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An astronaut en route to Mars develops severe abdominal pain, nausea, and vomiting. A fellow crew member examines him and finds significant tenderness and guarding in the right lower quadrant of his abdomen. The crew members teleconference with physicians on Earth, with a 20-minute communication delay because of the 140-million mile distance between them. The physicians confirm a probable diagnosis of appendicitis. Because the spaceship is more than 200 days away from Earth, the physicians instruct the crew to proceed with surgery and anesthesia in outer space.
Outer space medical care will certainly not resemble Dr. Leonard “Bones” McCoy on the original Star Trek, who waved his fictional handheld “tricorder” tool over a patient to diagnose and treat the patient’s illness.
How will astronauts conduct general anesthesia and surgery in outer space? Is an anesthesiologist required on board? Is a surgeon required on board? If the flight crew doesn’t include any physicians, how will the crew proceed to save the astronaut’s life?
Full disclosure: I’ve never given an anesthetic in outer space. But to date, no one else has given an anesthetic to a human in outer space either. Protocols regarding how to accomplish anesthesia in outer space exist in the medical literature.
For comprehensive reading I’d refer you to three papers by expert Matthieu Komorowski MD, an anesthesiologist, intensive care physician, and biomedical engineer at Imperial College London, and a former Research Fellow at the European Space Agency. Three of Komorowski’s key articles are: “Anaesthesia in outer space, the ultimate ambulatory setting?” in Current Opinion in Anaesthesiology; “Fundamentals of Anesthesiology for Spaceflight,” Journal of Cardiothoracic Vascular Anesthesia, and “Potential Anesthesia Protocols for Space Exploration Missions” in Aviation Space Environmental Medicine.
Distant space missions, known as exploration class missions (e.g. missions to the Moon and Mars) are planned in the coming decades. Staffing an astronaut/physician as one of the crew members on a mission to Mars is possible, but I have no information that the National Aeronautics and Space Administration (NASA) is grooming a combination astronaut/anesthesiologist at this time. In 2017, NASA created an Integrated Medical Model (IMM) as an evidence-based decision support tool to assess risks and design medical systems for extended space travel. The IMM includes 100 medical conditions that might commonly occur during space flight. Twenty-seven of these 100 conditions would require surgical treatment.
The most significant medical risks for space exploration missions are trauma, hemorrhagic shock, and infections. The risk of a medical emergency in space travel is estimated at one event per 68 person months. For a crew of six on a 900-day mission to Mars and back, at least one medical emergency would be expected. On a mission to Mars, the option of a stat return to Earth is impossible. Telemedicine can provide remote communication for medical consultation. While telecommunication between the Moon and Earth would have delays of only 2 seconds in each direction, for a Mars mission the delay in communications could reach up to 20 minutes in each direction, making real-time telemedicine impractical. The communications delay on a Mars mission would also mean that a surgical robot on board could not be controlled by a surgeon on Earth. The crew must be self-reliant.
Only physically and mentally fit candidates who are able to withstand the stresses of space travel are selected as astronauts. Physically and mentally fit candidates are at low risk for medical or surgical emergencies. But with the recent trend of privately funded space programs (e.g. SpaceX), some members of the general public may be offered the opportunity to experience space travel. Privately funded programs may push boundaries regarding the undesirable health status of candidates traveling into space.
PHYSIOLOGIC CHANGES IN SPACE
To devise safe anesthetic care for outer space, one must first understand the changes in an astronaut’s body during microgravity. The void of outer space provides a lack of barometric pressure, a lack of oxygen, severe extremes of temperature, and dangerous levels of radiation. Spacecraft are equipped with Environmental Control and Life Support Systems (ECLSS) to ensure livable conditions within the space capsule. Weightlessness and microgravity cause marked changes in human physiology, described by systems as follows:
Microgravity causes fluid to redistribute toward the upper half of the body, resulting in facial and airway edema (swelling), and diuresis (increased urination) which leads to an intravascular volume decrease of 10-15%. The systemic vascular resistance in the arterial system decreases about 14% because of dilatation of the blood vessels, but the left ventricular systolic function of the heart is maintained near normal.
