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Emergency medicine in space
Article in Journal of Emergency Medicine · February 2007
DOI: 10.1016/j.jemermed.2006.05.031 · Source: PubMed
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The Journal of Emergency Medicine, Vol. 32, No. 1, pp. 45–54, 2007
Copyright © 2007 Elsevier Inc.
Printed in the USA. All rights reserved
0736-4679/07 $–see front matter
doi:10.1016/j.jemermed.2006.05.031
Clinical
Communications
EMERGENCY MEDICINE IN SPACE
Lowan H. Stewart,
MD,*
Donald Trunkey,
MD,†
and G. Steve Rebagliati,
MD, MBA‡
*Department of Emergency Medicine, †Department of Surgery, and ‡Medical Affairs and Quality Management, Department of
Emergency Medicine, Oregon Health and Science University, Portland, Oregon
Reprint Address: Lowan H. Stewart, MD, Department of Emergency Medicine, Willamette Falls Hospital, 1500 Division St.,
Oregon City, OR 97045
e Abstract—Recent events, including the development of space
tourism and commercial spaceflight, have increased the need for
specialists in space medicine. With increased duration of missions
and distance from Earth, medical and surgical events will become
inevitable. Ground-based medical support will no longer be
adequate when return to Earth is not an option. Pending the
inclusion of sub-specialists, clinical skills and medical expertise
will be required that go beyond those of current physicianastronauts, yet are well within the scope of Emergency Medicine. Emergency physicians have the necessary broad knowledge base as well as proficiency in basic surgical skills and
management of the critically ill and injured. Space medicine
shares many attributes with extreme conditions and environments that many emergency physicians already specialize in.
This article is an introduction to space medicine, and a review
of current issues in the emergent management of medical and
surgical disease during spaceflight. © 2007 Elsevier Inc.
mental issues throughout the development of the Russian
and United States space programs, even before Yuri
Gagarin’s first flight. To this day, the effectiveness of
each mission to space depends on the health and wellbeing of each astronaut. The first successful Apollo mission, Apollo 7, became known as the “ten-day cold
capsule” after the entire crew developed viral upper
respiratory infections. The first deaths during spaceflight
occurred in 1971 when three cosmonauts died due to
rapid decompression of the Soyuz 11 capsule during
reentry. Some of the more common medical problems
encountered include minor trauma, burns, dermatologic
and musculoskeletal conditions, respiratory illness, headache, insomnia, and space motion sickness (2). The relatively benign nature of these problems has primarily
been a function of the short duration of individual spaceflights, careful selection of healthy astronauts, medical
prophylaxis, and rigorous countermeasures to the effects
of environmental factors and prolonged microgravity.
Predicting the expected incidence and character of medical events during extended spaceflight has been difficult
due to the small number of astronauts who have completed long-duration missions. Epidemiological data extrapolated from isolated U.S. Navy submariners suggest
one mission-impacting medical event per 6-month mission with a crew of seven astronauts (3). Similar work
has predicted a major surgical case to occur every 9 years
and acute appendicitis every 35 years (4). As we embark
upon a new era in space exploration, in which we expect
e Keywords—space; spaceflight; microgravity; emergency
medicine; emergency procedures
“Human beings are the product of a long evolutionary process that has made us fully adapted to the Earth
environment . . . When exposed to a space environment,
the human body reaches a new homeostasis . . .” A.I.
Grigoriev (1)
INTRODUCTION
Preventive medicine and contingency planning for acute
care of the human during spaceflight have been funda-
RECEIVED: 9 March 2005; FINAL
ACCEPTED: 9 May 2006
SUBMISSION RECEIVED:
26 September 2005;
45
46
L. H. Stewart et al.
continuous human inhabitation of the International Space
Station (ISS) and eventual extended manned missions to
the Moon and Mars, illness and injuries that once were
rare will be encountered routinely, and with time, those
scenarios merely probable will become certain. Earthbased medical support services at the American Mission
Control Center and the Institute for Biomedical Problems
in Russia will be increasingly augmented by telemedicine and intelligent computational neural networks, providing assistance to low-Earth orbit missions (5). Our
ability to provide advanced medical care for acute illness
and injury and safely return our astronauts to Earth is a
prerequisite to interplanetary travel and prolonged human spaceflight beyond low-Earth orbit. Current training
for astronaut crew medical officers only includes limited
medical instruction and minor surgical skills such as
basic suturing (6). As space vehicles move farther from
the Earth’s orbit, telemetric medical support and traditional communication traveling at the speed of light will
be significantly delayed. In the case of Mars, two-way
radio contact would take a minimum of 44 min. These
longer missions will require the presence of a physicianastronaut crewmember with a wide breadth of medical
knowledge who is skilled in basic surgical procedures
and the complex medical management of the acutely ill
and injured. Pending the ultimate sub-specialization of
medical care in space, when available resources might
allow for options such as a surgical suite on a Lunar or
Martian base, the next phase of space medicine will call
for versatile medical providers with familiarity with the
whole spectrum of human disease and disability. This article serves as an introduction to some of the current issues
in acute space medicine pertinent to the emergency physician, who has the ideal background training for this
specialized position. We will discuss the basics of space
medicine and physiology, environmental factors, and
some of the issues involved with the management of
medical and surgical emergencies during spaceflight.
THE HUMAN BODY IN SPACE
“While acknowledging that three types of basic interaction (strong, weak, and electromagnetic) are the true
fundamental prerequisites for life, as a quantitatively
new, high form of existence of matter, we must also note
that the fourth type of basic interaction— gravitational—
serves as a kind of sculptor or architect of the universe,
as well as of the varied forms of life and the substrate on
which they can develop.” I.D. Pestov (7)
In the decades since the first manned spaceflight by
Yuri Gagarin, we have accumulated a tremendous
amount of data regarding the human body in space (8).
During the early years of space exploration, the study of
space medicine and physiology uncovered a myriad of
seemingly pathological changes in the human body exposed to microgravity. Because of the changes, even the
physical examination itself must be adapted to this environment (9). Over time, a new paradigm has emerged,
with the weight of evidence suggesting that these changes
reflect adaptation to a unique environmental condition
rather than irreversible pathology. Whether this will hold
true remains one of the fundamental questions of space
biology, as we await a complete understanding of the
effects of long-duration exposure to microgravity. The
longest continuous inhabitation of space was performed
by the Russian physician-cosmonaut Valeri Polyakov,
when he lived aboard space station Mir for 438 days.
Very few people have spent more than a few months in
space, limiting our ability to accurately predict long-term
health risks. A more thorough understanding of physiologic changes during extended duration spaceflight is the
prerequisite to a safe transition to interplanetary travel,
such as a manned flight to Mars.
CARDIOVASCULAR SYSTEM
The human body consists of approximately 60% fluid.
Under different accelerational, positional, and gravitational conditions, the intravascular fluid exerts variable
hydrostatic pressure on the walls of elastic blood vessels,
triggering specific responses to maintain homeostasis in
the body. Upon entering the weightless environment of
space, the absence of gravity-induced hydrostatic forces
causes a cephalad shift and equilibration of intravascular
fluid from the lower extremities to the trunk and upper
extremities (approximately 2 L). This is followed by a
transcapillary shift of fluid from the extravascular compartment to the intravascular compartment in the lower
body, and from the blood vessels to the extravascular
compartment in the upper body. Space travelers experience this as a sensation of fullness in the head, nasal
congestion, facial edema, scleral and oral mucosal injection, and decreased leg circumference (what astronauts
refer to as “chicken legs”). These symptoms decrease
over time, but remain present throughout the course of
even very long space flights. The discomfort of the fluid
shift is transiently alleviated by lower body exercise. One
astronaut reported alleviation of symptoms after meals
(presumably from the shunting of blood to the gastrointestinal tract) (10).
During the first few days of space flight, there is an
average 2.5 kg body mass loss. This is a consequence of
fluid diureses, primarily from the extracellular compartment, and decreased fluid intake. Increased central venous pressure (CVP) is thought to stimulate cardiac
baroreceptors and initiate a reduction in plasma volume,
Emergency Medicine in Space
the so-called Henry-Gauer response, but studies including in-flight central venous catheterization have failed to
demonstrate elevated CVP (11). This may be secondary
to compensatory reactions during the pre-launch period
in the supine position, and is also complicated by the
practice of astronauts restricting fluid intake days before
flight to avoid the inconvenient diuresis first experienced
by Mercury astronauts on arrival to space.
Cardiac dynamics in space have been measured directly with echocardiography and electrocardiography.
