METHODS

For this study, 20 unique interviews were conducted with SMEs in spaceflight and analog domains. Analog domains were defined as environments with some overarching mission need that must be balanced against medical concerns that may arise, limited local ability for definitive medical care, and some complicating environmental factors for evacuation (e.g., terrain, weather, hostile actors, etc.). Given these criteria, six domains were identified from which to solicit SME input: wilderness/alpine exploration (wilderness), polar exploration and research (polar), military combat medicine (combat), civilian undersea operations/research (undersea), military submarine operations (submarine), and human spaceflight (space). For a description of study subjects, see Table I .

Table I. Description of Study Subjects.

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This study was reviewed by the National Aeronautics and Space Administration (NASA) Johnson Space Center Institutional Review Board and determined not to qualify as human subject research (exemption granted). Individuals with experience in medical care as well as evacuation planning, rehearsal, and execution in extreme environments were eligible for inclusion in the study. The decision was made to not collect/report several categories of data from subjects (e.g., age, sex, years of experience) in order to maintain anonymity in a relatively small community of extreme environment medicine.

After defining the major objectives of the study, an interview guide was created to focus the conversation rather than restrain it. Each interview was divided into two sections, with the first section asking subjects to describe a single or a few MEDEVAC experiences and the second querying the experts on their opinions about higher level principles that might guide future spaceflight MEDEVACs. Accordingly, this work represents what these experts described and is not an official NASA position. This was modeled after similar research undertaken by Eiding et al. in their investigation of interhospital transfers. ¹³

SMEs were recruited within a domain until there was saturation of the overall research questions, a common endpoint in Thematic Analysis, which is reached when additional interviews no longer yield new insights or themes, typically at two to five subjects per domain. ^{6 , 24} Interviews took place via video teleconference, voice calls, or via email exchange. Interviews were recorded, the audio anonymized, then transcribed by the NVivo automated software program (QSR International, Burlington MA, United States). Records of interviews were stored securely and stripped of identifying information. All interviews were conducted by 1 of 2 interviewers, with a single interviewer conducting the majority of the interviews (18 of 20). A common interview guide, pre-interview training, and post-interview debriefs were used to help minimize variability between the two interviewers. Following each interview, the team compared the information and major topics discussed with prior interviews using a constant comparative method. ¹⁵

Data analysis was performed by a single researcher using the Thematic Analysis approach. Due to the knowledge gap associated with this research topic focused on a historically rare event, Thematic Analysis was selected for its inductive or “bottom-up” approach. ⁷ Briefly, this method consists of identifying essential ideas, statements, or phrases within the text and labeling them with a summative description to create a “code.” Similar or related codes are then grouped together and labeled to create a “theme.” Associated or related themes can then be grouped further into “categories.” ³¹ Final themes and categories were defined with their respective key points, and representative statements were extracted from the data. A modified version of coding via “consensus, co-occurrence, and comparison” was employed to ensure external validity and credibility, with two additional researchers serving as reviewers of the results and analysis. ^{27 , 33} Methodological rigor was applied as follows using the criteria suggested by Nowell. ²⁷ Transferability was sought through the application of results to past events as seen in the discussion section. Confirmability and dependability were sought through the presentation of excerpted quotes and the retention of raw and complete anonymized transcripts, respectively. ²⁷ Similar versions of Thematic Analysis have been used to explore other emerging and less-defined spaceflight issues. ^{2 , 20 , 31}

RESULTS

Data collection yielded 20 SME interviews, totaling over 22 h of audio and over 250,000 words of transcription. Analysis of the data resulted in 18 themes expressed by the SMEs. These 18 themes were broken down by researchers into two main categories: 1) Primary Risk Considerations, and 2) Contributing Factors. These results can be seen in Table II .

Table II. Results Overview.

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Here the themes expressed by SMEs are listed and defined. Bullet statements below each definition explain the main aspects of each theme using both summative statements and direct SME quotes, focusing on unique, opposing, and even contradictory concepts expressed by multiple SMEs. There is considerable overlap and interplay between the themes, yet each attempts to describe and categorize only one domain of the complex problem.

Nine distinct themes from the SME interview data were categorized as Primary Risk Considerations. Researchers determined that SMEs expressed and emphasized these nine themes as the most important to consider when making a MEDEVAC decision. These themes, with definitions, summative analysis, and representative statements, are presented below and in consolidated fashion in Table III .

