Decompression sickness: diving, flying and recompression

A forty-one-year-old woman seeks the airport emergency department shortly after landing. She spent the week diving, made two dives the day before and boarded the next morning. During the flight, she felt pain in her right shoulder, which got worse, and now she notices tingling in her hand and unusual fatigue. She thinks she slept in an awkward position. The scene is fictional and was written for teaching. This text uses that picture as a clinical reasoning scenario: how to recognize decompression sickness, why flying after diving weighs on the history, what to do in the first hours and why recompression is the definitive treatment.

NEXO is a daily medical diagnosis game: one clinical case a day, up to six progressive clues, and ICD-10 proximity feedback across five levels.

This text is not a guide to hyperbaric medicine. Chamber treatment, transport and return to diving follow their own guidelines and depend on specialists. The interest here is the reasoning: why vague symptoms after a dive deserve attention, which questions help and which habits lead to a missed diagnosis. If you play the case of the day on NEXO, you will recognize the move: the clue that changes everything may be what the patient did the day before.

Key points

• Decompression sickness is caused by gas bubbles that form when the pressure around the body decreases.
• It can appear after diving, after a flight taken shortly after diving and, more rarely, in aviators and astronauts.
• Symptoms range from itching and joint pain to neurological deficits, circulatory collapse and death.
• First aid is oxygen at the highest possible concentration, and the definitive treatment is recompression in a hyperbaric chamber.
• Waiting a safe interval before flying after diving reduces the risk.

Why decompression sickness is a reasoning scenario

Vann and colleagues describe decompression sickness as a condition caused by bubbles inside or outside the vessels, formed when the ambient pressure decreases (Vann and colleagues, 2011). The term includes arterial gas embolism, in which gas reaches the arterial circulation, and decompression sickness proper, caused by bubbles that form in the tissues from dissolved inert gas. Both can occur in divers, compressed-air workers, aviators and astronauts.

For the clinician, this disease is a good scenario because the symptoms are common and misleading. Shoulder pain, fatigue and tingling have many explanations. The clue that changes everything is the sequence: dive, ascent to the surface and, sometimes, a flight soon after. Without the question about diving, the picture looks like nothing more than muscle pain.

What the scene teaches

In the opening scene, the week of diving, the two dives the day before, the morning flight and the symptoms that appeared on the plane form a pattern. No clue, on its own, defines the diagnosis. The post on signs, symptoms and history shows how context changes the weight of each finding. Here, the question "what have you done in the last few days?" is part of the examination.

Simple physics, complex clinical picture

During a dive, the body absorbs more inert gas, especially nitrogen, because the pressure is higher. On the ascent, this gas must leave gradually through breathing. Aerospace Medical Association guidance notes that exposure to the low pressure of flight shortly after the high pressure of diving favors nitrogen leaving as microbubbles in the tissues (Aerospace Medical Association, 2003). The physics is simple, but the way the bubbles distribute through the body explains the variety of symptoms.

What increases the risk

Vann and colleagues note that the risk of decompression sickness is affected by immersion, exercise and heat or cold (Vann and colleagues, 2011). Depth, bottom time, ascent speed and repeated dives also weigh. Aerospace Medical Association guidance notes that the disease can occur in any diver, even without a flight after diving, especially when dive tables are not followed (Aerospace Medical Association, 2003).

Patent foramen ovale

Abdelfattah and colleagues recall that patent foramen ovale, a communication between the heart's atria that persists in some people, raises the risk of decompression sickness by letting bubbles pass into the arterial circulation (Abdelfattah and colleagues, 2022). In the authors' analysis, closure of the foramen was associated with fewer episodes, but about 1 in 13 patients had an adverse event from the procedure. The decision is individual and belongs to specialists.

Freediving counts too

Schipke and colleagues reviewed cases of decompression sickness in freediving, without a tank (Schipke and colleagues, 2026). The authors describe that in this group, cerebral symptoms that can mimic a stroke predominate, often in young and healthy people. Short intervals between repeated dives, deep dives and rapid ascents are among the risk factors. The question about diving, therefore, is not limited to those who use a tank.

How the disease presents

Vann and colleagues describe manifestations ranging from itching and mild pain to neurological symptoms, cardiac collapse and death (Vann and colleagues, 2011). The Aerospace Medical Association guidance cites joint and muscle pain, pulmonary conditions, neurological dysfunction and circulatory collapse (Aerospace Medical Association, 2003).

