Sarah Spencer and Dr Lindsay Forbes shine some light on swimming-induced pulmonary oedema (SIPE) - a poorly understood but potentially deadly condition
Swimming induced pulmonary oedema (SIPE) is a condition that causes severe, sudden breathlessness during open water swimming. It appears to be fairly rare, but is seen more often as the popularity of open water swimming increases. SIPE can be described as an attack of shortness of breath that is out of proportion to the effort being put in, during or immediately after swimming. It can occur on its own or may include symptoms such as a whistling or crackling sound in the chest, an unexplained cough, coughing up phlegm or fluid and a feeling of tightness in the chest. SIPE is not normally linked to water inhalation and does not occur immediately on entering the water. Symptoms usually improve once on dry land. However, if someone is unaccompanied or cannot get out of the water quickly, it could be life-threatening.
Get out of the water
SIPE is an under-researched condition that is poorly understood. It is thought that the combination of water immersion, exposure to cold and exercise can increase the pressure in pulmonary capillaries (tiny blood vessels in the lungs) causing fluid to leak into the air spaces of the lung.
While SIPE can be experienced in all water temperatures, it seems to be more common in cooler water as the body reacts to cold by forcing blood away from the extremities into the chest
If you develop this type of shortness of breath while swimming, it is important to get out of the water as soon as possible. It is likely the symptoms will become more severe the longer you continue swimming. In most cases, the symptoms will resolve on their own once you are out of the water, usually within 24 hours. However, some swimmers may require medical attention on site or may need transferring to a hospital A&E department. Hospitalisation overnight is not usually necessary. Little is known about whether or not there are any long-term effects associated with SIPE, however one small study reported that lung function in some of the participants was worse in the week following SIPE.
Research shows that around 30% of people who had an episode of SIPE experienced it again. So far not much research has been carried out into the risk factors for SIPE but researchers are currently studying which factors might be the most important so that we can give good advice to people. Some of the latest research suggests that risk factors may include high blood pressure, taking fish oil supplements, long distance swims and female sex. Other hypothesised risk factors include cold water temperature, being aged over 40, wearing a tight wetsuit, over hydration, a high level of exertion, swimming position and lack of warm up. SIPE is thought to result from a number of these factors being present at the same time to create a “perfect storm”.
While SIPE can be experienced in all water temperatures, it seems to be more common in cooler water as the body reacts to cold by forcing blood away from the extremities into the chest. As a result, SIPE appears to occur more commonly during outdoor swimming in temperate climates rather than during pool swimming.
Reducing the risk
It may be possible to reduce the risk of a SIPE occurrence or recurrence by addressing some of the risk factors, however we cannot be sure that any of these things will definitely make a difference. The best advice at this stage is not to swim alone in open water. We don’t yet have a clear idea about treatment or prevention of SIPE, but there are interesting possibilities from surprising quarters. For example, Viagra may help prevent it. But the jury is still out on that - no robust studies yet have shown that it definitely works. But in the future we hope that we can offer a preventive treatment to people who have had a previous attack.