Table III. Consolidated Results—Primary Risk Considerations.

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Time

The duration of medical stability, procedures, MEDEVAC, resources, and decision space:

• Time in spaceflight is often determined by the consumption rate of resources and orbital dynamics.

• Time to a DMCF and in what environment needs to be considered.

• Most of the time, a split-second decision does not need to be made, and other decision makers at different levels with different information and considerations can be involved.

• Delays can expand decision space and improve MEDEVAC execution.

• “…time is a precious commodity. But I think if you can seek out more time to allow the decisions…to flourish, to grow, and eliminate avenues that now don’t make sense or provide more avenues that might give you a better answer. That’s good. But then you run into some of those hard balls of consumables that [don’t] allow you to expand your decision space time.”

Nine distinct themes from the SME interview data were categorized as Contributing Factors in a MEDEVAC decision. Researchers determined that SMEs expressed and emphasized these nine themes not to be of primary importance when making a MEDEVAC decision, but rather concepts that can both reduce risk and shape the environment for those decisions. These themes, with definitions, summative analysis, and representative statements, are presented below and in consolidated fashion in Table IV . Decision making is discussed separately.

Table IV. Consolidated Results—Contributing Factors.

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Decision Making

The theme of “Decision Making” was described by SMEs as having effects on both Primary Risk Considerations and Contributing Factors. This theme is concerned with how a MEDEVAC decision is made, by whom, at what level of an organization, and with what information. This theme was found to not only be necessary to consider when making a MEDEVAC risk decision, but also to impact how future decisions are made through organizational structure, decision making delegation, and the existence of standing guidelines (i.e., spaceflight “flight rules”) and rehearsals. Summative analysis and representative statements are presented below and in consolidated fashion in Table V :

• MEDEVAC decisions are often made with medical and operational inputs considered separately with a “firewall” between them.

• In organized structures, final decisions often rest offsite in the operational realm.

• Decision are made at higher levels if time allows.

• SMEs described that medical providers have significant influence over final decisions.

Table V. Consolidated Results—Decision Making.

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DISCUSSION

The main objective of this research was to determine what unique risk assessment principles are used to make MEDEVAC decisions in space and analog domains to better inform risk decisions and planning considerations for future space exploration missions. Through analyzing interviews with subject matter experts, 18 risk assessment themes were expressed, many with important and consequential connections, and several with unique applications for space exploration missions, illuminating the complex decision landscape.

To better prepare for future MEDEVAC scenarios, the 18 themes identified in this project (Table II) can serve as a starting point for establishing a MEDEVAC Concept of Operations and could aid in real time decision making. Currently, MEDEVACs in space are rare occurrences which SMEs described as generally considered on a case-by-case basis with little rehearsal or detailed planning. These emergencies are currently backstopped with ample offsite support, extensive resources, and the understanding that a DMCF can be reached from LEO in 24–48 h in a worst-case scenario. However, deliberate MEDEVAC decisions are difficult and become even more complex as human spaceflight transitions from LEO to the exploration of cislunar space and beyond. ¹⁹ Therefore, new tools are needed to assess the MEDEVAC risks in future exploration missions.

The Primary Risk Considerations themes have the greatest impact on a real-time MEDEVAC risk decision. When analyzing a mission concept for MEDEVAC risk, each phase of the mission could be assessed or quantitatively scored against these themes given some predefined objective criteria for each theme. Consider a hypothetical scenario with conflicting themes of Patient(s) and Mission. During the lunar surface phase of an Artemis mission, the MEDEVAC of an injured astronaut from the surface of the Moon to the Lunar Gateway station could present relatively high risk to the Mission if it means an end to the mission before the objectives were complete. However, the MEDEVAC could be relatively low risk for the Patient if there is increased diagnostic and treatment capability on the cis-lunar space station vs. the lunar surface. MEDEVAC to a DMCF on Earth from the Moon could also be assessed and compared. Weighting of each theme relative to the others according to some broader institutional guidance could enable even more critical analysis. In this way, MEDEVAC risk across multiple phases of a complex exploration mission could each be quantified and assessed prior to a mission’s execution.

With this approach, the Contributing Factors themes can be seen as the dials that can be turned which alter the Primary Risk Considerations within any given mission phase. Continuing the example, if the risk to the Patient(s) was determined to drive the MEDEVAC risk beyond some acceptable level, Medical Support Planning could be addressed through the addition of expanded treatment capability on the lunar surface vehicles.

