity. The finding comes as a new era of space exploration accelerates, with missions planned for the Moon and Mars that will take more people into space for longer than ever before. This research highlights a fundamental challenge in keeping humans alive millions of miles from an emergency room.
“Longer-lasting space missions in future and space tourism could increase the risks of a medical emergency occurring,” explained Nathan Reynette of the Cardiology Department at Université de Lorraine, a researcher on the project, in an Aug. 27 press release. While the risk to any individual astronaut is low, the increasing number of people traveling to space for longer periods means that a serious medical event like cardiac arrest is becoming an eventuality that space agencies must prepare for.
A problem of physics
The CPR problem is twofold, with distinct challenges for microgravity (in transit) and hypogravity (on a planetary surface).
The first problem — the one addressed by the French experiment in the jet — occurs in the weightlessness of spaceflight, where the basic physics of the procedure breaks down. Without weight, pushing on a patient’s chest simply sends both rescuer and patient floating apart. CPR requires both a compression force on the patient’s heart and a counter-force to hold the patient in place. On Earth, that counter-force is gravity. In a study presented at the 2025 European Society of Cardiology Congress, Reynette and his team investigated the effectiveness of the currently approved manual technique designed to overcome this problem.
For decades, the approved, albeit physically demanding, solution has been the “handstand” technique. This maneuver requires the rescuer to perform a modified handstand, placing their hands on the patient’s chest while bracing their feet against a wall or ceiling of the spacecraft to generate the necessary downward force for compressions.
Despite being the standard for years, the French study proved this acrobatic method falls short. The technique achieved a median compression depth of just 1.36 inches (34.5 millimeters), well below the 1.97- to 2.36-inch (50 to 60 millimeters) range required to keep blood flowing to the brain.
As a potential solution, the team tested three different Automatic Chest Compression Devices (ACCDs), machines already used on Earth in challenging environments like rescue helicopters. These devices solve the microgravity problem by creating a self-contained system. They are designed to be strapped securely around the patient’s torso, using their own frame to generate both the compression force and the counter-force, eliminating the need for rescuer weight and preventing the patient from floating away.
The study included two main types of machine. The most effective was a mechanical piston device, which features a backboard that slips under the patient and a motorized plunger that pushes down on the chest. The other was a compression band device, which uses a wide band that encircles the chest and rapidly constricts to perform compressions.
The results were clear: When tested on a CPR mannequin in parabolic flight, to mimic microgravity, the standard mechanical piston device was the only method that consistently achieved the required compression depth. This demonstrates that a technological solution to CPR in microgravity is not only viable, but superior to the manual alternative.
CPR on the Moon and Mars
But what happens when astronauts land on another planet and require CPR? This related problem — performing CPR in the hypogravity of the Moon or Mars — was the focus of a 2022 systematic review by Remco Overbeek and a team from several European institutions, published in the journal Life.
On a planetary surface, an astronaut has weight, but not nearly enough to perform CPR effectively. The gravity on the Moon is just 0.17 G (17% of Earth’s), and on Mars it’s 0.38 G (38% of Earth’s). This means a 150-pound (68 kilograms) astronaut would effectively weigh only about 26 pounds (12 kg) on the Moon and 57 pounds (26 kg) on Mars.
The review found that with so little body weight to use, rescuers cannot produce enough force with the traditional, locked-elbow technique. Instead, they must compensate by using pure muscle — actively bending their elbows to generate force with their arms and shoulders for every compression—leading to rapid fatigue and a swift decline in CPR quality.
To address this, the authors suggest that protocols be updated to require changes of the resuscitator after less than a minute, compared to every two minutes in traditional terrestrial CPR, and that alternative manual techniques should be investigated to improve stability.
One such technique is the Seated-Arm-Lock (or SEAL) method, where the rescuer straddles the patient and traps the patient’s arms behind the rescuer’s knees. Much like the ACCDs in microgravity, the SEAL maneuver creates a stable, closed system. By anchoring themselves to the patient, the rescuer can use upper body strength to generate force without being pushed away, improving the effectiveness of compressions.
While their analysis focused on improving these manual techniques, the authors also noted that ACCDs should be considered for planetary missions. Because these devices could remove rescuer weight and fatigue from the equation, they are a logical solution for hypogravity. However, since the studies included in the review did not test ACCDs in a hypogravity simulation, the authors could only point to them as a promising, but unproven, area for future research.
In some ways, the 2025 microgravity study provides the proof-of-concept that the earlier review identified as a critical missing piece, confirming the technology is effective in a nonterrestrial environment.
What happens to the human body in space?
These experiments highlight a fundamental truth: the human body is not built for space. According to a NASA overview of health in space, the moment gravity vanishes, bodily fluids shift upwards, causing astronauts to experience a “puffy face” and “a stuffy nose.” Without the constant load of gravity, bones in the legs, hips, and spine begin to lose mineral density, and muscles start to weaken. Looming over these challenges is the constant threat of space radiation, which increases cancer risk, and the unpredictable changes to the immune system. This array of ailments is why astronauts dedicate hours each day to rigorous exercise and undergo constant medical surveillance.
New challenges for a new space race
As the risk of a cardiac event grows — spurred on by what acting NASA Administrator Sean Duffy, has called a second space race, with China — researchers are urgently seeking solutions. The potential fix for microgravity, however, presents a new dilemma. Every ounce of mass and inch of space is precious on a spacecraft. While Reynette’s team did not specify the exact device used, a standard mechanical piston device on Earth typically weighs over 20 pounds.
This presents a difficult trade-off: is an effective, but bulky, device worth the cost for a low-probability event, especially when the desire to be among the stars pushes engineering to its limits? “It will be up to every space agency whether they want to include automatic chest compression devices in their emergency medical kit,” noted Reynette.
Ultimately, the research into CPR in space highlights the broader value of pushing the boundaries of medical science. “Space medicine often provides transferable lessons for emergency procedures in isolated environments on Earth, where space and clinical experience are also limited,” concluded Reynette. The challenges of keeping astronauts alive in orbit or on Mars force the development of technologies and procedures, like automated CPR devices, that could one day be used to save lives in the most remote and hostile environments on our own planet, from submarines deep in the ocean to arctic research bases.