BLUNT TRAUMA AND OPERATIVE CARE IN MICROGRAVITY: REVIEW OF MICROGRAVITY
PHYSIOLOGY AND SURGICAL INVESTIGATIONS WITH IMPLICATIONS FOR CRITICAL CARE AND
OPERATIVE TREATMENT IN SPACE
AW Kirkpatrick, MD, Departments of Critical Care and General Surgery, University of
Toronto, Toronto, Canada; MR Campbell, MD, FACS, Department of General Surgery, McCaiston
Regional Medical Center, Paris, Tex; O Novinkov, MD, PhD, Medical Operations Branch, KRUG
Life Sciences, Lyndon B. Johnson Space Center, Houston, Tex; I Goncharov, MD, PhD, and I
Kovachevich, MD, PhD, Medical Operations Branch, Institute of Biomedical Problems, Moscow,
Russia.
E-mail: andykirk@istar.ca.
Correspondence address: Andrew Kirkpatrick, MD, 590 Wellington St West, Toronto,
Ontario, M5V 2X5, Canada.
BACKGROUND: The assembly of the International Space Station in a low earth
orbit will soon become a reality. The National Aeronautics and Space
Administration envisions inhabited lunar bases and staffed missions to Mars in
the future. Increasing numbers of astronauts, construction of high-mass
structures, increased extra-vehicular activity, and prolonged if not prohibitive
medical evacuation times to earth underscore the need to address requirements
for trauma care in nonterrestrial environments.
STUDY DESIGN: A search was carried out to review the relevant literature in the
MEDLINE and SPACELINE databases. All related Technical, Corporate, and Flight Test Reports
in the KRUG Life Sciences corporate library were also reviewed. Bibliographies of all articles
were then reviewed from these papers to identify additional pertinent literature. Senior
Russian investigators reviewed the Russian literature and translated Russian publications
when appropriate. Personal communication and discussion with active microgravity
investigators and ongoing microgravity research supplemented published reports.
RESULTS: A large volume of data exist to document the multiple detrimental
physiologic effects of microgravity exposure on human physiology. Organs systems such as
cardiovascular, neurohumoral, immune, hematopoetic, and musculoskeletal systems may be
particularly affected. These physiologic changes suggest an impaired ability to withstand
major systemic trauma. Observational data also suggest adverse changes in numerous
aspects of response to wounding and injury, and in areas such as the behavior of
hemorrhage, microbiologic flora, and wound healing. In addition to an increased volume of
ongoing and anticipated basic science research in microgravity physiology, preliminary
studies of clinical diagnosis and therapy have been carried out in microgravity and
microgravity laboratories.
The feasibility of a wide range of ancillary critical care techniques has
been verified in the parabolic flight model of microgravity. Although Russian
investigators first performed laparotomies on rabbits in parabolic flight in
1967, only recently have American investigators demonstrated the reproducible
feasibility of open and endoscopic surgical procedures under general anesthetic
in animal models in a microgravity environment.
CONCLUSIONS: With appropriate instrumentation and personnel, the majority of
resuscitative and surgical interventions required to stabilize a severely injured astronaut are
feasible in a microgravity environment. Onboard
limitations in mass, volume, and power that are ever present in any spacecraft
design will limit the realistic capabilities of the medical system. Standard proved and tested
trauma and operative management protocols will constitute the basis for extra-terrestrial
care. Surgeons should familiarize themselves with the microgravity environment and remain
active in planning trauma care for the continued exploration of space.
The next
phase of staffed space exploration is an international effort to assemble an orbiting space
station in low earth orbit. The initial construction of the international space station will
require extensive extravehicular activity (EVA) that has an inherent risk of traumatic injury.
It will be necessary to be able to stabilize and support a seriously ill or injured crew member
until the space shuttle or a dedicated vehicle can return the patient to earth (1, 2). The
National Aeronautics and Space Administration (NASA) Space Exploration Initiative previously
envisioned inhabited lunar bases and staffed missions to Mars (3). The time to definitive
medical care on earth during future long-duration missions is anticipated to be 24 hours for
the international space station, 7 days for a lunar base, and 9 to 12 months for an
expedition to Mars (4). To venture beyond the relative safety of low earth orbit, the
requirements to limit mass, volume, power, and the level of onboard medical expertise must
be balanced against the requirement for more definitive medical therapy and operative
intervention. During the 21st century, medical providers must address the requirements for
trauma care in deep space, preferably before the exploration of the next frontier.