Heart rate is increased significantly during launch, orbit
entry, extravehicular activity (EVA), and reentry, attributed to cardiovascular deconditioning in weightlessness
and physical and autonomic stress (12–14). Measurements of cardiac output, stroke volume, and left ventricular end diastolic volume have not been significantly different from ground-based observations, however, some
recent data suggest decreased ejection fraction and reduction of overall cardiac function proportional to long
mission duration (15). Electrocardiography has demonstrated the presence of occasional premature atrial contractions (PAC) and premature ventricular contractions
(PVC). Observations during Space Shuttle EVA showed
that PACs or PVCs were present in 30% of astronauts at
some point during this period of strenuous activity in a
100% oxygen hypobaric environment (16). There have
been reports of electrocardiographic long QTc intervals
as well as brief episodes of ventricular tachycardia during extended spaceflights (17,18). These events may be
related in part to sympathetic tone and elevated catecholamine levels present during spaceflight (19). The ectopy
and brief dysrhythmias observed in astronauts are somewhat similar to those seen in healthy athletes during
physical stress, but are of uncertain clinical significance
in the space environment (20,21).
Upon return to Earth, there is decreased tolerance to
orthostatic stress. The cardiovascular system is unable to
maintain an adequate blood pressure in the upper body,
and symptoms of orthostasis have been observed, including diaphoresis, nausea, presyncope and syncope. G-suits
are used after landing, and measures such as exercise and
end-of-mission salt and volume loading are performed
prophylacticly. The cardiovascular system seems to respond appropriately and adequately to the physiologic
requirements of the weightless environment in space.
This new homeostatic set point becomes maladaptive
during the period of and soon after landing on Earth, but
normal function is regained over days to weeks.
ENDOCRINE AND ELECTROLYTE CHANGES
The fluid shift secondary to the reduction of hydrostatic
pressure gradients during spaceflight causes profound
47
changes in the physiologic systems regulating fluid balance. These hormone and electrolyte responses are further complicated by intimate connections with the systems involved in mineral homeostasis, which are also
perturbed by the effect of weightlessness on muscles and
bones. Over time, the initial diuresis stabilizes and urine
osmolarity is actually increased. Evaporative water loss
from sweat is decreased, even during exercise. This is
thought to be from the development of a sweat film on
the skin, inhibiting further sweating in the absence of
convective air movement. Renin, angiotensin, and aldosterone levels are elevated during spaceflight (22). Norepinephrine and antidiuretic hormone are also increased
(23). In conjunction with a “disuse atrophy” of the musculoskeletal system, spaceflight causes increased urinary
excretion of sodium, potassium, calcium, and phosphate
(24). Despite some departures from normal Earth-based
equilibrium during spaceflight, the observed changes in
the endocrine system and fluid and electrolyte balance
seem to establish a new non-pathologic steady state and
return to functionally normal values after return to the
Earth environment.
HEMATOLOGIC SYSTEM
Plasma volume and red blood cell (RBC) mass have been
shown to be decreased post-spaceflight (25). On arrival to a weightless environment, total vascular space is
reduced by the initial rapid diuresis. This results in
decreased plasma volume and increased hemoglobin
concentration, which is followed by a compensatory
decrease in erythropoietin production. An optimal equilibrium for the weightless environment is achieved with
smaller plasma volume and RBC mass. The functional
impairment of this “anemia of spaceflight” is not present
during normal spaceflight conditions, but contributes to
the orthostatic intolerance upon return to a 1 g environment (the Earth’s gravitational force at sea level g ⫽ 9.81
m/s2) during the first days to weeks after return to Earth.
A decreased reserve, however, might impair the physiologic response to hypovolemic shock in microgravity.
IMMUNE FUNCTION
Human and animal studies have described several factors
affecting the immune system during spaceflight. Altered
immune function has been linked to microgravity, hypokinesia, the neuroendocrine stress response, radiation
exposure, sleep disruption, isolation, and the effects of a
closed environment with various gases and airborne contaminants (26). Specific abnormalities in cellular immunity include alterations in leukocyte formation, cytokine
48
L. H. Stewart et al.
production, and natural killer cell activity during both
short-term and long-term flights (27–29). Down-regulation
of cellular immunity may contribute to the reactivation
of latent viral infections seen in some astronauts (30).
The question remains, however, as to what effect, if any,
these alterations have on host susceptibility to infection
or neoplasia during spaceflight (31).
motion sickness. Space motion sickness (SMS) is a subset of SAS and includes symptoms of flushing, anorexia,
nausea, vomiting, and malaise. Space motion sickness
usually begins within an hour of flight and lasts no longer
than 72 h. The incidence of SMS has been reported to be
50% and 35–70% of crewmembers based on Russian and
American experience, respectively (37). Intramuscular
promethazine is the current treatment of choice.
