Is There a Doctor Onboard? Medical Emergencies at 40,000 Feet




It is estimated 2.75 billion people travel aboard commercial airlines every year and 44,000 in-flight medical emergencies occur worldwide each year. Wilderness medicine requires a commonsense and improvisational approach to medical issues. A sudden call for assistance in the austere and unfamiliar surroundings of an airliner cabin may present the responding medical professional with a “wilderness medicine” experience. From resource management to equipment, this article sheds light on the unique conditions, challenges, and constraints of the flight environment.


Introduction


It is estimated 2.75 billion people travel aboard commercial airlines every year and 44,000 in-flight medical emergencies occur worldwide each year. Wilderness medicine requires a commonsense and improvisational approach to medical issues. A sudden call for assistance in the austere and unfamiliar surroundings of an airliner cabin may present the responding medical professional with a “wilderness medicine” experience. From resource management to equipment, this article sheds light on the unique conditions, challenges, and constraints of the flight environment.




The flight environment


Modern commercial aircraft fly at the interface between the troposphere and stratosphere, roughly equivalent to a cruising altitude of 32,000 to 45,000 feet. Above the troposphere, planes fly more smoothly and experience less turbulence and inclement weather. The height of the troposphere varies with altitude and season. Passengers are protected from high-altitude atmospheric conditions by a pressurized cabin environment that potentially creates its own medical ramifications.




The flight environment


Modern commercial aircraft fly at the interface between the troposphere and stratosphere, roughly equivalent to a cruising altitude of 32,000 to 45,000 feet. Above the troposphere, planes fly more smoothly and experience less turbulence and inclement weather. The height of the troposphere varies with altitude and season. Passengers are protected from high-altitude atmospheric conditions by a pressurized cabin environment that potentially creates its own medical ramifications.




Cabin altitude


The ambient atmospheric pressure at cruising altitude (30,000–40,000 feet) is about 200 to 300 hPa (roughly 0.2–0.3 atm). To allow passengers to survive and operate in this environment, the cabin must be pressurized. Despite pressurization, the internal cabin altitude is generally not maintained at sea level pressure because the aircraft structure required to maintain a sea level pressure would make the plane unacceptably heavy and expensive to build and operate. Thus, a compromise is made that is the most efficient for weight/strength/expense, while preventing passengers from becoming hypoxic. The aircraft cabin is typically pressurized between 6000 and 8000 feet above sea level. Newer aircraft, such as the Airbus A380 and Boeing 787 Dreamliner, can pressurize the cabin to lower altitudes, equal to about 6000 feet, even in the upper flight levels. In the United States, Federal Aviation Administration (FAA) requirements allow a maximum cabin altitude of 8000 feet.


Many people with heart and lung disease travel by commercial aircraft, and are unaware of the risk that is incurred. The fractional oxygen content of the air in the cabin is the same as that at sea level, approximately 21%. What changes with increasing cabin altitude is the atmospheric pressure. At a typical cruising altitude, the atmospheric pressure in the cabin is decreased by about 25% to 30% and results in a similar decrease in the partial pressure of inspired oxygen. The lower partial pressure of oxygen in the aircraft cabin results in slight hypoxemia, with a corresponding decrease in oxygen saturation and a mild compensatory hyperventilation and tachycardia. Medical personnel responding to onboard medical events should not be surprised by decreases in arterial oxygen saturation in the range of 3% to 5%, even in healthy individuals.




Pressure and dysbarism


Boyle’s law states that in a perfect gas where mass and temperature are kept constant, the volume of the gas varies inversely with the absolute pressure.


(P × V = P′ × V′)


Reduction in aircraft cabin pressure can lead to volume expansion of closed gas-containing compartments in the human body.


Middle Ear


Expanding volumes of air in the paranasal and frontal sinuses may produce symptoms, but the most common manifestation of dysbarism associated with the flight environment is barotitis media resulting in ear pain. Barotitis media is commonly related to eustachian tube congestion secondary to upper respiratory infections, middle ear infections, chronic effusions, or allergies. Mild barotrauma may occur as either pressure increase caused by expansion of gases as the aircraft ascends, or by decreased pressure in the middle ear as the aircraft descends. Although mild discomfort is the typical presentation, in rare cases, the changes in pressure can produce rupture of the tympanic membrane.


The most simple and commonly used method to open the eustachian tube is to swallow. Chewing gum or sucking on hard candy may facilitate this process. Infants should be given a bottle or pacifier to suck on to facilitate swallowing, especially during descent.


