For many years, long-term oxygen therapy (LTOT) users often faced myriad challenges when attempting to travel by air. Until the introduction of portable oxygen concentrators (POCs), compressed cylinders and/or portable liquid vessels were the only available lightweight, ambulatory oxygen systems. These devices contain bulk amounts of oxygen under pressure and can be considered hazardous. Therefore, they are not permitted on board any commercial aircraft. As a result, LTOT users wishing to travel by air were required to purchase oxygen for use in flight from the airline. Unfortunately, some airlines did not provide this service; and, of those that did, the cost of the in-flight oxygen could be quite expensive, often exceeding the ticket fare. This combination of complex rules and high cost often discouraged patients from air travel or, in the worst cases, forced some patients to travel without their needed oxygen.

Over the last decade, there have been a number of important advances in home oxygen technologies, and arguably, one major milestone has been the introduction of the portable oxygen concentrator, which for the purpose of this article includes both lightweight (<10 pounds) pulse-dose POCs and the larger, transportable POCs that can provide up to 3 LPM of continuous flow as well as pulse-dose oxygen delivery. The POCs are unique, because they introduced the first truly self-generating, portable oxygen system. The POC does not operate under high pressure, does not produce or store bulk amounts of oxygen, and operates on the same mechanical principles as stationary oxygen concentrators—systems that have a proven track record of high performance and clinical efficacy. These are some of the key reasons POCs proved safe and ideal for commercial air travel.

On July 12, 2005, the Federal Aviation Administration (FAA) published Special Federal Aviation Regulation (SFAR) 106 in the Federal Register.1 The regulation delineated the initial rules governing the safe use of POCs on board aircraft to the airlines, passengers, and oxygen device manufacturers. The initial rule also recognized the first two POCs the FAA approved for use. Numerous updates to SFAR 106 have added 10 more FAA-approved devices. The Table is a current list of the 12 POCs currently approved by the FAA. One major weakness of SFAR 106 was that the FAA could not mandate airlines to allow POCs on board; it simply approved the use and provided guidelines for the use of POCs on commercial aircraft. As a result, many airlines chose to continue their practice of not allowing POCs for use on board their aircraft.

The Department of Transportation (DOT) introduced a proposed rule in 2005 mandating POC use aboard commercial aircraft.2 The proposed rule, DOT NPRM Docket OST-2005-22298, was issued on September 7, 2005. After a long public comment period, DOT 14 CFR Part 382: Nondiscrimination on the Basis of Disability in Air Travel-Final Rule was published on May 13, 2008.3 This rule requires all commercial airlines taking off and landing in the United States to allow the use of FAA-approved POCs before and during takeoff/landing and in flight.

Like most government regulations, both SFAR 106 and the DOT rule are quite comprehensive. Here are some of the highlights from the regulations that most home oxygen users and providers should be familiar with:

  • Passengers should notify the airline of their intent to bring a POC on board at least 48 hours in advance of the planned flight.
  • Passengers using POCs may be restricted from sitting in an emergency exit row, or in a seat that restricts other passengers’ access to an emergency exit or aisle of the passenger compartment.
  • Approved POCs may be used in flight and during taxi, takeoff, and landing if required by physician’s statement.
  • Patients must possess a physician’s statement that includes documentation of three requirements:
    1. Ability to see/hear alarms and appropriately respond
    2. When oxygen is required (all or a portion of the trip)
    3. Maximum prescribed flow rate during flight
  • Patints are responsible for bringing a sufficient number of fully charged batteries to cover not less than 150% of the expected maximum flight duration.
  • Patients can use but must properly stow the POC during taxi, takeoff, and landing. This is typically in the carry-on storage area below the seat in front of the patient.
  • The DOT does not mandate that carriers allow users to plug the POC into the aircraft power supply.
Clinical Effects of Altitude

While the use of oxygen at ground level is well established, there are limited published data to guide the use of oxygen at altitude, particularly for patients who are hypoxemic at ground level. Most commercial aircraft keep the cabin pressure at or below 8,000 feet, although the pilot has the authority to increase the cabin pressure to 10,000 feet if required to fly at higher than typical altitudes. The partial pressure of oxygen in the ambient air is a product of the barometric pressure and the atmospheric fraction of oxygen (0.209) as represented in the equation: barometric pressure x 0.209 = atmospheric Po2. At sea level, this is represented as: 760 x 0.209 = 159 mm Hg.

