Airway Management in Space

It will be essential to have on board spacecraft astronauts who have requisite training in airway management, along with strategies for retaining these skills. However, success in applying some of the most effective methods of airway management requires frequent and regular practice, in the opinion of members of the committee who as part of their professional activities have expertise in airway management, and it is not likely that an individual with such characteristics will be on board the spacecraft. Therefore, techniques that are based on the likelihood of success should be chosen, and these should be consistent with the skills of the individuals on board. The types of airway equipment and techniques required will partly be based on the type of surgery and trauma anticipated. Decisions regarding long-term airway care need to be made before such equipment and techniques are selected. Lastly, because airway management is usually required for successful cardiopulmonary resuscitation, the need for airway management during anesthesia should be coordinated with the need for cardiopulmonary resuscitation.

To minimize morbidity and mortality, two approaches should be followed. The first is to use an anesthetic technique that does not require endotracheal intubation. The second is to avoid the use of neuromuscular system-blocking drugs. Anesthesia with the latter can facilitate an overall view of the trachea during endotracheal intubation, but if the trachea cannot be intubated, the patient is left totally dependent on the clinician for adequate ventilation. Controlling ventilation in a paralyzed individual is often difficult (Caplan et al., 1993; Parmet et al., 1998).

Little is known about airway management in an atmosphere of microgravity. Studies have been performed in simulated microgravity in a submerged full-scale model of a space module with neutrally buoyant equipment and personnel. The ability to control the airway in a free-floating submerged manikin was attempted with four different devices. Endotracheal intubation was unsuccessful in 10 to 15 percent of the situations, whereas other airway devices were more successfully implemented (Keller et al., 2000). Although this was useful initial information, the study with a manikin in no way simulates clinical conditions and the mental pressure associated with the need to control an airway in a life-and-death emergency.

These studies emphasize the potential for serious morbidity when intensive airway management is needed for either anesthesia or resuscitation. These clinical problems could contribute to the need for long-term care on board the spacecraft.

Because the possibility of failure of endotracheal intubation is real, less demanding techniques should be considered, even if they do not protect the airway from vomiting and aspiration as well as endotracheal intubation does. Insertion of a laryngeal mask is technically much easier, and it provides an excellent airway. In the simulated atmosphere of microgravity, use of a laryngeal mask has been more successful (Keller et al., 2000).

Anesthetics

Although inhaled anesthetics, both volatile and gaseous, are extremely useful and helpful, they should not be considered for use in space travel at this time, as stated above. Until the problems associated with gas-liquid interfaces in microgravity can be solved, intravenously administered anesthetics should probably be used. Although such anesthetics can be given by bolus administration, constant infusion achieves more sustained levels of anesthetic in the blood and brain, but constant infusion would require appropriate infusion pumps. These are small, however, and should be readily accommodated on a spacecraft. Nevertheless, basic technical procedures, such as procedures for the insertion of a reliable intravenous catheter, need to be reviewed, modified, or redesigned where necessary and need to be practiced.

In general, the drugs used should be associated with a rapid recovery and, preferably, should have an antagonist. These drugs should not cause significant cardiorespiratory depression. Unfortunately, no ideal drug with all of these characteristics exists at present.

Regional Anesthesia

The major advantage of regional anesthesia is that it anesthetizes only that part of the body that needs to be anesthetized and does not have the disadvantages associated with anesthetizing the entire body. It also has the advantages of maintaining the patient awake and facilitating a rapid recovery and postoperative analgesia.

Of prime importance on a spacecraft is what should be done if the regional anesthetic turns out to be inadequate for surgery. The nerve block procedure can be repeated (with the added potential complication of nerve toxicity), or a general anesthesia can be induced. Direct nerve injury and hematoma must be considered from use of the nerve-blocking procedure, although those are extremely rare complications on Earth. The team must be prepared to deal with central nervous system excitation and possible convulsions with short- or intermediate-action local anesthetics (e.g., lidocaine) and cardiotoxicity with the longer-acting drugs (e.g., bupivicaine).

Despite numerous potential problems, crew medical officers could be trained in the delivery of regional anesthesia in an effective manner. After conducting proper research on the effects of microgravity on the diffusion and nerve toxicities of local anesthetics, these will probably be the agents of choice.

Health Care Opportunity 16. Developing an anesthetic approach associated with rapid and comfortable recovery using anesthetic drugs with short durations of action or for which there are antagonists.