Older children and adults may benefit from performing a Valsalva maneuver. This is achieved by pinching the nostrils and attempting exhalation through the nose. This maneuver is familiar to most scuba divers, because the same technique is used for equalizing ears during descent. Another useful technique is to have the patient swallow while pinching the nostrils closed. Other pressure equalization techniques include the following:




  • Voluntary tubal opening: Attempt to yawn or wiggle the jaw



  • Valsalva maneuver: Pinch your nostrils, and gently blow through your nose



  • Toynbee maneuver: Pinch your nostrils and swallow (good technique if equalization is needed during ascent)



  • Frenzel maneuver: Pinch your nostrils while contracting your throat muscles, and make the sound of the letter “k”



  • Lowry technique: Pinch your nostrils, and gently try to blow air out of your nose while swallowing



  • Edmonds technique: Push your jaw forward, and use the Valsalva maneuver or the Frenzel maneuver



Dental


Cabin pressure changes may cause toothaches in patients with pre-existing dental disease, such as a dental abscess (barodontalgia).


Abdomen


Occasionally, intraluminal gas expansion caused by decreased cabin pressure may cause abdominal discomfort. The surgical literature contains references regarding complications during flight subsequent to recent abdominal surgery. Travelers should be advised to check with their surgeon. The British Civil Aviation Authority publishes the following recommendations.




  • Travel should be avoided for 10 days following abdominal surgery.



  • Following procedures, such as colonoscopy, where a large amount of gas has been introduced into the colon, it is advisable to avoid travel by air for 24 hours.



  • It is advisable to avoid flying for approximately 24 hours after laparoscopic intervention, because of the residual CO 2 gas, which may be in the intra-abdominal cavity.



  • Neurosurgical intervention may leave gas trapped within the skull, which may expand at altitude. It is therefore advisable to avoid air travel for approximately 7 days following this type of procedure.



  • Ophthalmologic procedures for retinal detachment involve the introduction of gas by intraocular injections, which temporarily increase intraocular pressure. Depending on the gas, it may be necessary to delay travel for approximately 2 weeks if sulfur hexafluoride is used and 6 weeks pursuant to the use of perfluoropropane. For other intraocular procedures and penetrating eye injuries, 1 week should elapse before flying.



Gas Expansion and Medical Devices


Various medical devices that trap fixed quantities of expandable air must be considered when transporting patients aboard aircraft. Expanding trapped gas within these devices has been known to cause barotrauma during rapid ascent in unpressurized and pressurized aircraft. A partial list of these devices includes pneumatic splints (air splints), feeding tubes, urinary catheters, cuffed endotracheal tubes, and cuffed tracheostomy tubes.


If not contraindicated, the effects of gas expansion can be eliminated by installation of water rather than air during flight. These devices require careful monitoring; partial deflation should be considered if overexpansion is suspected. Feeding and infusion tubes should be capped off.


Pneumothorax


Travelers with pre-existing pulmonary disease are at risk for flight-related pneumothorax. A patient with a small, asymptomatic pneumothorax can develop a more significant pneumothorax as air expands within the pleural space during ascent. Risk of pneumothorax during air travel is increased in patients with cystic lung disease, recent pneumothorax, thoracic surgery, and chronic pneumothorax.




Flying after scuba diving


Guidelines for Postdive Air Travel


The Divers Alert Network and the Undersea Hyperbaric Medical Society convened a workshop in 2002 to review the available data regarding postdive air travel. The published guidelines ( Table 1 ) do not guarantee that one will avoid decompression sickness. Allowing even longer surface intervals than the recommended minimums further reduces the risk of decompression sickness.



Table 1

Divers Alert Network guidelines for flying after diving



















Dive Profile Minimum Preflight Surface Interval Suggestion
Single no-decompression dive 12 h or more
Multiple dives in a day 18 h or more
Multiple days of diving 18 h or more
Dives requiring decompression stops Substantially longer than 18 h

From Flying after scuba diving: how long should I wait? Divers Alert Network; 2016; and Data from DAN Medical Frequently Asked Questions. Available at: www.diversalertnetwork.org/medical/faq/Flying_After_Diving .


There are additional considerations regarding the Divers Alert Network/Undersea Hyperbaric Medical Society flying after diving guidelines. It is prudent to wait longer than the suggested minimum interval. Recent studies show that flying in a commercial aircraft, even after a 24-hour surface interval, can produce bubbles in a diver’s blood; therefore, Divers Alert Network advises that one exercise caution by maintaining more conservative dive profiles during the final day of diving and plan for a 24-hour surface interval before flight. Any postdive ascent to a higher altitude—even using ground transportation—increases decompression stress, so one should follow the same guidelines if heading by car, bus, or foot from a dive site to the mountains.