SPACE TRAUMA OVERVIEW Experts at NASA studied a graph depicting the "probable incidence
versus impact on mission and health" for space missions and concluded that
trauma is rated at the highest level (5). Dramatic unsurvivable accidents such
as the explosion of the Challenger Space Shuttle demonstrate graphically that
traumatic injury is a real risk of space exploration. Traumatic injuries
requiring medical treatment are likely to be blunt. Penetrating injuries,
however, can also occur during EVA, with violation of the protective space suit
by a micrometeorite or local space hardware, which would produce an explosive
decompression. Environmental exposure to extremes of ambient pressure,
temperature, hypoxia, and radiation could also result. These insults are likely
to be lethal, precluding the requirement for medical care. Explosive
decompression to a vacuum would allow dissolved gases to enter the gaseous
state. From the results of animal studies, we can infer that after a complete
explosive decompression in space, vapor bubbles would appear in the great
vessels and heart, with resultant complete cardiac standstill after 10 to 15
seconds (6). Other injuries include pulmonary barotrauma, such as pneumothorax and
pneumomediastinum, and the effects of gas emboli (6, 7).
Throughout human history, accidents during construction and exploration have caused
death and disability. Additional exploration of space and the
construction of the space station will present similar risks. The risk and
severity of injury will be more increased because of the increased numbers of
person hours spent in space and in EVA, the requirement for movement and
construction of high mass hardware, vehicle docking and refueling, the advancing age of the
astronaut population when highly specialized persons are selected for specific missions, and
an array of space-induced physiologic and pathologic changes (3, 8, 9).
Objects,
structures, or humans, once accelerated in weightlessness, could deliver crushing or
lacerating blows (10, 11) because objects in weightlessness retain their mass, which is
independent of gravitational changes. Force can then be developed by any acceleration
imparted to an object. The force devel oped is determined by the equation,
Force=Mas x Acceleration
with the kinetic energy that can be transmitted to a subject, independent of
gravity, described by the equation,
Energy Kinetic=1/2 (Mass) (Velocity2 ).
This risk may be accentuated by decreased perception of the risk of unintended
acceleration because of the lack of apparent weight (11). Testing
during spaceflight has confirmed that gravity plays an essential role in weight
discrimination. Without weight as we know it on earth, humans are not as
sensitive to inertial mass judgments when asked to discern apparent weights of
objects (12, 13) and have shown decrements in proprioceptive ability (14).
The possibility of a serious traumatic injury occurring in space is real. Original plans for
the space station specified medical care similar to that provided by the emergency,
operating, and critical care units of a terrestrial level III hospital (1). This is not feasible
given present mass, volume, and power restraints. This level of care will remain a distant,
highly desirable standard because the immediate capability to return to earth may not exist,
or the patient could be nontransportable or unable to withstand the shock of the landing
(15). The ability to correctly diagnose and adequately treat injuries in space will be beneficial
beyond reducing the cost in human morbidity and mortality. Previous estimates were that
an unscheduled medical evacuation to earth would cost at least $250 million in 1987 dollars
(16, 17). These costs have not decreased.
MICROGRAVITY AND MICROGRAVITY LABORATORIES Most of the people space experience has occurred during orbital flight around the
earth. In this microgravity environment, the earth's gravitational force provides the
centripetal force necessary to continuously change the tangential momentum of an object
into a circular or elliptical orbit, with the gravitational force vector negated by a centrifugal
force vector (18). Weightlessness of an object is the result of the absence of acceleration
vectors on this object. No actual or simulated operative procedures have been performed
during spaceflight, although an increasing amount of life sciences data from Russian and US
space programs is applicable to critical care and surgery.
Except for space itself, the only other true microgravity laboratory available to surgical
investigators has been parabolic flight. Surgical investigations have been conducted on the
KC-135 aircraft, a modified Boeing 707 aircraft used extensively by NASA. By flying a ballistic
(projectile) parabolic trajectory, the contents and passengers of the KC-135 are subjected to
weightlessness because they are experiencing no accelerative force vectors relative to the
aircraft (19). This weightless state can be maintained for up to 30-second intervals.
Disadvantages of parabolic flight include short windows of 0g followed by windows of 1.8g
during pull-up maneuvers, great financial expense, and the need for logistically simple
experiments. Surgical experiments have also been performed underwater with specially
designed instruments and equipment to simulate weightlessness as a space analogue (20).
Disadvantages of neutral buoyancy include water resistance that would not be present in
space, substances (solutions or blood) interacting and dissolving with the water, difficulties
in making each piece of hardware neutrally buoyant, and organs floating or sinking
underwater because of individual densities.
