Swimming Induced Pulmonary Edema (SIPE)


I’ve been learning about swimming induced pulmonary edema (SIPE) and I thought I’d offer an introduction here based on my reading and conversations with experts in the field as well as affected athletes.

The problem of SIPE, or immersion pulmonary edema (IPE) as it was first known, was recognized at least as far back as the mid-1990s. Early reports in the scientific literature focused primarily on a small number of healthy scuba divers who experienced problems with unusual breathlessness (dyspnea), particularly when diving in cold water. Medical evaluation for the problem showed that the divers had low levels of oxygen in the blood (hypoxemia), often reported coughing up frothy, blood-tinged secretions, and had findings on chest x-ray that suggested pulmonary edema. In the setting of immersion in cold water, this collection of difficulties–dyspnea, hypoxemia, excess lung secretions, and pulmonary edema–became known as IPE.

Interestingly, the victims of IPE were often very experienced swimmers who had difficulties only with swimming and/or diving in cold water (~50-60 degrees Fahrenheit).

It’s worth taking a moment to review a few important facts about the anatomy and physiology of the lungs. We have two lungs, each about the size and shape of a 2-liter soda bottle. Healthy lungs are extraordinarily light and very spongy. For our discussion today, it will help to think of the lungs as sponges. The lungs are ordinarily almost colorless, but take on a pink hue because of blood that flows throughout the lung tissue.

The right ventricle of the heart pumps blood to the lungs through the pulmonary arteries which branch into smaller and smaller branches and eventually into miscrosopically small capillaries which come into contact with the air-filled spaces in the lungs. It’s here where the blood unloads carbon dioxide and picks up oxygen. The blood then flows into increasingly larger veins and eventually into the pulmonary veins that carry the blood back to the left side of the heart where it is pumped to the rest of the body.

Like I mentioned, the lungs are usually extraordinarily light. But when fluid escapes the bloodstream and collects in the spongy lung tissue outside the blood vessels, the lungs become water-logged, much the way that a sponge becomes heavy once it soaks up water. One of the consequences is that it is much more difficult for oxygen to get into the bloodstream and much more difficult for carbon dioxide to get out. We call this situation pulmonary edema.

There are many causes of pulmonary edema. The most commonly encountered cases are due to heart problems of one sort or another (eg, heart valve problems, weakness of the left ventricle), but other causes include: reactions to blood transfusion, direct injury to the lungs, infection, and perhaps various inflammatory conditions.

The exact cause of pulmonary edema with SIPE is not completely understood, but experts suspect that a combination of increased bloodflow into the lungs due to immersion combines with increased pressure in the pulmonary arteries and veins (because of exercise) to cause a leak of fluid out of the bloodstream and into the lung tissue.

It is not clear if exercise-induced pulmonary edema occurs on land.


SIPE and Triathlon

As many readers here will know, there have been a number of episodes of sudden cardiac death (SCD) in triathlons in recent years, and these episodes have occurred with a preponderance during the swim portion of triathlon events. The cause of most of these deaths appears to be typical sports-related SCD due to a sudden arrhythmia, but some have wondered if SIPE could have played a role. There have been a handful of thoughtful opinion pieces about this possibility and I’d refer you to one such article by Rudy Dressendorfer in a recent edition of Sports Medicine Bulletin, entitled “Triathlon Swim Deaths: Initial Steps Toward Prevention.” This article lays out one view on the issue. In my opinion, though, it is not at all clear that SIPE has had a role in triathlon-related swim deaths.

Charles Miller and colleagues at Texas Tech University Health Sciences Center published an interesting report in 2009 that dealt with the possibility of SIPE in triathletes. During late 2008, they distributed a questionnaire to the membership of USA Triathlon asking about athletes’ experiences with “swim-related breathing problems.” The response rate to the survey was tiny–at only 1.3%–and it’s important to remember that the low response rate might have tremendous bias with the results. Nonetheless, about 1.4% of respondents reported having a swim-related episode of “pink frothy or blood-tinged secretions” that was suggestive of pulmonary edema. Moreover, the authors identified several risk factors for this occurrence, including high blood pressure, female gender, increasing length of the swim, and use of fish oil supplements. Only a minority of reported episodes suggestive of SIPE occurred in the absence of one or more of these 4 risk factors.

