The combination of an ongoing global increase in airline passengers and an aging population with more comorbidities means increasing numbers of patients with preexisting medical conditions are traveling by air.  Basic knowledge of how to assess fitness to fly on commercial airlines and how to respond to inflight medical events is therefore of increasing relevance to clinicians.
Space medicine is the practice of medicine on astronauts during spaceflight and involves the prevention and treatment of common illnesses in space. Stressors unique to space include effects of microgravity, spatial confinement, and limitations of remote help. There is a strong emphasis on prevention and preflight screenings because of limited medical equipment, diagnostic capabilities, and medications during spaceflight.
- Clinicians may be asked by the airline to provide a “Medical Certificate” regarding their patient's fitness to fly.
- The International Air Transport Association (IATA) recommends that such certificates be regarded as advisory only, with the airlines' own medical representatives ultimately being responsible for deciding whether a passenger is permitted to fly. This is because clinicians who are not specialized in aviation medicine are unlikely to be fully familiar with either the particular medical concerns of air travel or the medical capacities onboard, and medical clearance procedures differ significantly between airlines and internationally. 
- While this section outlines key areas to consider when assessing fitness to fly, concerns should always be discussed with the airline's designated medical representatives.
- Preexisting medical conditions: potential inflight deterioration; limited inflight emergency medical resources (see “Inflight medical events”)
- Medications: dosage, timing, potential disruptive effects of travel
- Patients should be advised to carry medications and basic medical records (e.g., medication schedules) in their hand luggage.
- Need for assistance or special services such as wheelchairs, stretchers, lifting services, special meals, special seating, early boarding, and supplemental oxygen
- Public health concerns (e.g., communicable diseases, vaccination status)
Relevant systems and conditions
|System-based approach to preflight screening |
|System||Key conditions/events||Pathophysiology||Investigations and patient advice|
|Communicable diseases|| || |
|Endocrine|| || |
|Psychiatric|| || |
|Surgical|| || |
|Otolaryngological|| || |
|Miscellaneous|| || |
Although inflight medical events (IFMEs) are relatively rare, there is a realistic chance that clinicians will have to provide onboard medical assistance within their lifetime. IFMEs pose a special challenge because of limited patient information and medical equipment, confined space, language barriers, and legal uncertainties.
Incidence of IFME 
- 1 per 604 flights
- 24–130 per 1 million passengers.
- Aircraft diversion (i.e., landing of the aircraft at a destination other than the scheduled one because of a medical emergency) occurs in ∼ 4.4% of IFMEs. 
- Mortality from IFME: only 0.3% of IFMEs result in death 
Risk factors in the cabin environment for an IFME
- Low cabin pressure: Reduced air pressure leads to an expansion of gases in closed gas or air containing compartments of the body (e.g., sinuses, middle ear; nonphysiological spaces such as pneumothorax or postsurgical gas collections).
- Low partial pressure of oxygen: Mild hypoxia (blood oxygen saturation ∼ 90%) leads to compensatory hyperventilation and tachycardia.
- Immobilization: hydrostatic edema of the lower limbs
- Low cabin air humidity: In combination with hyperventilation, this can precipitate dehydration or exacerbation of respiratory conditions.
Most common IFMEs 
- Syncope or near syncope (30%): see “Differential diagnoses” in “Syncope”
- Gastrointestinal symptoms (15%): see “Nausea and vomiting”, “Dyspepsia”, and “Diarrhea”
- Respiratory symptoms (10%): see “Dyspnea”, “Bronchospasm”, and “Asthma”
- Cardiovascular symptoms (7%): see “Acute coronary syndrome”, “Overview of cardiac arrhythmias”, “Chest pain” and “Dyspepsia”
- Stroke or stroke-like symptoms (5%): see “Stroke”
- Seizure (5%): see “Seizure disorders”
- Trauma (5%): see “Management of trauma patients”
- Psychiatric symptoms (3%): see “Panic disorder” and “Specific phobia”
- Substance abuse or withdrawal (3%): see “Substance-related and addictive disorders”
- Allergic reaction (2%): see “Anaphylaxis”
- Obstetric emergencies (1%): see “Childbirth” and “Antepartum hemorrhage”
- Cardiac arrest (0.2%): see “Cardiopulmonary resuscitation”
General considerations for IFME management
Ground-based medical support 
- Many airlines work with ground-based physicians who are trained in aviation and emergency medicine. These physicians are contacted via radio or satellite telephone by the pilot and can provide guidance to medical volunteers or cabin crew in case of IFMEs.
