Selecting Medical Conditions Relevant to Exploration Spaceflight to Create the IMPACT 1.0 Medical Condition List
INTRODUCTION: Medical conditions occurring in spaceflight pose risks to the crew and the mission and these risks will be exacerbated during exploration-class missions. Probabilistic risk assessment is a method used at NASA to quantify this risk for low-Earth orbit operations. Informing Mission Planning via Analysis of Complex Tradespaces (IMPACT) is a next-generation tool suite that will perform these assessments for exploration-class missions. It will require a robust list of medical conditions of significant likelihood and/or consequence to exploration-class missions to accurately inform the tool suite.
METHODS: The IMPACT 1.0 Medical Condition List (ICL 1.0) contains 120 conditions selected in the context of a 210-d cis-lunar, Mars analog design reference mission. The conditions were selected via a systematic process that preserved institutional knowledge from nine prior condition lists. Conditions were prioritized for inclusion in the ICL 1.0 based on history of occurrence in spaceflight, concurrence among the nine source lists, and concurrence among subject matter experts.
DISCUSSION: The ICL 1.0 has notable advantages over its predecessor lists in that it is more specific to exploration-class missions, contains a greater number, breadth, and depth of conditions, and was derived via consensus across multiple medical specialties.
Kreykes AJ, Suresh R, Levin D, Hilmers DC. Selecting medical conditions relevant to exploration spaceflight to create the IMPACT 1.0 Medical Condition List. Aerosp Med Hum Perform. 2023; 94(7):550–557.
Medical conditions occurring in spaceflight can pose risks to the crew and the mission. Constraints of exploration-class spaceflight missions will exacerbate these risks. These constraints include communication delays, lack of resupply, limited or no opportunity for evacuation, restricted mass and volume, and unprecedented mission lengths. To mitigate medical risk posed to the crew and mission, it is necessary for mission planners to first identify medical conditions of significance for exploration-class missions. A spectrum of conditions exists from low likelihood, low consequence, to high likelihood, high consequence. Those of high likelihood or high consequence must be considered for appropriate mission planning. The National Aeronautics and Space Administration (NASA) has produced several lists of spaceflight medical conditions in the past that have been leveraged to create the Informing Mission Planning via Analysis of Complex Tradespaces (IMPACT) 1.0 Medical Condition List. 5 The purpose of this paper is to describe the IMPACT 1.0 Medical Condition List (ICL 1.0), how it was derived, and its application to exploration-class spaceflight missions.
NASA’s Integrated Medical Model (IMM) is currently used for medical trade space assessments for the International Space Station (ISS). 2 – 4 It was the first attempt to apply probabilistic risk assessment (PRA) to medical system design. PRA modeling runs hundreds of thousands of simulated missions to estimate risks of crewmembers being afflicted by medical conditions and models subsequent health outcomes. To do so, the model must have a pool of medical conditions from which to select. The IMM was based on a list of 100 medical conditions known as the “IMM Medical Condition List” (IMCL). 2 IMM’s successor is IMPACT, a novel tool suite developed by NASA’s Human Research Program, Exploration Medical Capability Element, to apply PRA to medical system design for exploration-class missions. 5 During PRA, conditions that affect crewmembers are based on a predetermined spaceflight incidence. The essential elements of the model for each medical condition consist of condition incidence, duration of illness or injury, capabilities and resources deemed necessary for treatment of that condition, probability of the need for escalation of care, probability of mortality resulting from the condition, and impaired ability to perform mission specific tasks due to the condition. These elements are collectively known as the “Evidence Library” (EL). Based on these inputs, the IMPACT model can provide various outputs beyond the scope of this paper which inform resource planning, design, and mission risk. The ICL 1.0 was created in the context of IMPACT and provides the pool of possible medical conditions that may affect crewmembers during the PRA modeling for exploration-class missions.
The ICL 1.0 contains 120 conditions (
Fig. 1
). This limit was established by project leadership as a schedule- and resource-feasible goal for IMPACT version 1.0. The ICL 1.0 development effort occurred under the context of a 210-d mission to cis-lunar space, a design reference mission (DRM) analog for future Mars missions. This mission includes 150–180 d in transit or halo orbit and 30–60 d on the lunar surface, with both transit/orbital and surface operations inclusive of extravehicular activity (EVA). Anticipated crew exposures were based on this DRM to inform included conditions.