I’ve heard from several triathletes about their personal experiences with SIPE and I thought I’d share their stories here.

Nathan Farrugia, an avid runner and triathlete from Malta, shares his story at his blog. He describes his experience of discovering the problem in 2009 and then learning about SIPE and eventually traveling to Duke University for detailed physiologic testing. He’s very thoughtful about the physiology of the condition and the factors that might promote SIPE while racing.

Katherine Calder-Becker, a triathlete from Montreal, wrote to me to share stories about her struggle with SIPE. You can read about her discovery of the problem, how it’s affected her triathlon racing, her visit to Duke University for testing, and her recipe for heading off the problem now at her website. In addition to her personal story, she shares useful links to additional scientific articles and press reports for those who might want to do some additional reading. Those of you with a physiology background, in particular, will enjoy reading about her visit to Duke Dive Medicine to participate in a study of athletes with SIPE.

I gather that Nathan’s and Katherine’s stories are typical. I know of other athletes who have experienced similar symptoms during open water swimming, particularly during races, who received medical attention, at the scene or the hospital, who were suspected of having pulmonary edema. Supportive care with rest and oxygen, if needed, resulted in a resolution of the symptoms. I’m not aware of any triathlon-related death where clinical or autopsy findings specifically suggested SIPE as a cause.

Athletes who have been bothered by SIPE have offered a variety of suggestions for how to avoid trouble. These are also summarized in the article by Dressendorfer:

1. Avoid overhydration on race morning (to limit the immersion-related increase in bloodflow to the lungs).

2. Become acclimated to the water conditions, and particularly the water temperature, immediately before a race with a gentle warm-up swim.

3. Avoid using a wetsuit that has a restrictive fit at the neck.

4. Think to signal and request assistance during the swim if symptoms of unusual breathlessness develop.

SIPE is an area of ongoing basic investigation. One prominent group of investigators is headed by Dr. Richard E. Moon at the Duke University Center for Hyperbaric Medicine and Environmental Physiology. This group continues to study (in human subjects) the various physiologic changes that accompany SIPE, trying to identify the causative mechanisms that are responsible. I’ve had a chance to speak with Dr. Moon recently and I’m encouraged that his team’s work will be productive in defining this condition more precisely, identifying the causes and risk factors, and suggesting ways to avoid or alleviate the problem among triathletes.

That’s what I can offer in the way of an introduction to this topic. It would be great to hear from readers who can share their experiences with SIPE so that we might all learn more about this condition.

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  1. says

    I am 69 years old and a returning to triathlons after a 29 year layoff. My first triathlon was this month and I wore a full wetsuit, and within 300 yards of 1/2 mile swim I was gasping for breath and running out of energy. I finished the swim and the triathlon but at a much reduced pace. I believed it was the chest compression of the wetsuit and still do. I bought another better fitting wesuit and went for a training swim 5 days later and had a repeat of the sysmptoms. this included the post swim lung gurgles that last for about 18 hours. I then modified an older wetsuit by removing the sleeves and cutting it off at the knees. it was open at the sides of the chest and didn’t create any chest compression. I swam hard for 1/2 hour and never felt so good. I am convinced it was the chest compression of the wesuit that caused my problem.

  2. says


    Most of the (reported) exercise-related cases of SIPE seem to occur in triathletes. I don’t know that I’ve ever heard of a case in long-distance open water swimming (2-20 mile races, done without wetsuits). Is that your understanding as well?


  3. says


    There is precious little in the medical literature about SIPE in any individuals outside the military or scuba communities.

    Like you say, I can’t put my finger on a case report of SIPE in a (non-wetsuite) open water swimmer in the medical literature.

    I’ve heard a bunch of stories from triathletes who’ve had unexplained shortness of breath during/after a triathlon swim, but only a small number of stories where advanced (hospital) medical care was provided and the diagnosis of SIPE was suggested by x-ray and laboratory data. The reports seem to suggest that, while SIPE was originally described in scuba divers in cold water, the condition can occur with water temperatures that are relatively warm as well.

    Like with triathlon, there is no governing body or government that seems to be collecting reports on this issue and I suspect that we’ll learn slowly about this condition.

