Altitude pulmonary edema in high-altitude crew

A 35-year-old flight attendant is on the second night of a layover in a city more than 3500 meters above sea level. On the first day, she walked up a long slope with the crew and felt more tired than her colleagues. On the second night, she wakes up with a dry cough and shortness of breath even while lying down. The doctor called to the hotel hears crackles at the right base, measures a temperature slightly above normal and sees on the oximeter a saturation well below what is expected, even for the altitude. The scene is fictional and was written for teaching.

This text uses the picture as a setting for clinical reasoning. The trap is tempting: cough, low fever and crackles at the base suggest pneumonia, and the natural course would be antibiotics and rest at the hotel. If the picture is high-altitude pulmonary edema, staying at altitude is the mistake. The text is not a summary of crew layover rules. If you play the case of the day on NEXO, you will recognize the challenge: where the person is changes the most likely diagnosis.

Key points

• High-altitude pulmonary edema appears above 2500 to 3000 meters, usually within 1 to 5 days.
• The first signs are shortness of breath on greater exertion than colleagues, mild cough and chest tightness.
• Low fever and crackles are part of the picture and can mimic pneumonia.
• Descending or giving oxygen is the main treatment.
• Extended-release nifedipine is the vasodilator most used when descent and oxygen are not available.
• Diuretics are not part of standard treatment.

Why this is a reasoning setting

The case brings together an environment that changes physiology, a healthy person and a respiratory picture that looks common. A review on acute altitude illnesses describes that, between 1 and 5 days after arriving at altitudes of 2500 meters or more, a person is at risk of three forms of illness: acute mountain sickness, cerebral edema and high-altitude pulmonary edema (Luks, Swenson and Bärtsch, 2017). The flight attendant is exactly in that window.

Crews who lay over at high-altitude airports arrive without acclimatization, often after a night of work and with little sleep. The same authors note that lack of acclimatization is the main risk factor and that rapid ascent is the most important factor for the illness (Luks, Swenson and Bärtsch, 2017). A flight takes a person from sea level to altitude in a few hours, with no adaptation at all.

What the scene teaches

The flight attendant brings a clue from exertion on the first day and a clue from rest on the second. The progression is typical. The post on signs, symptoms and history shows how the sequence of symptoms can be more informative than any isolated finding.

When and in whom it happens

The review by Luks and colleagues places high-altitude pulmonary edema in healthy people above 2500 to 3000 meters, within 1 to 5 days of arrival (Luks, Swenson and Bärtsch, 2017). A more recent review on environment-induced pulmonary edema describes that the picture usually develops within 1 to 2 days above 3000 meters and that it can affect healthy and often young people (Tetzlaff, Swenson and Bärtsch, 2022).

Susceptibility varies widely between people. In the same review, the frequency in those who ascend to 4559 meters in 24 hours is about 6 in 100 among mountaineers with no prior history and 62 in 100 among those who have had the picture before (Tetzlaff, Swenson and Bärtsch, 2022). Luks and colleagues describe a probability of 60 in 100 of repeating the edema with a 1 to 2 day ascent to the same altitude in those who have had the documented picture (Luks, Swenson and Bärtsch, 2017).

Frequency also depends on the rate of ascent. An Indian review estimates edema in 0.01 to 0.1 per 100 visitors to Colorado ski resorts, in about 4 per 100 among those who climb more than 600 meters per day in the Himalayas and the Alps, and in up to 15 per 100 soldiers flown to 5500 meters (Paralikar, 2012). Direct air travel to a high city is precisely the rapid ascent that increases the risk.

The question about previous layovers

For the flight attendant, this makes one question essential: has she ever had shortness of breath, cough or unusual fatigue on previous layovers in the same city? A positive history greatly increases the probability of the diagnosis now and changes the planning of upcoming layovers. The post about base rate in diagnosis recalls that the frequency of a disease in a specific group weighs in before any test.