Citation: Aerospace Medicine and Human Performance 94, 7; 10.3357/AMHP.6199.2023
METHODS
Evidence Library Team
The Exploration Medical Capability Element (ExMC) of the Human Research Program at NASA’s Johnson Space Center in Houston, TX, created the ICL 1.0 for IMPACT. ExMC’s EL condition list development team (the “EL Team”) represented a collaborative effort inclusive of subject matter experts (SMEs) from the following backgrounds: Physician—Aerospace Medicine, Family Medicine, Internal Medicine, Emergency Medicine, Pain Medicine, Pathology, Physical Medicine and Rehabilitation, Sports Medicine, Wilderness Medicine, and Public Health; Nursing—Registered Nurse, Master of Science in Nursing (emergency nursing, critical care, nursing informatics); Epidemiology; Pharmacy; and Clinical Science.
In addition, the EL Team conferred with spaceflight and operational SMEs in the following fields regarding relevant conditions: Obstetrics and Gynecology, Dentistry, Behavioral Health and Performance, Undersea and Hyperbaric Medicine, Extravehicular Activity Physiology, Musculoskeletal Medicine and Rehabilitation, Optometry, Toxicology, and Life Sciences Research. Notably, the Behavioral Health and Performance Element (BHP) at NASA’s Johnson Space Center was consulted regarding all behavioral health-related conditions. BHP prioritized eight conditions as candidates for inclusion in the ICL 1.0 and assisted in writing the definitions for these conditions.
Condition List Sources
Multiple groups within NASA are involved in developing systems to support human health in spaceflight. Thus, several spaceflight medical condition lists currently exist within the agency. These lists provide valuable perspective regarding conditions posing medical risk to crew and spaceflight missions. Legacy data from the nine source lists in
Table I
were combined to create a master list of over 400 conditions to leverage this institutional knowledge. A brief description of these lists follows.
The IMCL of 100 medical conditions was the foundation for the ICL 1.0. 2 Conditions from the IMCL that had occurred in spaceflight were considered the highest priority for inclusion. The EL Team supplemented these conditions by performing a pilot project that created four additional unique medical condition lists for exploration-class missions. These included a list of toxic exposures and injuries, common conditions that occurred terrestrially in a population restricted to mimic the demographics of the astronaut corps which was drawn from the Rochester Epidemiology Project database, 7 and two SME-created lists of conditions relevant to spaceflight and exploration-class mission environments. Additionally, the Exploration Medical Condition List was used as a source. 1 This is a condition list that was created to define the set of medical conditions most likely to occur during the following mission profiles: lunar sortie, lunar outpost, and near-Earth asteroid missions. The draft Artemis Phase I: Functional Medical Concept of Operations was also reviewed, and relevant medical conditions were identified. Finally, the Lunar EVA Incapacitation Condition List was drawn from an existing effort at NASA to identify potentially incapacitating events during lunar EVAs.
All unique conditions on the nine sources lists were combined and approximately 30 additional conditions relevant to exploration-class spaceflight were added by SMEs during EL Team meetings. Examples of added conditions include: “Behavioral Health and Performance (BHP)—Grief Reaction,” “EVA Related Shoulder Injury,” and “Gravity Well—Entry Motion Sickness/Neurovestibular Disturbance.” These additions completed the creation of a working “master condition list” (MCL) pool from which the ultimate 120 conditions on the ICL 1.0 were selected.
Concurrence Ranking Across the Source Lists
Every condition was assigned a concurrence ranking. Each source list on which a condition appeared was counted toward that condition’s concurrence ranking (i.e., if a condition occurred on five of the nine lists, it received a concurrence ranking of 5). The maximum possible concurrence ranking was a score of 9 and scores spanned from 1–9. All conditions with a concurrence ranking of 3 or higher were discussed to consensus in EL Team meetings. Select conditions with a concurrence ranking of 1 or 2 were also discussed to consensus in EL Team meetings due to potential relevance for the cis-lunar DRM for IMPACT 1.0 (e.g., “EVA-Related Dehydration”).