Physiological Responses to Injury

The physiological alterations that accompany long-duration space missions may well affect homeostasis, wound healing, and resistance to infection, all of which are crucial for recovery from trauma or surgery. Any wound sets into motion a complex series of events under neurohumoral system control termed the “response to injury.” The time course has been fairly well delineated in the normal Earth environment, and the routines of postoperative and postinjury care are based upon the assumptions implicit in this model of events (Greenfield, 1996). The initial studies upon which this model is based were performed in the 1930s and have been refined by innumerable clinical and laboratory observations over the intervening decades to derive assumptions about fluid and electrolyte balance, changes in hormone levels, metabolic changes, cytokine activation, and immunological alterations after injury. Essentially nothing is known about how this neurohumoral response to injury is modified by microgravity.

Although it may not be realistic to replicate these myriad physiological studies during the postoperative period, carefully designed experiments with simple outcomes measures (supplemented by highly selected physiological, histological, or metabolic studies) performed in a microgravity environment such as the ISS after surgery in animals might yield significant information of value.

Take one example: the response to hemorrhage and fluid resuscitation. Cardiovascular adaptations and changes associated with microgravity will probably alter the response to hemorrhage and fluid resuscitation. Without gravitational pooling, will fluid volumes required for resuscitation from a standard hemorrhage be the same, greater than, or less than those required on Earth? What fluids should be used, and at what volume? What (if any) blood substitutes should be used? Would the use of a counterpressure device (such as military antishock trousers) help? Or would the use of such a device prove detrimental or nonproductive in an environment lacking the capability to obtain definitive control of hemorrhage?

To stop bleeding and achieve homeostasis, the surgeon applies mechanical methods (ligatures, cautery, hemostatic clips) that are likely to be quite effective in microgravity (Campbell and Billica, 1992; Colvard et al., 1992; Campbell et al., 1993, 1996; Campbell, 1999). In addition, new methods are continually being devised; for example, an ultrasound-activated method of sealing blood vessels has been demonstrated to have significant advantages in minimal-access surgery, supplanting the traditional electrocautery for many applications (Gossot et al., 1999). Continued developments can be anticipated, as this is a major area of focus in civilian and military medical practice.

Similarly, new methods of wound closure are continually being devised as alternatives to sutures or staples. For example, both biological and artificial adhesives are under continual improvement (Quinn et al., 1998; UHSC, 1999). These may be supplemented, when necessary, by a surgical zipper applied in such a fashion as to pull the edges of the wound together. This provides mechanical support for a “sutureless” closure (Mulvihill, 1999) that is quick and painless and that may be more resistant to infection than the closures achieved by more conventional methods.

Surgical homeostasis requires not only mechanical control of bleeding but also complex interrelated mechanisms of blood coagulation and fibrinolysis. As an example of unexpected issues that may emerge when actual surgery is performed or major injuries are treated, Campbell and colleagues (1993) noted that venous bleeding appeared to increase during surgery performed during parabolic flight. They hypothesized that gravitational forces on tissues normally contribute to the collapse of veins and help staunch the flow of blood when surgery is performed on Earth. In microgravity, however, such forces on tissue are nonexistent and external compression must be supplied. Practical lessons such as those about venous bleeding are best learned by carefully designed studies with animals.

Although immediate control of bleeding in microgravity has been demonstrated to be achievable by conventional means, it is not known whether long-duration space missions may result in subtle alterations in blood coagulation activity (e.g., platelet dysfunction or hyperfibrinolysis) that might require additional hemostatic maneuvers or the use of topical hemostatic agents. Anecdotal experience from Mir suggests that minor cuts take longer to heal, but it is dangerous to generalize this to an assumption that wound healing may be prolonged. Incomplete healing has been observed for muscles and bones injured in rats before spaceflight in the Cosmos biosatellite series, and brief daily exposure to near-infrared light appears to promote epithelial wound healing (Baibekov et al., 1995; Korolev and Zagorskaia, 1996).

Of greater concern than soft-tissue healing is the probable impact of bone demineralization upon healing of fractures. Fractures may be casted, internally fixed, or externally fixed. Although each of these methods has its advantages, neither casting nor external fixation would seem to allow access to a pressure suit, should this be required. Better information about how bone heals in microgravity would be extremely helpful. Innovative methods such as percutaneous injection of bone adhesives or growth factors-growth promoters might be available (AAOS, 1996).