How the condition presents

The initial symptoms described by Luks and colleagues are shortness of breath on exertion out of proportion to companions, mild cough, chest tightness and a drop in physical performance (Luks, Swenson and Bärtsch, 2017). As the edema advances, cough and dyspnea worsen and orthopnea appears. Gurgling in the chest and pink, frothy sputum indicate advanced cases.

The examination shows cyanosis, tachypnea, tachycardia, slightly raised temperature and crackles on auscultation (Luks, Swenson and Bärtsch, 2017). In this case, the flight attendant had greater fatigue than her colleagues on the first day and, on the second, cough and dyspnea at rest with crackles and low-grade fever. The presentation is the one described in the review, not an atypical picture.

The hidden severity

Hypoxemia can be very intense. The review by Luks and colleagues reports that, in advanced cases at 4559 meters, the mean arterial oxygen pressure was around the low 20s mmHg, against 35 to 45 mmHg in healthy controls at the same altitude (Luks, Swenson and Bärtsch, 2017). Tetzlaff and colleagues estimate a mortality of about 50 per 100 without adequate treatment, and note that the symptoms, except for reduced exercise tolerance, disappear within hours after a rapid descent (Tetzlaff, Swenson and Bärtsch, 2022).

Pathophysiology: a leak driven by pressure

The core of the mechanism is hypoxic pulmonary vasoconstriction. In response to air with less oxygen, the pulmonary arterioles contract. In susceptible people, this response is exaggerated and uneven. The review by Luks and colleagues describes that the exaggerated rise in pulmonary artery pressure comes with microvascular pressure above 20 mmHg, a threshold for the formation of alveolar edema (Luks, Swenson and Bärtsch, 2017).

The authors cite three proposed mechanisms: leakage in the arterioles, uneven hypoxic vasoconstriction between regions and constriction of the veins (Luks, Swenson and Bärtsch, 2017). If the vasoconstriction is uneven, flow concentrates where it is lower, capillary pressure rises and fluid leaks out. In a Swiss study with mountaineers who climbed to 4559 meters, the 8 who had edema, on the second or third day, already showed before the evident picture a greater drop in forced vital capacity than the 10 controls and lower nocturnal saturation (Clarenbach and colleagues, 2012). The changes are consistent with a less compliant lung and impaired gas exchange.

Edema without inflammation at the start

The fluid from bronchoalveolar lavage in early edema shows a pattern of noncardiogenic, noninflammatory hydrostatic edema (Luks, Swenson and Bärtsch, 2017). The pressure alters the permeability of the barrier between alveolus and capillary or causes direct mechanical injury, which the authors call capillary stress failure. This explains why the distribution on imaging is irregular and why lowering pulmonary artery pressure, with descent, oxygen or a vasodilator, works.

The post about linking mechanism and symptom shows how this kind of reasoning helps predict treatment. If the problem is pressure, the solution is to lower the pressure. If it were infection, the treatment would be different.

The differential diagnosis

Cough, dyspnea, low-grade fever and crackles have several explanations. The hypotheses the scene requires considering are:

• High-altitude pulmonary edema.
• Community-acquired pneumonia.
• Decompensated heart failure.
• Pulmonary embolism, especially after a long flight.
• Viral respiratory infection, including COVID.
• Asthma or bronchospasm worsened by cold, dry air.

Pneumonia is the most dangerous differential to confuse, because the wrong treatment keeps the person at altitude. Low-grade fever and crackles appear in both conditions. What weighs in favor of edema is the context: recent arrival at altitude, worsening on exertion on the first day and progression to dyspnea at rest on the second.

Altitude edema is not COVID

During the pandemic, the idea arose of treating COVID lung injury as if it were altitude edema. Luks and Swenson argue that, despite similarities such as hypoxemia, opacities on imaging and changes in lung compliance, the mechanisms of the two conditions are fundamentally different and cannot be seen as equivalent (Luks and Swenson, 2020). The authors warn that vasodilators and acetazolamide, useful at altitude, should not be used in COVID.

The reasoning works both ways. A flight attendant with a positive test for a respiratory virus in a high-altitude city can have both things, and treating one does not replace treating the other. The post on differential diagnosis with clues shows how to keep hypotheses open until context and tests decide.