Consensus Evidence Library Team Meeting Approach
All conditions were initially reviewed individually by EL Team SMEs who provided annotations to the Condition List Lead. The Condition List Lead compiled these comments for discussion. The EL Team then met for approximately 25 h of consensus meetings comprised of a minimum of four SMEs. Notably, conditions were created by EL Team consensus during these meetings to fill gaps unaddressed by the original conditions in the MCL. In the event that consensus could not be reached among the EL Team, the ExMC Element Scientist and Deputy Element Scientist were consulted for resolution.
Stratification of Conditions from the Master Condition List
Fig. 2
provides a graphical overview of the process of selecting conditions for the ICL 1.0. The highest priority for inclusion of a condition was prior occurrence in spaceflight. All conditions from the IMCL that had occurred previously in spaceflight were included on the ICL 1.0. The next consideration was concurrence between the nine source lists (Table I). Review of the MCL occurred sequentially during EL Team meetings, starting with conditions with the highest concurrence ranking. If all EL Team SMEs supported inclusion of the condition in the ICL 1.0, then the condition was included. If a condition needed only minor edits (e.g., renaming of the condition “Visual Impairment/Intracranial Pressure Syndrome” to reflect the current nomenclature, “Spaceflight-Associated Neuro-ocular Syndrome”) and the EL Team otherwise unanimously supported inclusion, then the change was made and the condition was included in the ICL 1.0.
Citation: Aerospace Medicine and Human Performance 94, 7; 10.3357/AMHP.6199.2023
Most conditions required further discussion in EL Team meetings. SME comments primarily encompassed conditions being too broad and requiring further stratification, conditions being too narrow and allowing combination with other relevant conditions, or conditions in need of revised definitions. Conditions accordingly underwent the following changes during EL Team meetings:
- 1)
Definitions of the condition were updated to better match current literature.
- 2)
Broad conditions were split into more granular conditions (e.g., “Abdominal Injury” was divided into two separate conditions, blunt and penetrating abdominal trauma).
- 3)
Similar and/or overlapping conditions were combined into more broad conditions when the EL Team felt it was appropriate based on similarity in medical management or perceived lack of granularity in supporting literature. For example, shoulder, elbow, and wrist sprain/strain were combined into the condition “Upper Extremity Sprains/Strains.” (After combination, shoulder, elbow, and wrist sprain/strain were each moved to the “Removed Conditions List”).
When the ICL 1.0 reached 117 conditions, the EL Team again reviewed the full list to assess whether any existing conditions should be deferred or any conditions were missing. Two conditions were deferred to the Proposed Future Conditions List, described below, as a result. The condition “Dental Caries” was deferred based on spaceflight operational dentist SME opinion that caries would be unlikely to develop in astronauts during the defined DRM due to their excellent dental hygiene, preflight screening, the 210-d length of the DRM, and the carefully controlled dietary intake during spaceflight missions. The condition “Ovarian Cyst” was deferred based on EL Team SME consensus. After these changes the ICL 1.0 consisted of 115 conditions, leaving room for 5 additional conditions to reach the project goal of 120 conditions. Thus 12 candidate conditions were selected. The final five conditions were identified via majority vote by the EL Team.
Product Condition Lists
During EL Team meetings, three product condition lists were created in addition to the ICL 1.0. Conditions on all product lists were labeled with unique identifiers to allow traceability.
- 1)
Proposed Future Conditions List (PFCL): The PFCL contains conditions that the EL team felt were relevant, but excluded from the ICL 1.0 due to the aforementioned project time and resource constraints. These conditions were felt to be less likely to occur and/or less severe. Many of these conditions have direct relevance for exploration missions, particularly to Mars DRMs. Inclusion of these additional conditions is recommended for future iterations of the ICL.
- 2)
Removed Conditions List: This list contains conditions that were identified as potential candidates during initial list development, but were subsequently removed from consideration because they were addressed by existing ICL 1.0 condition definitions, or they were nonspecific, limiting ability to identify supporting medical literature, obtain incidence data, and assign medical resources (e.g., “Non-specific musculoskeletal pain”). Note that for most of these conditions, similar but more specific conditions were included in the ICL 1.0.
- 3)
All Remaining Conditions List (ARCL): The ARCL contains all conditions that were considered for ICL 1.0, but were not included on any of the aforementioned lists. These conditions should also be considered for inclusion in subsequent iterations of the ICL, but are a lower priority than the PFCL conditions. The ARCL contains only conditions with a concurrence ranking of 1–2.