At 8,000 feet, the partial pressure of O2 in the cabin is 564 mm Hg x 0.209 = 118 mm Hg. Gas density at 8,000 feet is almost 30% lower than at sea level. With less driving pressure available, the clinical effect is similar to that if breathing approximately 15.1% O2 at sea level.4 For most healthy people, there are few noticeable symptoms associated with short-term exposure to altitude. Normal cardiopulmonary responses to altitude include:

  • Modest fall in Pao2
  • Increased respiratory rate
  • Increased tidal volume (and therefore an increasedminute ventilation)
  • Increased heart rate
  • Increased cardiac output
  • Preferential redistribution of perfusion to essential organs and diminished perfusion to other organs
  • Vasoconstriction of the pulmonary arteries

For many travelers, the only noticeable side effects of short-term altitude exposure are headache, fatigue, and some mild dehydration. It is possible that a small percentage of patients on very long flights (ie, >15 hours) may be at risk for developing altitude sickness, although data supporting this is very limited.

Oxygen Use in Flight

There is no single, evidence-based method of predicting blood oxygen levels at altitude, especially for patients with chronic lung disease. As a general rule of thumb, it is estimated that inspired Pao2 declines approximately 5 mm Hg per 1,000 feet ascended. Unfortunately, there is no such general rule governing potential changes to Spo2 among people with lung disease traveling at altitude for brief periods. One recent study examining the effects of aircraft-cabin altitude on the oxygen levels of healthy subjects suggests that altitude lowered blood oxygen saturation by 4% when compared to their baseline, ground level Spo2.5 There have been a number of predictive, regression equations derived from various clinical studies, but they may not prove accurate or effective as part of an individual patient evaluation for predicting blood oxygen levels during flight.6-8 A hypobaric challenge, also referred to as a high altitude simulation test or HAST (having a patient breathe 15.1% gas), while at sea level may prove to serve as an effective predictor of blood oxygen levels during flight. Unfortunately, HAST is not commonly used because of the need for specialty gases and a closed breathing system.

LTOT Patients and Air Travel

For patients prescribed LTOT for use at home, there is no evidence-based or expert consensus guideline for prescribing oxygen for use in flight. A patient’s baseline hypoxemia, oxygen prescription at ground level, respiratory reserve, level of hemoglobin, and general clinical condition prior to flight are all key variables influencing in-flight oxygen use. Stoller9 notes that despite the protean effects of altitude exposure, relatively brief exposure to altitude (<12 hours) encountered during commercial flights seems to be well tolerated, even among patients with chronic lung disease.

It is generally accepted that patients with a ground level Pao2 of >80 mm Hg will experience no difficulty during flight and patients with a Pao2 of <60 mm Hg at ground level will need oxygen at altitude. Patients predicted to have an in-flight Pao2 ≤50 mm Hg are clearly candidates for using supplemental oxygen during flight.9 Depending on their clinical condition at the time of flight, LTOT users may need to increase their oxygen dose (flow setting or setting on the oxygen conserving device) to ensure adequate oxygenation during flight, as their fraction of inspired oxygen (Fio2) will likely decline due to the lower molar volume of oxygen in the ambient cabin gas at altitude.

The decision to prescribe oxygen during flight for a patient who is normoxic at ground level or the decision to alter an LTOT patient’s ground level oxygen prescription for use during flight is one best made by the patient’s attending physician after an evaluation. It is prudent and good practice that all patients with chronic lung disease be seen and evaluated by their physician prior to scheduling any air travel.