Pain that has no other explanation

Joint pain, especially in the shoulder and elbow, is a classic form. The patient usually attributes it to the effort of carrying equipment or to a bad position on the plane. The clue lies in the lack of another explanation and in the link to diving. Mitchell and colleagues recall that girdle pain around the trunk suggests spinal cord involvement and does not count as limb pain, and that mild pain that keeps getting worse cannot be considered mild until it stabilizes or starts to recede (Mitchell and colleagues, 2018).

Subtle neurological signs

Tingling, weakness, dizziness, difficulty concentrating and intense fatigue can be signs of neurological involvement. In the scene, tingling in the hand changes the severity of the case. The post about diagnostic uncertainty helps you think about how to act when vague symptoms may hide a serious condition.

Arterial gas embolism

Vann and colleagues recall that arterial gas embolism can happen when gas from the alveoli, or bubbles that were in the veins, reaches the arterial circulation (Vann and colleagues, 2011). In diving, this is usually linked to a rapid ascent with air trapped in the lungs. Symptoms tend to appear soon after reaching the surface and may include confusion, loss of consciousness, weakness on one side of the body and seizures. The authors recall that arterial gas embolism also has causes unrelated to diving, linked to medical procedures. For reasoning, the time between the ascent and the symptoms is an important clue: minutes suggest embolism, hours suggest bubbles formed in the tissues.

Presentations in a table

The table below summarizes, in a didactic way, presentations of decompression sickness and other causes that can confuse. It simplifies a complex topic and does not replace the assessment of a diving medicine specialist.

Presentation	What suggests decompression sickness	What can confuse
Joint pain	Appears hours after the dive or during the flight, without trauma	Effort with equipment, muscle injury
Itching or skin spots	Appear after the dive	Allergy, marine animal sting
Tingling or weakness	Appears after the dive, sometimes irregularly	Nerve compression, anxiety
Dizziness or vertigo	After the dive, with or without hearing loss	Ear barotrauma, nausea
Shortness of breath or chest pain	Right after the ascent	Heart problem, partial drowning
Confusion or loss of consciousness	Minutes after the ascent	Arterial gas embolism, hypoglycemia, other neurological causes

A neurological exam that cannot be rushed

Because neurological signs can be subtle, the exam must be complete: strength in each muscle group, sensation, reflexes, coordination, gait, balance and mental status. Mitchell and colleagues note that the category of mild cases, used to decide when recompression may not be necessary in remote locations, includes limb pain, general symptoms such as fatigue, some changes in skin sensation, spots and swelling under the skin, provided these findings are stable or improving and that significant neurological dysfunction has been ruled out (Mitchell and colleagues, 2018). The authors warn that tingling in both feet can signal spinal cord involvement and should not be considered mild, and that a neurological exam performed by a physician is the most reliable way to rule out important signs. As a clinical criterion, weakness and changes in balance, coordination or mental status are neurological dysfunction and take the case out of the mild category. In practice, a rushed exam can classify as muscle pain a condition that already involves spinal cord impairment. Repeating the exam after some time also helps, because symptoms can change in the first hours.

Flying after diving

The Aerospace Medical Association guidance notes that most divers fly to their destination and fly home, and that the problem is flying too soon after diving (Aerospace Medical Association, 2003). The recommendation cited by the association, based on guidelines from diving medicine organizations, is a minimum interval of 12 hours before ascending to altitude after a single dive per day, and a longer interval for those who dive several times a day, over several days or with decompression stops.

What the experiments showed

Vann and colleagues ran chamber experiments with dives followed by exposure to an altitude equivalent to the cabin of commercial aircraft (Vann and colleagues, 2004). The occurrence of decompression sickness fell as the interval before flying increased, and repeated dives required longer intervals than a single dive. In a later study, the same authors showed that the safe interval seemed to depend on bottom time, repetition and decompression stops, and noted that the tests were done in dry, resting conditions (Vann and colleagues, 2007).

No rule guarantees

The Aerospace Medical Association guidance acknowledges that no interval guarantees prevention and that there will always be divers who develop the disease even when following the recommendations (Aerospace Medical Association, 2003). Cialoni and colleagues examined divers with echocardiography during the return flight, after a week of diving and a 24-hour interval (Cialoni and colleagues, 2014). Most had no bubbles, but the few who did were the same ones who formed bubbles after each dive. The association recommends leaving the last day of the trip dive-free and notes that, if there are symptoms after diving, flying is contraindicated before treatment.