Conditions Not Explicitly Stated
The ICL 1.0 consists of 120 named conditions, but it should be noted that some condition definitions encompass a spectrum of disease that includes another condition (e.g., “transient ischemic attack” is included in the definition spectrum for “cerebral vascular accident”). These conditions were tracked and are included in the evidence for each condition under the heading “Conditions Included, But Not Explicitly Stated (CNES).” The ICL 1.0 contains 123 CNES (
Fig. 3
).
Citation: Aerospace Medicine and Human Performance 94, 7; 10.3357/AMHP.6199.2023
Internal Review and Versioning
After the completion of ICL 1.0 version 1, three SMEs reviewed the list and provided comments regarding condition definitions. Changes were made to incorporate their comments in version 1. These SMEs were an astronaut physician and two operational flight surgeons from the NASA Johnson Space Center.
During the process of data collection for the Evidence Library (condition incidence, duration, treatment capabilities and resources, probability of need for escalation of care, probability of mortality resulting from the condition, and impaired ability to perform mission specific tasks due to the condition), several changes were made to the ICL 1.0. Three conditions were removed. The conditions “Cold Injury—Chilblains/Frostbite” and “Hypothermia” were removed because of the paucity of data related to spaceflight incidence, dependence of cold injury on mission phase, and significant operational and engineering mitigations resulting in any cold injury being expected to result in the loss of the crew. The condition “Vertebral Disc Disorder” was also removed because all published cases of in-flight back pain during U.S. spaceflight were captured by other conditions (“Sprain/Strain—Back” and “Space Adaptation—Back Pain”). Therefore, there was no added value of including “Vertebral Disc Disorder” in the ICL 1.0.
Three conditions were added to again bring the total number of conditions on the current ICL 1.0 final version to 120. “BHP—Spaceflight Related Relationship Problems” narrowly missed being included in the first version of the ICL 1.0. When “Vertebral Disc Disorder” was removed, this condition was added. “Gravity-Well—Entry Motion Sickness” was initially included in the condition definition spectrum with another condition, “Gravity Well—Neurovestibular Disturbance.” While gathering the evidence for the condition, it was determined that it was not possible to combine entry motion sickness and neurovestibular disturbance into one condition. Thus, the conditions were split. Finally, “Pregnancy, First Trimester” was added to the ICL 1.0 to augment the existing condition, “Pregnancy, Risk For.” The current version of the ICL 1.0 is listed in Fig. 1.
DISCUSSION
The Exploration Medical Capability Element of NASA’s Human Research Program is designing IMPACT, a next-generation tool suite that will be used to apply probabilistic risk assessment to medical system design for exploration-class spaceflight missions. The model relies on a list of medical conditions of significant likelihood and/or consequence to these missions. The IMPACT 1.0 Medical Condition List (ICL 1.0) provides these conditions.
The ICL 1.0, designed specifically for exploration-class missions, has notable enhancements as compared to the predecessor list used for probabilistic risk assessment related to low-Earth orbit missions on the International Space Station. First, it was created for a 210-d cis-lunar Mars analog DRM, which is more applicable to exploration-class missions. Second, the ICL 1.0 contains 120 conditions, a 20% increase from its predecessor. In addition to these named conditions, within the condition definitions it includes an additional 123 “Conditions Not Explicitly Stated,” expanding the breadth of the list. Third, the ICL 1.0 includes more EVA-related and Behavioral Health and Performance related conditions than its predecessor. It also includes dust exposure and gravity-well conditions that will be specific to exploration-class missions. These additions further enhance the depth and relevance of this list for exploration spaceflight. Fourth, the process used nine existing source condition lists drawing on existing institutional knowledge. History of condition occurrence in spaceflight and concurrence among these source lists carried the highest weighting for condition inclusion. Fifth, condition definitions were updated to make a more discrete connection with necessary in-flight diagnostic and treatment capabilities, as well as making the definitions more closely aligned with reported evidence used for risk estimation. Sixth, the conditions included on the ICL 1.0 were selected via consensus from ExMC’s Evidence Library Team. The EL Team is comprised of a diverse background of medical specialties and additional expertise was sought in many spaceflight specific areas such as Behavioral Health and Performance and EVA-related concerns. Lastly, the final list was independently reviewed by operational flight surgeons and a physician astronaut not involved in the original selection process. This interdisciplinary expertise enhanced the quality of conditions and the breadth of their associated definitions.