Using POCs in Flight

POCs operate on the same mechanical basis as standard concentrators: pressure swing adsorption (PSA). Since PSA systems separate the nitrogen from the oxygen, the performance at ground level is essentially the same as the performance at altitude, although working with fewer total moles of oxygen. While the commercially available POCs operate from the same mechanical and theoretical platform, all have slightly different performance specifications, although the majority of commercially available devices are rated for use at altitudes of 8,000 feet or higher. Like many oxygen and respiratory technologies, all devices may not be ideal for all patients under all circumstances. It is important to remember that patients using a nasal cannula typically derive >90% of their inspired gas volume from the ambient gas, which has much more influence over the Fio2 than the oxygen delivered from the cannula. Therefore, patients prescribed a POC for air travel should be educated and evaluated with the specific device being used. They should also be informed that their prescription at altitude may differ from that at ground level due to breathing the lower partial pressure of oxygen in the ambient gas at altitude.

Summary

It has been more than 5 years since the FAA approved POCs for use on commercial aircraft. Although there is no published data, there are thousands of anecdotal reports of LTOT users experiencing smooth and very successful trips using a POC in flight and during their travels. Despite the DOT and FAA rules, there remains some occasional confusion or misinformation regarding the use of POCs on commercial aircraft. There are a number of excellent resources available to help patients and providers navigate the system. Most POC manufacturers have detailed information about their products and the FAA and DOT rules on their Web sites. Patient organizations, such as the National Home Oxygen Patient Association (NHOPA), provide LTOT users with travel information via their Web site, www.homeoxygen.org.

The founding fathers of LTOT always envisioned lightweight, self-generating oxygen technologies that would empower oxygen users with the ability to live an active and productive life. Modern home oxygen therapy systems can help a patient live a life close to the way they did before they needed a prescription for oxygen, including travel by air.

Joseph Lewarski, BS, RRT, FAARC, is vice president of clinical affairs, and Robert Messenger, BS, RRT, is respiratory clinical education specialist, Invacare Corp, Elyria, Ohio. For further information, contact [email protected].

References
  1. Use of Certain Portable Oxygen Concentrator Devices Onboard Aircraft; Final Rule. Fed Regist. 2005;70(132):40158-40164.
  2. Nondiscrimination on the Basis of Disability in Air Travel—Medical Oxygen and Portable Respiration Assistive Devices. Proposed Rules. Fed Regist. 2005;70(172):53108-53117.
  3. Nondiscrimination on the Basis of Disability in Air Travel; Final Rule. Fed Regist. 2008;73(93):27614-27687.
  4. Seccombe LM, Kelly PT, Wong CK, Rogers PG, Lim S, Peters MJ. Effect of simulated commercial flight on oxygenation in patients with interstitial lung disease and chronic obstructive lung disease. Thorax. 2004;59:966-70.
  5. Muhm JM, Rock PB, McMullin DL, et al. Effect of aircraft-cabin altitude on passenger discomfort. N Engl J Med. 2007;357:18-27.
  6. Mortazavi A, Eisenberg MJ, Langlebe D, Ernst P, Schiff RL. Altitude-related hypoxia: risk assessment and management for passengers on commercial aircraft. Aviat Space Environ Med. 2003;74:922.
  7. Dillard TA, Moores LK, Bilello KL, Phillips YY. The preflight evaluation: a comparison of the hypoxia inhalation test with hypobaric exposure. Chest. 1995;107:352.
  8. Gong H, Tashkin DP, Lee EY, Simmons MS. Hypoxia altitude simulation test. Evaluation of patients with chronic airway obstruction. Am Rev Respir Dis. 1984;130:980-6.
  9. Stoller JK. Oxygen and air travel. Respir Care. 2000;45:214-21.