Adequate nutritional support has revolutionized the management of surgical illnesses ranging from burns through trauma and infection. The neurohumoral response described above increases metabolic demands by 15 to 25 percent for a fracture of a major long bone (e.g., the femur) and 50 percent for multiple trauma (Greenfield, 1996). Ileus commonly accompanies burns, trauma, and surgical illness and may be exacerbated by the hypomotility associated with microgravity (Harris et al., 1997). This may make it impossible to maintain caloric intake; hence, short-term nutritional support may be needed during recovery from an acute illness or trauma. Consideration should be given to ways in which this might be accomplished within the realistic constraints of the mission. A simple way to monitor the adequacy of nutritional support, for example, urinary nitrogen excretion as a measure of nitrogen balance, would be helpful if it could be validated in microgravity.

Surgical Skills and Training

A word about remote or telepresence surgery is in order. By this method of surgery, a surgeon in a remote location controls robotic instruments that perform the actual surgery. It has been demonstrated to be feasible and is being explored for some applications in remote locations on Earth. However, even the slight transmission delay involved in transcontinental distances has proved problematic (DiGioia et al., 1998; Satava and Jones, 1998). Thus, in a mission beyond Earth orbit, transmission blackouts and delays will certainly limit its usefulness. Therefore, the roundtrip time lag (40 minutes or so once the mission is near Mars) negates the use of telesurgery and even real-time telementoring at this time, even though these methods have proved feasible on Earth.

Robotic surgery has captured public interest and enthusiasm. At present, surgical robots operate under the direct control of a human surgeon, who is usually in the same room. Currently, they are dependent on gravity. The robotic assistant is used to scale down movement and eliminate unwanted motions, allowing smaller, more precise sutures to be placed (Satava and Jones, 1998; Borst, 2000). Although rapid developments in this field are anticipated (Campbell et al., 1996; Satava and Jones, 1998; Campbell, 1999, Maniscalco-Theberge and Elliott, 1999), the application of robotic assistance to long-duration space missions is uncertain. Combinations of ultrasound-based diagnosis with computer-assisted positioning of therapeutic instrumentation may, in the future, make robotics a valuable technology for space medicine. A combination of computer-guided, robotic, and human hands-on expertise—including crew medical officer training and proficiency in evolving, minimally invasive surgical techniques such as laparoscopy—will be necessary, backed by data in an onboard computer might provide the best solution for complex low-probability problems.

Surgical Equipment

What surgical equipment should be taken on a space mission beyond Earth orbit several decades from now? Therapeutic options will be limited by the available drugs, equipment, and supplies. Thus, the choice of surgical equipment and supplies and the choice of procedures that will be performed seem to be inextricably linked. Yet, with computer-assisted design and computer-assisted manipulation (CAD-CAM) technology, it is possible to fabricate small parts to order from specifications contained in an onboard database or transmitted from Earth (Heissler et al., 1998; Okumura et al., 1999). Thus, it is conceivable that a seldom used surgical instrument (or an implant needed to stabilize a fracture) could be fabricated as needed and then recycled when it was no longer needed. Such technology is already available, and future application to surgical parts and instruments is likely a cost-effective way to achieve a just-in-time solution to a major problem on a spacecraft: the lack of hospital supplies. CAD-CAM equipment may well be included in a Mars mission for other (nonmedical) purposes; the task would thus be ensuring that materials and specifications were consistent with medical applications as well. The availability of this kind of technology dramatically expands therapeutic possibilities and emphasizes the need for skills acquisition by space crews.

By using today's standard of care as a guide, basic diagnostic equipment would include a high-resolution imaging system, an ultrasound unit, or conceivably, a compact magnetic resonance imager. This allows the detection of abscesses, bleeding, and pneumothorax and the performance of image-guided interventions (see Management of Abscesses and Soft-Tissue Infections below). In current trauma practice, a focused ultrasound evaluation has proved to be rapid and reliable in ruling in or out certain kinds of injuries (Bode et al., 1999; McCarter et al., 2000). This is another area in which multiple civilian applications are driving a rapid pace of technological innovation that could be adapted for use in space medicine if it is validated in microgravity. Whatever system is chosen may well need to be tested on healthy human subjects in microgravity, as anatomic landmarks shift without the constraints of gravity.