PHYSIOLOGIC CHANGES PERTINENT TO CRITICAL CARE AND TRAUMA The weightless environment has a myriad of physiologic effects on living
creatures accustomed to the Earth's environment of reference gravitational force
(1g). Some of these physiologic effects of microgravity, such as the cardiovascular and
neurovestibular effects, occur almost immediately after the
astronaut leaves earth (21). Cardiovascular changes likely begin to occur even
during the prelaunch phase because of the inverted posture that is typically
assumed while awaiting launch. Other physiologic changes, such as loss of calcium and lean
body mass, possible loss of red blood cell mass, and cumulative radiation effects, occur later
during the flight (21). Many physiologic changes observed during human spaceflight suggest
an impaired ability for an astronaut to withstand major systemic trauma. Although the
diverse range of physiologic changes described to date are beyond the scope of this article,
the most pertinent for injury survival are discussed.
Cardiovascular and neurohumoral changes. In the (1g) standing state, a large
component of blood volume resides in the peripheral vascular space because of
gravitationally induced hydrostatic forces. In microgravity, these forces are removed,
resulting in translocation of fluids from the lower to the upper part of the body (22). This
translocation has the net effect of reducing total body
water to an earth-equivalent hypovolemic state (11, 21, 23-26). The translocated
fluid is believed to expand the central blood volume transiently, with excess
volume rapidly reduced through the homeostatic responses of diuresis and reduced thirst
(27, 28). Early (day 2) stroke volumes of 150 percent of the preflight standing controls that
progressively fell throughout flight were detected on the Space Life Sciences (SLS)-1 mission
(29). As a result, astronauts have been reported to lose between 10 percent and 23 percent
of the circulating volume during space flight (30-32). During long-term space habitation on
the Russian space station MIR, cardiac stroke volumes decreased by 10 percent to 20 percent
(23-30). Recent reviews further support the occurrence of cardiac deconditioning (9, 11,
28).
The impaired ability of returning astronauts to tolerate reintroduction of
normal gravitational forces on return to the earth is a comparable model for
hypovolemia. The stress of hemorrhage is analogous to the stress of gravity
imposed by returning to earth. Syncope and presyncopal symptoms, reflecting
cerebral hypoperfusion, are well described in these circumstances (27). Adverse
cardiovascular responses, observed to decrease the negative pressure applied to the body in
space causing caudal displacement of body fluids, further
demonstrate impaired cardiovascular reserves (26, 33).
In the microgravity environment, these changes may be an adaptive response to
decreased cardiovascular demands and a relatively expanded plasma volume immediately
after launch, but would reduce the hemodynamic reserves when faced with major trauma. A
circulating volume deficit of just 15 percent corresponds with a class I hemorrhage on earth,
according to advanced trauma life support guidelines (34). With these baseline deficits, the
needs of the recipient for resuscitative fluids and blood products may be increased relative
to a similar injury on earth (10, 11).
Central control of hemodynamics could also be affected by spaceflight. Investigators
noting reductions in baroreceptor responses, which persisted up to
10 days after landing, and in the normalization of blood volume interpreted these findings as
evidence of an intrinsic loss of vagal control over the sinus node (27, 35). Other investigators
view attenuation of vagally mediated cardiac baroreceptor function as only one marker of a
larger global autonomic readaptation to microgravity (36). After reviewing the pertinent
literature, Robertson and colleagues believe that during most of spaceflight, sympathetic
activity is reduced and levels of circulating catecholamines are low (36). They
postulated multiple effects of decreased levels of catecholamines, including reduced heart
rate, loss of renal sodium-retaining capability and a resultant increased diuresis, reduced
erythropoietin levels, and up-regulation of beta-adrenergic receptors. Attenuation of cardiac
chronotropic responses and the enhanced beta rather than alpha nature of the autonomic
nervous system, would reduce the ability to maintain blood pressure in response to
hypovolemic stress (36, 37).
Immune function. Spaceflight has long raised concerns about decreased immune
responses (9, 11, 25, 28, 30, 38, 39). Consistent effects of microgravity on the immune
system include neutrophilia, lymphocytopenia, eosinopenia , and a range of functional
impairments in cell-mediated immunity (40). Numbers of circulating monocytes are
reported by some to decrease during spaceflight (31), while others have found increased
counts but altered characteristics, including smaller size, reduced granularity, and reduced
numbers of receptors (40-42). These findings may have implications for wound healing (43).
