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Immersion pulmonary oedema risk when diving and snorkelling

Issued: 27/10/2022
Last Updated: 27/10/2022

The purpose of this safety alert is to inform businesses that provide diving and snorkelling activities of the risks of participants suffering from immersion pulmonary oedema (IPO).


In June 2022 a woman participating in snorkelling activities began to feel unwell and struggled to breathe. She exited the water and was provided first aid, but tragically died. It is believed that she may have suffered IPO.

IPO is a condition where the lungs fill with fluid, the person struggles to breathe and consequently the body struggles to get enough oxygen. If the condition is not corrected, it can cause death. Fatal cases of IPO can be confused with drowning as both will result in fluid collecting in the lungs. It is believed that the number of cases of IPO remains underreported.

IPO may be confused with other conditions such as:

  • drowning
  • salt water aspiration
  • respiratory infection
  • cardiac insufficiency
  • acute asthma.

IPO can occur suddenly and with immersion at any depth, including at the surface.

Contributing factors

The cause of IPO is complex and still being researched, however there are several factors that can influence whether or not a person suffers from the condition:

  • When a body is immersed in water, changes in hydrostatic pressure causes blood which would normally pool in the legs and arms to move to the chest. This increases the central blood volume and can cause fluid to leak into the lungs.
  • People who suffer high blood pressure (hypertension) and other cardiac conditions are particularly susceptible to IPO due to increased alveolar pressure.
  • Breathing through a snorkel or a diving regulator can generate resistance to inhalation and can result in negative thoracic pressure, creating a vacuum phenomenon which can draw fluids into the lungs. Lying in a prone position whilst immersed can increase the risks of IPO (although scuba divers' symptoms can arise with the vertical posture during ascent).
  • Strenuous exercise and feeling anxious can increase the risk of an IPO.
  • Older people are more susceptible to IPO and it is overrepresented in women.
  • Cold water causes vascular constriction which will increase the pressure in alveolar capillaries and increase the risk of IPO, however IPO does occur in warmer waters as well.
  • Overhydration has an additive effect on the increase in alveolar capillary pressure resulting from immersion and can increase the risk of an IPO occurring.
  • Tight wetsuits can result in an increase in capillary pressure making a person more susceptible to IPO.
  • If a diver develops IPO at depth and then ascends, they are at risk of unconsciousness as the partial pressure of oxygen decreases on ascent in addition to the postural change.

It is often a combination of factors that increases the alveolar capillary pressure to a point that it causes IPO.

High blood pressure appears to be a common predisposing factor, however other heart and lung abnormalities may increase a person’s risk of suffering IPO.


The onset of IPO can be sudden and is usually precipitated by a feeling of breathlessness. Divers with breathing difficulties may have uneven or rapid breathing. Divers will often signal a problem with their regulator or ’out of air’ and may reject an alternate air source when provided. Snorkellers may move upright in the water and remove their snorkel from their mouths.

Uncontrolled coughing is also an indicator that a person may be suffering IPO. It often starts as a small tickle in the back of the throat but is persistent and can’t be resolved. Sufferers of IPO may cough up blood or have a frothy sputum. They may also describe a tightness in the chest and crackling sounds may be heard from their lungs.

The reduction in oxygen will often cause cyanosis (blueness of lips and tongue), confusion and people suffering IPO may appear to be intoxicated or function abnormally.

Action required

The primary treatment is to remove the person from the water and place them on oxygen as quickly as possible to reverse the effects caused by immersion.

If conscious, they should be kept in a comfortable position, often sitting or semi-reclined to assist their breathing.

The person should be provided with high concentration oxygen as soon as possible. This should be delivered by constant flow rather than a demand valve to reduce breathing resistance. IPO sufferers often improve when provided with oxygen.

An individual who has experienced IPO should be taken to hospital for further assessment and treatment.

Advice to workers

  • Continue to screen participants for medical conditions including high blood pressure and be aware that these participants are more at risk of an IPO. A history of previous shortness of breath with immersion is a strong indicator of the potential for IPO.
  • Be aware of the environmental conditions and stronger currents that can increase the physical exertion of participants.
  • If a participant is complaining of breathlessness, make it a priority to remove them from the water.
  • If a diver is signalling a malfunctioning regulator/distress/inability to breathe, IPO is possible, and the diver should be accompanied back to the surface.
  • Once removed from the water, sufferers should be provided with high concentration oxygen and kept in a comfortable position whilst conscious.
  • IPO sufferers should be kept thermally comfortable to reduce the vasoconstriction.
  • People who have suffered a suspected IPO should seek medical attention.

Further information

Further information can be obtained from the following: