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Evaluation of patients for supplemental oxygen during air travel

Evaluation of patients for supplemental oxygen during air travel
Literature review current through: Jan 2024.
This topic last updated: Nov 17, 2023.

INTRODUCTION — It is estimated that 1.5 to 4.5 billion passengers travel by air each year [1]. Flying at a high altitude can induce significant hypoxemia in patients with underlying lung disease, despite pressurization of airliner cabins. A large number of air travelers have underlying medical conditions, including pulmonary disease, and are at risk for adverse cardiopulmonary effects related to oxygen desaturation [2-5].

The evaluation of patients for potential in-flight hypoxemia and the prescription of supplemental oxygen for air travel are reviewed here. General assessment and counseling prior to air travel and the prescription of long-term supplemental oxygen are discussed separately. (See "Assessment of adult patients for air travel" and "Pneumothorax and air travel" and "Long-term supplemental oxygen therapy" and "Prevention of venous thromboembolism in adult travelers".)

EFFECTS OF AIR TRAVEL — In-flight medical events (IFMEs) have been reported to occur at a rate of approximately 15 to 100 per million passengers [6,7]. The precise incidence of IFMEs is unknown because there is no mandatory reporting system. Deaths (all cause) are estimated to occur at a rate of 0.1 to 1 per million passengers [6-9]. Respiratory events are estimated to account for 12 percent of IFMEs [6]. Changes in atmospheric pressure and oxygen tension are thought to contribute to these events. (See "Management of inflight medical events on commercial airlines", section on 'Epidemiology'.)

Altitude and oxygen tension — Commercial aircraft typically operate at cruising altitudes of 30,000 to 40,000 feet (9144 to 12,192 meters) [8,10]. As altitude increases, ambient air pressure decreases, leading to a decrease in the oxygen tension (also known as the partial pressure of oxygen) of inspired air (table 1).

Pressurization of cabins on commercial airliners limits the decrease in air pressure, allowing the airplane or jet to cruise at altitudes up to 40,000 feet (12,192 meters) without inducing extreme hypobaric stress in the passengers [11]. Regulatory government agencies, such as the Federal Aviation Administration, require that airliner cabins be pressurized to simulate an altitude (so-called cabin altitude) below 8000 feet (2438 meters) and allow only brief diversions to a cabin altitude of 10,000 feet (3048 meters) for safety (eg, to avoid adverse weather).

The changes in inspired oxygen tension (PiO2) due to changes in altitude can be determined by the equation:

PiO2 = FiO2 x (Patm - PH2O)

where FiO2 is the fraction of inspired oxygen (0.21 in atmospheric air), Patm is the atmospheric pressure (760 mmHg at sea level; 564 at cabin altitude), and PH2O is the partial pressure of water (47 mmHg at 37°C) [3,8,12]. (See "Measures of oxygenation and mechanisms of hypoxemia", section on 'Reduced inspired oxygen tension'.)

At cabin altitudes between 5000 and 8000 feet, the PiO2 is calculated to be between 108 and 122 mmHg [13]. The resulting arterial partial pressure of oxygen (PaO2) varies due to individual variation in baseline lung function and the ventilatory response to hypoxia.

Clinical effects — Individuals with normal cardiorespiratory function typically experience a decrease in PaO2 from above 95 mmHg (12.7 kPa) to between 53 and 75 mmHg (7.1 to 10.0 kPa) when going from sea level to a cabin pressure that simulates an altitude of 8000 feet (2438 meters) [13-15]. This change in PaO2 is on the upper, flat portion of the oxyhemoglobin curve, so the decrease in oxygen saturation is only 3 to 4 percent and not associated with symptoms.

For patients who have a PaO2 below 95 mmHg at sea level, the decrease in PaO2 at a cabin altitude of 8000 feet (2438 meters) is on the steeper portion of the oxyhemoglobin saturation curve (figure 1), so it will be associated with a greater fall in oxygen saturation [14]. As an example, a patient with chronic obstructive pulmonary disease (COPD) and a PaO2 of 70 mmHg (9.33 kPa) at sea level would be likely to have a decrease in PaO2 to 53 mmHg (7.06 kPa) and a decrease in oxyhemoglobin saturation to 84 percent at a cabin altitude of 8000 feet [14], which may be associated with symptoms, ranging from mild cognitive dysfunction to marked dyspnea, chest pain, or confusion.

Air travelers are usually sedentary during flight, thus reducing the likelihood of symptoms associated with a lower PaO2. However, even modest exercise under hypobaric conditions may be associated with substantial worsening of hypoxemia. In a study of 24 patients with various lung diseases, more than 80 percent experienced a decrease in PaO2 to less than 50 mmHg (6.67 kPa) during exercise in a chamber simulating a cabin altitude of 8000 feet [16].