MUSCULOSKELETAL SYSTEM
The absence of weight loading and relative hypokinesia
in space results in muscle atony and decreased protein
synthesis (32). The tonic effect of passive stretch is also
lost. Lower extremity weight-bearing muscles important
for ambulation on Earth lose this function in microgravity and therefore undergo significant atrophy. The vertebral column lengthens up to 7 cm in space, and over
two-thirds of astronauts report low back pain (33). Like
muscle, bone is not static tissue but an active and dynamic organ involved in mineral homeostasis and hematopoiesis, in addition to providing mechanical support for
movement. In microgravity, bone mineral density in the
legs, pelvis, and lumbar vertebrae decreases by about 1%
per month, secondary to both increased bone resorption
and decreased formation (34). It is currently unknown
whether there is a ceiling to this effect by reaching a new
equilibrium during long-duration spaceflights, or if the
osteopenia will progress to become a limiting factor on
mission duration. The primary effect of lost bone mass
would be a substantial increased risk of fracture during
strenuous activity and trauma. Extensive research on
bed-rest and hypokinesia on Earth suggests that osteopenia can be countered by physical exercise, mineral
supplements, and drugs such as bisphosphonates (35).
However, data on the recovery of bone mass of astronauts upon return to a 1 g environment are sparse and
highly variable between individuals. Early development
of osteoporosis on Earth may be a significant concern
regarding mission duration.
SPACE ADAPTATION SYNDROME
Exposure to microgravity provides unique and highly
unusual stimuli to human skin, muscle, joint, visual, and
vestibular receptors. Until they can adapt to the new
environment, space travelers experience abnormalities in
movement, coordination, visual gaze, and can have illusions of motion. These physiologic responses to the
environment of microgravity have been collectively
termed space adaptation syndrome (SAS) (36). The most
acutely uncomfortable aspects of SAS are the sensory
and autonomic responses that are similar to terrestrial
SPACEFLIGHT AND
SPACECRAFT ENVIRONMENT
The closed cabin spacecraft environment is somewhat
similar to that of submarines and to large buildings with
the sealed recirculated air responsible for what is known
as “tight” or “sick” building syndrome. Even very low
levels of volatile organic compounds in recirculated areas have been shown to be deleterious to memory (38).
General factors affecting astronaut health include high
levels of physical and psychological stressors, and exposure to noise, vibration, and long periods of isolation.
Countermeasures to the development of psychological
stress include ground-based support and the performance
of multiple tasks to stay active. Sleep patterns are disturbed and shortened in duration, with altered circadian
zeitgeibers in the spacecraft environment where the Sun
appears to “set” approximately every 90 min (39).
The low barometric pressure and artificial gas composition of some spacecraft atmospheres can expose
crew to factors such as hyper- or hypoxia, hypercapnea,
lung atelectasis, altitude decompression sickness, possible explosive decompression, fire, and abnormal heat
balance. Toxic exposures are a continuous threat from
gaseous and particulate contaminants resulting from human metabolism and waste, chemicals in the spacecraft,
propellants, coolants, off-gassing from plastics, and particulate matter (which does not fall to the floor in microgravity). Shuttle astronauts in the 1980s reported mild
coughing and eye irritation from dust while exchanging
lithium hydroxide air filter cartridges. During the 1975
Apollo-Soyuz mission, an open cabin valve on reentry
exposed three crewmembers to nitrogen tetroxide and
monomethyl hydrazine. One astronaut lost consciousness; all developed chemical pneumonitis and were hospitalized with pulmonary edema (40). Table 1 lists some
potentially toxic substances of particular concern on
spacecrafts.
Space crews are exposed to significant acceleration
vector forces or “g-forces” during routine spaceflight.
