Extraterrestrial resuscitation of hemorrhagic shock: fluids

Facing Trauma and Surgical Emergency in Space: Hemorrhagic Shock

Although the risk of trauma in space is low, unpredictable events can occur that may require surgical treatment. Hemorrhage can be a life-threatening condition while traveling to another planet and after landing on it. These exploration missions call for a different approach than rapid return to Earth, which is the policy currently adopted on the International Space Station (ISS) in low Earth orbit (LEO). Consequences are difficult to predict, given the still scarce knowledge of human physiology in such environments. Blood loss in space can deplete the affected astronaut’s physiological reserves and all stored crew supplies. In this review, we will describe different aspects of hemorrhage in space, and by comparison with terrestrial conditions, the possible solutions to be adopted, and the current state of the art.

Do we have the guts to go? The abdominal compartment, intra-abdominal hypertension, the human microbiome and exploration class space missions

Humans are destined to explore space, yet critical illness and injury may be catastrophically limiting for extraterrestrial travel. Humans are superorganisms living in symbiosis with their microbiomes, whose genetic diversity dwarfs that of humans. Symbiosis is critical and imbalances are associated with disease, occurring within hours of serious illness and injury. There are many characteristics of space flight that negatively influence the microbiome, especially deep space itself, with its increased radiation and absence of gravity. Prolonged weightlessness causes many physiologic changes that are detrimental; some resemble aging and will adversely affect the ability to tolerate critical illness or injury and subsequent treatment. Critical illness-induced intra-abdominal hypertension (IAH) may induce malperfusion of both the viscera and microbiome, with potentially catastrophic effects. Evidence from animal models confirms profound IAH effects on the gut, namely ischemia and disruption of barrier function, mechanistically linking IAH to resultant organ dysfunction. Therefore, a pathologic dysbiome, space-induced immune dysfunction and a diminished cardiorespiratory reserve with exacerbated susceptibility to IAH, imply that a space-deconditioned astronaut will be vulnerable to IAH-induced gut malperfusion. This sets the stage for severe gut ischemia and massive biomediator generation in an astronaut with reduced cardiorespiratory/immunological capacity. Fortunately, experiments in weightless analogue environments suggest that IAH may be ameliorated by conformational abdominal wall changes and a resetting of thoracoabdominal mechanics. Thus, review of the interactions of physiologic changes with prolonged weightlessness and IAH is required to identify appropriate questions for planning exploration class space surgical care.

Point-of-care resuscitation research: From extreme to mainstream: Trauma Association of Canada Fraser Gurd Lecture 2019

The Gurd Family surgical legacy was deeply intertwined with National service in both World Wars. My own personal research mission has attempted to emulate such service, by enhancing the tools and techniques available to facilitate point-of-care diagnosis and resuscitation in extreme and adverse environments. Our efforts involving point-of-care diagnosis/resuscitation and the telementored guidance of those remotely responding to catastrophic injury have included collaborations with National Aeronautics and Space Administration (NASA) the Canadian Space Agency, the Canadian Forces, its democratic allies, and non-governmental surgical organizations. Research has been conducted in resuscitative suites and operating theaters, research laboratories, parabolic flight aircraft, on humanitarian surgical missions, and from ski-hills and firehalls. The initial phases of these efforts involved inaugural studies in resuscitative sonography including defining the Extended Focused Assessment with Sonography for Trauma (EFAST) examination. Although the original work was commissioned for Space Medicine, generalization to mainstream practice further justifies space medicine research. Iterative steps in advancing telementored resuscitation have subsequently involved the maturation of space-mandated telementored ultrasound support (TMUS), exploration of TMUS in terrestrial clinical practice, and the creation of increasingly mobile (hand-held) TMUS solutions. Subsequently it was recognized that teleultrasound is simply one informatic dimension of remote telemedicine, and current efforts are focused in a Program known as TeleMentored Ultrasound Supported Medical Interactions (TMUSMI) of remote responders required to intervene with catastrophic trauma. While this research program has yielded many techniques and findings that have benefited mainstream terrestrial practice, these investigations are currently ongoing, and we hope to demonstrate that TMUSMI may benefit all Canadians especially those in remote areas, as well as potentially every global inhabitant without immediate access to care. Further, we propose that to fully utilize these techniques, a new specialty, that of the remote medical mentor will be required, a new specialty that will require the creation and scientific validation of its principles and techniques.