Despite this degree of hypoxemia, patients with COPD who are exposed to high altitude for several hours are unlikely to experience adverse clinical events [8,17]. Possible reasons for the low morbidity associated with air travel are that patients compensate for decreased oxygen tension by hyperventilating and are relatively inactive in-flight [18].

Another consequence of the decrease in ambient pressure is that gas in trapped spaces (eg, paranasal sinuses, abdominal viscera, lung bullae, and pleural space) expands (table 1). Expansion of air within a bulla can cause tissue separation, leading to a pneumothorax. Thus, in addition to the direct effects of decreased oxygen tension, hypoxemia may be caused by barotrauma. (See "Pneumothorax and air travel".)

SCREENING FOR IN-FLIGHT HYPOXEMIA — The British Thoracic Society (BTS) 2022 guidelines for screening patients for potential in-flight hypoxemia (defined as an arterial partial pressure of oxygen [PaO2] <50 mmHg [6.6 kPa] or pulse oxygen saturation [SpO2] <85 percent) advise using a combination of clinical assessment of dyspnea and resting pulse oximetry to guide initial decision-making [5].

Indications for screening — While exact criteria for screening for in-flight hypoxemia are lacking, the following are considered to be risk factors for in-flight respiratory symptoms or hypoxemia [5,8,19-21]:

Respiratory conditions with potential for acute deterioration or need for medical intervention:

Severe (FEV1 <50 percent predicted) or poorly controlled obstructive airways disease

Symptomatic restrictive chest wall condition or respiratory muscle weakness (vital capacity <1 liter)

Interstitial lung disease with SpO2 ≤95 percent or diffusing capacity of the lung for carbon monoxide (DLCO) ≤50 percent of predicted

Pulmonary hypertension

Hospitalization for respiratory illness within six weeks of intended air travel

Requirement for continuous positive airway pressure (CPAP) or noninvasive ventilation

Active cancer with lung involvement

Comorbid conditions that may be worsened by hypoxemia (eg, cardiac or cerebrovascular disease)

Requirement for long-term oxygen therapy, CPAP, or noninvasive ventilation (NIV)

Pneumothorax within six weeks of intended air travel, increased risk of pneumothorax (cystic lung disease or recurrent pneumothorax)

Trapped lung with chronic pneumothorax

Pulmonary embolism or deep venous thrombosis within six weeks or increased risk of venous thromboembolism

Individuals with bothersome cardiorespiratory symptoms during prior air travel

A number of studies have reported that resting pulse oxygen saturation is not fully predictive of in-flight hypoxemia [8,22-24]. Thus, in addition to assessment of the type and severity of underlying lung disease, we often use pulse oximetry during a six-minute walk test (6MWT) to guide selection of patients for further testing (algorithm 1). While this approach has not been specifically validated, it is based upon similar algorithms [5,8,23].

Patients requiring supplemental oxygen at baseline — Patients who require supplemental oxygen at rest are at risk for in-flight hypoxemia. If the oxygen requirement at rest is >4 L/minute, it may be difficult to ensure adequate supplemental oxygen in flight. For such patients, the clinician must assure that the battery life (including back-up batteries) is sufficient for the entire flight duration, allowing extra time for in-flight delays, or advise against air travel.

For patients whose oxygen requirement is ≤4 L/minute at rest, guidelines advise increasing the oxygen flow by 1 to 2 L/minute while in flight [5]. If the destination is at altitude, a similar adjustment will be needed during their stay.

Indications for further evaluation — Various methods have been suggested for selection of patients who need specific testing for in-flight hypoxemia, such as hypoxia altitude simulation testing (HAST; also called hypoxic challenge test). The BTS guidelines suggest using a combination of a resting SpO2 <95 percent at sea level and risk factors that would increase the likelihood of in-flight hypoxemia to guide the need for HAST [5]. However, one study found that a third of patients with SpO2 92 to 95 percent and none of these risk factors desaturated during HAST [25]. An alternative is to assess oxygenation during a 6MWT and use the results to guide referral for HAST (algorithm 1) [8,23,26]. This approach has the advantage of improving sensitivity for patients at risk for hypoxemia and reducing the overall number of patients referred for HAST.

As noted above, the 6MWT can also be used to guide referral for HAST among patients with SpO2 >95 percent and one or more of the risk factors noted [22]. (See 'Resting pulse oximetry' below.)