Connections and overlaps between the emerging themes were common. Some of these connections were direct and logical (e.g., more patients require more resources), while others were determined to be causal through analysis of SME inputs. When considering the risks associated with any single principle or theme, it is also important to consider the connection and drivers behind those principles.

While it may seem duplicative to enumerate the connections between the two categories, the impacts that Contributing Factors themes have on Primary Risk Considerations are a fundamental result from this study. While the Primary Risk Considerations may prove to be a helpful context for assessing MEDEVAC risk in an exploration mission, they alone are likely not enough to help adjust that risk. Pairing the Primary Risk Considerations with the Contributing Factors provides a basis for adjusting MEDEVAC risks, ideally prior to a mission, and helping reduce the overall risk an exploration mission may present. In other words, the connections make the results of this work not only explanatory, but actionable. Below is a discussion of those principles with significant or unique connections between the premission Contributing Factor themes and real-time Primary Risk Consideration themes as illustrated in Fig. 1 .

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The Contributing Factor with the most connections to Primary Risk Considerations is Medical Support Preparation. Since this theme is defined as the “prior considerations, planning, and rehearsals for medical scenarios through both training and mission/vehicle design,” some connections are clearly logical. The amount of planning and rehearsals for medical contingencies directly influences the Experience of the crew, risk to the Patient(s) through treatment or MEDEVAC, and the skills of the Provider, including the risk they incur if they themselves are the patient and need to be treated by the other crewmembers. Less obviously, medical support preparation, particularly when considering the design and functionality of a vehicle or medical support system, can impact the constructed Environment. Finally, the considerations for what medical conditions are worthwhile to plan and resource has an obvious and direct impact on the Resources available. Through these connections, Medical Support Preparation is the most impactful Contributing Factor and, therefore, one of the most important principles for affecting the risks associated with a MEDEVAC.

The Contributing Factor MEDEVAC Preparation also impacts many Primary Risk Considerations. Defined as “prior considerations, planning, and rehearsals for MEDEVAC execution through both training and mission/vehicle design,” it also has many connections that are clearly logical (e.g., Experience, Environment, etc.). MEDEVAC Preparation also has a direct impact on the risk the actual Execution of a MEDEVAC presents. SMEs described how practice and rehearsal mitigates risks through identifying “stress points” and exploring the impact of “stacked failures” until the dangerous activities are “muscle memory.” Together, the Medical Support Preparation and MEDEVAC Preparation contributing factors have large impacts on the ultimate risks associated with a MEDEVAC.

Several of the themes are notable for having unique aspects when considering exploration missions vs. LEO spaceflight. These unique aspects are driven by both the physical differences in traveling beyond LEO and the broad societal impacts such missions are likely to have.

Longer times for Patient(s) transport to a DMCF will require expanded CMO training in prolonged care, more onboard resources, and autonomous decision making compared to the current LEO paradigm. ³² Any medical contingency will also likely place an increased burden on the Crew to care for a patient and assume their critical duties, as well as introduce the possibility of continuing a lengthy mission after the loss of a crewmate. ¹⁸ The delayed physical and possible psychological impacts on the crew must be considered in any exploration MEDEVAC decision as well as when designing exploration medical support systems.

Exploration missions to cislunar space and beyond involve increased distances that directly impact the themes of Time (via increased travel times) and Communication (via the introduction of extended latencies). ¹² Increased communication latencies have been shown to complicate the use of Offsite Support, as was also highlighted in conversation with spaceflight SMEs. ¹⁴ The current paradigm for LEO medical support relies heavily on offsite support with CMOs explicitly assisting ground-based flight surgeons in evaluating and treating medical problems. ³² Increased communication times will uniquely hinder, or outright prevent, exploration CMOs from utilizing offsite support in this way, requiring adjustments to the Medical Support Considerations Contributing Factor in the form of increased training or decision support tools to help mitigate the risks associated with the Provider. Indeed, Medical Support Considerations in the form of increased medical training for the entire crew will likely be needed. The current paradigm relies heavily on ad hoc and just-in-time training, with one SME describing having to create “cheat sheet[s] for the rest of the crew” when they themselves became the patient, to handle the crew’s concerns of “what do we do, or how do we know if this gets worse?”