Intra-abdominal pressure effects on porcine thoracic compliance in weightlessness: implications for physiologic tolerance of laparoscopic surgery in space

OBJECTIVE

Laparoscopic surgery (LS) is envisioned as an option for spaceflight, but requires intra-abdominal hypertension (IAH) to create the surgical domain. Prolonged weightlessness induces physiologic deconditioning that questions the ability of ill or injured astronauts to tolerate IAH. On earth, IAH results in marked ventilatory embarrassment. As there has been no previous study of physiologic changes related to LS in weightlessness, we studied anesthetized pigs in parabolic flight.

DESIGN

Parabolic flight research laboratory.

SUBJECTS

Five anesthetized Yorkshire pigs.

INTERVENTIONS

Subjects were transported from an animal care facility and secured aboard an aircraft capable of generating hypergravity and weightlessness. Mechanical ventilation was performed using pressure control and positive end-expiratory pressure at 15 and 2 cm H2O, respectively; rate 12 breaths/min. Three abdominal conditions were used during LS: insufflation to produce IAH, abdominal wall retraction (AWR), and no abdominal wall manipulation (baseline). During each parabola breath by breath-tidal volumes (Vt) were recorded by a transport ventilator (HT-50 Newport Medical).

MEASUREMENTS AND MAIN RESULTS

Least square means (LS-means) of weight corrected Vt (milliliter per kilogram) by gravity (g) and abdominal condition were determined using a mixed effects model for repeated measures analysis. Increasing gravity (g) consistently reduced Vt (p = 0.0011) as did insufflation (p < 0.0001). In 1g, Vt (LS-mean 13.7, 95% confidence interval [CI]: 12.4-15.0) was relatively unaffected by AWR (LS-mean 12.8, 95% CI: 11.5-14.00), but markedly decreased by IAH (LS-mean 10.00, 95% CI: 8.9-11.1), an effect accentuated in hypergravity (LS-mean 8.1, 95% CI: 6.4-9.8). In weightlessness, Vt reduction during insufflation was near obviated (LS-mean 12.3, 95% CI: 10.6-14.1), and AWR regularly but inconsistently increased the Vt above 1g baseline (LS-mean 13.7, 95% CI: 11.7-15.8).

CONCLUSIONS

Weightlessness protects against thoracic compliance changes that are inherent in IAH during induced pneumoperitoneum in gravity. The technique-related physiologic cost of performing LS in space deconditioned astronauts should be incorporated into design concepts for space surgery systems.

Severe traumatic injury during long duration spaceflight: Light years beyond ATLS

Traumatic injury strikes unexpectedly among the healthiest members of the human population, and has been an inevitable companion of exploration throughout history. In space flight beyond the Earth's orbit, NASA considers trauma to be the highest level of concern regarding the probable incidence versus impact on mission and health. Because of limited resources, medical care will have to focus on the conditions most likely to occur, as well as those with the most significant impact on the crew and mission. Although the relative risk of disabling injuries is significantly higher than traumatic deaths on earth, either issue would have catastrophic implications during space flight. As a result this review focuses on serious life-threatening injuries during space flight as determined by a NASA consensus conference attended by experts in all aspects of injury and space flight.In addition to discussing the impact of various mission profiles on the risk of injury, this manuscript outlines all issues relevant to trauma during space flight. These include the epidemiology of trauma, the pathophysiology of injury during weightlessness, pre-hospital issues, novel technologies, the concept of a space surgeon, appropriate training for a space physician, resuscitation of injured astronauts, hemorrhage control (cavitary and external), surgery in space (open and minimally invasive), postoperative care, vascular access, interventional radiology and pharmacology.Given the risks and isolation inherent in long duration space flight, a well trained surgeon and/or surgical capability will be required onboard any exploration vessel. More specifically, a broadly-trained surgically capable emergency/critical care specialist with innate capabilities to problem-solve and improvise would be desirable. It will be the ultimate remote setting, and hopefully one in which the most advanced of our societies' technologies can be pre-positioned to safeguard precious astronaut lives. Like so many previous space-related technologies, these developments will also greatly improve terrestrial care on earth.