Reduced numbers of T lymphocytes have been consistently observed after spaceflight (40), as
have alterations in the relative T4 and T8 cell populations (3, 23, 31, 41, 44). Decreased
numbers and activity of natural killer cells were detected in cosmonauts and space shuttle
crew members (40, 41, 45, 46). In vivo flight assessments of the cell-mediated immunity of
shuttle crew members revealed substantial decreases in reactivity with delayed cutaneous
hypersensitivity reactions (40, 45). The response of T cells to mitogenic stimulation has
proved markedly attenuated during and after spaceflight (23, 47, 48); in one case,
microgravity cultures showed less than 3 percent of 1g control activity (49). Substantial
decreases in interleukin production (especially interleukin-2) and interferon-gamma have
been reported in animals and cosmonauts after prolonged microgravity exposure (45).
These findings must be interpreted with consideration of the remarkable
complexity and redundancy in the human immune system, the rapid advances in our
understanding of the immune system since the space program began, and similar alterations
noted in immune function after a variety of terrestrial stresses
(40). Additional studies are needed. Many putative immune defects are remarkably similar to
some of the immunologic defects that can be induced in laboratory animals by traumatic
shock (eg, skin test anergy, decreased T4-T8 ratios, decreased blastogenesis) and are
correlated with undesirable clinical outcomes (44, 50).
Red blood cell mass. A consistently decreased red blood cell volume on the order
of 1 percent per day in flights up to 10 days was noted by American and Russian
investigators after spaceflight (32). Reduced red blood cell mass on
return to Earth has been labeled the anemia of spaceflight; a maximum decrease
is reached at 40 to 60 days of spaceflight (21, 36, 40, 51). The mechanism seems to be
related to normal destruction of red blood cells with suppressed
erythropoiesis, as indicated by reticulocytopenia, erythroid hypoplasia of the
marrow, and erythropoietin levels in microgravity of 31 percent of preflight
values (32, 51). These changes likely reflect physiologic adaptation to
polycythemia induced by blood volume shifts soon after leaving earth's gravity
(32), but they leave the person with less reserve to undergo and survive a
hemorrhagic injury.
Respiratory system. The respiratory system could benefit from a weightless
environment. The lung is exquisitely sensitive to gravity, which induces large gradients in
blood flow, alveolar size, ventilation, and gas exchange (29, 52). Microgravity experiments
during parabolic flight and spaceflight have shown that topographic differences of lung
expansion, ventilation distribution, and pulmonary blood flow are reduced, as expected, but
not abolished (52-56). Lung
volume measurements also revealed the average functional residual capacity
(FRC), expiratory reserve volume, total lung capacity, residual volume, and inspiratory vital
capacity, reduced from 1g standing volumes (57). These changes
are likely a result of a cranial shift of the diaphragm because the abdominal
cavity is no longer pulled cephalic by gravity (some more than others), increased
intrathoracic blood volume, and more uniform alveolar expansion (57).
In injured patients, these same lung volumes in microgravity were increased over
the corresponding supine values (57), which reflects the usual positioning of
critically ill and postoperative patients on Earth. Aboard the SLS-1, the average FRC and
expiratory reserve volume in microgravity were 650 mL and 850 mL
increased over those measured in the 1g supine posture (57). So, while supine
lung volumes in space would not match peak standing values before spaceflight,
the lung volumes in space would be greater than those found in the supine
position on Earth.
Closing capacity designates lung volume below which dependent airways begin to close,
with resultant air trapping in small airways (58, 59). Functional
residual capacity designates lung volume at the end of a normal tidal expiration.
Postoperative respiratory failure in the terrestrial environment has been associated with
lung closing volumes below FRCs. Reduced FRCs are associated with increased age, smoking,
obesity, general anesthesia, thoracic and abdominal operative procedures, and supine
positioning (59, 60). When the tidal breathing range is wholly or party below the closing
capacity, dependent airways remain closed, resulting in perfusion to inadequately ventilated
lung units or even development of shunting (56, 58). Shunting causes hypoxemia that is
difficult to treat by using only supplemental oxygen. With an increased postoperative FRC in
space, many of the well-known hazards of supine positioning in the treatment of critically ill
patients (eg, increased atelectasis, ventilation and perfusion mismatch, increased shunting)
(60), could be ameliorated.
Musculoskeletal system. Loss of bone density during microgravity persists
throughout flight and seems to be proportional to the duration of exposure, without a
self-limiting plateau (21, 30, 39). This loss of bony mass, which can reach 5 percent per
month in certain weight-bearing bones (11, 26), would increase the risk of fractures (3, 30),
and visceral injury. In blunt thoracic trauma, rib fractures are the most common injury (61).