Decompression sickness without diving

The disease also appears in aviation. Kutz and colleagues reviewed cases treated as aviation decompression sickness in high-performance aircraft crew members, after rapid cabin pressure losses (Kutz and colleagues, 2023). The authors note that the mechanism is the same as in diving, but that the condition is less predictable and less familiar, because it sits between aerospace and hyperbaric medicine.

When the hypothesis is not confirmed

In the same series, reviewers trained in both areas attributed more than half of the cases to another diagnosis (Kutz and colleagues, 2023). Decompression sickness was less likely when the event happened at lower flight altitudes or with small pressure variations. The post on differential diagnosis shows how to keep other hypotheses open without losing the urgency.

Other low-pressure situations

Vann and colleagues recall that the disease also occurs in compressed-air workers, such as in tunnel and foundation construction, and in astronauts during activities outside the spacecraft (Vann and colleagues, 2011). In all these situations, the question is the same: was there a pressure change shortly before the symptoms? For the clinician in an ordinary service, this includes asking about work in pressurized chambers, trips to very high regions right after diving, and any rapid descent or ascent in environments with a different pressure.

What to do in the first hours

Vann and colleagues describe one hundred percent oxygen as the first aid and recompression, breathing pure oxygen, as the definitive treatment (Vann and colleagues, 2011). Adjuvant measures, such as hydration and prevention of thrombosis in patients with paralysis, are also recommended.

Oxygen as soon as possible

Longphre and colleagues analyzed reports of diving accidents gathered by a diving safety organization (Longphre and colleagues, 2007). First-aid oxygen increased the effectiveness of recompression and reduced the number of sessions needed when it was given in the first four hours after the ascent. Mitchell and colleagues recommend that divers be trained to administer oxygen and that it be kept up during transport, if possible (Mitchell and colleagues, 2018).

Position, fluids and temperature

Mitchell and colleagues recall that the head-down position is no longer recommended, that oral hydration is indicated if the patient is fully conscious, with non-carbonated fluids without caffeine or alcohol, and that the diver should be kept at a comfortable temperature, warmed without overheating (Mitchell and colleagues, 2018). The authors advise against intravenous glucose solutions and consider that there is not enough evidence to recommend or reject other drugs used in some services.

Talk early with whoever treats

Mitchell and colleagues recommend that the decision about transport and recompression be made in conversation with a diving medicine physician (Mitchell and colleagues, 2018). The authors describe that some mild cases, in remote locations, can be treated without recompression, but that recompression speeds recovery when it is available. Severe cases need recompression as soon as possible.

Recompression and what comes after

Vann and colleagues report that the treatment is effective in most cases, but that there can be sequelae in severe cases, even after several recompression sessions (Vann and colleagues, 2011). Abdelfattah and colleagues recall that complications can persist after hyperbaric oxygen treatment and affect quality of life, including limiting diving (Abdelfattah and colleagues, 2022).

Flying and diving again

Returning to diving after an episode, investigating patent foramen ovale and when to fly after treatment are decisions for specialists. The post on clinical decision-making shows how to weigh benefits and risks when each option has a different cost for the patient. For the first-response clinician, the most important thing is to recognize the picture, start oxygen and talk early with whoever treats.

The biases that leave diving out

Decompression sickness rarely goes unnoticed for lack of knowledge. It usually slips by through predictable habits and biases:

1. Not asking about diving in the days before the symptom.
2. Attributing shoulder pain to exertion with the equipment without further investigation.
3. Considering subtle neurological symptoms, such as tingling and fatigue, to be mild.
4. Thinking that following the dive table rules out the disease.
5. Clearing the patient to fly without specialized assessment.

Croskerry describes anchoring and premature closure among the most frequent cognitive errors in diagnosis (Croskerry, 2003). The post on the diagnostic pause shows how a short moment of checking helps to notice what was left out.

What to ask the diver

Some questions organize the history and help the specialist who will receive the case:

• How many dives did you make, over how many days, and when was the last one?
• What was the maximum depth and the bottom time?
• Was there a rapid ascent, shortness of breath during the dive or a missed decompression stop?
• Did you fly or go up to a high region after diving?
• When did the symptoms start and how have they changed since then?