  4. Mark Hamilton says

    Just swam open water sea swim yesterday ,my first time really in the sea. Had wet suit,felt it was restricting my breathing and tight around neck , i completed swim at a struggle and the swim was nothing like my training in the pool,one person commented how blue i looked(face) above wet suit when i got out, almost straight away i would cough lung secretions,not much,but had frank blood in it,4hours later i was still coughing up secretions with frank blood. Got up this morning and cleared my lungs and coughed up secretions dark red congealed blood,not much,size of teaspoon.i thought i had torn something in upper airway with coughing on sea water during swim but after reading i feel its pulmonary edema. The whole swim was unpleasant ,even after few min,just determinetion got me through,thanks for article it enlightened me.

    • Larry Creswell, MD says

      Thanks for sharing your experience, Mark. Those are the kind of symptoms that deserve to be checked out by your doctor.

  5. Jeff Rodney says


    I appreciate the insight.

    I am 46 and in my third year of Olympic distance triathlons. I have read several articles on SIPE and although I have yet to experience any pink lung discharge, I have experienced extreme difficulties in breathing disproportionate to physical exertion, followed by 12-24 hour headaches. So I suspect that I am experiencing a mild case of SIPE. This only occurs during OW swims and while wearing a wetsuit. I have recently been refitted with a new sleeveless wetsuit which I hope will significantly reduce chest and shoulder constriction.


  6. Judy says

    I have had a few SIPE experiences, all while wearing wet suits. I have had non SIPE swims with the wet suit on, but the last time was too scary. I’ve decided to forgo the suit and swim without. My longest distance is Olympic. I may not be as fast as those with the suit, but I prefer to breathe.

    I am so thankful for the person from a tri-group who was able to tell me that what I was experiencing was SIPE. I thought it was all in my head!


  7. Denise horton says

    Swim for lls across rhe hudson. i do not wear a wetsuit ( half canadien and half well insulated) was recently diagnosed with exercise asthma but will be sending this article to my doc. I do not run so my only cardio is swiming. I had an attack in the pool recently that doc says could have beed chlorine induced… Thanks for the article
    Cheers denise

  8. Lisa Bennett says

    Hi Larry
    I’ve had symptoms before whilst swimming in a chlorinated pool about a year ago. On a couple of occasions whilst swimming a distance of 3 km… I noticed that I felt as though I had secretions in my upper airway. The first time it occurred I wanted to cough to try and clear my throat. I thought that maybe I’d inhaled some water. I didn’t have any shortness of breath or breathing difficulties but felt as though I had fines crackles coming from my throat when forcing a breath out. The second time it happened I had the same experience however I was bringing up brownish tinged seemingly frothy secretions. No breathlessness. I have done two 1 km ocean swims without any issues.
    I also run and race distances up to 21 km without any problems . The reason I am looking at your article is now I have just had another experience of this yesterday evening. I was swimming in an ocean pool… A total of 1800 m and towards the end of the swim I felt fatigued as it felt like I was really working hard. I attributed this to the difference in swimming in the sea with the swell and having to look up and out for swimmers getting I’m my way. I felt like I had possibly inhaled water and wanted to cough to clear my throat. I felt like the secretions were a bit frothy but didn’t spit it out to look. I have woken at 2am to find the same kind of fine crackly sound if I forced the air out of my lungs… Like huffing. Once again I do not have breathlessness or pain etc.
    I have never been to the doctor to investigate this complaint.
    It really is an interesting issue and I’m not sure what my doctor would say considering the nature of the incidence of my symptoms and also the fact that they have been only on a few occasions!
    Kind regards Lisa

    • Larry Creswell, MD says

      Thanks for sharing your story. Your experience may be valuable to other readers.

      SIPE is a bit mysterious, I must say. I do think it’s important to get checked out if you have any breathing problems that turn up while swimming.