Technical Aspects of Surgery

In a microgravity environment, special mechanical problems such as anchoring both the patient and the operating team, maintaining a sterile field, and controlling blood and body fluids can be anticipated (Kirkpatrick et al., 1997). The mechanics of both open and laparoscopic techniques have been explored during parabolic flight, and the feasibility of these techniques with suitable modifications has been demonstrated. During open surgery, control of body fluids with sponges and suction appears to be adequate if the patient has normal hemostatic capabilities (Campbell and Billica, 1992; Colvard et al., 1992; Campbell et al., 1993, 1996; Campbell, 1999). Special adjuncts such as transparent plastic shields to provide containment of arterial bleeding can easily be designed and tested either in parabolic flight or on the ISS.

Laparoscopic surgery is an attractive option that has been demonstrated to be feasible in a porcine model during parabolic flight (Campbell et al., 1996). Other forms of minimal-access surgery may similarly prove to be both feasible and advantageous. Because the incisions used are small, recovery is usually rapid and limitations of physical activities are minimized. Better containment of body fluids is an additional advantage when working in microgravity. Minimal-access surgical simulators are already available, and it may be particularly easy for those who already have excellent eye-hand coordination skills to learn the techniques.

The preceding information and examples illustrate the accelerating integration of engineering and biology. The committee encourages the National Aeronautics and Space Administration (NASA) to track these and other emerging opportunities closely to apply them to space medicine as the technology develops to meet the need.

Prevention of Infection

Accidental wounds (such as lacerations and open fractures) are considered contaminated and require therapeutic administration of antibiotics as well as judicious surgical management to prevent devastating infectious complications in the best of circumstances (Singer et al., 1997; Luchette et al., 2000). Infection is possible even after clean, elective surgery. This may be more likely when surgery is performed during a mission. Breaks in sterile technique may be more likely in microgravity, the microflora is altered among individuals in close confinement (i.e., individuals share microorganisms), and there may be alterations in immune function in astronauts. Prophylactic antibiotics have been shown to decrease the probability of wound infection and are commonly used in current surgical practice (McCuaig, 1992; Bold et al., 1998; Weigelt and Faro, 1998). Selection of antibiotics for prophylactic and therapeutic purposes should be based upon knowledge of the microfloras that colonize the skin and gastrointestinal tract, coupled with pharmacological considerations (e.g., frequency and ease of administration and potential toxicity).

Management of Common Surgical Emergencies

Although one can anticipate the most common surgical emergencies from demographic and analog-environment data, unanticipated events can and do occur. A subarachnoid hemorrhage was managed by physicians in Antarctica, despite inadequate facilities, through ingenuity and innovation (Pardoe, 1965). Whether such a heroic effort could be undertaken or should be undertaken in the context of a space mission is doubtful, but it serves to show the human drive to preserve life, even against all odds. It also demonstrated how improvisation led to a successful outcome. Although it is not possible to plan for all emergencies, it may be possible to facilitate improvisation by providing the basic materials.

Fairly good data on the incidence of likely surgical emergencies are available from demographic and analog environments (Lugg, 2000). Anticipated emergencies include acute appendicitis, abscesses, incarcerated hernias, and trauma. Acute appendicitis is of particular interest because it provides a clear example of a common surgical emergency that has been approached in various ways over the past decades in an effort to avoid the necessity of an untrained person performing an appendectomy in a remote environment. In 1979, studies in Antarctica documented an increased incidence of acute appendicitis (Lugg, 1979) and led to the recommendation that the team physician undergo prophylactic appendectomy. The spectrum of measures available to avoid performance of an appendectomy in a remote environment ranges from prophylactic appendectomy before the mission to treatment of appendicitis with antibiotics with later (interval) appendectomy and to the use of antibiotics supplemented by percutaneous drainage of any abscess that might form.

Management of Abscesses and Soft-Tissue Infections

Abscesses and other soft-tissue infections are treated with antibiotics and by drainage or debridement, as needed. Image-guided (probably ultrasound-guided) percutaneous drainage (Nakamoto and Haaga, 1995; Montgomery and Wilson, 1996; Shuler et al., 1996; Miller et al., 1997; Scott et al., 1997; Wroblicka and Kuligowska, 1998; D'Agostino, 1999) would seem to be an ideal method for the management of deep-seated abscesses (as well as some less common conditions such as acute cholecystitis refractory to antibiotics). This technology is well proven as a safe and effective alternative to surgical drainage under the proper conditions and with concurrent antibiotic therapy.

