Cite as: Dumont J, Brownbridge R, Bailey JG. Blocking beyond: regional anesthesia in space. ASRA Pain Medicine News2025;50. https://doi.org/10.52211/asra080125.008.

Introduction

The next decade is expected to witness a resurgence of crewed space travel with preparations intensifying for deep space travel to Mars. NASA’s Artemis program aims to send astronauts back to the Moon’s surface, culminating in human exploration of Mars and permanent bases on the Moon.¹ Other national space agencies and private companies are similarly strategizing to send humans beyond Low Earth Orbit (LEO; ~400 km) in the near future. To date, only 24 people have left LEO,² but this number is expected to rise significantly. Unlike LEO missions, deep space missions offer no option for evacuation to Earth in a medical emergency,³ necessitating comprehensive medical strategies to address astronaut health issues. These efforts must mitigate the physiological impacts of microgravity, communication delays, and resource limitations.

More frequent space travel and a greater number of humans operating beyond LEO raise the probability of traumatic injury and a potential rise in the prevalence and incidence of disease in space. Crews in comparable isolated environments, such as Antarctic research stations and submarines, have encountered medical issues like strokes, appendicitis, fractures, cancer, intracerebral hemorrhages, psychiatric disorders, and kidney stones.⁴

Over the past 50 years of space exploration, NASA has selected 360 astronaut candidates, 33 of whom have been physicians. On most missions, one astronaut is designated as the “Chief Medical Officer” (CMO). CMOs receive only 40 hours of pre-mission basic medical training on using essential on-orbit medical equipment and recognizing various medical conditions.⁵

Ultimately, the unique physiologic changes associated with microgravity, combined with equipment and expertise restrictions, present numerous challenges to the provision of medical care in this austere environment. The minimal resource requirements and the lack of significant systemic physiological effects make regional anesthesia a promising option for anesthesia and analgesia in space.

Physiological Changes in Microgravity

Extended exposure to microgravity alters nearly every organ system with implications for anesthesia. Understanding these changes is vital for planning safe and effective interventions during missions. Table 1 summarizes these changes and their relevance to medical care.^6-9

Practicality: Regional Anesthesia (RA) vs. General Anesthesia (GA)

Several unique factors complicate the provision of anesthesia and analgesia during deep-space missions. Supplies are constrained by limited space, payload, and storage requirements, making it impractical to transport cumbersome ventilators, airway equipment, and numerous medications, which may degrade more rapidly in space. Furthermore, medical procedures are likely to be conducted by practitioners with limited expertise. Communication with crews on Mars could take anywhere between 3.5 to 22 minutes for a one-way trip,¹⁰ making real-time consultation with flight surgeons impractical, requiring crews to respond to emergencies independently. RA offers a more practical and resource-efficient alternative in this environment, minimizing risks associated with both systemic analgesics and microgravity-induced physiological changes (Table 2).^11-13

While we have primarily compared RA to GA in this article, a more practical comparison would be to systemic analgesics that could cause hallucinations and delirium at worst, and sedation and mental fogging at best. RA would not only allow procedures (eg, fracture reduction, incision, and drainage) but also provide longer-term analgesia with minimal systemic effects.

Current Research: Neutral Buoyancy Experiments

Microgravity also impairs eye-hand coordination and the central executive and psychomotor functioning of the caretaker.¹⁴ Ergonomic challenges include a lack of counterforce, atypical orientation, and independent movement of the patient. To assess feasibility, our research team conducted an experiment using simulated nerve blocks, comparing free-floating underwater conditions with those of Earth's gravity.¹⁵ Ultrasound-guided nerve blocks were performed using a validated meat model, prepared with bovine muscle and tendon, encased in ballistic gel.¹⁶ Dye was injected into the models and later assessed for the accuracy of injection. The median time to block was 35 seconds in simulated microgravity, comparable to 27 seconds under normal gravity. Success rates of 85% in microgravity and 80% in normal gravity demonstrated that the challenges posed by free-floating conditions did not significantly affect outcomes. No difference in ease of image acquisition or needle placement was observed between conditions. These findings suggest that RA is feasible under simulated microgravity conditions.

The minimal resource requirements and the lack of significant systemic physiological effects make regional anesthesia a promising option for anesthesia and analgesia in space.

A free-floating underwater environment offers a cost-effective method to assess procedural feasibility, but has additional ergonomic challenges (Video 1). Stabilization of the model and equipment was critical to success, mimicking the need for similar considerations during spaceflight. Due to the inability to verbally communicate underwater, the team relied on prearranged hand signals, which reduced the efficiency of communication. Maintaining neutral buoyancy required breath control, a task unnecessary in true microgravity. Wearing masks underwater potentially affects image clarity.

Next Steps: Parabolic Flights

While neutral buoyancy offers valuable insights, parabolic flights simulate near-microgravity and offer additional advantages that make them essential for further validation. Parabolic flights generate brief periods of true free-fall, lasting approximately 22 seconds per parabola. For experiments involving RA, parabolic flights enable detailed observation of operator movements, precision of needle placement, and the behaviour of injectates under true microgravity conditions. Unlike underwater conditions, parabolic flights eliminate resistance from the surrounding medium, allowing for unrestricted mobility and more accurate replication of free-floating procedures. The lack of goggles and diving gear also enhances visual clarity and procedural accuracy, and the absence of buoyancy-related breathing challenges enables operators to focus entirely on the task. Immediate future research should focus on:

1. Conducting RA procedures during parabolic flights to assess operator ergonomics and success rates.
2. Exploring strategies to make the block achievable by nonmedical professionals, including
   • Testing non-experts to assess if they can perform blocks effectively during parabolic flights.
   • Integrating automated guidance systems to assist non-expert operators.
   • Identifying the amount of training required for non-experts to perform the block successfully.