Resting pulse oximetry — For patients who do not require supplemental oxygen at rest, measurement of SpO2 is performed while the patient is resting and breathing room air (algorithm 1). The values described here presume that the patient is assessed at sea level.

SpO2 ≥95 percent – For most patients with a resting room air SpO2 ≥95 percent at sea level, it is unlikely that their PaO2 will decrease below 55 mmHg (7.3 kPa) at cruising altitude, so in-flight oxygen is generally not needed [5]. However, patients with a Medical Research Council dyspnea score ≥3 (calculator 1) should undergo further study, preferably with a six-minute walk test (6MWT) or shuttle walk test [5]. If the SpO2 is <84 percent during one of these tests, empiric supplemental in-flight oxygen or HAST (if hypercapnia is a concern) is advised.

A prospective study of patients with a variety of lung diseases found that 23 percent of those with a SpO2 >95 percent experienced a decrease in PaO2 to below 50 mmHg (6.6 kPa) while breathing a hypoxic gas mixture that simulated airline cruising altitude [22]. While none of these patients developed significant respiratory distress in-flight, we have a low threshold for proceeding to additional assessment (eg, 6MWT) when patients have underlying lung disease. (See 'Further assessment to determine in-flight need for oxygen' below.)

SpO2 92 to 95 percent – Patients with a resting room air SpO2 92 to 95 percent at sea level are assessed for risk factors (see 'Indications for screening' above) for in-flight hypoxemia and for desaturation on 6MWT to determine the need for further testing. Alternatively, the BTS guidelines suggest providing supplemental oxygen in flight or proceeding to HAST in patients with SpO2 <95 percent [5]. In a study of patients with chronic obstructive pulmonary disease (COPD) and a SpO2 92 to 95 percent, 67 percent of those without risk factors for in-flight hypoxemia and 70 percent of those with risk factors developed desaturation to PaO2 <50 mmHg (6.67 kPa) during HAST [27], suggesting that risk factors may be inaccurate in predicting the likelihood of in-flight hypoxemia.

Pulse oximetry saturation values of 92 to 96 percent are also less likely to assure adequate oxygenation (ie, an arterial saturation >88 percent) in Black individuals, where occult hypoxemia (ie, an arterial saturation <88 percent) with SpO2 values of 92 to 96 percent can be threefold more common (ie, 17 versus 6.2 percent) than in White individuals [28].

SpO2 <92 percent – Patients with a resting room air SpO2 <92 percent at sea level are candidates for supplemental oxygen in-flight. The Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines suggest prescribing oxygen at 3 L/min via nasal cannula or 31 percent by Venturi facemask without additional testing [29], although an alternative is to perform HAST on these patients to confirm the need for in-flight supplemental oxygen [8]. In contrast, the BTS guidelines suggest in-flight oxygen for patients already on long-term oxygen therapy (LTOT; presumably room air SpO2 <89 percent) at 2 L/minute greater than their LTOT prescription [5]. (See 'Estimating in-flight oxygen requirement' below.)

Six minute walk test — For patients with COPD and a resting SpO2 ≥92 percent, pre-flight (sea level) assessment with a 6MWT has been proposed to guide the need for HAST (algorithm 1) [23].

Patients with a resting SpO2 92 to 95 percent plus a 6MWT SpO2 <84 percent are prescribed supplemental oxygen for air travel without further testing. An oxygen flow rate of 2 L/min is reasonable.

Patients with a resting SpO2 of 92 to 95 percent and a 6MWT SpO2 ≥84 percent are referred for HAST.

Patients with a resting SpO2 >95 percent and a 6MWT SpO2 <84 percent are referred for HAST.

In a series of 100 patients with COPD, use of 6MWT results according to these thresholds resulted in 100 percent sensitivity for needing in-flight oxygen and 90 percent specificity and lessened the frequency with which HAST was needed to 33 percent of assessed patients [23]. A small portion of patients with underlying lung disease and a resting SpO2 >95 percent desaturated during the 6MWT to SpO2 <84 percent and were referred for HAST. Such patients were a minority of those tested in the study, and it is unclear what portion of patients with a resting SpO2 >95 percent are at risk for clinically important in-flight desaturation. For patients with underlying lung disease and dyspnea when walking on level ground, it is reasonable to monitor oxygen saturation during a 6MWT to assess the need for additional testing. (See 'Hypoxia altitude simulation test' below.)