Closing too early

The hotel doctor sees a woman with fever, cough and crackles at the base. Pneumonia is the first explanation that comes to mind. A Turkish review on altitude illnesses recalls that the drop in physical performance and dry cough are the earliest symptoms of pulmonary edema, and that it can lead to death within hours to days if not recognized (Aksel et al., 2019). The post on diagnostic pause helps build the habit of asking "what else could it be?" before closing.

Tests: what helps on site

At altitude, resources are limited and the diagnosis is mostly clinical. Radiography and CT in symptomatic edema show an irregular, peripheral and nodular distribution of edema (Luks, Swenson and Bärtsch, 2017). The image from the review shows a mountaineer with predominantly right-sided edema, which reminds us that asymmetry does not rule out the diagnosis.

Chest ultrasound has been studied on site. In a prospective Chinese study of 148 patients with suspected high-altitude pulmonary edema, 126 had the diagnosis confirmed, and ultrasound had a sensitivity of about 98 and a specificity of about 91 in every 100. It was more sensitive than crackles and than radiography, and tracked improvement well after treatment (Yang et al., 2018). There is one caveat: in a study of 42 healthy visitors at 2745 meters, all had B-lines at the lung bases on the third day (Lahham et al., 2023). Some B-lines alone, without a clinical picture, do not close the diagnosis.

The oximeter as an ally

Oxygen saturation at altitude is lower than at sea level in anyone. What draws attention is a saturation much lower than that of colleagues at the same altitude, and a saturation that improves little with rest. In this case, the flight attendant's saturation was well below that of her colleagues, which reinforces the diagnosis. The sources read do not define a numerical saturation target for this scenario, and so the text does not give that number.

Clue	Favors high-altitude pulmonary edema	Source
Recent arrival above 2500 to 3000 meters	Window of 1 to 5 days	Luks, Swenson and Bärtsch, 2017
Dyspnea on exertion greater than that of companions	Typical initial symptom	Luks, Swenson and Bärtsch, 2017
Low-grade fever and crackles	Part of the picture	Luks, Swenson and Bärtsch, 2017
Irregular, peripheral edema on imaging	Pattern described on radiography and CT	Luks, Swenson and Bärtsch, 2017
Previous episode on a similar ascent	Frequent recurrence	Tetzlaff, Swenson and Bärtsch, 2022
Improvement within hours with descent	Reinforces the diagnosis	Tetzlaff, Swenson and Bärtsch, 2022

Treatment: descend, oxygen and vasodilator

Treatment depends on the setting. Luks et al. describe that conscious patients with access to health services often do not need to descend and can be treated with supplemental oxygen and close observation (Luks, Swenson and Bärtsch, 2017). In remote or low-resource settings, the person should descend or, if that is not possible, receive oxygen or stay in a portable hyperbaric chamber, along with a pulmonary vasodilator.

Luks and Swenson sum up the same principle: the main treatment is supplemental oxygen or, when it is lacking, descent (Luks and Swenson, 2020). For the flight attendant in a city with a hospital, oxygen and observation may be enough. If no oxygen is available, the flight back to a lower altitude becomes part of the treatment.

Nifedipine and tadalafil

When descent and oxygen are not available, extended-release nifedipine is the preferred agent for treatment, according to the review (Luks, Swenson and Bärtsch, 2017). The medication table in the same review lists extended-release nifedipine 30 mg every 12 hours for treatment and tadalafil 10 mg every 12 hours as an alternative, with the warning that tadalafil should not be combined with nifedipine.

The evidence base is small. The authors support the preference for nifedipine with a small study without a control group, and they describe the use of phosphodiesterase 5 inhibitors based on isolated reports (Luks, Swenson and Bärtsch, 2017). A review of the evidence notes that, without treatment, mortality approaches 50 in every 100 and that descending to a lower altitude is curative (Woods and Alcock, 2021).