  9. Juan says

    This year I started training for my first Triathlon at age 56. I consider myself to be in good shape. In the past 30 yrs I’ve run numerous marathons and 100’s if smaller road races. I began training in December 2014, swimming, biking and running 3x/wk for each. Running and biking I had no problems. However, I developed SIPE during my 3rd month of swimming. I started w/a 1/4 mile and worked up to a mile swim. The 2nd time I swam a mile it hit me real bad and I stopped all training for medical advise. After all test (ct scan, stress test, echo, and x-rays) my cardiologist said my heart was in very good condition. I’m still running and biking with no side effects from IPE. I would still like to compete and finish a triathlon but not sure on how to train for the swim. Any advise you can give me will be appreciated. Can people overcome SIPE?

    • Larry Creswell, MD says

      I don’t have personal experience working with athletes who have documented SIPE.

      Perhaps other readers can chime in with experiences that can be helpful.

  10. Theo says

    More research is needed on SIPE. I am reading everything there is online but not much there in terms of prevention or treatments available.

    I thought I would drown in today’s half Ironman race in St Pölten, Austria. I started coughing up pink froth already 150 yards into the swim. I had to alternate between breast stroke and simply floating on my back for the remaining distance.

    The bike leg was ok even though I found it harder to breath going uphill. I also did not push as I usually do on the flat since my sub 5 hr goal had already been dismissed due to a 56 minute swim (vs 38 in my last half Ironman race in Mallorca, Spain).

    The run! Usually when I experience SIPE the symptoms are reversed rather quickly once I am out of the water. Not today! I should be able to run the half-marathon leg in 90 minutes rather comfortably but took 1:48 today. I could only run half a mile at a time and then had to walk for 30 seconds to cough up more froth and let my racing heart slow down before starting running again.

    The race finish was 5 hours ago and I am still coughing extensively in my hotel bed which I do not intend to leave until tomorrow.

    My biggest concern is the full Ironman race I have signed up for in late June. I need advoce beyond Viagra, cutting off arms and legs of my wet suit, warming up and not over-hydrating! Has anyone tried something else that seem to work?

    Any advice much appreciated.

    Btw, I am a 42 yo male training on average 7-12 hours per week consistently and consider myself to be in pretty good shape. Recent marathon time of sub 3-hrs for ex..

    • Larry Creswell, MD says

      Thanks for sharing your experience. Perhaps other readers will offer suggestions.

      Breathing problems can be scary any time, but particularly during a race. My best advice is to STOP at the first dignity of breathing difficulties.

  11. Mark says

    Yesterday I had my first experience with SIPE…I’m a diver who treasure hunts with a hooded vest and a wetsuit and a weighted vest…all this can be considered constricting…my activities underwater take a great deal of energy and exertion…last night when I was lying flat on my back in bed I had the feeling of water in my lungs…rattling,crackling,bubbling sounds and shortness of breath…it was quite alarming. ..today I feel fine…thanks for all the previous posts, now I will be more aware of the contributing factors and will try to correct my actions.
    I’ll post Any follow up experiences or personal insights.

  12. Brian O'Donnell MD says

    Hi Larry, I’m an attending anesthesiologist from Ireland, keen marathon and trail runner and recently moved to triathlon this year. Having conquered the swim in the pool I moved to the open water with a little trepidation but quickly became comfortable at distances of up to 2km. Having just returned from a trail running trip in the French Alps, I yesterday joined my tri-club members for an open water sea swim. The plan was to do a leisurely 30 minutes (usually 1700-2000m). The water temperature was a balmy 50F and I wore my usual wetsuit. After 300m and in deep water I became suddenly short of breath and unable put my head in water. Realising impending problems I then made a beeline for shore and signalled to my partners that I was in trouble. What then followed was a struggle to breast stroke against a falling tide toward shore with an unceasing level of respiratory distress culminating in an onshore collapse with copious amounts of pink frothy sputum. Having become aware of SIPE and now having experienced it myself I must congratulate you and contributors for sharing their stories. I’m unsure what to do next other than to NEVER swim alone!

    • Larry Creswell, MD says

      Thanks for sharing your story, Brian.

      Never swimming alone is good advice for anybody!

      Did you get evaluated after your episode? Did things return quickly to normal?

      • Brian O'Donnell says

        Hi Larry, I had cold cyanosed peripheries and a mild sinus tachycardia (hr 80-100 bpm) for some hours following, accompanied by dyspnoea and rattling breathing with blood tinged sputum. This persisted for 24 hours. On waking 36 hours after the event my resting heart rate had resolved to its usual 38 bpm and I felt better.