FURTHER ASSESSMENT TO DETERMINE IN-FLIGHT NEED FOR OXYGEN

Selecting a method — For patients who need further evaluation based on inconclusive pulse oximetry (eg, pulse oxygen saturation [SpO2] between 92 and 95 percent at sea level), risk factor(s) for in-flight hypoxemia, or desaturation on six-minute walk testing (6MWT), our preferred method of predicting in-flight arterial partial pressure of oxygen (PaO2) is the hypoxia altitude simulation test (HAST), because it is more commonly available than hypobaric chamber testing and more accurate than regression equations [8]. Measurement of PaO2 under hypobaric conditions, either during actual ascent to altitude (eg, on a mountain or in an unpressurized aircraft) or in a hypobaric chamber is likely most accurate, but generally only available for research purposes [30-34].

Our approach is described in the algorithm (algorithm 1).

Comparative studies of the various methods, while limited, include the following:

Prediction of in-flight PaO2 by inhalation of a hypoxic gas mixture (HAST) was compared with prediction using mathematical equations in a retrospective study of 45 patients with chronic obstructive pulmonary disease (COPD), interstitial lung disease, or cystic fibrosis [35]. Inhalation of a hypoxic gas mixture predicted a higher in-flight PaO2 than that predicted by any of the mathematical equations used. This suggests that the mathematical equations might lead to a prescription for in-flight supplemental oxygen therapy more often than actually necessary, although confirmation with in-flight oxygenation was not performed.

In contrast, underestimation of in-flight PaO2 by 16 regression equations was noted in 27 subjects with COPD [36]. The prediction equations were inaccurate in predicting the PaO2 during HAST, and almost a third of patients predicted to maintain adequate oxygenation by the equations became hypoxemic during HAST.

In a study of 13 passengers with COPD, the pulse oxygen saturation during HAST was compared with results obtained during air travel [37]. The mean oxygen saturation during HAST was comparable to the mean in-flight oxygen saturation. However, the nadir oxygen saturation was lower during flight than during the HAST (78 versus 84 percent, respectively). This discrepancy was attributed to activity during the flight.

Few studies directly compare the HAST with in-flight measurements of oxygenation [35-37]. Additional research using larger, prospective studies that include patients with a variety of lung diseases and compare the estimated in-flight PaO2 with the actual in-flight value would be helpful to guide selection of the optimal sequence of tests.

Hypoxia altitude simulation test — The hypoxia altitude simulation test (HAST, also known as high altitude simulation test or hypoxia challenge test) involves inhalation of a mixture of nitrogen with oxygen at a concentration of 15.1 percent [30,37-39]. This oxygen concentration is chosen as it simulates the oxygen concentration that an individual would breathe at an in-flight cabin altitude of 8000 feet (2438 meters). An alternate method for delivering a hypoxic gas mixture is to use a 40 percent Venturi mask with nitrogen as the driving gas [5]. This will yield a 15 to 16 percent oxygen mixture. In the authors’ experience, this method is rarely used.

Baseline testing – At the beginning of the HAST, a sample of arterial blood is obtained for measurement of PaO2 and carbon dioxide tension (PaCO2) [39]. The patient's SpO2 and electrocardiogram are monitored continuously during the test. Nasal cannula are in place in case supplemental oxygen is needed.

Administration of hypoxic mixture – A 15.1 percent oxygen mixture is administered via a tight-fitting mask or mouthpiece. The patient is monitored closely for dyspnea, chest pain, or other change in symptoms or vital signs. Dyspnea can be monitored with use of the Borg scale (table 2). If the pulse oximeter shows oxygen desaturation below 85 percent, an arterial blood gas sample is obtained for confirmation of hypoxemia.

Arterial blood gas at end of test – If the SpO2 remains at 88 or above while breathing the hypoxic mixture, an arterial blood gas sample (or capillary blood gas in children) is obtained after 20 minutes (table 3) [5]. If the PaO2 at the end of the HAST is greater than 50 mmHg (6.6 kPa, approximately a SpO2 of 88), supplemental oxygen is NOT needed for air travel. If the PaO2 decreases to <50 mmHg (6.6 kPa, approximately a SpO2 of 85), supplemental oxygen is advised for future air travel.

Repeat oxygenation assessment during exertion for indeterminate result – As the HAST is somewhat imprecise, some experts consider it borderline if the PaO2 is 50 to 55 mmHg (6.6 to 7.4 kPa) and obtain an additional arterial blood gas sample or pulse oxygen saturation during mild exertion (eg, walking, sit-to-stand, or step exercises) while the patient is breathing the hypoxic mixture.

Hypobaric chamber — Some studies have used a hypobaric chamber to simulate an airline cabin altitude of 8000 feet (2438 meters) [16,30-34]. However, hypobaric chambers have limited availability.