After the flight crew requests medical assistance:
- Assess your capability of helping the patient. Did you consume alcoholic beverages or take medications that might impair your judgment?
- Introduce yourself to the cabin crew and describe your medical qualifications.
- Some airlines require proof of medical license.
- Ask for a medical emergency kit.
- Introduce yourself to the patient in a calm manner.
- Obtain the patient’s consent if possible; crew members can serve as witnesses.
- Communication may be difficult due to language barriers. If a language interpreter is needed, consider patient privacy.
- Take patient history, perform a focused physical examination, and obtain vital signs.
- Administer treatments (in coordination with ground-based medical support if available and within your expertise).
- If the necessary medication is not included in the airplane emergency kit, ask the patient if they have their own medications. Consider asking other passengers if the patient does not have medications with them.
- Ensure proper positioning of the patient: seated if possible, but if there is impaired consciousness or the condition is potentially life-threatening, supine in a more spacious area such as the kitchen or lavatory area, to allow any necessary resuscitative measures
- Discuss your assessment with the pilot and ground-based medical support and recommend aircraft diversion if the patient is critically unwell.
- Provide care until the patient is stabilized or you are able to transfer care to other medical personnel.
- Document your medical assistance (some airlines provide standardized forms).
A pulse oximeter reading of ∼ 90% is normal at standard cabin air pressure.
Auscultation will likely be more difficult due to the noise and vibration of the aircraft.
Aircraft diversion 
The pilot makes the ultimate decision to divert the aircraft. All other personnel involved, including ground-based physicians, flight staff, and medical volunteers onboard, act in a purely advisory capacity. Volunteer care providers are not usually knowledgeable about many of the factors involved in deciding aircraft diversion (e.g., medical capabilities of the nearest airports, operational risks of landing at particular sites).
Contents of medical emergency kits 
All US airlines must have an emergency kit on board that fulfills the minimum requirements of the Federal Aviation Administration (FAA). These emergency kits include:
- Equipment for basic medical assessment, hemorrhage control, and intravenous fluid and medication administration
- Medications to treat common medical conditions, including severe symptoms (e.g., mild pain, allergic reactions, bronchoconstriction, hypoglycemia, dehydration, certain cardiac conditions)
- An automated external defibrillator
- Some airlines provide a wider selection of devices and medications. Common supplementary devices and medications include a glucometer, urinary catheter, antiemetic and anticonvulsant medications, and an expanded selection of analgesic and cardiac medications.
- Oxygen bottles available on commercial aircraft usually provide an oxygen flow of 2 L/min (low) or 4 L/min (high). Oxygen supplies may not be sufficient for the full duration of the flight, even for a single passenger.
|FAA-mandated medical emergency kit|
| || |
Pulse oximetry equipment is not mandated by the FAA!
Legal considerations 
- In general, the country under which the airline operates has jurisdiction.
- In the US, Canada, England, and Singapore, physicians are not legally bound to provide medical assistance unless there is a preexisting physician-patient relationship. In contrast, Australia and many European, Middle Eastern, and Asian countries have laws that require physicians to help in case of medical emergencies.
- Legal liability:
- In the United States, clinicians providing medical assistance are protected from legal liability by the Aviation Medical Assistance Act (i.e., “Good Samaritan” law), except in cases of gross negligence or willful misconduct.
- Some international airlines provide “declarations of assumptions of legal liability” to protect medical volunteers from legal action.
- In practice, the risk of legal action after inflight medical assistance is minimal.
- Clinicians who provide medical assistance should not be under the influence of alcohol, illicit drugs, or sedating medications.
- Basic first aid and CPR/AED training for the cabin crew is required in the US.
In practice, the risk of legal action after inflight medical assistance is minimal.
|Common complications of space travel  |
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|Cardiovascular|| || |
|Immune system|| || || |
|Vestibular|| || |
|Visual|| || |
|Neurologic|| || |
|Multisystem involvement|| || |