Loss of the protection of the rib cage would increase the degree of injury to viscera, such as
the liver, spleen, lungs, and mediastinal structures, that are normally protected by the
axial bony skeleton.
WOUND HEALING Wound healing and tissue repair are crucial for recovery from traumatic injury and
from operative interventions necessitated by trauma. Preliminary investigations of certain
aspects of tissue repair in microgravity suggest that many changes have not been fully
defined (4). Histologic and tensiometric analysis of full-thickness abdominal skin incisions in
rats flown aboard the space shuttle Endeavour revealed greater inflammatory responses,
increased fibroplasia, abnormal arrangements of collagen fibers, reduced stress at maximum
load, and a reduced Young's modulus compared with the findings in ground-based controls
subjected to otherwise similar flight conditions (Bolton and colleagues' [62], unpublished
observations). Sears and Argenyi have briefly reviewed pertinent studies and discussed
alterations in macrophage, fibronectin, and collagen composition in microgravity (43). Bone
healing in rat models flown aboard Soviet spacecraft was impaired, with reduced callus
formation and reduced angiogenesis (63, 64). Rat studies conducted in space and on Earth
with prolonged head-down bed rest also revealed disruptions in the microvasculature of
injured muscles, with a paucity of recognizable capillaries (65), suggestions of less organized
muscle repair, and delays in the repair process (66). Wound healing and tissue repair remain
a crucial area requiring more study.
HEMORRHAGE In addition to the microgravity-induced changes occurring in healthy astronauts,
microgravity would affect the mechanisms of injury. The characteristics of hemorrhage
would be different during weightlessness. With external bleeding in microgravity, surface
tension and Newton's first law of motion (a body in motion continues in motion unless
disturbed) seem to be the predominant physical forces acting on shed blood (8, 11, 20, 67).
Most intraoperative bleeding results in fluid domes that remain at the site of bleeding or
adhere to adjacent objects, such as gloves and instruments, rather than free bleeding (20,
26, 68). Particularly brisk arterial bleeding occasionally forms streams of droplets that travel
until reaching a barrier, but more often forms large fluid domes at the source of the
bleeding (11, 26, 67-69). Studies of operative procedures in microgravity have shown
subjective increases in the force and volume of venous bleeding compared with that at 1g
(67,70).
MICROBIOLOGIC CHANGES Bacterial infection can be a major cause of morbidity after any traumatic injury, but
trauma during spaceflight may substantially increase the infectious risk. The airborne route
of infection may be a relatively greater cause of wound contamination and infection than it
is on Earth. The closed environment of a space station may be susceptible to overgrowth by
potentially harmful bacteria (26); without the settling effect of gravity, these bacteria could
contaminate open wounds sooner than in the terrestrial environment. Larger airborne
particles normally settle quickly, a function of gravity (71, 72). Airborne microorganisms are
known to be associated with large airborne particle size (8, 71). In microgravity, instead of
settling, all particles remain airborne unless constrained by a surface, such as an open
wound or mucous membrane (73). Particle count specifications for the planned space station
Freedom were still 5 to 10 times those observed in terrestrial operating rooms, despite
planned filtering and air quality systems (8). Growth rates of bacteria have been reported in
some spaceflight investigations as greater than those of terrestrial controls (74, 75). During
spaceflight, lower efficacy of antibiotics, with higher minimal inhibitory concentrations have
been reproducibly noted for Escherichia coli and Staphylococcus aureus (74,
76-78). Substantial increases in the thickness of the cell wall also occur during an infection
with S. aureus (76). Bacteria collected on the bodies of crew members during the
Apollo-Soyouz Test Project exhibited a pronounced antibiotic resistance compared with
preflight and postflight collections (77). In an operative environment or in a wound, more
physically larger particles and more pathogenic microorganisms may be present. These
possibilities are concerning because conservative or modified therapeutic approaches to
many potentially surgical conditions presuppose effective antimicrobial action.
PREOPERATIVE RESUSCITATIVE CARE Resuscitation, preoperative, and postoperative care in space can be expected to follow
the same principles established for terrestrial medicine, with allowances for
equipment-related and environmental factors. The most current specifications for the
international space station mandate the ability to comply with the standard resuscitative
guidelines of basic life and basic cardiac life support, advanced cardiac life support, and
advanced trauma life support courses (1, 79). Simulations performed aboard the KC-135
have demonstrated the ability to perform endotracheal intubation, mechanical ventilation,
and cardiopulmonary resuscitation, to obtain intravenous access and infuse fluids and
medications, and to insert urinary and nasogastric catheters into training mannequins (26).