Finally, exploration missions are likely to differ from current LEO spaceflight in their impact on society at large. An estimated 650 million people worldwide watched the first steps on the lunar surface in 1969, and it is likely that a return to the Moon will again raise excitement and interest in human spaceflight, to say nothing of a mission to Mars. ^{8 , 21 , 26} Furthermore, any contingency scenario will likely draw even more attention, with popular culture having shown enthusiasm for tales of astronauts stranded or injured far from home. ³⁰ This anticipated public visibility and the objectively high resource costs of such a mission highlight the impact the theme of Political Considerations will have as a Contributing Factor to any MEDEVAC decision. ⁴ These unique political pressures impact the Decision Making and Philosophical approaches organizations should take when handling MEDEVAC risk decisions and dictate the need for a methodical approach to these difficult calls.

Taken as a whole, this study finds future exploration missions beyond LEO will require unique MEDEVAC risk assessments. The Primary Risk Consideration themes identified in this study, along with the Contributing Factors, offer an organizational framework to plan for and execute exploration spaceflight MEDEVACs. The unique distances and impacts associated with these missions also require increased focus on medical and psychological autonomy and training provided to CMOs and the crew. These distances and impacts also require advanced development of deliberate philosophies that pertain to how prioritizations are made and the acceptability of risk and mission loss.

The applications of this study are limited principally by the qualitative nature of the research. The research team has significant prior knowledge about extreme environments (including human spaceflight) and medical evacuations, which may have shaped the results. Furthermore, SMEs were recruited in a stepwise fashion, with many being known to the research team or other subjects. Although attempts were made to ensure saturation of each domain, there are undoubtedly opinions and experiences that were not captured.

The three prior medical evacuations from space offer the opportunity to check the face validity of the framework described herein by retrospective application. Each scenario will be presented with a vignette followed by a brief discussion of the relevant themes from the MEDEVAC framework.

The first scenario involved a MEDEVAC from Salyut 5 in 1976 due to toxic environmental exposures. A summary of the mission and MEDEVAC is reproduced from the “Handbook of Bioastronautics”:

The crew was exposed to acrid odors apparently caused by nitric acid fumes leaking from propellant tanks. There were also reports the crew didn’t follow their exercise program and were sleep deprived. Mission psychologists felt there were “interpersonal issues” between the crew. Vitali Zholobov had space motion sickness as well as the aforementioned psychological issues. The crew returned on day 49 of a planned 54-d mission. Because of the early return, the recovery conditions were not optimal, and included strong winds, which caused uneven firing of the braking rockets, resulting in a hard landing at night. ¹⁰

Several Primary Risk Consideration themes from this study are apparent in this vignette. Here the medical incident (an environmental exposure) put the Patient(s) at risk during the time between the exposure and the eventual MEDEVAC. The theme of Execution also contributed significantly, with the decision to evacuate before the planned return [Patient(s) over Mission], resulting in executing the MEDEVAC in suboptimal return conditions, increasing the risk to the Crew. Adjusting the Contributing Factors of Medical Support Preparation (through increased toxic exposure prevention or treatment capability), Team Cohesion (hopefully mitigating the “interpersonal issues”), and Psychological Considerations (through increased sleep planning and support) prior to launch could potentially have changed the scenario, possibly alleviating the need for what was ultimately an off-nominal, and possibly more hazardous, return to Earth. This vignette also presents interesting parallels for a future lunar mission. Here a toxic exposure rendered the entire crew as Patients with no true “healthy” Provider or Crew while nevertheless requiring the entire Crew to act as Providers for themselves and each other. This is similar to what will be encountered by long-duration lunar exploration crews inevitably dealing with chronic lunar dust exposure. ⁹

The second scenario is from Salyut 7 in 1985 which involved a crewmember with a urinary and prostate infection. A summary of the mission and MEDEVAC is reproduced from the “Handbook of Bioastronautics”:

[Vladimir] Vasyutin fell ill soon after arriving at the station and was unable to perform his duties as station commander. The mission was originally scheduled for a 216-day stay, but his illness forced an early mission termination. The illness was probably prostatitis, and he had pain and a fever as high as 104 degrees F. Savinyikh, Vasyutin, and Volkov returned to Earth on 21 November 1985 after 65 days. Vasyutin spent a month in hospital on return to Earth. ^{10 , 17}

Here again, the Principal Risk Considerations of Mission and Patient are in tension with the ultimate decision to return, prioritizing the Patient over the Mission. The Crew also likely experienced increased risk during the time the Patient was unable to execute his duties as station commander. An increased focus on the Medical Support Considerations Contributing Factor theme could have adjusted the risk a prostate and urinary infection posed to the Patient and perhaps enabled the Mission to continue to its planned duration.