Cabin air


Despite the pervasive antipathy expressed by airline passengers, there is little clinical evidence to suggest that cabin air quality on modern jets is potentially harmful. Many airline passengers have anecdotes about getting sick following a long duration flight. The risk of contracting an infection during a commercial flight arises from the close proximity to potentially germ-laden fellow passengers, and not from the quality of aircraft cabin air. A crowded airplane poses no greater risk than other enclosed spaces.


A portion of the cabin air (no more than 40%–50%) is recirculated and passes through high-efficiency particulate air filters. According to Boeing, between 94% and 99.9% of all airborne microbes are filtered during this process. The other source of cabin air is “bleed air” that is obtained when outside air is compressed by the aircraft’s engines. The incoming bleed air is plumbed into air conditioning units for cooling. This mix of recirculated cabin air and outside bleed air makes it possible to efficiently regulate temperature and humidity.


Newer aircraft use high-efficiency particulate filters to remove gaseous contaminants, including some volatile organic compounds that may act as mild respiratory irritants.


Fume Events


In the event of an oil leak, bleed air may be exposed to gasses that could potentially expose passengers to neurotoxins. Such events are rare, but have reportedly triggered neurologic symptoms, such as headaches and dizziness in crewmembers and passengers. Jet engine oils contain synthetic hydrocarbons and other additives, including the organophosphate tricresyl phosphate, which acts as a high-pressure lubricant. Most studies indicate that total tricresyl phosphate concentrations occurring during so-called fume events remain below threshold limits for causing neurologic symptomatology. The concentration of organophosphates that aircraft crewmembers and passengers could be exposed to is insufficient to produce neurotoxicity. A recent guide for health care providers concluded that “there are currently no tests of sufficient sensitivity and specificity to assess exposure/health effects outcomes.”


The newest Boeing airliner, the 787 Dreamliner, uses a no-bleed systems architecture that replaces the conventional pneumatic bleed air system with a high-power electrical compressor system that avoids any mixing of engine-based bleed air with internal cabin air.


Infectious Disease and Air Travel


Although modern airliners provide clean cabin air, air travelers are still subjected to long periods in enclosed spaces, which facilitates the spread of infectious disease. Multiple outbreaks of serious infectious diseases have been reported aboard commercial airlines including influenza, food poisoning, measles, tuberculosis, viral enteritis, severe acute respiratory syndrome, and smallpox.


The risk of cross-infection from airborne pathogens in aircraft cabins seems to be related to the duration of the flight (with 8 or more hours producing an increased risk), and proximity of the index passenger (seating within two rows associated with an increased risk).


If a contagious disease is suspected, ask the ill passenger to use a facemask. A mask should be available in the medical kit and/or the first aid kit. Use of a facemask by the ill passenger is recommended by the World Health Organization. Attempt to isolate the patient and relocate neighboring passengers. Discuss quarantining the passenger with the flight crew and any reporting requirements.


Low Humidity of Cabin Air


Airliner cabins are dry. Typical humidity levels in most airliners are about 2%. Airplane designers are happy to minimize moisture to help inhibit structural corrosion. Maintaining optimal cabin humidity (40%–70%) is prohibitive because of the increased cost and weight of equipment. The newer Boeing 787 does not use engine bleed air to pressurize the cabin. The 787 cabin contains 6% to 7% humidity, which according to studies done by Boeing improves the passenger experience. Low cabin humidity levels can lead to dehydration, so passengers are encouraged to increase water intake. Dry eyes can be especially problematic for travelers with pre-existing conditions and for soft contact lens wearers. Carrying “artificial tears” or contact rewetting drops is of benefit. Dry inflamed upper respiratory mucosa can produce cough and exacerbate reactive airway disease.




Cosmic-radiation exposure


Cosmic radiation originates from powerful events, such as star collisions, gamma ray bursts, black holes, and supernovae. Particles released by solar flares are another source. The earth’s magnetic field and atmosphere shield the planet from 99.9% of cosmic radiation; however, for travelers outside the protection of Earth’s magnetic field, space radiation becomes a more potential hazard. Exposure levels also rise when we travel by plane, especially at higher altitudes and latitudes.