Cabin altitude simulation to 8000 feet (2438 meters) using a hypobaric chamber led to oxygen desaturation (PaO2 78 to 49 mmHg [10.4 to 6.5 kPa]) in 17 patients with restrictive ventilatory impairment (eg, kyphoscoliosis, interstitial lung disease). A further decline in PaO2 to 38 mmHg (5.1 kPa) occurred with 20 watt exercise (walking slowly) at cabin altitude.

Prediction equations lack accuracy — Several regression equations have been developed to predict whether the in-flight PaO2 of normal travelers or those with pulmonary disease will fall below 50 mmHg (6.67 kPa) at 8000 feet (2438 meters) [30,31,40-43]. Depending on the equation used, values of the PaO2 at ground level, forced expiratory volume in one second/forced vital capacity (FEV1/FVC) ratio (without bronchodilators), and diffusing capacity of carbon monoxide (DLCO) are included. While these equations provide a good estimation on average, this is the least accurate method for predicting in-flight hypoxemia in individuals, and we prefer use of other methods. (See 'Selecting a method' above.)

ARRANGING FOR PORTABLE OXYGEN DURING FLIGHT

Estimating in-flight oxygen requirement — Supplemental oxygen is suggested for individuals whose in-flight resting arterial partial pressure of oxygen (PaO2) is predicted to be ≤50 mmHg (6.6 kPa) [3-5,10]. This includes patients who require long-term oxygen therapy at baseline.

Once it has been determined that the patient should have in-flight supplemental oxygen, the next step is to determine the supplemental oxygen flow rate that will result in adequate protection against hypoxemia during the flight.

Assessed during HAST – Supplemental oxygen can be titrated during a repeat high altitude simulation test (HAST) [39,44], although this method may underestimate oxygen requirements due to accumulation of oxygen from the nasal cannula in the mask [19]. (See 'Hypoxia altitude simulation test' above.)

To assess oxygen supplementation during HAST, the patient breathes the same hypoxic mixture of nitrogen with 15.1 percent oxygen, while their pulse oxygen saturation (SpO2) is monitored. Supplemental oxygen is delivered through a nasal cannula, preferably from the portable oxygen concentrator (POC) that will be used in flight. The oxygen flow required to maintain adequate oxygenation during flight can then be estimated by measuring SpO2 or PaO2 at different flow rates. Most POCs use pulsed delivery, although some can deliver continuous oxygen up to 3 L/minute [5]. (See 'Hypoxia altitude simulation test' above.)

Empiric oxygen supplementation – For patients who do not have resting hypoxemia at baseline, but are predicted to desaturate at altitude or in-flight, supplemental oxygen at 2 L/minute is generally sufficient to maintain adequate in-flight oxygenation [8]. In the absence of HAST testing, we suggest an empiric oxygen flow of 2 L/minute, based on the observation that this flow rate restored adequate oxygenation in patients whose SpO2 was below 90 percent during HAST [44,45]. In one study, an oxygen flow rate of 2 L/min was sufficient in 20 travelers with either obstructive or restrictive lung disease, although one patient with severe chronic obstructive pulmonary disease (COPD) and an arterial oxygen of 70 percent during HAST required oxygen at 3 L/minute to achieve a SpO2 over 90 percent [45]. Similarly, in a study that used hypoxic gases to simulate altitudes of 6700 and 10,000 feet, supplemental oxygen via nasal cannula at rates of 1.2 and 1.5 L/minute, respectively, restored baseline oxygen saturation in 11 patients with COPD [44].

For patients who require long-term supplemental oxygen at sea level, guidelines suggest increasing the oxygen flow 1 to 2 L/minute over baseline while in flight [5,39]. Alternatively, the liter flow requirements and, for patients at risk of hypercapnia, changes in arterial tension of carbon dioxide (PaCO2) can be determined by direct measurement during HAST, as described above [5]. (See 'Hypoxia altitude simulation test' above.)

Oxygen delivery system — Federal Aviation Administration (FAA) rules prohibit travelers from carrying their own oxygen tanks (cylinders) aboard commercial aircraft. Most patients can use an FAA-approved battery-powered portable oxygen concentrator (POC), as airlines landing in the United States are now required to allow use of these devices throughout the flight [46].

Outside the United States, regulations may differ. Several web sites offer a list of current air carriers' policies regarding use of in-flight oxygen and allowable equipment [47-50]. The European Lung Foundation has compiled information on European airlines, whose rules and charges regarding in–flight oxygen may differ from those of American carriers [49]. Efforts are underway to devise uniform standards for the use of medical oxygen in airports and on commercial aircraft [51,52].

