BSAC Update on Immersion Pulmonary Oedema Risk to Divers

immersion pulmonary oedema lungs

Image: Magic mine/

The British Sub-Aqua Club (BSAC) has released updated guidelines for divers on dealing with Immersion Pulmonary Oedema/Edema (IPO/IPE) which, according to the UK Diving Medical Committee (UKDMC), may be the most common cause of fatal incidents in amateur scuba divers.

Pulmonary Oedema is caused by a build-up of fluid in the lungs. It has a range of causative factors but is often associated with cardiovascular conditions such as coronary artery disease and high blood pressure. Underwater, IPO may be exacerbated by cold water, overexertion and excess fluids taken prior to a dive, leading to breathing difficulties, confusion and, if unrecognised, death.

IPO was identified among swimmers and divers in the 1980s but was thought to be a rare occurrence in scuba divers until the last few years. This is probably because fatal incidences of IPO have been mistaken for drowning, as both result in fluid-filled lungs. However, research conducted by BSAC identified 24 cases within its database of annual diving incident reports (1997-2018) where IPO has been confirmed. Between 2016 and 2018, a further 29 incidents have been identified where IPO is suspected of being a causative factor.

pulmonary oedema image

The build-up of fluid in the lungs causes hypoxia leading to confusion and unconsciousness (Image:

Causes of IPO

As all divers know, immersion in water increases the hydrostatic pressure to which the body is subjected to. This is why we have to equalise our ear spaces during descent and be wary of diving too deep for too long. This pressure also causes blood to be squeezed from around the body towards the chest. Over time, this increase in blood volume around the chest area can force fluid into the pulmonary alveoli, the small air sacs in the lungs where gas exchange takes place as we breathe. Left unchecked, this fluid build-up can eventually lead to IPO, and certain factors can exacerbate the process in divers, including: 

  • High blood pressure (or other pre-existing cardiovascular problem)
  • Cold water
  • Excessive hydration prior to a dive
  • Overexertion during a dive, regardless of fitness level
  • Stress

Recognition and Symptoms of IPO

The build-up of fluid in the lungs leads to hypoxia (lack of oxygen reaching the bloodstream) and can lead to breathing difficulties, confusion and a sense that the diver's breathing apparatus is not functioning correctly. Signs that a diver may be experiencing IPO include:

  • Divers with breathing difficulties when not exercising particularly strenuously. Breathing difficulties may be indicated by rapid, uneven or heavy breathing, or coughing uncontrollably.
  • Confusion, swimming in the wrong or random directions (similar to a CO2 hit for rebreather divers).
  • Inability to carry out normal functions, while appearing to have to concentrate on breathing.
  • Belief that a regulator is not working properly.
  • Indication of ‘out of gas’ when their regulator(s) are found to be working correctly and with adequate gas supplies.
  • Divers refusing or rejecting an alternate air source when ‘out of gas’.
  • Indication of difficulty of breathing at the surface.
  • Uncontrollable coughing at the surface accompanied by frothy sputum which may contain blood

(Source: BSAC Diver Guidance for IPO)

Treatment of IPO

Should any of the above factors be recognised in a diver then the immediate priority it to surface the diver and seek immediate medical assistance. It is worth noting that the UKDMC report mentions that a hypoxic diver may lose consciousness during ascent as the partial pressure of oxygen in the lungs is reduced. Should IPO in a diver be suspected then the advice is to:

  • Surface the diver safely and exit the water
  • Keep the diver sitting still and upright if they are conscious
  • Keep the diver warm to maintain blood flow
  • Administer 100% oxygen
  • Do not administer fluids
  • Seek emergency medical assistance

Recurrence of IPO

Individuals who have had Immersion Pulmonary Oedema are likely to suffer repeat occurrences, and the general advice is that the diver should not return to the water. It is essential that a thorough medical investigation is conducted following a case of IPO, as it may reveal underlying conditions which predisposed the diver to IPO and which pose a significant threat to the individual's overall health, particularly with regards to life-threatening cardiac diseases. Even should no other condition be found, individuals who have exhibited symptoms of IPO at any time should seek detailed medical advice before diving again.


For more information on Immersion Pulmonary Oedema:




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