Researchers will need to address procedural barriers to optimize the experimental setup and data collection process during parabolic flights. Key considerations include determining how and when to collect data efficiently during the short parabolas, how to reset the experiment during the 90-second intervals between parabolas, and the feasibility of breaking procedures into manageable segments across multiple parabolas.

Further Research Before Practical Application

Before RA can be confidently applied in actual deep-space missions, significant further research is necessary to address additional challenges:

1. Pharmacokinetics in microgravity
   • Analyze drug dispersion, absorption, and efficacy in microgravity environments.
   • Address potential local anesthetic degradation due to radiation and long-term storage.
2. Safety and complication rates
   • Study the feasibility of continuous peripheral nerve block catheters to provide long-term analgesia during extended space missions, including sterility of procedures.
   • Evaluate the risk of local anesthetic systemic toxicity due to altered metabolism, volume status, and cardiovascular changes.
3. Crew training and automation
   • Develop advanced training protocols for non-expert crew members.
   • Develop protocols for emergency RA interventions during extended missions.

Conclusion

The demonstrated feasibility of RA in underwater simulated microgravity highlights its potential as a cornerstone of deep-space analgesia. Further validation in parabolic flights will be necessary to refine techniques and evaluate the feasibility under more accurate microgravity conditions. By advancing RA techniques and technologies, we not only prepare for space exploration but also improve care for patients in isolated communities. Validating these methods for terrestrial remote and underserved healthcare settings and adapting portable and autonomous RA systems for extreme environments on Earth bridges the gap between space innovation and practical applications that benefit humanity.

References

1. Carruth AR. Artemis II map. The National Aeronautics and Space Administration. https://www.nasa.gov/missions/artemis/artemis-ii-map. Published March 9, 2023. Accessed November 12, 2024.
2. National Aeronautics and Space Administration. 50 years ago: Apollo astronauts land, take first steps on moon. https://www.nasa.gov/centers-and-facilities/kennedy/50-years-ago-apollo-astronauts-land-take-first-steps-on-moon. Published July 20, 2019. Accessed November 12, 2024.
3. Anderton R, Posselt B, Komorowski M, et al. Medical considerations for a return to the Moon. Occup Med (Lond) 2019;69(5):311-3. https://doi.org/10.1093/occmed/kqz099
4. Expert Group on the Potential Canadian Healthcare and Biomedical Roles for Deep-Space Human Spaceflight. Canadian Healthcare in Deep Space: Advancing our country’s leadership in autonomous care in space and on Earth. March 2019.
5. Blue R, Bridge L, Chough N, et al. Identification of Medical Training Methods for Exploration Missions. National Aeronautics and Space Administration (NASA); 2014.
6. Scarpa J, Wu CL. The role for regional anesthesia in medical emergencies during deep space flight. Reg Anesth Pain Med 2021;46(10):919-22. https://doi.org/10.1136/rapm-2021-102710
7. Baker ES, Barratt MR, Sams CF, et al. Human response to space flight. In: Barratt MR, Baker ES, Pool SL, eds. Principles of Clinical Medicine for Space Flight. 2nd ed. New York, NY: Springer; 2019.
8. Komorowski M, Fleming S, Mawkin M, et al. Anaesthesia in austere environments: literature review and considerations for future space exploration missions. NPJ Microgravity 2018;4(1):5. https://doi.org/10.1038/s41526-018-0039-y
9. Komorowski M, Thierry S, Stark C, et al. On the challenges of anesthesia and surgery during interplanetary spaceflight. Anesthesiology 2021;135(1):155-63. https://doi.org/10.1097/ALN.0000000000003789
10. European Space Agency (ESA). Enabling effective communication for human space exploration beyond Low Earth Orbit. 2023. Available at: https://nebula.esa.int/sites/default/files/neb_study/3142/C4000136202ESR.pdf. Accessed January 9, 2025.
11. Taddeo TA, Gilmore S, Armstrong CW. Spaceflight medical systems. In: Barratt MR, Baker ES, Pool SL, eds. Principles of Clinical Medicine for Space Flight. 2nd ed. New York, NY: Springer; 2019.
12. Reichard JF, Phelps SE, Lehnhardt KR, et al. The effect of long-term spaceflight on drug potency and the risk of medication failure. NPJ Microgravity 2023;9(1):35. https://doi.org/10.1038/s41526-023-00271-6
13. Kohn FPM, Hauslage J. The gravity dependence of pharmacodynamics. NPJ Microgravity 2019;5(5). https://doi.org/10.1038/s41526-019-0064-5
14. Fiore S, Wiltshire T, Sanz E, et al. Critical team cognitive processes for long-duration exploration missions d final report 2015. NASA/TM-2015-218583
15. Kiberd MB, Brownbridge R, Mackin M, et al. Feasibility of ultrasound-guided nerve blocks in simulated microgravity: a proof-of-concept study for regional anaesthesia during deep space missions. Br J Anaesth2024;133(6):1276-83. https://doi.org/10.1016/j.bja.2024.07.034
16. Brownbridge RG, Kiberd MB, Werry D, et al. Discriminative ability of dye injected into a meat model to determine accuracy of ultrasound-guided injection. Simul Healthc 2025;20(1):54-60. https://doi.org/10.1097/SIH.0000000000000799