The third scenario is from Mir EO-2 and involved a crewmember with a cardiac dysrhythmia. A summary of the mission and MEDEVAC is reproduced from the “Handbook of Bioastronautics”:

[Aleksandr] Laveykin performed a strenuous EVA and developed a cardiac tachyarrhythmia that persisted for several days before returning to normal. The dysrhythmia recurred and mission control recommended he return before the planned December 1987 return date. He was replaced by Aleksandr Aleksandrov and returned on 30 July 1987, having spent 174 days 3 h 25 min in space. He was later returned to flight status. ¹⁰

This vignette shows how risk assessments can change as a situation develops. Initially, the risk a cardiac dysrhythmia posed to the Patient was apparently deemed below the risk a MEDEVAC would pose to the Mission. As Time continued the condition apparently did not completely resolve and the risk to the Patient rose to outweigh the Mission, resulting in an early return. However, the manner of MEDEVAC Execution likely helped reduce the risk to the Mission, as the choice was made to evacuate the Patient in conjunction with a flight to bring a replacement crewmember. Also interesting in this vignette is the role Offsite Support and the context around Decision Making played in the eventual MEDEVAC. Had no Offsite Support in the form of cardiac monitoring and evaluation been in place, the dysrhythmia might never have been discovered, leaving the Patient at risk during the execution of the Mission. While it is possible that the crew could have discovered and diagnosed the dysrhythmia themselves, it was the Decision Makers on the ground that apparently made the call to have the crewmember return. Had the ultimate decision rested with the crew, the outcome could have been quite different.

It is also important that this framework be applicable to scenarios where MEDEVAC is considered even if not ultimately undertaken. A dental abscess nearly caused the return of a cosmonaut; however, appropriate Medical Support Considerations enabled his treatment with analgesia. ¹⁰ Another cosmonaut’s ingestion of toxic ethylene glycol resulted in facial and upper-airway dermatitis, with the onboard Provider treating the cosmonaut in flight. ¹⁰ A case of abdominal pain caused the planning of an early return for fear of an acute appendicitis which might require a surgery that was outside the Resources and Provider capability onboard. However, the Patient’s illness subsided and was found to be a case of nephrolithiasis. ¹⁰

Within the U.S. space program, an astronaut was discovered to have a deep vein thrombosis in their internal jugular vein. ⁵ The diagnosis and treatment of the Patient was done through extensive use of Offsite Support with experts on Earth providing diagnosis, prognosis, treatment plans, and even remotely guiding diagnostic use of the ultrasound. ⁵ Appropriate Resources also had to be flown to the International Space Station in the form of anticoagulants. ⁵ These close calls and vignettes above show how themes from this study can be used to analyze medical events and MEDEVAC risk assessments.

This qualitative survey of spaceflight MEDEVAC principles is well suited to aid future mission planning by pairing with quantitative risk assessment tools. One such tool, NASA’s Informing Mission Planning via Analysis of Complex Tradespaces (known as IMPACT), is designed to estimate medical risk and generate recommendations for medical system resource sets within user-specified inputs and constraints (e.g., mission duration, number of crew, system mass). ^{3 , 23}

IMPACT can identify phases of exploration missions with high likelihoods of a medical event or evacuation, driving a detailed MEDEVAC risk assessment. ²⁵ The themes detailed herein can then serve as the basis for objective criteria to break down these risks, perhaps in a manner similar to the creation of likelihood vs. consequence risk matrices used by the Department of Defense and NASA. ¹¹ Mission phases with a resulting MEDEVAC risk assessment above a predetermined threshold could then be assessed for adjustment of one or more of the associated Contributing Factors to mitigate the likelihood or consequence of a medical event or evacuation.

Ultimately, this work enumerates the specific themes that should be considered in MEDEVAC planning for human space exploration. Although the results are generalized, defining them in a rigorous fashion is a necessary precondition for development of objective and quantitative criteria for specific missions. Future work using these results as a basis for analysis can lead to the development of high-level consensus recommendations for medical evacuation in spaceflight as well as the creation of specific guidelines for particular mission profiles. Indeed, a clear understanding of all the factors to be considered in a spaceflight MEDEVAC decision will decrease the risk faced by exploration crews and enable even greater discoveries for all of humanity.