Weightlessness causes a combination of decreased gastric motility and increased gastric acidity. If an astronaut requires general anesthesia, one must assume the patient has a full stomach and is at risk for aspiration.
Microgravity leads to an increase in respiratory rate and a decrease in tidal volume, resulting in near normal ventilation.
Microgravity interferes with inner ear function, and causes disturbances in balance and vestibular function. Constant exposure to artificial lighting alters sleep rhythms, and predisposes the crew to impaired mental acuity and depression.
Weightlessness and inactivity cause an increase in bone resorption. Bone density decreases by about 1% per month, which predisposes astronauts to long bone fractures and kidney stones secondary to increased calcium excretion. Prolonged microgravity leads to deconditioning of the muscular system with skeletal muscle atrophy. This is most marked in the lower body, as the legs become “effectively redundant.”
REGIONAL ANESTHESIA VERSUS GENERAL ANESTHESIA
Every anesthetic, regional or general, will require the patient to have an intravenous line, usually in their arm. Astronauts will be trained in the insertion of IV cannulae, and the sampling of blood for diagnostic tests. Storage of prepackaged intravenous fluids can occupy a large volume of precious cargo space. An exploration class mission may require up to 100 liters of IV fluids in case of severe burn injuries. Scientists have developed a system named IVGEN (Intravenous Fluid Generation) to prepare sterile IV normal saline from space station drinking water.
Bubbles in the IV fluids are dangerous, and are filtered out by the system, because bubbles could form air emboli and cause a stroke or a heart attack if they entered the body. Transfusable blood products have a limited shelf life, which makes an onboard blood bank impractical for prolonged space travel. Medical checklists will aim to ensure patient safety and help the astronauts gain familiarity with medical equipment and drugs. Medical kits on board will include a basic vital signs monitor, a mechanical ventilator, an ultrasound machine, suction, airway equipment, and a limited range of drugs with protocols regarding how to use them.
Standard patient monitoring would include ECG, non-invasive blood pressure cuff, oxygen saturation, end-tidal CO2, and temperature. Preoperative ultrasound examination can be applied for diagnostic use, the assessment of cardiac function and fluid status, and assistance in visualizing blood vessels for peripheral or central line placement.
A regional technique offers simplicity over general anesthesia, but a successful regional anesthetic requires skill, experience, training, and regular use of such skills. Studies on Earth show that an average of 20 procedures are required to reach a learning curve plateau. A practitioner must be schooled in regional anesthesia techniques on Earth prior to the space flight. The three suggested regional blocks to treat the majority of conditions expected to be encountered in space include femoral, sciatic, and brachial plexus nerve blocks. The blocks would be ultrasound-guided, and there is hope that AI-imbedded ultrasound technology will be available in the future to localize relevant structures such as nerves and blood vessels. The injection of a local anesthetic such as ropivacaine for a regional techniques carries the inherent risk of local anesthetic toxicity. The antidote for local anesthetic toxicity is lipid emulsion, which could occupy valuable space on board, and has a shelf life of only 24 months. Spinal blocks are impractical, as the use of typical hyperbaric local anesthesia such as 0.75% bupivicaine has not been investigated in microgravity to date.
General anesthesia has the advantages of a quick and reliable onset. The physiologic changes during microgravity predispose a general anesthesia patient to both aspiration of stomach contents and hypotension due to low intravascular volume. Each general anesthetic would require a preinduction loading with intravenous fluid replacement, followed by a rapid sequence induction and endotracheal intubation. In the absence of gravity, restraints will be required to keep the patient immobile for intubation.