        Tomorrow I will see a colleague for an stress test and echo to rule out any other precipitating factors. Having spent the past 5 years driving an otherwise fit cardiovascular engine to extremes I was completely taken by surprise at how quickly this manifested less than 10 minutes into an otherwise unremarkable swim.

        Please do keep this thread open and visible as I am aware of two other triathlon club members who have experienced similar problems recently. If what I experienced was indeed SIPE, it is potentially as big and under-reported a problem as hyponatraemia and over hydration in endurance sport.

        Keep up the good work, Brian

  13. RJ says

    I’m a 44 yr old triathlete, good fitness levels and compete in 4-6 triathlons per year. After a good winter in the pool my first two open water training swims with wetsuit this summer were unusually horrendous. Could not pull the skin off a rice pudding and much slower than I should be. I even had to resort to breastroke. Could feel fluid build up in lungs and chest was rattling for 24hrs afterwards. Researching my symptoms lead me to self diagnose SIPE. However I have since done another training swim and a race SIPE free by making sure I do a ten minute jog to warm up properly before entering the water, and not over hydrating plus making sure my stomach wasnt too full with food. That seems to work for me. Not sure which of the three is most important but gut feeling is the warm up. Just my experience.

  14. Dave says

    I’m a very strong swimmer and have high confidence in open water. 50yrs. I’m an iron distance athlete. Once in a while, for reasons unknown in the swim, I get what I used to call “panic attacks” for lack of a better description. I think is som level of SIPE. I’ve had them in cold and warm water but always in a wetsuit. I simply can’t get enough air Even though I’m taking huge breaths and exhales. But It’s not a restriction of airflow. When I flip on my back it settles down. Roll over and it ramps back up. Never had the pink spittle. I usually can settle back down and finish the swim but I know it’s not going to be an A race.
    This weekend I did my first race with a garmin sHrM. I had another “panic attack”, first in over a year. I was in the first wave with clear water. After the race when I looked at my HR stats I couldn’t believe my heart rate. It spiked above my highest ever recorded max HR test and stayed there for a long time. I stayed in an elevated HR (and it felt like zone5 also not a battery issue) through transition and about 20 minutes into bike. I was hitting my normalize power numbers and even with cardiac drift at the end of 3 hrs my Hr gets up to zone 3.5. This time my Hr continued to drop steadily from z5 until it settled at 3.5. I was also breathing very labored for most of the bike. Like training at a super high elevation. But was just about at sea level. Very strange but common feeling from other races. My heart is very healthy according to cardiologist. No high blood pressure. No asthma. Anyway. Good to know its not just me. I’ll be paying attention and won’t discard it as mearly a panic issue.

  15. Darrel Schultz says

    I’m a 61 year old triathlete.with a history of supra ventricular tachycardia…heart gets to racing from time to time. Usually I can slow it with deep coughing. In 2005 I did a half iron…cold water, no warm up. Within minutes of the start I was experiencing difficulty breathing and had no idea why. I eventually tried unzipping my wetsuit and so floundered on, unable to do a proper stroke. A kayaker kept their eye on me and I survived the long slow swim. With a mysterious rattle in my chest and only able to take half breaths I somehow staggered through the rest of the race to claim the t-shirt. After that experience I was at a loss to understand what happened to me, wondering if it was heart related. The symptoms, however, were unlike a heart episode. For the next decade I focussed on cycling and running events. This year I decided to go back into triathlon and began training for the Vancouver Ironman Olympic distance. Had a few D good, cold lake swims in a new wetsuit. 3rd lake swim and shortly after starting had the old familiar feeling of breathing difficulty. Stopped and rested after 150M then tried to soldier on. Things went downhill and by the time I floundered to the other side (600M), my buddies had to help me out of the water. My chest was rattling and I was spitting pink flem. After resting tried to swim back but couldn’t and struggled to shore. That night went on the Internet and found out about SIPE. Felt like I was reading my circumstances to a tee. Rented a more flexible wetsuit and 2 days later did the swim no problem. Did the Olympic swim in ocean temp of about 49 degrees and through pre swim run and water acclimatizing and lower hydration…no problems. Getting ready for next Tri in September and had some good lake swims. Then 2 nights ago had a recurrence about 500M into swim. Coughing pink and rested out of water before getting back in. Had to stop at shore every 150M to cough and try to clear out lungs so I could continue. Found this to help me make it through. Now I’m wrestling with what is triggering since I’m in an expensive wetsuit, water temp not overly cold, slow strokes to start, didn’t over-hydrate. I ate an hour before the swim. Thinking about a sleeveless wetsuit or no wetsuit. This is frustrating! Any suggestions welcome!

