In-flight medical events are increasingly frequent because a growing number of individuals with pre-existing medical conditions travel by air. Also new aircraft such as the Airbus A380 and the Boeing 777 LR —are now capable of extending flight times to 18�� h, therefore, an increasing number of travellers with various underlying medical conditions could face environmental and physiological changes associated with the flight. The issues are discussed in a Review on the medical issues associated with commercial flights, written by Dr Mark Gendreau, Lahey Clinic Medical Center, Burlington, MA, USA, and colleagues.
Many passengers with pre-existing cardiac, pulmonary, and blood conditions have a reduced arterial oxygen partial pressure, so reduced cabin pressure leads to further reduction of oxygen saturation in the blood. This decreases further with increasing flight times. The decreased oxygen saturation can exacerbate medical conditions. For example, a recent prospective observational study showed that 18% of passengers with chronic obstructive pulmonary disease have at least mild respiratory distress during a flight. The cabin pressure experienced at cruising altitude causes gases in the body to expand by 30%. For health passengers, this can manifest as cramping or ear trauma, but for others – for example those who have had recent surgery – air expansion can be a major problem and thus air travel should be delayed for at least 14 days after major surgery.
Overall, studies show an association between venous thromboembolism and long-haul air travel, with risk up to four-fold, depending on study methods. Risk peaks when flight duration is more than eight hours; a population-based study showed that risk started to increase when flight duration exceeded four hours. Business-class versus economy-class travel has no effect on venous thromboembolism incidence. Immobilisation has been linked to 75% of air-travel cases of venous thromboembolism, with the long-flight thrombosis study (LONFLIT) showing the greatest frequency of venous thromboembolism occurring in non-aisle seating where passengers tend to move less. Recommendations to reduce the risk of developing venous thromboembolism during air travel are based more on common sense than on evidence and include: being well-hydrated, reducing alcohol and caffeine consumption, changing positions or walking throughout the cabin, and doing periodic calf-muscle exercises to reduce venous stasis. Use of graduated compression stockings with an ankle pressure of 17�� mm Hg can reduce risk during air travel. Many doctors also seem to recommend aspirin before air travel for individuals at moderate risk of venous thromboembolism. However, because of scarce evidence showing substantial benefit, aspirin is not recommended alone as prophylaxis for any air traveller.
Jet lag, or a disruption of the body's day night cycle, is a phenomenon that affects many passengers. Travellers have greater difficulty falling asleep after an eastward travel than after a westward travel because of the internal clock's natural tendency to resist shortening the 24-h day cycle. Re-entrainment (synchronisation) typically takes one day for every time zone crossed westward or 1•5 days for every time zone crossed eastward. A Cochrane meta-analysis of ten trials concluded that taking 0•5�� mg of melatonin at the desired destination bedtime is effective for reducing or preventing jet lag.
Air travellers spend long periods in enclosed spaces, which facilitates the spread of infectious diseases. Since 1946, several outbreaks of serious infectious diseases have been reported aboard commercial airlines, including influenza, measles, severe acute respiratory syndrome (SARS), tuberculosis, food poisoning, viral enteritis, and small pox. Risk of onboard transmission of infection is mainly restricted to individuals with either close personal contact or seated within two rows of an index passenger. Whether reducing the number of flights during a large-scale epidemic or pandemic would slow the spread of an infectious-disease outbreak remains unclear. An observational study, however, showed that the peak date of the US influenza season was delayed 13 days after the terrorist attacks of Sept 11, 2001, consistent with a greatly reduced number of flights during that time.
Many in-flight medical events arise aboard commercial airlines and most are minor. Cardiac, neurological, and respiratory complaints are the most serious in-flight medical events, with cardiac and neurological complaints accounting for most diversions. Passengers older than 70 years have the highest rates of in-flight medical events, but the mean age of passengers with an in-flight medical event is 44 years for men and 49 years for women. Medical assistance during an in-flight medical event is protected under Good Samaritan laws, and no physician has ever been held liable for his or her actions while providing medical care. Commercial aircraft have medical kits (1�� first-aid kits and at least one enhanced emergency medical kit), as required by aviation regulatory agencies. Emergency medical kits vary from carrier to carrier and can be extensively complex. Most commercial flights also carry an automated external defibrillator. Most commercial air carriers use on-ground telemedical assistance to medically assess at the gate passengers who seem unfit for travel, and to provide medical advice and support during in-flight medical events. With regard to fitness to travel, passengers should be able to walk a distance of 50m and climb one flight of stairs without angina or severe shortness of breath.
The Review concludes by looking at future directions. Cabin air quality remains an issue, and it has been linked to passenger and flight crew complaints of dry eyes, stuffy nose, and skin irritation, as well as headaches, lightheadedness, and confusion. Peer-reviewed studies on the effect of vaporised organic compounds, such as tricresyl phosphate, that have led to reported cases of crew and passenger incapacitation, are needed. These vaporised organic compounds come from burning jet fuel which then enters the cabin air supply. New aircrafts, such as the Airbus A380 and Boeing 787, are being designed to operate at cabin altitude of 1829 m compared with the current altitude of 2438 m, in addition to having improved cabin air quality and passenger seating. The authors say: "The molecular basis for circadian-rhythm disorders has been recently clarified and future clinical application might lead to new treatments for jet lag. The risk that commercial aircrafts are vehicles of influenza pandemic spread is real and opportunities exist to keep the risk to a minimum."
They conclude: "In the modern travel era, clear understanding of the medical consequences of commercial flights has become increasingly important. Individuals need to be aware of the possible medical complications of air travel, and physicians should identify people at potential risk from air travel and advise them of any necessary treatments to travel safely."
For Dr Mark Gendreau, Lahey Clinic Medical Center, Burlington, MA, USA please contact Margie Coloian T) +1 781 744-3859 E) Mark.A.Gendreau@lahey.org / margie.coloian@lahey.org
For full Review see: http://press.thelancet.com/airtravelreviewfinal.pdf
Journal
The Lancet