Splinting and casting limbs was possible but somewhat more difficult under weightless
conditions (26). In parabolic flights since 1992 in the same aircraft, while investigating actual
operative procedures in microgravity, Campbell and colleagues used live animal models (67).
They demonstrated the feasibility of mechanical ventilation, intravenous anesthetic
techniques, central arterial and venous and intracerebral pressure monitoring, and urinary
bladder catheterization (67) (M. R. Campbell, MD, unpublished data, 1996.)
ANESTHESIA FOR OPERATIVE PROCEDURES Local and intravenous anesthetic agents are the preferred method of delivering
anesthesia for major emergency operations in space (3, 11). Standard anesthetic gas
machines and spinal anesthetics require gravity. Inhalational anesthetics typically require a
liquid-gas interface for adequate provision of anesthesia, and spinal anesthetics require
accurate control of the dermatome level, both functions of gravity (3). Furthermore, leakage
of gas into a closed environment could not be permitted (3, 11, 25). Regional and epidural
anesthetic techniques are theoretically possible (38), but would likely be limited by the
absence of an operator skilled in their use and by the inherent limitations of these methods
in abdominal and thoracic operative procedures. The adequacy of an intravenous anesthetic
based on barbiturates, benzodiazepines, and narcotics administered by trained personnel
during operative interventions performed on animals in microgravity aboard the KC-135
aircraft has been reproducibly demonstrated (2, 67).
PHARMACOLOGY Reviews of the pharmacodynamics (80), pharmacokinetics (81), and bioavailability (82)
of medications in microgravity stress the limited investigational data available. Based on
studies in animals, increased sensitivity to benzodiazepines and barbiturates is expected in
microgravity, but a large component of this effect could be from the known decrease in
plasma volume during spaceflight (80). In astronauts, greater irregularity in acetaminophen
levels occurred during spaceflight than during preflight, possibly because of
microgravity-induced changes in gastrointestinal function (83). Irregular pharmacodynamics
and the requirement for higher minimal inhibitory concentrations to treat bacterial
infections are concerns (73). If mission constraints and reduced surgical capability prompt
reliance on nonoperative or limited operative therapy for conditions that would require
operative treatment on earth, the optimal dosage of therapeutic agents will be
imperative.
SURGICAL PREPARATION AND CONTAINMENT Maintenance of sterile technique will be essential with potentially larger numbers of
antibiotic-resistant bacteria (on the skin of astronauts, in the environment in which the
wounds occur, and in the atmosphere); potentially weakened host-immune defenses; and
limitations in surgical capability, instrumentation, and assistance. Fortunately, investigations
conducted aboard the KC-135 have demonstrated the ability to gown, glove, and drape an
operative field and surgical team (11, 26). Antiseptic agents in routine clinical use in
terrestrial operating rooms have surface tension characteristics that permit their use in
microgravity (3).
Several versions of the surgical overhead canopy (SOC) with laminar airflow capabilities
have been demonstrated in parabolic flight for containment of body fluids and isolation of
violated cavities and organs from environmental contaminants (67, 84). Mutke found a
contained transparent plastic surgical container intended for space use satisfactory for
childbirth on earth (85). Campbell and associates used an SOC equipped with laminar airflow
in 1991 experiments during abdominal operations in rabbits and found that it protected the
cabin atmosphere from contamination, controlled stray instruments, and helped maintain
sterility (67). They showed that because of the effect of surface tension, local methods, such
as cautery and the use of sponges and specially designed suction devices, effectively
controlled most intraoperative bleeding, without using an SOC. The exceptions were cases
associated with large arterial droplet streams, purulent wounds, or when large amounts of
irrigation fluid were required (67). Because these factors are likely to be encountered during
operative treat<%1>ment of trauma, an SOC-type device may be required.
SURGICAL INVESTIGATIONS Although no operative procedures have been required in space, the United States and
the former Union of Soviet Socialist Republics have performed operative procedures in the
microgravity environment of parabolic flight (2, 25, 67). Russian investigators first performed
laparotomies on rabbits in 1967, effectively initiating the practice of microgravity surgery
(86). Satava performed a range of major abdominal operative procedures on rats submerged
and ventilated in an underwater tank while he operated from the side of the tank (20). He
noted that certain features of weightlessness were beneficial, such as the improved exposure
by evisceration of the abdominal contents, but emphasized altered proprioceptive changes,
such as "past-pointing" and decreased tactile sensation as potential problems to be
expected in microgravity (20). In 1991, Markham and Rock performed simple procedures,
such as debriding, suturing, and cleansing, in parabolic flight using laceration and burn
models (84). They reported that these procedures could be performed with ease after a short
period of acclimatization.