  16. Scott says

    41 year old in decent tri shape first year in sprint and intermediate Tris. Swimming in the pool has not been a problem putting out decent 1000 (14-16min) and 1600 times not blow your doors off but decent
    Noticed it the first time when I went with my wife for her first open water swim in the spring she was starting to panic so we made it to shore I ditched the boat and went out for 1/2 mile with her. (NO WET SUIT, GOGGLES, JUST SHORTS) Noticed on the way out I developed a frog in my throat didn’t pay that much attention until I started having a hard time getting full breaths told my wife to finish and I’d limp in with breast stroke as I got closer to shore started spiting up orange then red flem. by the time I reached shore it was bloody not tinged but bloody and my wife saw it I was on my way to ER.

    Knowing what I know now they miss diagnosed me with Pneumonia after seeing a chest xray showing fluid on my lungs.

    Things cleared up but still had a lingering cough with little junk I attributed to allergies. Did a Sprint no problem great race….
    Swam in pool was doing well breathing, fine no issues “good to go” this past weekend, 2 months later, did an intermediate was feeling good for 1/4 mile then felt short on breath could not keep my head under for 15 yards or so. kept popping up trying to catch my breath then the cough started and I knew exactly what was happening and went to breath stroke, slowed and made shore, really slow. Got on bike cleared up but felt weaker than normal (i consider my self above avg in biking but it wasn’t there) and run was okay. Flem was pink this time not full of blood coming out of the water.
    (So going into this I was calm, did small warm up, Had wet suit on this time, trigger may have been stress had someone that decided to use me as test dummy and kept running into me, swim a few feet away and run into me after this is when things went down hill)

    One thing I need to note is that I hydrated with Gatorade and each time I felt as if I was tasting Gatorade so I didn’t pay as much attention to it thinking the salty taste was just from the drink. The sprint I did I forgot to hydrate and didn’t have the problem. This is my norm before biking or running haven’t had time to play with it in swimming may ditch this practice and see if it helps swim,
    my wife pointed out I do not hydrate before training, yup always try something new on race day just made sense being I was going to be exerting myself.

    Last but not least to all that read this it’s not something to fool around with on the water we (triathletes) are stubborn at a fault on finishing but if this happens to you get you head out of the water get comfortable as you can and take note of all the boats positioned around you, you may need them it can come on suddenly and you feel helpless even if your in great shape, also if you can get their attention so they know you may need help it might not hurt. People have apparently died from this be cautious.

    • Brian O'Donnell says

      Hey Scott, sounds remarkably similar to my episode 18 months ago, which thankfully hasn’t recurred (and I’ve completed 2 long course ironman events since then). Cold water (12 deg centigrade), tight wetsuit, over hydration and sudden increase in effort level may have all contributed to my episode. Couldn’t agree more with your advice…if you feel this coming on, alert your swimming buddies and get to shore asap. Keep well, brian.

  17. chris day says

    I’m a slow swimmer (20-22min for 1km) but have been swimming distance with confidence in pool through winter. Tri season just started & experienced wheezing, rattling while swimming open water. I’m putting it down to tight wetsuit & cold water. More the wetsuit though as swam over 1km fine in cold water & no wetsuit. Knew breathe wasnt right as really struggled to get out that long relaxed exhale …which was how i thought to fix shortness of breath. I thought i wasnt doing this right or not relaxing properly …it is some relief that prob wasnt doing anything wrong during swim & that stopping, doing breaststroke, lowering HR were all smart moves. Wearing a looser wet suit & having a longer warm up hopefully will resolve this. Not sure when to train again now after this happened today. No pink spit though. Def alot of rattle & don’t think swallowed water.


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