Portable oxygen concentrators – Approved POCs (eg, Inogen One, Airsep Lifestyle, DeVilbiss Healthcare iGo) are generally available for rental from oxygen supply companies. Travelers should check with the manufacturer to determine whether their specific POC is approved for in-flight use. POCs typically provide up to 3 L/minute of continuous flow [46].

Battery power is needed for operation, so patients typically need to bring enough 12-cell batteries for 1.5 times the anticipated duration of the flight. Available POCs differ in their ability to raise oxygen saturation and the duration of battery charge [53].

The charging cord should be kept with the device rather than in checked luggage in case the POC battery needs to be recharged during a layover or delivery of checked luggage is delayed. Outlet adapters may be needed in the destination country.

In-flight oxygen – Outside the United States, airline practices about the availability and cost of in–flight oxygen are not standardized, so clinicians and patients may need to consult information for specific carriers. In situations where oxygen is supplied by the airline, practical details such as the interface (eg, mask or nasal cannula) and liter flow options are likely to vary among carriers. Prospective oxygen-using travelers are advised to seek comparative, current information when planning a trip. (See 'Traveler resources' below.)

Transport of oxygen cylinders – For patients who will require oxygen at their destination, either the POC can be used or arrangements can often be made with a local oxygen supplier for delivery of oxygen cylinders.

Transport of oxygen cylinders in checked baggage for use at a destination may not be allowed or may require packaging in a flame proof "super box," depending on airline regulations.

Communication with the airlines — Patients should be encouraged to contact their airline well in advance (at least two weeks) of anticipated air travel, which means that the evaluation of supplemental oxygen requirements must be performed at least two to three weeks before actual travel [46].

The traveler will need to inform the Transportation Security Administration (TSA) official during screening that they have a POC and whether they can disconnect from oxygen during screening. Communication with the airline and TSA officials is facilitated by a clinician's letter (figure 2) and/or a TSA notification card specifying the underlying pulmonary condition, the prescribed liter flow, and whether supplemental oxygen is required just during flight or throughout the day.

PATIENT AND DISEASE SPECIFIC CONSIDERATIONS — Most of the data on the effects of air travel on oxygenation come from studies of adults with chronic obstructive pulmonary disease (COPD). However, children and adults with other lung diseases (eg, cystic fibrosis, pulmonary hypertension, pulmonary lymphangioleiomyomatosis [LAM]) may have disease-specific issues related to air travel. In addition, the accuracy of methods to predict hypoxemia in-flight has not been well studied in these patient populations.

Children — Limited guidance is available for children and infants with respiratory disease. The British Thoracic Society (BTS) guidelines suggest empiric availability of in-flight oxygen at 1 to 2 L/minute for infants born prematurely who have not yet reached their delivery date and hypoxia altitude simulation testing (HAST) in a plethysmography box for older infants and children with a history of respiratory disease [5]. For children and infants with lung disease who require oxygen at baseline, a reasonable course is to double their usual oxygen flow, although supportive data are limited; alternatively, a respiratory pediatrician should be consulted and HAST obtained if feasible [5].

Cystic fibrosis — Patients with cystic fibrosis tend to have few symptoms related to oxygen desaturation at altitude, possibly due to chronically lower oxygen saturation at sea level. The consequences of brief periods of asymptomatic hypoxemia in these relatively young patients without concomitant heart disease are not known. In the absence of clear data, the same guidelines for supplemental oxygen are used for patients with cystic fibrosis as for other patients. (See 'Indications for further evaluation' above.)

An observational study evaluated oxygenation and lung function at an altitude of 8694 feet (2650 meters) in 36 patients with cystic fibrosis [54]. An arterial partial pressure of oxygen (PaO2) less than 50 mmHg (6.67 kPa) at rest was observed in one-third at rest and in two-thirds during low level exercise (30 watts), the equivalent of walking down the aisle. None of the patients had symptoms at rest and only one patient experienced light-headedness with exercise, even with hypoxemia. Patients with a baseline PaO2 of 60 mmHg (8 kPa) or higher tolerated several hours of exposure to an altitude of 8694 feet without symptoms. However, patients with more severe airflow obstruction tended to have a greater degree of desaturation at altitude.

A separate study evaluated 30 adult patients with cystic fibrosis, of whom 16 had a baseline pulse oxygen saturation (SpO2) <95 percent, and 15 had a forced expiratory volume in one second (FEV1) <50 percent of predicted [55]. A moderate correlation was noted between FEV1 and desaturation during HAST, but no correlation was noted between baseline SpO2 and HAST SpO2. A better correlation was noted between SpO2 during maximal exercise and HAST PaO2. (See 'Hypoxia altitude simulation test' above.)