The same year, the first North American surgical investigations in microgravity were
conducted on a rabbit model aboard the KC-135 aircraft (67). Because of the inherent
limitations of brief (25-30 second) intervals of microgravity on the KC-135, routine portions
of the operative procedures were performed during the intervals between microgravity, and
the designated crucial portions of the procedures were performed during microgravity.
Procedures performed included exploratory laparotomy, mesenteric vein ligation and repair,
incision and repair of the renal and carotid arteries and the aorta, and closure of the
laparotomy incision (67). These same investigators later evaluated laparoscopy and
laparoscopic operative techniques and the clinical behavior of a hemoperitoneum (2). In
addition, they have evaluated thoracentesis, tube thoracostomy, thoracoscopy, thorascopic
techniques, such as pericardiotomy, and the clinical behavior of hemothorax (M. R. Campbell,
MD, unpublished data). The later studies used a larger pig model and showed that
performance of these procedures in microgravity was technically feasible and that the
standard operative procedures were no more difficult to perform than in the 1g
environment.
The ability to perform these procedures has, in part, depended on careful
attention to restraint of the patient, operators, and surgical and anesthetic equipment by
using a number of ingenious systems (2, 8, 11). The use of lasers has not been reported in a
microgravity environment, although medical lasers have been used to perform laparotomies
on rats onboard the KC-135 aircraft during 1g flight (87). Although these studies have been
essential for advancing the knowledge, techniques, and principles of operative treatment in
microgravity, the microgravity studies have all been limited by the episodic nature of the
investigational microgravity provided by parabolic flight.
MEDICAL CAPABILITIES OF SPACE CREW PERSONNEL Medical training of the personnel designated as crew medical officers onboard the space
shuttle may be only 16 to 18 hours of cursory medical training (88, 89), a clearly inadequate
level. No requirement is planned for physicians onboard spaceflights at present or in the
near future. Although an operationally experienced space expert might be trained to perform
minor operative procedures, the length of formal training needed to acquire surgical
proficiency would require the introduction of trained surgeons to the space environment
(10). Medical care onboard the space station will rely heavily on "telemedicine" technology to
provide remote expertise in management decisions (2-4, 88). By using this technology,
making an internist out of a surgeon would be easier than the converse because of the
ability to remotely transfer information but not mechanical skills (3, 11, 17). Hardware
specifications of space craft design that preclude formal operative intervention must be
addressed and overcome to support exploration beyond Earth's orbit.
OPERATIVE PROCEDURES IN EARTH'S ORBIT Prediction of the exact scope of life-saving operative procedures that might be
required onboard a space station is impossible. In a partially analogous setting, reviews of
preventable deaths in isolated and rural treatment facilities have emphasized inadequate
volume resuscitation and airway control and lack of urgent operative intervention in
treatable hemoperitoneum as the main causes of potentially preventable death (10, 90-93).
Presumably, identification of the major causes of preventable mortality on earth should set
the eventual minimum requirements for trauma care in space.
Reports reveal that only 10 percent of patients with blunt abdominal trauma with
hemoperitoneum from intra-abdominal injury remain hypotensive despite aggressive fluid
resuscitation and, thus, require urgent life-saving laparotomy (94, 95). Although complex
and devastating injuries are encountered in blunt abdominal trauma, many causes of
hemoperitoneum that is fatal if untreated, are technically easy to remedy. Splenic trauma is
the most common manifestation of blunt abdominal trauma and represents a major cause of
massive intraperitoneal bleeding that can be treated easily by splenectomy or other
operative techniques performed by trained physicians (95-97). As early as 1983, a council of
trauma surgeons, space physicians, and biomedical engineers specifically noted that if
physical and technical limitations prevented definitive management of all possible injuries,
at the minimum, capability of performing routine celiotomy onboard a space station before
any transfer to earth would be lifesaving (10). Chest injuries account for about 25 percent of
all trauma deaths, but most thoracic injuries are adequately treated by chest drainage alone
and do not require a thoracotomy (98-100). Thoracotomy is only occasionally required in
patients with ongoing thoracic blood loss or evidence of cardiac tamponade, and, in these
cases, the procedure may be lifesaving.
Current approaches in trauma care are constantly being redefined. Blunt injuries can be
successfully managed nonoperatively by skilled practitioners. Nonoperative management for
traumatic injuries that only a few years earlier would have mandated immediate operative
therapy now exists. Examples include treatment of splenic and hepatic injuries (101-103)
and contained rupture of the thoracic aorta (104). A caveat in all these cases is that the
physician managing the injury should have the experience, ability, and resources to
recognize and intervene operatively whenever stability of the patient's condition is in
question (101-103). The obvious desire to avoid potential operative complications with this
approach must be weighed against the heavy reliance of recent nonoperative approaches on
availability of accurate imaging techniques, invasive monitoring devices, and
around-the-clock experienced critical care nurses, none of which is available in space.