Limitations
The ICL 1.0 is limited to 120 conditions. This number was selected to keep the initial data collection within budget and schedule constraints. While it does not capture all medical conditions anticipated in future exploration missions, it is comprised of conditions with a suspected significant likelihood of occurrence or mission consequence. Future iterations should expand the conditions and associated evidence to further define medical risk in the exploration spaceflight environment.
The ICL 1.0 is limited to medical conditions known to researchers, but there are “unknown unknowns,” including the risk of conditions that have yet to occur during spaceflight. Increasing mission durations beyond 1 yr—the current maximum experience for human spaceflight—will result in diminished ability to conduct routine medical surveillance and risk mitigation. This may result in novel incidence or increased incidence of conditions that would otherwise be identified and mitigated preflight. Insight into novel spaceflight medical conditions is provided by continued spaceflight experience and vigilance in the aerospace medicine community. Recognition of such “new” conditions or disease processes should drive future iterations of the ICL 1.0.
Condition definitions are assumed to be mutually exclusive but pose the possibility of overlap. This is particularly true with Behavioral Health and Performance conditions. This may affect the incidence and outcomes related to overlapping conditions during PRA.
Common side effects of frequently used pharmaceuticals have not been considered in the ICL 1.0. A more extensive formulary is anticipated to be carried onboard during exploration missions. It is likely that more undesirable medication side effects will be encountered. Serious side effects from medications are recommended to be considered for inclusion in future versions of the ICL 1.0, along with appropriate treatment resourcing. This is also true for complications of diagnostic or therapeutic procedures.
Hematologic and metabolic analysis diagnostic tools are being actively investigated for use in exploration missions. While these are excellent for nonspecific complaints (e.g., fatigue), they pose a dilemma when abnormal values are encountered. Incidental findings such as thrombocytopenia, anemia, hyperkalemia, hyponatremia, and others may occur during routine testing. It is recommended that consideration be given to adding some of the more common and consequential of these incidental diagnostic findings to the ICL 1.0 in the future.
Conclusions
The IMPACT 1.0 Medical Condition List (ICL 1.0), developed by the Exploration Medical Capability Element of NASA’s Human Research Program, will serve as the foundation for applying probabilistic risk assessment to medical system design for exploration-class missions. This list of 120 named medical conditions, encompassing an additional 123 medical conditions within the condition definitions (CNES), was developed systematically using nine condition source lists. It represents the most comprehensive condition list developed for exploration-class missions.
Future efforts should expand upon this list. Given the ever-increasing body of knowledge of Aerospace Medicine, the “Proposed Future Conditions List” and the “All Remaining Conditions List” will need to be periodically reviewed and updated. Input from operational SMEs should drive consideration for inclusion of additional conditions or updates to existing conditions. Refinement of future condition lists should consider the relative priority of condition types (e.g., adequately balancing musculoskeletal conditions vs. EVA-related conditions vs. Behavioral Health and Performance conditions). Definitions should be created and modified as necessary so that conditions are mutually exclusive, thereby reducing “double counting” of medical events and allowing for accurate representation of their incidence. As humans gain more experience with exploration-class missions, novel conditions in spaceflight should be added to this list. Associated evidence, such as condition incidence, duration, treatment capabilities and resources, probability of need for escalation of care, probability of mortality resulting from the condition, and impaired ability to perform mission specific tasks due to the condition, should be modified accordingly. Models that have been developed to predict the incidence of medical conditions can be validated or refined using flight experience. Finally, future iterations of this list should consider including more chronic conditions as these conditions are anticipated to be more common with longer, exploration-class missions.
IMPACT 1.0 Medical Condition List (ICL 1.0). BHP: Behavioral Health and Performance; EVA: extravehicular activity.
IMPACT 1.0 Medical Condition List refinement methodology overview. All conditions included in ICL 1.0 had definitions updated. IMCL: IMM Medical Condition List; EL: Evidence Library; CL: condition list; EMCL: Exploration Medical Condition List; ConOps: concept of operations; EVA: extravehicular activity. *Additional conditions added during splitting/combining process.
Conditions included, but not explicitly stated (CNES) in the condition title on the ICL 1.0. LE: lower extremity; LRI: lower respiratory infection; URI: upper respiratory infection.
Contributor Notes