Patients with cystic fibrosis who anticipate a long flight may need to bring a portable, battery-powered nebulizer for administration of medication in-flight. All medications and spacer devices should be carried in hand luggage. The use of a portable nebulizer in-flight often requires prior permission from the airline. (See "Cystic fibrosis: Overview of the treatment of lung disease".)

Pulmonary hypertension — Patients with pulmonary hypertension may be at particular risk for in-flight hypoxemia, as a low inspired oxygen tension can trigger pulmonary artery vasoconstriction and exacerbate hypoxemia [21,56]. The combination of exertion and low in-flight oxygen tension may lead to further oxygen desaturation.

In the absence of simulation testing, provision of supplemental oxygen in-flight is reasonable for those with a mean pulmonary artery (PA) pressure of 35 mmHg or higher or a systolic PA pressure of 50 mmHg (6.67 kPa) or higher [21].

Patients with more severe pulmonary hypertension may need to completely avoid air travel, although minimal data are available to guide the clinician in this decision. It has been suggested that patients with New York Heart Association Class III and IV disease (table 4) avoid air travel and that those with less severe disease undergo hypoxia altitude simulation testing [13,21] (see 'Hypoxia altitude simulation test' above). A small study evaluated 34 patients with pulmonary hypertension (47 percent were Class III or IV) during commercial flights and found that 38 percent developed respiratory symptoms in-flight [56]. Desaturation was common, occurring in 26 percent, and the overall mean decline in oxygen saturation during flight was 4.9 percent.

Pulmonary lymphangioleiomyomatosis — Patients with LAM are at risk of hypoxemia and pneumothorax during air travel and should be screened for possible in-flight hypoxemia, as described above. (See 'Screening for in-flight hypoxemia' above.)

Details regarding the risk and safety of air travel in patients with LAM are discussed separately. (See "Sporadic lymphangioleiomyomatosis: Treatment and prognosis", section on 'Air travel'.)

Interstitial lung disease — Patients with ILD compensate for hypoxemia by increasing minute ventilation and heart rate; in advanced ILD, patients may not be able to increase minute ventilation sufficiently [5]. Studies of the effects of altitude and air travel in ILD are limited [24,57,58]. It seems likely that supplemental oxygen is not needed in patients with baseline SpO2 >95 percent at rest and ≥95 percent on six-minute walk test (6MWT) or shuttle walk test [5].

Based on data from 88 patients with ILD, patients with both a sea level PaO2 ≤70.6 mmHg [9.42 kPa] and a DLCO ≤50 percent of predicted should use supplemental oxygen in flight [5,57]. Patients with either a sea level PaO2 ≤70.6 mmHg [9.42 kPa] or DLCO ≤50 percent of predicted (but not both) should undergo HAST.

ADDITIONAL TRAVEL CONSIDERATIONS

Access to medications — Travelers should ensure easy access to necessary medications (eg, inhalers), in case of travel delays or lost luggage, by keeping these medications in carry-on luggage. It is prudent to carry an extra copy of prescriptions for necessary medications and an emergency supply of "contingency" medications (perhaps a course of an antibiotic and a systemic glucocorticoid, as appropriate). A list of clinicians in locations along the travel route is also helpful.

As noted above, patients with cystic fibrosis may need access to a portable nebulizer for delivery of medication in-flight. (See 'Cystic fibrosis' above.)

Infection, pneumothorax, and VTE

Exposure to respiratory viruses and influenza can be a particular problem for patients with lung disease. Hand hygiene, seasonal influenza vaccination, and SARS-CoV-2 vaccination can mitigate the risk of infection. (See "Seasonal influenza vaccination in adults" and "Seasonal influenza in children: Prevention with vaccines".)

The exact risk of pneumothorax for patients with cystic or emphysematous lung disease is not known, but is thought to be low except in patients with a prior pneumothorax who have not undergone surgical or video-assisted thoracoscopic pleurodesis. Pneumothorax with a persistent air leak is considered a contraindication to air travel, and recent pneumothorax needs individualized assessment. (See 'Clinical effects' above and "Pneumothorax and air travel".)

Air travel increases the risk of venous thromboembolism (VTE), especially with prolonged travel (eg, more than four to six hours), although the absolute risk remains low in the absence of other risk factors. Thromboprophylaxis with general measures, such as avoidance of dehydration and frequent ambulation or flexion-extension of the ankles and knees, are adequate for most patients with lung disease other than prior VTE. Graduated compression stockings may be beneficial in patients at higher risk. Pharmacologic prophylaxis is usually reserved for travelers at particularly high risk and is described separately. (See "Prevention of venous thromboembolism in adult travelers".)

