Breathing difficulties underwater are among the most frightening situations a scuba diver can face. While equipment problems may be the first suspected cause, another potentially life-threatening condition deserves recognition: immersion pulmonary oedema (IPO).
IPO develops when fluid moves from the blood vessels in the lungs into their surrounding air spaces during immersion, compromising gas exchange. It can occur rapidly and may affect both novice and experienced divers, including those who appear healthy.
The Scuba News asked Dr John Lippmann OAM FUHM, Chairman and CEO of the Australasian Diving Safety Foundation (ADSF), to explain the condition, warning signs, risk factors and appropriate response. His comments concern IPO generally and do not assess any particular diving incident.
What Happens in the Lungs?
Immersion redistributes blood from the limbs towards the chest, increasing the load on the heart and pressure within the lung’s capillaries.
Dr Lippmann explains that negative pressure in the lung air spaces may also arise because of a diver’s body position or resistance when breathing through a regulator or snorkel. Together, these changes can promote movement of fluid into the alveoli, the tiny air sacs where oxygen and carbon dioxide are exchanged.
The resulting congestion can make breathing increasingly difficult. Unlike inhalation of surrounding water, the fluid involved in IPO originates within the body’s circulation.
The mechanisms are consistent with the 2024 joint position statement from the South Pacific Underwater Medicine Society (SPUMS) and the UK Diving Medical Committee (UKDMC).
Warning Signs That Should Not Be Ignored
Dr Lippmann identifies shortness of breath, coughing, sometimes with blood-stained sputum, wheezing, chest tightness and marked distress as important warning signs.
Bluish colour around the lips or tongue may appear in severe cases, and respiratory arrest followed by cardiac arrest can occur.
One particularly concerning scenario is a diver reporting that they cannot get enough air from their regulator, even though sufficient gas is available and changing to another functioning regulator does not resolve the problem.
Panic can follow the breathing difficulty, rather than being its initial cause.
Symptoms are not diagnostic on their own. Equipment faults, aspiration, cardiac disease, asthma and other diving emergencies can present similarly.
The practical rule is that unexplained breathing difficulty underwater warrants immediate action, not an attempt to continue the dive.
Who May Be More Susceptible?
Dr Lippmann identifies older age, high blood pressure, underlying heart disease (a diver may have an unrecognised cardiovascular condition despite feeling fit), cold water, exertion, increased breathing resistance, excessive hydration and extreme anxiety as potential contributors.
Female sex has also been associated with higher risk.
These factors certainly do not mean IPO is inevitable, but represent an increased risk.
A previous IPO episode is especially important because recurrence may occur. A diver should not regard the disappearance of symptoms after leaving the water as proof that the problem is resolved or that further diving is safe.
What to Do if IPO Is Suspected
Suspected IPO is a potential medical emergency.
The affected diver should end the dive, alert their buddy and be assisted towards the surface as quickly and safely as circumstances permit.
Avoid routine safety stops; mandatory decompression obligations can create difficult competing risks that require trained emergency judgement.
At the surface, keep the diver positively buoyant and remove them from the water promptly.
Activate emergency medical services, provide high-concentration emergency oxygen using appropriate equipment and trained personnel, and allow a conscious diver to sit upright or remain in a position that makes breathing easier.
Loosen restrictive equipment, protect against cold and monitor breathing and responsiveness.
If the diver is unresponsive and not breathing normally, begin CPR and follow current resuscitation and emergency-response guidance, preferably including supplemental oxygen.
Dr Lippmann notes that symptoms can worsen during or after ascent as oxygen partial pressure falls.
Even if symptoms appear to improve, urgent medical assessment is warranted to evaluate IPO and other possible diving-related emergencies.
Reducing Risk and Returning to Diving
There is no guaranteed prevention strategy, but appropriate medical assessment and sensible diving practices matter.
Divers with previous unexplained breathing problems in the water should consult a doctor trained in diving medicine and may need specialist investigation.
Dr Lippmann recommends a fitness-to-dive assessment by a doctor with dive medical training for all divers aged 45 or older, and those with heart disease or dysfunction or other significant chronic conditions.
This age threshold is the recommendation of the South Pacific Underwater Medicine Society (SPUMS), not a universal legal requirement.
Divers treated for hypertension should review the suitability of their medications with a diving-medicine physician, rather than changing treatment themselves.
Avoid unnecessary heavy exertion, use appropriate protection against cold, ensure breathing equipment is maintained, and avoid deliberate overhydration before diving.
The 2024 SPUMS/UKDMC joint position statement strongly advises against further compressed-gas diving after an IPO episode because recurrence may be severe or fatal.
A cardiovascular and respiratory investigation is necessary, and any decisions about future diving require specialist medical advice. Improvement of symptoms alone does not constitute clearance.
Why Awareness Matters
For instructors, buddies and dive operators, the lesson is that not every breathing emergency is caused by insufficient gas or panic.
Rescue readiness, emergency oxygen, clear communication and access to medical help are important.
Dr Lippmann believes awareness of IPO is increasing, but still has a long way to go, particularly as recreational divers age and may have diagnosed or undiagnosed health conditions.
He also advocates a measured response: education should improve recognition and preparedness without making exaggerated claims or discouraging safe participation in diving.
A Practical Safety Message
Unexplained breathlessness, coughing or chest tightness while immersed should prompt a timely, controlled end to the dive and emergency evaluation.
Divers who have previously experienced these symptoms should seek diving-medical advice before returning to the water.
Recognising a possible medical emergency can be just as important as identifying an equipment problem.
About the Expert
Dr John Lippmann OAM FUHM is Chairman and CEO of the Australasian Diving Safety Foundation, an Adjunct Senior Research Fellow at Monash University and a Senior Research Fellow with the Royal Life Saving Society.
He founded Divers Alert Network (DAN) Asia-Pacific, which he oversaw for 25 years.
His comments were provided to The Scuba News in written correspondence on 28 September 2026.
Sources and Further Reading
- Australasian Diving Safety Foundation
- SPUMS/UKDMC Joint Position Statement on Immersion Pulmonary Oedema and Diving (2024)
- Divers Alert Network: Immersion Pulmonary Edema
Additional editorial source: Dr Lippmann’s written responses to six questions supplied to The Scuba News on 28 September 2026, held on file.
This article is for diving-safety education. It does not replace individual medical advice, emergency care or rescue training.