What not to do

The review by Luks and colleagues states that diuretics are not part of standard protocols, because many patients have depleted volume at the time of illness and the diuretic increases the risk of hypotension (Luks, Swenson and Bärtsch, 2017). The logic of cardiogenic edema does not apply here, because the heart is not the cause. An antibiotic may make sense if there is real doubt about pneumonia, but it does not replace descending or giving oxygen.

Prevention on the next layovers

The best prevention is not a drug. Luks and colleagues state that, since climbing too fast remains the main risk factor, a slow ascent to the final altitude is the best method to prevent the illness (Luks, Swenson and Bärtsch, 2017). For a crew that arrives by plane, a slow ascent is not possible, which makes personal history and layover planning even more important.

For people who have already had high-altitude pulmonary edema, preventive medication has evidence. A 2026 clinical review summarizes the 1991 randomized trial with 21 mountaineers with a history of edema: on a new ascent to 4559 meters, the condition appeared in 7 of 11 who received placebo and in 1 of 10 who received nifedipine (Adhikari and colleagues, 2026). Luks and colleagues describe that tadalafil, dexamethasone and salmeterol also prevented edema in susceptible people, the latter with a smaller effect (Luks, Swenson and Bärtsch, 2017).

How the review organizes prevention

Table 2 of the review by Luks and colleagues gives the same treatment doses for prevention, extended-release nifedipine 30 mg every 12 hours or tadalafil 10 mg every 12 hours, and reserves preventive medication mainly for those who have already had the condition (Luks, Swenson and Bärtsch, 2017). The 2026 review, based on the wilderness medical society guideline, describes starting 24 hours before the ascent and continuing until the start of descent, or for 4 to 7 days after reaching the maximum altitude, whichever comes first (Adhikari and colleagues, 2026). It also notes that, in most European countries, these medications are not approved for preventing altitude illness.

For the flight attendant, this means a conversation with the occupational physician about future layovers. The decision involves the city's altitude, the length of stay, personal history and the company's rules, which this text does not summarize. The post on prognostic reasoning shows how today's diagnosis changes tomorrow's planning.

The scene reviewed hour by hour

Rereading the case in order helps show where each clue came in. On the first day, the flight attendant arrived by plane, without acclimatization, after a work shift. Walking up the hill with the crew and feeling more tired than her colleagues is exactly the exertional dyspnea out of proportion that the review describes as an initial symptom (Luks, Swenson and Bärtsch, 2017). At that moment, no one would think of illness, and that is why the clue is usually lost.

On the first night, she slept at altitude. The review reminds us that the risk altitudes refer to the altitude at which the person sleeps (Luks, Swenson and Bärtsch, 2017). A rotation that includes an overnight stay in a high city exposes the crew in a different way than a short stop at the airport.

On the second night, the dry cough and shortness of breath when lying down show progression to orthopnea. Crackles at the right base and a low fever complete the clinical picture described in the review. The saturation far below that of colleagues indicates that gas exchange is already compromised. Each clue alone would have another explanation, but together, at the right time and in the right place, they point to edema.

What the hotel doctor can do

The practical decision has few steps. Ask for oxygen and an evaluation at a health service, if one is available. If there is no oxygen, arrange the descent, which for a crew may be the flight to a lower city, with monitoring. Keep pneumonia as an associated hypothesis, without letting it delay the main measure. Record the episode for planning future rotations.

The post about signs, symptoms and history is useful again here: a set of signs, taken together, is worth more than each one alone.

Reasoning: what remains from the case

The scenario teaches you to read the place as part of the diagnosis. The same symptoms at sea level and at 3500 meters point to different diseases. The second lesson is about the mechanism: understanding that edema is a pressure leak explains why descending, giving oxygen or using a vasodilator works, and why a diuretic does not help.

The third lesson is about urgency. A disease that can kill in a few days and improves in hours with descent calls for a quick decision, even with doubt. The post about diagnostic uncertainty discusses how to act when doubt cannot wait, and the text about clinical decision-making shows how to choose the approach that protects the patient from the two main hypotheses.

How NEXO helps train this reasoning

To use the case of the day as training, try three habits. Before the first guess, ask where the person is and how long they have been there. With each clue, see whether it changes the approach or only confirms what you already thought. After the result, note whether the first plausible diagnosis closed your list.