Traveler resources

Federal Aviation Administration (FAA). Acceptance Criteria for Portable Oxygen Concentrators (March 22,2022)

Transportation Security Administration (TSA). Portable oxygen concentrators (March 22,2022)

Alpha-1 Foundation. www.alphaone.org (March 22, 2022)

British Lung Foundation. https://www.blf.org.uk/support-for-you/going-on-holiday/flying-with-a-lung-condition (March 22, 2022)

European Federation of Allergy and Airways Diseases Patients’ Associations. Enabling Air Travel with Oxygen in Europe (March 22, 2022)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Supplemental oxygen" and "Society guideline links: Management of inflight medical events".)

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Beyond the Basics topics (see "Patient education: Supplemental oxygen on commercial airlines (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

Despite pressurization of airliner cabins, flying at a high altitude can induce significant hypoxemia in patients with underlying lung disease. Patients who are at risk of becoming hypoxemic (arterial partial pressure of oxygen [PaO2] <50 mmHg [<6.6 kPa] or pulse oxygen saturation [SpO2] <85 percent) are candidates for supplemental oxygen during the flight. (See 'Effects of air travel' above.)

Our approach to identifying patients with lung disease who are at increased risk of in-flight hypoxemia is described in the algorithm (algorithm 1). We use an initial assessment of underlying lung disease and SpO2 to determine which patients need additional testing and which clearly do or do not need in-flight oxygen without further testing. (See 'Screening for in-flight hypoxemia' above.)

For those who need further assessment, hypoxia altitude simulation testing (HAST), which involves breathing 15.1 percent oxygen for 20 minutes, is preferred as it is reasonably accurate and broadly available. Hypobaric chamber testing is most accurate, but has limited availability. Regression equations that incorporate baseline oxygenation and pulmonary function test parameters are not sufficiently accurate. (See 'Further assessment to determine in-flight need for oxygen' above.)

For patients who require long-term supplemental oxygen at baseline, we suggest using an increased liter flow while in-flight (Grade 2C). The baseline oxygen flow can be empirically increased by 1 to 2 L/minute over baseline. Alternatively, the liter flow requirement can be determined by direct measurement during a HAST. (See 'Estimating in-flight oxygen requirement' above.)

For patients who do not require supplemental oxygen at baseline, resting pulse oximetry at sea level and assessment of the underlying lung disease are used to screen for likelihood of in-flight hypoxemia (algorithm 1).

For patients with a resting SpO2 <92 percent, we suggest use of supplemental oxygen in-flight (Grade 2C). (See 'Screening for in-flight hypoxemia' above.)

Patients who have a SpO2 of 95 or higher at sea level are unlikely to have significant hypoxemia during air travel. To identify the minority of such patients who are at risk of in-flight hypoxemia, such as those with prior in-flight symptoms or baseline exertional dyspnea, a six-minute walk test (6MWT) can be performed. If the SpO2 decreases to <84 percent during the 6MWT, HAST is needed to determine likelihood of in-flight hypoxemia. If 6MWT SpO2 remains ≥84 percent, supplemental oxygen is not needed during air travel. (See 'Resting pulse oximetry' above.)

Patients who have a resting SpO2 between 92 and 95 percent at sea level should undergo a 6MWT with pulse oximetry. Desaturation to a SpO2 <84 percent indicates the need for in-flight oxygen. For those with a 6MWT SpO2 ≥84 percent, a HAST should be done to determine the need for in-flight supplemental oxygen. When available, the HAST is preferred over regression equations for determining the need for in-flight supplemental oxygen. (See 'Indications for further evaluation' above and 'Hypoxia altitude simulation test' above.)

For patients who are predicted to require supplemental oxygen during air travel, the oxygen flow rate required to prevent hypoxemia can be determined during a repeat HAST with supplemental oxygen administered by nasal cannula. If hypercapnia is a concern (eg, current or prior hypercapnia), arterial tension of carbon dioxide (PaCO2) can be assessed by arterial blood gas or end-tidal CO2 during administration of supplemental oxygen. Alternatively, an oxygen flow of 2 L/minute is generally sufficient. (See 'Estimating in-flight oxygen requirement' above.)

Federal Aviation Administration (FAA) rules prohibit travelers from carrying their own oxygen tanks (cylinders) aboard commercial aircraft. Airlines landing in the United States are now required to allow use of FAA-approved, battery-powered, portable oxygen concentrators (POCs) throughout the flight. However, a prescription is needed from the clinician (figure 2) and prior approval is needed from the airline. Outside the United States, airline practices about in–flight oxygen are not standardized, and patients will need to obtain information for the specific country and airline. (See 'Arranging for portable oxygen during flight' above.)

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