Launch can achieve up to 5 g (5 ⫻ 9.81 m/s2). Descent
and landing generate 3– 8 g, but steep emergency trajectories can lead to more than 20 g (41). Depending on
Emergency Medicine in Space
49
Table 1. Potentially Toxic Substances in the
Spacecraft Environment
Acetaldehyde
Acrolein
Ammonia
1,3-Butadiene
Carbon dioxide
Carbon monoxide
Dichloroacetylene
1,2-Dichloroethane
2-Ethoxyethanol
Formaldehyde
Freon 113
Hydrazine
Hydrogen
Indole
Mercury
Methane
Methanol
Methyl ethyl ketone
Methyl hydrazine
Methylene chloride
Nitromethane
Octamethyltrisiloxane
2-Propanol
Toluene
Trichloroethylene
Trimethylsilanol
Vinyl chloride
Xylene
multiple factors, a force as little as 4 g is capable of
inducing syncope.
Radiation exposure is an important occupational
risk affecting virtually all of the organ systems. The
main sources of ionizing space radiation are the trappedradiation belts, galactic cosmic rays, and solar particle
events from solar flares. Significant protection from ionizing radiation is provided by the Earth’s magnetosphere
when in near-Earth orbit, but this shield is lost during
interplanetary travel. The National Aeronautics and Space
Administration (NASA) identified radiation exposure as
one of the most pressing challenges to the human space
program (42). Efforts to minimize damage include
careful navigation planning, antioxidant vitamin supplementation, and repositioning of spacecraft during
solar flares. Due to multiple confounding factors and a
small experimental population, the long-term genetic
and carcinogenic risks are unclear. For practical purposes, the current accepted risk for astronauts is a career
limit 3% increased risk of cancer mortality from space
activities (43).
MEDICAL EMERGENCIES
General Considerations
Medical equipment, supplies, and hardware selected for
use in space must fulfill rigorous specific characteristic
requirements based on the remote, isolated, and dangerous environment (44). There are significant space, power,
and weight constraints, as well as formative launch costs
to put supplies in orbit (approximately $20,000/kg). With
the Space Medicine and Healthcare Systems Office,
NASA Medical Operations continues to define the optimal training and equipment required for spaceflight.
Since Normand Thagard became the first American physician to fly in space, approximately 20 physicians have
flown. Despite requests from many of the NASA Medi-
cal Operations staff to include physicians in the ISS
crew, the crew medical officer currently receives only 20
or 60 h of medical training to serve on the Shuttle and
ISS, respectively (analogous to the training of an independent duty corpsman on small naval vessels). As such,
the Space Shuttle and ISS are equipped for only minor
procedures and basic medical treatment using the supplies manifested on the Shuttle Orbiter Medical System
and the ISS Crew Health Care System (45). Table 2 lists
examples of the types of oral and parenteral medications
currently available. Longer and more remote missions
will require more intensive medical training for crew
medical officers as well as the other astronauts, who may
need to assist during a medical emergency.
Imaging
Ultrasonography is currently the clinical imaging modality of choice for spaceflight, and is integrated with remote telemetry on the ISS. The equipment is light and
useful in a broad range of clinical situations. Unlike
radiography, ultrasound images are not affected by the
ubiquitous space radiation. Both modalities are subject to
the unique physical parameters of microgravity, i.e., there
are no air/fluid “levels” and all such familiar gravitydependent radiological signs are unavailable (46). Because ultrasound cannot penetrate bone or lung parenchyma, some form of radiography will likely be part of
any self-sufficient medical facility in space. One such
Digital Radiographic Imaging System was dropped from
the ISS design, due to the power and weight constraints
discussed previously (47).
Pharmacology
Pharmacological aids for space medicine must be selected based on their usefulness for a wide range of
indications, effective use in combination, stability in the
space environment, and the expected probability of spe-
Table 2. Typical Medications Currently Available
During Spaceflight
Acetaminophen
Ampicillin
Atropine
Dexamethasone
Diazepam
Diphenhydramine
Donnatal
Epinephrine
Erythromycin
Hydroxyzine
Cephalexin
Lidocaine
Meperidine
Morphine
Nitroglycerine
Penicillin
Prochlorperazine
Promethazine
Tetracycline
50
cific disease states. Our knowledge of pharmacodynamics and pharmacokinetics of therapeutic agents in vivo
during spaceflight is limited. What we do know suggests
that the blood levels of medications may not be predictable using Earth-based data (48). There are numerous
factors that may influence drug efficacy, including the
many physiologic changes and environmental factors
discussed previously. Another important issue is the disturbance of endogenous endocrine and metabolic circadian rhythms. As we gather more data and experience
with larger numbers of astronauts and longer missions,
an evidence-based approach for medication selection
will be desirable.