In 1991, the International Commission on Radiological Protection declared cosmic radiation an occupational risk for flight crews. Since that time, exposure monitoring and maximum dose guidelines have been developed. Current recommendations are to limit annual crew exposure to 20 mSv/y averaged over 5 years (total of 100 mSv in 5 years). Even frequent flyers and aircrews typically remain well below this limit.


Concerns increase when considering the developing fetus during pregnancy. The National Council on Radiation Protection and Measurements recommends a monthly limit of 0.5 mSv, whereas the International Commission on Radiological Protection recommends a radiation limit of 1 mSv during the entire pregnancy. These recommendations would place limits on pregnant crewmembers and frequent air travelers, because flying roughly 15 long-haul round trips would expose a fetus to more than 1 mSv. To avoid risk to the fetus, the FAA recommends pregnant crewmembers take shorter, low-altitude, low-latitude flights.


The Centers for Disease Control and Prevention recommends that if you are pregnant and aware of an ongoing solar particle event, that you reschedule your flight. A National Institute for Occupational Safety and Health (NIOSH) study found that flight attendants exposed to 0.36 mSv or more of cosmic radiation in the first trimester may have a higher risk of miscarriage. Although flying through a solar particle event is rare, a NIOSH and National Aeronautics and Space Administration study found that a pregnant flight attendant who flies through a solar particle event can receive more radiation than is recommended during pregnancy by national and international agencies.


How to Reduce Exposure


Ultimately the amount of cosmic radiation exposure received while flying depends on the amount of time in the air, altitude, latitude, and solar activity. Lowest dose rates at a given altitude are found close to the equator and intensify with increasing latitude. For any location at commercial flight altitudes, a higher altitude incurs a higher dose rate. Reducing aircraft altitude can significantly reduce radiation exposure during a solar radiation event in high-latitude areas. With regard to solar particle events, the Centers for Disease Control and Prevention states




  • NIOSH has estimated that pilots fly through about six solar particle events in an average 28-year career.



  • Avoiding exposure to solar particle events is difficult because they often happen with little warning. One can find out whether a solar particle event is currently active through these sources:




    • The National Aeronautics and Space Administration Nowcast of Atmospheric Ionizing Radiation System is being developed to report potentially harmful flight radiation levels to flight crews and passengers.



    • National Aeronautics and Space Administration Nowcast of Atmospheric Ionizing Radiation System: current radiation dose rate forecast.



    • A space weather app for the iPhone offers current information on solar activity (developed by Stellar North LLC).



    • The National Oceanic and Atmospheric Administration Space Weather Prediction Center’s Aviation Community Dashboard includes a forecast for solar particle events.



    • A useful tool to estimate an individual’s exposure to cosmic radiation from a specific flight is available from the FAA on its Web site ( jag.cami.jccbi.gov/cariprofile.asp ).






Emotional and physical stress during air travel


Travelers are often subject to conditions that increase anxiety and overall dysphoria during air travel, including the following:




  • Time pressures of travel



  • Airport congestion



  • Rushing to make connecting flights



  • Stress and anxiety associated with business travel



  • Stress and anxiety associated with family-related events, such as reunions, weddings, and funerals



  • Psychosocial disruptions in circadian rhythms (discussed next)



  • Emotional effects of lack of sleep and dehydration



  • Stress and anxiety associated with missed and canceled flights



  • Unexpected layovers





Jet lag


Circadian Rhythm Sleep Disorder (Jet Lag)


Jet lag is a sleep disorder occurring in travelers who transit across three or more time zones. Jet lag occurs when the internal circadian rhythm “clock” adjusts slowly to the destination time. This disruption causes circadian rhythms to become out of synchronization with the destination time zone.


The pineal gland is highly involved with regulating the sleep-wake cycle by secreting melatonin. The synthesis and release of melatonin is stimulated by darkness and suppressed by light.


Symptoms


Symptoms may include poor sleep, including sleep-onset insomnia, fractionated sleep, and early awakening; fatigue; mood changes; headache; irritability; poor concentration; depression; and mild anorexia.


Clinical Considerations


Although there is substantial individual variability in the severity of jet lag symptoms, the direction of travel and the number of time zones crossed are important factors to consider. Specifically, westward travel generally causes less disruption than eastward travel.




  • Eastward travel is associated with difficulty falling asleep at the destination bedtime and difficulty arising in the morning.



  • Westward travel is associated with early evening sleepiness and predawn awakening at the travel destination.



  • Travelers flying within the same time zone typically experience the fewest problems, such as nonspecific travel fatigue.



  • Crossing more time zones or traveling eastward generally increases the time required for adaptation.