Emergency medicine in space

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 physician-astronauts, 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.

Emergencies in Space

Manned spaceflight is inherently risky and results in unique problems from a trauma and medical perspective. Emergency care under these special physiologic and environmental conditions calls for novel techniques for diagnosis and therapy.

The role of the vagus nerve in hypertonic resuscitation of hemorrhagic shocked dogs

Previous studies have suggested a critical role for the vagi during the hypertonic resuscitation of hemorrhagic shocked dogs. Vagal blockade prevented the full hemodynamic and metabolic recovery and increased mortality. This interpretation, however, was challenged on the grounds that the blockade also abolished critical compensatory mechanisms and therefore the animals would die regardless of treatment. To test this hypothesis, 29 dogs were bled (46.0 +/- 6.2 ml/kg, enough to reduce the mean arterial pressure to 40 mmHg) and held hypotensive for 45 min. After 40 min, vagal activity was blocked in a reversible manner (0 masculine C/15 min) and animals were resuscitated with 7.5% NaCl (4 ml/kg), 0.9% NaCl (32 ml/kg), or the total volume of shed blood. In the vagal blocked isotonic saline group, 9 of 9 dogs, and in the vagal blocked replaced blood group, 11 of 11 dogs survived, with full hemodynamic and metabolic recovery. However, in the hypertonic vagal blocked group, 8 of 9 dogs died within 96 h. Survival of shocked dogs which received hypertonic saline solution was dependent on vagal integrity, while animals which received isotonic solution or blood did not need this neural component. Therefore, we conclude that hypertonic resuscitation is dependent on a neural component and not only on the transient plasma volume expansion or direct effects of hyperosmolarity on vascular reactivity or changes in myocardial contraction observed immediately after the beginning of infusion.

Effects of crystalloid and colloid resuscitation on hemorrhage-induced vascular hyporesponsiveness to norepinephrine in the rat

BACKGROUND

We have shown previously that hemorrhagic hypotension is associated with a progressive development of vascular hyporeactivity to norepinephrine (NE). The present study investigated whether select crystalloid or colloid resuscitation fluids would ameliorate this effect.

METHOD

Anesthetized male rats were hemorrhaged to and maintained at a mean arterial pressure (MAP) of 50 mm Hg for 60 minutes. Rats (n = 7 per group) were then resuscitated with lactated Ringer's (LR), 7.5% hypertonic saline (HS) for 1 hour followed by LR (HS-LR), Hespan, or Hextend to restore and maintain MAP to 70 mm Hg over 4 hours. Additional hemorrhaged groups were resuscitated with LR to the baseline MAP (LR-BL) or received no resuscitation. A sham hemorrhage group served as controls. The responses of MAP and the blood flow of the superior mesenteric, celiac, left renal, and left femoral arteries to NE (3 microg/kg administered intravenously) were measured at BL (prehemorrhage); at the end of the hypotensive period; and at 1, 2, and 4 hours after resuscitation.

RESULTS

Hemorrhagic hypotension significantly (p < 0.01) reduced the NE-induced pressor response in MAP and significantly reduced the contractile responses (reflected by the reduction of blood flow after NE administration) of the four arteries to NE. Hespan and Hextend infusion improved the NE response of MAP and the contractile responses of the observed arteries to NE significantly better than LR, HS-LR, or LR-BL. The colloids improved the vascular contractile responses to NE in the superior mesenteric and left femoral arteries and the pressor response of MAP to NE, to 80% to 90% of their basal response level compared with 40% to 60% with the crystalloid fluids (p < 0.05). LR-BL infusion resulted in hemodilution, with no added benefit to vascular responsiveness.

CONCLUSION

These data suggest that hypotensive resuscitation to 70 mm Hg with colloids was better than crystalloids in improving vascular responsiveness to the pressor effects of NE and required smaller volumes. Normotensive resuscitation with LR was not better than hypotensive resuscitation. Not all vasculatures improved equally after fluid resuscitation.