Potent anesthetic gases such as sevoflurane cannot be used in outer space, as vaporizers will not function properly in microgravity. General anesthesia will include intravenous medications only. Ketamine will be the preferred drug of choice for induction of general anesthesia, as spontaneous respiration and cardiovascular stability are maintained. Ketamine induces both a dissociative state and analgesia, and has an extended shelf life of around 20 years in powder form. It’s currently used in remote locations on Earth where there is limited equipment and monitoring (e.g. combat anesthesia in low-income countries). The unpleasant psychomimetic side effects of ketamine are negated by the co-administration of an IV benzodiazepine such as midazolam or Valium. Intravenous atropine will also be administered to minimize the increased oral secretions produced by ketamine.
A muscle relaxant/paralytic drug is recommended to facilitate endotracheal intubation. Succinylcholine will not be used because of its ability to cause hyperkalemia. Rocuronium at a modified rapid sequence dose of 1mg/kg is recommended. A checklist and a PowerPoint presentation on the sequence of drugs and procedures needed to initiate general anesthesia will be available for the astronauts to read prior to and during the administration of general anesthesia. A video laryngoscope will be available, as it is recognized as an easier technique for inexperienced practitioners to complete successful endotracheal intubation. A publication by Komorowski and Fleming, “Intubation after rapid sequence induction performed by non-medical personnel during space exploration missions: a simulation pilot study in a Mars analogue environment,” demonstrated that intubation can be done by non-medical staff with little or no training via instructions from PowerPoint slides.
An intravenous infusion of ketamine is recommended for the maintenance of general anesthesia. Opioids are unlikely to be carried on a spacecraft. It’s likely the analgesic effects of ketamine will be used for acute pain relief. Sugammadex will be available to reverse the neuromuscular blockade from rocuronium, and neuromuscular monitoring will be utilized prior to extubation.
SURGERY IN SPACE
Restraining the surgeon, the patient, and the surgical tools against floating around the room in zero gravity are challenges to overcome in outer space. Magnetizing the surgical tools so they stick to the operating room table, and restraining the astronaut/surgeon and the patient are important adjustments. Surgery involving anesthesia was successfully performed on rodents for the first time in 1990 on the STS-90 Neurolab Space Shuttle. Astronauts repaired rat tails and performed laparoscopy on rodents in microgravity. It’s possible that insufflation of the human abdomen with carbon dioxide gas during laparoscopy in microgravity may cause changes in cardiac or respiratory function. During open abdominal surgery in microgravity, a patient’s intestines would float around and could obscure the view of the surgical field. Because of the large array of surgical equipment necessary for any specific surgery, a 3D printer on the spacecraft may be the solution to create tools as needed.
Bleeding in microgravity causes domes to form around the bleeding site. The domes are held in that shape because of surface tension. Enclosed surgical chambers have been developed to protect the sterile surgical field and the cabin environment during open surgeries in zero gravity. A hermetically sealed expandable surgical chamber for microgravity is called a “surgical overhead canopy” (SOC). The surgical repair can be performed within the canopy, and the canopy prevents organs or blood from floating about the cabin.
Anesthesia in Outer Space – Conclusion
For the appendicitis case introduced in paragraph one, the anesthetic would include the IV loading of 500 ml of normal saline; a rapid sequence intravenous induction of general anesthesia using ketamine, midazolam, atropine, and rocuronium; placement of an endotracheal tube into the patient; and an IV ketamine infusion for the maintenance of anesthesia. Once the patient is anesthetized, the surgery could either proceed as an open abdomen under a sterile surgical canopy, or a laparoscopy with the abdomen remaining closed, depending on the skillset and the surgical equipment available to the surgeon/astronaut on board.
One day an astronaut will perform the first anesthetic on a human in outer space. The astronaut will most likely not be a board-certified anesthesiologist, and he or she will likely follow a PowerPoint slide show demonstrating the sequence of procedures and pharmacology for successful anesthesia. Expect the first anesthetic in space to be a tense, exciting, and dramatic event in the history of medicine.
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