Open water swimming: identifying and managing SIPE

Regarded as one of the world’s most iconic ocean swims, the 20 km Rottnest Channel Swim (RCS) from Cottesloe Beach to Rottnest Island off the coast of Western Australia attracts thousands of participants each year.

This year, for the first time in the history of the 34-year-old event, the RCS organisers were forced to cancel the event mid-swim due to dangerous and unsafe weather conditions.

SIPE — what do we know?

The race may have been called off, but research for a rare but life-threatening condition, swimming induced pulmonary oedema (SIPE), associated with open water swimming, did go ahead.

SIPE occurs when excess fluid accumulates in the lungs, causing acute shortness of breath during or immediately after swimming. It may include symptoms such as a whistling or crackling sound in the chest, an unexplained cough, coughing up phlegm or tightness in the chest.

It is a serious and potentially fatal condition, but there is not enough data on incidence rate and a lot remains unknown, particularly in terms of its pathophysiology, according to the researchers.

To get insights on the incidence rate of SIPE in public open water swimming, UWA researchers led by Associate Professor Louise Naylor, with support from Royal Perth Hospital, Fiona Stanley Hospitals and Curtin University, are conducting a study in both competitive and community-based marathon swimming events, specifically the RCS.

Identifying risk factors

The researchers are using the RCS cohort of 400+ athlete volunteers for their study for identifying risk factors. Dr Sebastian Knudsen, intensive care specialist at Royal Perth Hospital, was one of the solo participants at the event last year. Solo competitors typically spend between four (race leader) and 12 hours (last finishers) in water.

UWA senior researcher and PhD candidate Julie Collis, Naylor, Knudsen and team are hoping that their research will identify factors that can help people be screened and managed both in and out of the water.

In 2022, around 55% of surveyed swimmers who took part in the solo crossing for the swim reported at least one symptom of SIPE, and there have been individuals who have been hospitalised due to this condition at many crossings.

This study is being conducted in collaboration with Philips, with the company supplying a range of cardiac and lung ultrasound equipment (Philips Epiq CVx, Affiniti CVx ultrasound system, Compact 5500CV and Lumify systems) over the last two years.

Preventative treatments

Identifying risk factors for SIPE would allow the reduction in the risk of incidence occurrence via educating athletes and support crew, potentially guiding preventative treatments in at-risk athletes, and allowing for more targeted research into the pathophysiology in the future, the researchers suggest.

Naylor and her team believe that a combination of water pressure on the body as well as exposure to cold and prolonged exercise forces blood from the extremities into the chest, thus increasing the pressure in the tiny capillaries in the lungs — this can lead to pulmonary oedema.

While the initial study target was to check for pre-clinical SIPE in 350–400 solo swimmers at the Rottnest Channel Swim, the numbers and study plans are being revised following the cancellation of the swim.

The RCS was suspended four hours after commencement, but the researchers were lucky to have a few participants who had almost hit Rottnest Island jump on a boat and reach the tent for testing.

Image: Supplied.

“As part of the study, participants came in for pre-event testing, including an echocardiogram at rest and under stress conditions. They were to be tested again immediately post-race when they arrived on Rottnest Island. Based on pilot work from last year, swimmers who had evidence of edema in the lungs (that is, preclinical or pre-symptomatic SIPE) were more likely to be female, had lower body fat and showed higher RV GLS (ie, 31 vs 29) compared to the group average after the marathon swim,” Naylor said.

The researchers will either be testing the same number of volunteer athletes at next year’s Rottnest Channel Swim or split this number amongst smaller events throughout the year. Collis said the study findings will help researchers determine any sport-specific cardiac adaptations to marathon swimming.

Need to raise awareness

With the increasing popularity of open water swimming, there is a growing need to better understand and raise awareness of SIPE and the associated risk factors for the condition, the researchers suggest.

Identifying risk factors for SIPE is a great first step, which would allow the reduction in the risk of a SIPE occurrence through athlete screening as well as potentially guiding preventative treatments in at-risk athletes, they said.

“Due to its somewhat insidious presentation and a lack of understanding around the condition, it is often overlooked until an athlete is extremely unwell. It is often only in retrospect that swimmers can say, ‘Oh, I was getting pain/shortness of breath/feeling unwell, but I just thought that was how I would feel after swimming 17km!’

“Added to this is the fact that many high-level athletes will want to push themselves to the limit, and many more part-time athletes will be reluctant to stop given the huge sacrifices they have made to train for big events. Better knowledge of SIPE and its risk factors will help in making the big decision to pull a swimmer out of the water,” the researchers concluded.

The study authors have already been invited to attend and research other similar events and with the recent cancellation of RSC, they are investigating other options. “However, the logistics in trying to replicate an echo lab in the field on an island, with the correct scanning beds, participant privacy, machines etc are significant,” Collis said.

“For the baseline assessments, and last year post marathon I used the premium machines, The Epiq, as the 3D imaging provides a unique assessment of the cardiac mechanics and volumes. We had them barged over to the island ready for this year as well. We would need to review these logistics for smaller and subsequent events.”

SIPE may seem to be rare but UWA researchers suspect the cases are underreported with symptoms often easily ignored by participants. Their research hopes to change this, improving prognosis, prevention and outcomes.

Top image credit: iStock.com/Alexmumu