Back to the scene

In the opening scene, the doctor who asks about the week of dives and the morning flight does not treat the shoulder pain as muscle pain. He carefully examines strength and sensation, starts oxygen, keeps the patient warm and hydrated, contacts a hyperbaric medicine service and arranges transport. The tingling changes the priority of the case. She is also advised not to board a flight again, not even a short one, until the specialist's assessment. The reasoning starts with the history, not with the pain. The question about the day before, asked right at the start, saved precious hours.

How NEXO helps train this reasoning

In NEXO, the case of the day is fictional, with a real clinical presentation and up to six progressive clues. You propose a diagnosis by searching for the code in ICD-10 and receive proximity feedback in five levels, which shows whether the guess landed on the exact code, the same category, the same group, the same chapter or a different chapter. This format speaks to the theme of this text: a clue about the day before can move the guess from a muscle disease to the chapter of injuries and other consequences of external causes.

To use the case of the day as training, try three habits. Before each guess, ask what the patient did in the previous days. When a vague symptom appears, ask what exposure could explain it. After the result, note which clue would have anticipated the diagnosis.

Three exercises with cases

Ask about the day before. In each case, imagine what the patient did in the last 48 hours and see what changes.

Put the symptoms together. Reread a case asking whether vague and different symptoms could have a common cause.

Think about transport. Faced with a serious diagnosis, ask what needs to happen before the patient reaches definitive treatment.

The post about case-based learning in clinical practice shows how cases help fix patterns that rarely appear in daily practice.

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

What is decompression sickness?

It is a condition caused by gas bubbles that form in the blood and tissues when the pressure around the body decreases, as on the ascent from a dive or at altitude.

What are the symptoms?

They range from itching, skin marks and joint pain to tingling, weakness, shortness of breath, confusion and circulatory collapse.

Why does flying after diving increase the risk?

Because cabin pressure is lower than at sea level, which favors the release of accumulated nitrogen in the form of bubbles.

How long should you wait to fly after diving?

The cited recommendations call for at least 12 hours after a single dive per day and longer after several dives. No interval guarantees full protection.

What is the first aid?

Oxygen at the highest possible concentration, as soon as possible, with the person lying down, warm and hydrated if conscious, and contact with a dive medicine service.

What is the definitive treatment?

Recompression in a hyperbaric chamber, breathing oxygen, indicated and conducted by specialists.

Final checklist

• I asked about dives in the previous days and about flights or ascents after them.
• I carefully examined strength, sensation, balance and mental state.
• I did not treat subtle neurological symptoms as mild.
• I started oxygen at the highest possible concentration as soon as possible.
• I contacted a dive medicine service to decide on transport and recompression.
• I advised not to fly before assessment and treatment.

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

References

1. Abdelfattah OM, Sayed A, Elgendy IY, et al. Patent foramen ovale closure and decompression sickness among divers. Cardiovasc Revasc Med. 2022. PMID 34810112.
2. Aerospace Medical Association. Decompression illness (DCI). Medical guidelines for airline travel. 2003. Document.
3. Cialoni D, Pieri M, Balestra C, et al. Flying after diving: in-flight echocardiography after a scuba diving week. Aviat Space Environ Med. 2014. PMID 25245898.
4. Croskerry P. The importance of cognitive errors in diagnosis and strategies to minimize them. Acad Med. 2003. PMID 12915363.
5. Kutz CJ, Kirby IJ, Grover IR, Tanaka HL. Aviation decompression sickness in aerospace and hyperbaric medicine. Aerosp Med Hum Perform. 2023. PMID 36757235.
6. Longphre JM, Denoble PJ, Moon RE, et al. First aid normobaric oxygen for the treatment of recreational diving injuries. Undersea Hyperb Med. 2007. PMID 17393938.
7. Mitchell SJ, Bennett MH, Bryson P, et al. Pre-hospital management of decompression illness: expert review of key principles and controversies. Diving Hyperb Med. 2018. PMID 29557102.
8. Schipke JD, Limper U, Tetzlaff K. Breath-hold diving and decompression sickness. Am J Med. 2026. PMID 41397651.
9. Vann RD, Butler FK, Mitchell SJ, Moon RE. Decompression illness. Lancet. 2011. PMID 21215883.
10. Vann RD, Gerth WA, Denoble PJ, et al. Experimental trials to assess the risks of decompression sickness in flying after diving. Undersea Hyperb Med. 2004. PMID 15686274.
11. Vann RD, Pollock NW, Freiberger JJ, et al. Influence of bottom time on preflight surface intervals before flying after diving. Undersea Hyperb Med. 2007. PMID 17672177.