When operative therapy was required, it could be as abbreviated as possible,
encompassing only the procedures necessary to prevent ongoing bleeding and prevent
leakage of enteric and urinary contents. Although "damage-control" abbreviated laparotomy
was originally used for severely injured patients, demonstrating the limits of physiologic
reserve through hypothermia, acidosis, and coagulopathies (105-108), the same principles
and techniques would serve the needs of an injured astronaut who requires only
resuscitation and stabilization, to allow safe transport to definitive care on earth. Time and
labor saving techniques described include the surgical packing of hepatic or retrohepatic
venous injuries, temporary closure of the lumen of injured bowel without resection, tying off
of an injured ureter, nonanatomic stapled lung resection, balloon tamponade of bleeding
cavities and inaccessible vessels, and simple skin closure with towel clips (105, 109, 110).
These measures are expected to stabilize the condition of the severely injured patient long
enough for transport to earth for definitive operative treatment by fully equipped and
prepared surgical teams. Essential requirements would be stabilization of oxygen transport,
coagulation, and thermoregulation before reoperation (107, 111).
Minimal access surgery uses the general principle of minimizing access incisions and
permitting complex operative procedures within a closed physiologic environment (112). To
minimize operative trauma and environmental contamination, minimally invasive procedures
could also be used when deemed safe for the patient (113). Endoscopic investigations may
play a greater role in space trauma if standard imaging devices are unavailable, such as
computed tomographic and ultrasonographic scans on which trauma surgeons have relied so
heavily. Endoscopic techniques will also protect the patient from environmental
contamination and will protect the environment from contamination by the patient (2).
Endoscopy, laparoscopy (114-117), and thoracoscopy (98, 100, 118, 119) are increasingly
discussed as investigative and therapeutic tools. Laparoscopy and thoracoscopy have been
termed cavitary endoscopy (117). A crucial principle remains that the procedure be
converted to an open procedure if proper treatment of the pathologic condition or patient
safety is compromised by reduced exposure, especially in operative treatment of trauma in
which exposure has traditionally been of paramount importance.
A distinct advantage of cavitary endoscopy over standard laparotomy and thoracotomy is
that laparoscopy (2, 113, 115, 120) and thoracoscopy (98) may be performed safely using
local anesthesia in patients in stable condition. Possible uses of laparoscopy include control
of hepatic and splenic hemorrhage, blood salvage, and diagnosis of diaphragmatic rupture
(116, 117). Possible uses of thoracoscopy include diagnosis of occult cardiac and
diaphragmatic injuries, drainage of hemothorax, and cauterization of persistently bleeding
intercostal vessels (98, 117). Intercostal vessel bleeding is among the most common causes
of ongoing intrathoracic bleeding. Jones and colleagues reported successful
electrocoagulation of intercostal bleeding in two of three patients who otherwise would have
required thoracotomy (98). Remarkably, these thoracoscopies were performed without
intubation and ventilation of the patient (98).
Operative procedures should be performed when necessary to save a life. The extent of
these procedures should be as minimal as possible, but of sufficient magnitude to provide
hemodynamic stability and prevent ongoing contamination. The focus is to buy time to allow
transfer and definitive reoperation on Earth. Endoscopic procedures under local anesthetic
are desirable when feasible.
CONCLUSIONS The unique weightless environment of microgravity has produced an array of
physiologic changes that could adversely affect the ability to withstand traumatic injury.
Initial investigations into the requirements and techniques of critical care and trauma
management have been performed in microgravity environments. Planning and investigations
should continue to address the needs for basic resuscitation and operative intervention in
low earth orbit as minimum requirements for care. The principles and techniques of
emergency operative intervention will be better learned in a space research setting than if
discovered in the emergency clinical setting in response to a traumatic injury. Knowledge
gained in these investigations will allow critical care surgeons to remain intimately involved
in medical research and planning for future space exploration. With continued expansion of
exploration and eventual habitation of Earth's orbit, the lunar base, and Mars, a more
permanent medical and surgical facility may be required in space.
ACKNOWLEDGMENT We thank MO Meade, MD, Departments of Medicine and Critical Care, The
Toronto Hospital, Toronto, Ontario, Canada, for reviewing the manuscript.
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