Airway
Although airway management has never been necessary
during the history of manned spaceflight, there have been
cases of aspiration, chemical pneumonitis, and smoke
inhalation. As we extend the duration of our orbital
missions and embark on interplanetary travel, airway
management during respiratory failure, anesthesia for
surgical procedures, and treatment of traumatic injuries
will be inevitable. A comparison of airway devices using
a water immersion model demonstrated no differences in
difficulty of placement of the cuffed oropharyngeal airway, laryngeal mask airway, and intubating laryngeal
mask airway, with or without stabilizing restraints (49).
Laryngoscopy for placement of an endotracheal tube was
more prone to failure during free-floating conditions.
Based on experience during parabolic flight, grasping the
head with one’s knees has been suggested as a technique
L. H. Stewart et al.
to facilitate laryngoscopy of the unrestrained patient in
microgravity (50) (Figure 1).
Anesthesia
Although there are no direct observations of anesthetic
use during human spaceflight, it is clear that astronauts
are a unique population subject to significant physiologic
and environmental stressors. Anesthetic agents in space
must therefore be used with the expectation of a hypovolemic patient with altered regulatory systems and significant skeletal muscle atrophy. It has been suggested
that after significant exposure to microgravity, induction
be performed with etomidate and midazolam to avoid the
hemodynamic effects of other agents (51). In the setting
of up to 20% muscle atrophy, succinylcholine use may
be relatively contraindicated to avoid hyperkalemia. Unlike the 100% oxygen atmosphere that caused a deadly
fire in the Mercury project, supplemental oxygen is safe
in the Earth-like atmosphere on current spacecraft. Gas
anesthesia cannot be used due to the risk of contamination of the closed-loop atmosphere in a spacecraft. More
benign nebulized medications could be used cautiously,
with attention to airflow and perhaps using a mask or
specialized hood if needed. Spinal anesthetics can flow
cephalad in weightlessness and are therefore unpredictable. Therefore, the only practical means of anesthesia in
space are local, regional, and intravenous medication
delivery (52). Simple procedures such as starting an
intravenous line and administering fluids are feasible but
have unique technical considerations in the absence of
gravity. For example, there is no air-fluid separation in a
bag of saline. In space, the air must first be removed, and
a pressurized system is necessary for flow.
SPECIFIC MEDICAL EMERGENCIES
Cardiovascular Emergencies
Figure 1. Endotracheal intubation in simulated microgravity
during parabolic flight. Used with permission from Dr. William Norfleet and Lippincott Williams and Wilkins, Inc.: (48)
Norfleet WT. Anesthetic concerns of spaceflight. Anesthesiology 2000;92(5):1219 –22.
The high incidence of ectopy, tachycardia, and other
minor dysrhythmias observed during spaceflight have an
uncertain etiology but may be related to high catecholamine levels. The predominately young and healthy crew
have tolerated these episodes, but the cardiovascular
effects of long-duration spaceflight are largely unknown.
With the recent advent of commercial space tourism,
older and less physically conditioned astronauts will be
more commonplace. Burt Rutan’s SpaceshipOne launched
the first private astronaut into space in 2004, and Richard
Branson plans to develop the ship for ticketed passengers
on the first space airline, Virgin Galactic. Eventually,
more significant and deleterious cardiac events are ex-
Emergency Medicine in Space
pected. The ISS has cardiac telemetry capability, and the
advanced cardiac life support procedures such as cardiac
defibrillation could all be performed. Cardiopulmonary
resuscitation (CPR), vascular access, intravenous fluid
infusion, bladder catheterization, and gastric tube placement have all been demonstrated experimentally in microgravity (53). Although these procedures can be performed on a spacecraft, modifications are invariably
necessary to adapt to the unique environment. For example, in the absence of gravitational assistance, conventional CPR technique is ineffective in generating
adequate intrathoracic pressure. Work with mannequins
and swine in microgravity suggests the best technique is
chest compression of a restrained patient by a rescuer in
an upside-down handstand position with arms extended
and using the knees to push off the “ceiling” of the
spacecraft (Figure 2) (54,55). Although most of the car-
51
diac changes noted in astronauts have been either transient or benign, halogenated hydrocarbons in the environment could theoretically sensitize the myocardium in
the setting of a toxic contamination. An automatic external cardiac defibrillator is currently available on the ISS
alone. The Space Shuttle cannot be used for emergent
evacuation of a critical patient because it takes more than
a month to ready the vehicle, and the currently utilized
Russian Soyuz escape capsule can take only three persons in a sitting position with no room for any cardiac or
other medical support equipment.