  • After eastward flights, jet lag lasts for the number of days roughly equal to two-thirds the number of time zones crossed; after westward flights, the number of days is roughly half the number of time zones.



  • The intensity and duration of jet lag are related to the number of time zones crossed, the direction of travel, the ability to sleep while traveling, the availability and intensity of local circadian time cues at the destination, and individual differences in phase tolerance.



Prevention


Travelers can minimize jet lag by doing the following before travel :




  • Shift the timing of sleep to 1 to 2 hours later for a few days before traveling westward



  • Shift the timing of sleep to 1 to 2 hours earlier for a few days before traveling eastward



  • Shift mealtimes to hours that coincide with the previous changes



  • Seek exposure to bright light in the evening if traveling westward, in the morning if traveling eastward



  • Mobile apps, such as Jet Lag Rooster and Entrain, are available to help travelers calculate and adhere to a light/dark schedule



  • Web sites, such as Jet Lag Advisor ( www.britishairways.com/travel/drsleep/public/en_gb ), offer similar services online; travelers answer a few simple questions regarding planned flights and advice is then calculated to minimize jet lag



Pharmacologic Treatment


The use of the nutritional supplement melatonin is controversial for preventing jet lag. Some clinicians advocate the use of 0.5 to 5.0 mg of melatonin during the first few days of travel, and data suggest its efficacy. The production of melatonin is not regulated by the Food and Drug Administration and commercially available products have demonstrated impurities. Additionally, current data also do not support the use of special diets to ameliorate jet lag. If used, timed treatment with melatonin in the early morning of the departure time zone (westward) or the very early evening of the departure time zone (eastward) preflight and postflight may improve initiation and maintenance of the desired phase shift.


Newer melatonin receptor agonists, such as ramelteon, have recently been approved for the treatment of insomnia, but have not been well studied for use in jet lag.


The 2008 American Academy of Sleep Medicine recommendations include the following:




  • Promote sleep with hypnotic medication, although the effects of hypnotics on daytime symptoms of jet lag have not been well studied.



  • Nonaddictive sedative hypnotics (nonbenzodiazepines), such as zolpidem, have been shown in some studies to promote longer periods of high-quality sleep. If a benzodiazepine is preferred, a short-acting one, such as temazepam, is recommended to minimize oversedation the following day. Because alcohol intake is often high during international travel, the risk of interaction with hypnotics should be emphasized with patients.



  • If necessary, promote daytime alertness with a stimulant, such as caffeine in limited quantities. Avoid caffeine after midday.



  • Take short naps (20–30 minutes), shower, and spend time in the afternoon sun.





Health issues associated with commercial air travel


Airlines are not required to report emergencies unless they require actual diversion of the flight. A recent article provides an extensive review of in-flight emergencies. This article reviewed records of in-flight medical emergency calls from five domestic and international airlines to a physician-directed medical communication center from January 1, 2008, through October 31, 2010. During the study period there were approximately 744 million airline passengers who traveled on commercial airline flights. The communications center received 11,920 in-flight medical emergency calls (a rate of 16 medical emergencies per 1 million passengers). The incidence of in-flight medical emergencies was one in-flight medical emergency per 604 flights. The most common medical problems were syncope or presyncope (37.4%), respiratory symptoms (12.1%), and nausea or vomiting (9.5%).


Aircraft diversion occurred in 7.3% of cases, whereas 1.2% of patients resolved sufficiently before landing to negate the need for emergency medical service (EMS) services on landing. Only 37.3% of patients evaluated by EMS personnel after landing were transported to a hospital emergency department.


Medical problems that were associated with the highest rates of hospital admission were stroke-like symptoms (23.5%), obstetric or gynecologic symptoms (23.4%), and cardiac symptoms (21%). Although most of the medications that were used are available in the FAA emergency medical kit (EMK) (discussed later), some medications came from other passengers or the patient themselves. The most commonly used medications were oxygen (49.9%), intravenous (IV) normal saline (5.2%), and aspirin (5%).


Automated External Defibrillators


An automated external defibrillator (AED) was used on 137 patients (1.3%). An AED was applied in 24 cases of cardiac arrest but shock delivered in only five cases. The return of spontaneous circulation occurred in one patient receiving defibrillation. For eight other patients, an AED was used but no shock was indicated.


Death Rate


The death rate among all patients with in-flight medical emergencies was 0.3%. Table 2 shows medical emergencies according to medical problem and outcome.


Dec 2, 2017 | Posted by in Uncategorized | Comments Off on Is There a Doctor Onboard? Medical Emergencies at 40,000 Feet
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