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The Transferrer’s Guide To The Galaxy

So - how would you transfer a patient through outer space?!
© UCL

Dr Sindujen Sriharan, Diving/Hyperbaric Registrar at the Alfred Hyperbaric Unit/ICU, in Melbourne, Australia talks us through his special interest in aerospace medicine, and what transfers in outer space look like…

This article will reference current practices of medical evacuation from the International Space Station (ISS) which resides in low-earth orbit, as seen above.

As of February 2024, 644 people have flown to space, which remains one of the most harsh, extreme and isolated environments that humans have travelled to. Astronauts inhabit the ISS which resides approximately 400km above us and is in constant orbit of Earth.

Ground Control To Major Tom…

  • It is estimated that the risk of a serious medical event which requires advanced and invasive care during a mission to be around 0.06 per person-year of flight, which corresponds to 1 event per 2.8 years for a crew of 6.
To date, there have only been three medical repatriations back to Earth, in the 1980s.
  • Governmental astronauts are rigorously screened, trained and prepared for months prior to their missions, which has reduced the risk of medical events occurring in space and the need for medical evacuation.
  • However, companies like SpaceX and Virgin Galactic have created a new demographic of space tourists – including older individuals with a number of co-morbidities.
  • This renewed interest in space travel means that an increasing number of individuals will be going into space over the next 20 years. The unlikely need for medical evacuation will become more of a reality and contingencies and medical protocols must be in place to allow the safe repatriation of these travellers.

Physiological Effects

Space Physiology & Medicine: AE Nicogossian, CL Huntoon, SL Pool – 1989
  • The austere environment of space has a number of effects on the human body, with the predominant effect being due to the loss of gravity, also known as microgravity, an understanding of which can help us predict illnesses that might occur more commonly.
  • In addition, physiological deconditioning and altered cardiovascular and respiratory dynamics can make a transfer back to Earth a lot more risky.
  • Numerous body systems are affected over different timeframes. The table below helps to summarise some of these effects:
CARDIOVASCULAR RESPIRATORY MUSCULOSKELETAL
Cephalad fluid shift: 1-2L from capacitance vessels into thorax, neck and face Increased RR (9%) but reduced VT (7%). Overall minimal change to MV Increased bone resorption and attenuated response to bone formation
CO increases earlier by up to 30% with SVR reduced by 24% to maintain MAP and HR Initial 5% reduction in VC, FRC reduced by 500ml, RV reduced by 18% Regional bone loss of over 1% per month
Cardiac atrophy – up to 9% reduction in LV mass related to mission duration Increased abdominal compliance thus increased abdo breathing (from 38% to 50%) Regional reductions in muscle mass – quadriceps and soleus/gastrocnemius
Reduced plasma volume (12-15%) and reduced red cell mass by 10% Increased AP diameter – reduced chest wall compliance Initial decline in VO2max. Over 6 months, a return to pre-flight baseline levels
Arterial baroreflex desensitisation leading to postural hypotension (upon return to Earth) Uniform pulmonary perfusion and ventilation with improved gas exchange  
Increased SNS activity with increased catecholamine release Reduced deposition of particles but in different locations in the airway tree  
Space Associated Neuro-ocular syndrome (SANS)    

There’s A Starman Waiting In The Sky…

  • Common minor conditions like headaches, space motion sickness (yes!) and back pain can be treated on the ISS. However, more serious pathologies like appendicitis or a clinically deteriorating astronaut, warrant urgent medical transfer back to Earth.
  • At its most efficient, this ‘scoop and run’ technique still takes approximately 3 to 6 hours for return to Earth and around 24 hours to a definitive medical care facility. Extensive logistical planning is required in combination with ground-control to ensure re-entry and landing in accordance with the orbit position of the ISS.
  • Currently, medical transfer back to Earth is carried out using the Soyuz space capsule as pictured above (more recently, the SpaceX Dragon capsule has come into use but the Soyuz remains the primary capsule for evacuation). To date, there have only been a handful of medical evacuations back to Earth; for a short-run of tachydysrrhythmia (which self-resolved prior to transfer) and prostatitis.
  • This is only really viable for relatively well patients who do not need continuous monitoring. The reduced internal size of the Soyuz of only 4m3 means that astronauts must be able to sit down and conform to the shape of the capsule, which can be difficult if they are injured or unwell.
  • There have been no critically unwell patients transferred back from space. With patients who are critically unwell and need transfer in the Soyuz, it would be very difficult for them to lie supine or for them to be monitored. They are also subject to high levels of G-forces upon re-entry to Earth which can cause significant haemodynamic and respiratory compromise leading to cardiac arrest. There has been some evidence using animal models that despite these high G-forces there is a high survivability rate, even in non-resuscitated haemorrhagic shock subjects.

Resusci-space-tion

  • Overall, all this warrants a need for an astronaut to be resuscitated and treated prior to transfer. The ability to provide adequate medical care is complicated by limited on-board equipment and astronaut skill set.
  • Astronauts are taught a number of medical procedures and protocols to ensure the safety of their team. Currently, the assigned crew medical officer (CMO) undergoes approximately 80hr of training specific to medical protocols, but they may not have a medical background beyond this point. Managing a critically ill patient may be pushing the boundaries of what they have been trained to do, even with the help of telemedicine from ground-control.
  • In addition, sending a second astronaut to accompany the unwell individual renders an already-small team on the ISS potentially unable to continue their mission.
The provision for resuscitation and critical care onboard the ISS does exist, but it is short-lived given the finite resources available.
  • The current US medical kit used on the ISS comprises numerous sub-kits used for a range of examinations and procedures. There are over 190 medications which include ketamine but no other anaesthetic agents. Vapour anaesthesia cannot be used given the risk of contaminating the ISS environment.
  • Anaesthetic agents have been used in animal models but some studies have shown that, in conjunction with the microgravity-induced cardiovascular alterations that occur, there could be precipitous reductions in cardiac output.
  • There is approximately 12L worth of crystalloid fluid available, which must be given with a pressure bag due to the loss of gravity-facilitated fluid movement and a discerning eye towards gas bubbles that can exist diffusely throughout the fluid (as pictured).
  • An Autovent 2000 basic ventilator is also present but it is not clear how it would function under varying G-force conditions upon re-entry back to Earth.
LifePak Image (Creative Commons license)
  • In the event of further deterioration, there is a semi-automatic defibrillator available (LifePak 1000). Numerous CPR methods have also been trialled to ensure adequate chest compressions can be performed in the event of a cardiac arrest.

To Boldly Go…

  • In the early 2000s, an Assured Return Crew Vehicle (ARCV) was proposed, which would have increased space available and improved re-entry G-profiles, putting significantly less haemodynamic demand on an unwell astronaut. This may be the potential future solution, given an increasing demand for safe space travel – not only for astronauts but for commercial self-funding space tourists too.

In conclusion, medical evacuations from the ISS remain rare but are a critical aspect of ensuring the health and safety of space travellers in orbit. The process involves a coordinated effort between the ISS crew, ground control, and the various space agencies involved, but despite existing medical equipment and protocols available on the ISS it is still currently not possible to transfer a critically unwell patient from space back to Earth before adequate resuscitation back to astronaut self-sufficiency.

…and so, like many Earth-bound transfers, where is the point in space where the transfer becomes riskier than the acceptance of a likely fatal outcome without one?

REFERENCES

© UCL
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