Infection
Despite numerous countermeasures, bacteria, fungi, and
viruses are ubiquitous inhabitants of spacecraft. Some of
the microorganisms found on spacecraft include Bacillus, Corynebacterium, Enterobacter, Escherichia, Klebsiella, Staphylococcus, Streptococcus, Aspergillus, Mycoplasma, Candida, and Penicillium. Humans are the
main source of these organisms. It has been estimated
that the average person sheds about 40 billion bacteria
daily from skin particles alone (56). All of the Apollo 11
crew reported symptoms suggestive of a viral upper
respiratory infection (57). After Apollo 13, routine preflight quarantines have significantly reduced the incidence of infectious diseases during spaceflight. Since
then, primarily minor infections such as boils, sty formation, and gingivitis have been reported (58). The depressed immune system in microgravity might result in
more serious infections on longer flights.
Extravehicular Activity and Dysbarism
Figure 2. Chest compressions in simulated microgravity during parabolic flight. Used with permission from Dr. Gregory
D. Jay and the Aerospace Medical Society: (54) Jay GD, Lee
PHU, Goldsmith H, et al. CPR effectiveness in microgravity:
comparison of three positions and a mechanical device.
Aviat Space Environ Med 2003;74:1183–9.
Since Alexi Leonov made the first “spacewalk” in 1965,
extravehicular activity (EVA) has been recognized as
one of the most strenuous space environments. Astronauts working outside spacecraft are exposed to higher
levels of radiation, increased physical workload with
deconditioned and atrophic muscles, altered thermoregulation, and hypobaria. The American space suit for
EVA is called the extravehicular mobility unit. It weighs
113 kg on Earth and is difficult to maneuver even in
microgravity. To reduce the work required to move in the
suit, the internal pressurization is kept at only about 30%
of the sea level pressure within the Shuttle. This pressure
differential creates the possibility of decompression sickness (DCS). Decompression sickness results from the
formation of gas bubbles in tissues exposed to relatively
hypobaric environments. The symptoms can be divided
into the joint and musculoskeletal pain known as the
“bends” (DCS type I), and severe pulmonary, cardiovas-
52
cular and neurologic events (DCS type II). Experimental
work in hypobaric chambers suggests an expected 17%
incidence of DCS symptoms under simulated space extravehicular activity (59). Perhaps due to the difficulty of
differentiating the musculoskeletal discomfort of working during EVA and the symptoms of mild DCS, astronauts have not reported DCS (60). Another confounding
factor is astronaut reluctance to report minor medical
problems due to concern they might not be selected for
future missions. Currently, there is no equipment available for hyperbaric therapy on the ISS. On missions out
of near-Earth orbit, a portable hyperbaric chamber could
be life-saving. Ultrasonography potentially could be used
to detect intravascular bubbles, however, the mere presence of bubbles does not define the clinical syndrome
of DCS.
Urologic Emergencies
The negative calcium balance induced by bone remodeling in space leads to increased urinary calcium. Urine
pH and citrate are reduced favoring saturation of calcium
salts and the formation of renal calculi (61). Renal colic
has occurred during spaceflight and will need to be
managed effectively both prophylactically and medically. During the Apollo 13 mission, two astronauts
developed urinary tract infections. In-flight treatment
with tetracycline was ineffective, and their urine later
grew out Pseudomonas aeruginosa (62).
Trauma and Surgical Emergencies
Although there are significant technical barriers to performing surgery in space, it is feasible. The question is,
at what point would it be necessary to have a surgical
suite. This threshold becomes lower when evacuation is
impossible in the case of interplanetary travel, and extended missions of larger numbers astronauts.
Surgery has yet to be performed during spaceflight.
One mission was nearly aborted when a cosmonaut developed right lower quadrant abdominal pain thought to
be appendicitis, but resolved as an uncomplicated ureterolithiasis (63). The likelihood of a surgical event is
expected to increase proportional to the duration of
spaceflight. Traumatic injury will be one of the greatest
risks to human space exploration, secondary to its expected incidence and the resulting impact on crew health
and mission (64).