Development of a Space Medicine Catalog and Database

During the space mission, routine surveillance of health measures should be conducted and all episodes of illness and injury should be recorded. Systematic record keeping with a computerized database will be necessary so that data can be accessed periodically and also used for identification of diagnostic and therapeutic errors and continued health care planning. Sex and cultural differences should be identified as part of surveillance of health measures. A centralized catalogue for all peer-reviewed manuscripts, abstracts, reports, handouts, mission log summaries, and monographs related to space biomedical research, health care, and relevant studies in analog environments (Lugg and Shepanek, 1999) should be developed. Access should be maintained through a centralized database with contemporary medical information on personnel and equipment. All material should contain the date and the responsible author(s). This is important, because resources could well be available but not used because they are not accessible and because promising information regarding countermeasures or important biomedical associations could be missed because the material is unknown or unavailable. The databases on board the spacecraft could be continuously updated as newer scientific information becomes available.

The Australian National Antarctic Research Expeditions Health Register is one model for such a database (Sullivan et al., 1991; Sullivan and Gormley, 1999). The database system should include descriptions of the illnesses and injuries that occur in microgravity, track normal health status measures, assess the types of illnesses and injuries and risks of exposure, determine the effectiveness of exposure modifications, track procedures performed by individuals and by the group, track the therapeutic agents that have been administered, and have a system for the coding of each episode of illness and injury according to the International Classification of Diseases and emergency medical code groupings. These codes should be expanded to include codes for dental problems. New emergency medical codes will likely need to be developed for the microgravity environment. Standardized rates for reporting of incidents, such as the numbers of incidents per person-day, should be adopted so that rates from different missions can be compared.

Health Care Opportunity 19. Recording routine surveillance of health status measures, incidents of illnesses and injuries, and their treatments in a database with standardized rates of occurrence so that data between studies and missions can be compared.

Health Care Opportunity 20. Developing and maintaining a centralized catalogue of all written materials related to space and analog-environment biomedical research and experience according to current medical informatics standards.

The health care opportunities that are described in this chapter and that may be explored to increase the future effectiveness of managing risks to the health of astronauts during space travel are listed in Box 4–1. These should be evaluated in addition to the health care opportunities provided in Chapter 3. Further opportunities will accrue as the field of space medicine continues to develop. As health care opportunities during space missions are explored, they will contribute substantially to the evidence base for the development of the appropriate means of management of medical events considered to be within the scope of care for long-duration space travel.

Conclusion

Exploratory missions with humans involve a high degree of humanmachine interaction. The human factor will become more important as the durations of missions into deep space with humans increase and as the spacecraft crew functions more autonomously, adapts to unexpected situations, and makes real-time decisions.

• NASA, because of its mission and history, has tended to be an insular organization dominated by traditional engineering. Because of the engineering problems associated with early space endeavors, the historical approach to solving problems has been that of engineering. Long-duration space travel will require a different approach, one requiring wider participation of those with expertise in divergent, emerging, and evolving fields. NASA has only recently begun to recognize this insufficiency and to reach out to communities, both domestic and international, to gain expertise on how to remedy it.
• Engineering and biology are increasingly integrated at NASA, and this integration will be of benefit to the flexibility and control of long-duration missions into deep space. NASA's structure does not, however, easily support the rapidly advancing integration of engineering and biology that is occurring throughout the engineering world outside NASA. NASA does not have a single entity that has authority over all aspects of astronaut health, health care, habitability, and safety that could facilitate integration of astronaut health and health care with engineering.
• The human being must be integrated into the space mission in the same way in which all other aspects of the mission are integrated. A comprehensive organizational and functional strategy is needed to coordinate engineering and human needs.

Recommendation

NASA should accelerate integration of its engineering and health sciences cultures.

• Human habitability should become a priority in the engineering aspects of the space mission, including the design of spacecraft.
• Investigators in engineering and biology should continue to explore together and embrace emerging technologies that incorporate appropriate advances in biotechnology, nanotechnology, space worthy medical devices, “smart” systems, medical informatics, information technology, and other areas to provide a safe and healthy environment for the space crew.
• More partnerships in this area of integration of engineering and health sciences should be made with industry, academic institutions, and agencies of the federal government.

Figure

Mission Control, Johnson Space Center, Houston, Texas, during the early portion of space shuttle mission STS-95 on October 29, 1998, overlooking the Flight Director (FD) and the Spacecraft Communicator (CAPCOM) consoles. NASA image.

Figure

Dr. Paul Stoner (left) and Dr. Jeff Jones, on-duty flight surgeons in Houston's Mission Control Center during the April 24, 2000, launch attempt of space shuttle Atlantis during mission STS-101. NASA image.