Three exercises with cases

Ask about the place. For each case, write down the altitude, the weather and the time since arrival.

Link mechanism and approach. Write the mechanism of the main hypothesis and the treatment that follows from it.

Test the opposite approach. Ask what would happen if you treated the neighboring hypothesis instead of the main one.

The post about learning based on clinical cases shows how cases help fix this habit.

The limits on using the game are described on the NEXO economy page. If you research the teaching of clinical reasoning, the page for researchers explains how to get in touch. Professionals who write or review cases find information under curation and under creators, and institutions can learn about the proposal on the partnerships page.

Frequently asked questions

Can high-altitude pulmonary edema happen in healthy people?

Yes. It occurs in healthy people above 2500 to 3000 meters, within 1 to 5 days (Luks, Swenson and Bärtsch, 2017).

Can a low fever be part of the picture?

Yes. A slightly raised temperature and crackles are among the examination findings (Luks, Swenson and Bärtsch, 2017).

Can oxygen and observation be enough near a hospital?

Yes. Conscious patients with access to a health service are often treated with oxygen and close observation (Luks, Swenson and Bärtsch, 2017).

Does nifedipine help when there is no oxygen and no descent?

Yes. Extended-release nifedipine is the preferred agent in this situation (Luks, Swenson and Bärtsch, 2017).

Can someone who has already had the condition prevent it?

Yes. Nifedipine and tadalafil prevented edema in susceptible people (Luks, Swenson and Bärtsch, 2017; Adhikari and colleagues, 2026).

Final checklist

• I asked about the altitude and how long the person had been there.
• I asked about similar episodes on previous climbs or trips.
• I took seriously the shortness of breath on greater exertion than that of colleagues.
• I remembered that low-grade fever and crackles are part of altitude edema.
• I kept pneumonia, heart failure and embolism in the differential.
• I compared the saturation with that of colleagues at the same altitude.
• I offered oxygen and observation, or organized the descent.
• I reserved nifedipine for when oxygen or descent are lacking.
• I avoided diuretics.
• I planned prevention for the next climbs with the occupational physician.

Want to practice reasoning with progressive clues? Play the case of the day.

References

1. Adhikari S, Zimmer R, Brugger H, et al. Prevention of altitude illness in adults: preparing people for travel to high altitude. BMJ. 2026. PMID 42686358.
2. Aksel G, Çorbacıoğlu ŞK, Özen C. High-altitude illness: Management approach. Turk J Emerg Med. 2019. PMID 31687609.
3. Clarenbach CF, Senn O, Christ AL, et al. Lung function and breathing pattern in subjects developing high altitude pulmonary edema. PLoS One. 2012. PMID 22829927.
4. Lahham S, Moeller J, Choi H, et al. Application of Point-of-care Ultrasound for Screening Climbers at High Altitude for Pulmonary B-lines. West J Emerg Med. 2023. PMID 36976605.
5. Luks AM, Swenson ER, Bärtsch P. Acute high-altitude sickness. Eur Respir Rev. 2017. PMID 28143879.
6. Luks AM, Swenson ER. COVID-19 Lung Injury and High-Altitude Pulmonary Edema. A False Equation with Dangerous Implications. Ann Am Thorac Soc. 2020. PMID 32735170.
7. Paralikar SJ. High altitude pulmonary edema-clinical features, pathophysiology, prevention and treatment. Indian J Occup Environ Med. 2012. PMID 23580834.
8. Tetzlaff K, Swenson ER, Bärtsch P. An update on environment-induced pulmonary edema: "When the lungs leak under water and in thin air". Front Physiol. 2022. PMID 36277204.
9. Woods P, Alcock J. High-altitude pulmonary edema. Evol Med Public Health. 2021. PMID 33732460.
10. Yang W, Wang Y, Qiu Z, et al. Lung Ultrasound Is Accurate for the Diagnosis of High-Altitude Pulmonary Edema: A Prospective Study. Can Respir J. 2018. PMID 30364105.