Penetrating trauma will likely occur during EVA,
resulting in rapid decompression and death when the
space suit integrity is disrupted. This leaves blunt trauma
(also most likely during EVA) and subsequent organ
L. H. Stewart et al.
damage and hemorrhagic shock as the primary concerns
during extraterrestrial trauma. The goal of management
of traumatic injuries and other serious surgical problems
that occur during near-Earth spaceflight is stabilization
and damage control pending rapid and safe return to
Earth. The Space Shuttle and ISS are only equipped for
minor surgical procedures. In the absence of comprehensive onboard surgical capabilities, treatment of severe
traumatic injuries will focus on temporizing measures.
During long missions when return to Earth is not an
option, the most serious traumatic injuries may necessitate comfort care. British and American submarine experience has also shown that many surgical diseases can
be approached medically in remote and isolated conditions. Indeed, the current US Navy protocol for appendicitis has a 75% success rate with i.v. antibiotics (65).
This could be augmented by percutaneous ultrasound
guided catheter drainage if an abscess were to develop on
an extended mission.
Since the first report of animal laparotomy in the
experimental microgravity of parabolic flight in 1967,
much work has been done to develop the techniques,
procedures and equipment necessary to perform basic
surgery in space (66). Some of the important logistic
issues include careful restraint of the physician, patient
and supplies during weightlessness, maintenance of sterile technique, and trash disposal (67). Due to the lack of
gravity, the atmospheric particle count on the ISS is
almost 10 times that of a conventional operating room
(68). Because of surface tension and the formation of
fluid domes, hemorrhage is easily located and does not
contaminate the environment. Laparotomy, large vessel
repair and wound closure have not been found to be
significantly more difficult during weightlessness despite
the tendency of the bowels to float up against the abdominal wall (69). On the STS-90 Neurolab Shuttle
mission, astronauts working with rats demonstrated intramuscular anesthesia, dissection, hemostatis, and wound
closure to be feasible and no more difficult than in a 1 g
environment (70).
The standard advanced trauma life support (ATLS)
procedures have been demonstrated to be feasible in
microgravity, using animal models and standard equipment manifested on the ISS (71). Procedures that were
not significantly more technically difficult to perform in
microgravity than in a 1 g environment included: intravenous fluid infusion, Foley catheter drainage, laceration
closure, artificial endotracheal ventilation, chest tube insertion and suction, percutaneous tracheostomy, and crichothyrotomy. Percutaneous diagnostic peritoneal lavage
had an increased risk of bowel perforation secondary to
the bowel floating up against the anterior peritoneum in
the 0 g environment. This procedure may be replaced by
Emergency Medicine in Space
abdominal sonography for the identification of intraperitoneal fluid in space.
Because hemorrhage is the primary cause of death
from traumatic injuries on Earth, effective fluid resuscitation will likely be vital to the management of trauma
victims in space. Currently, normal saline is the only
intravenous fluid manifested on the Space Shuttle and
ISS. Hypertonic saline and hemoglobin-based oxygen
carriers may eventually replace normal saline, with the
goal of selecting therapies with the greatest efficacy to
mass ratio (72). An important consideration during extraterrestrial shock is the exposure to g-forces if emergency descent is necessary. A crew member with decreased intravascular volume already in shock might
then sustain significant secondary end-organ insult with
prolonged tissue hypoxia. Hypoxic and traumatic brain
injury could also be exacerbated by the underlying decreased cerebrovascular tone that has been noted, as well
as the inability to “elevate” the head to decrease intracranial pressure in space (73).
CONCLUSIONS
Spaceflight presents a unique and challenging medical
setting with complex physiologic changes and extreme
environmental conditions. Over the last century we have
learned a tremendous amount about human adaptation to
microgravity and the rigors of spaceflight. But this is
only the beginning of this frontier of medicine; and there
is much to learn as more humans travel to and spend
more time in space. Selection of preventive and therapeutic strategies for illness has long been driven by
Earth-based medical support. This has worked well for
near-Earth orbit missions, when consultation can be obtained, communication is relatively constant, and reentry to Earth is a viable possibility. Nevertheless, the
presence of a physician will always broaden the capabilities of in-flight medical care independent of the availability of ground support. As we explore further into our
solar system, ground-based medical support will no
longer be possible when acute medical decision-making
is required and return to Earth is not an option. Pending
the permanent inhabitation of space stations or lunar
bases with sub-specialized physicians and advanced surgical equipment, a broadly trained physician will be
needed with a diverse range of medical and surgical
capabilities. Emergency physicians possess these diverse
skills and would be well suited to fill the function of a
physician-astronaut in the unique medical environment
of space.
53
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