I saw this week that there was an important new paper on swimming induced pulmonary edema (SIPE). Richard Moon, MD, and his colleagues at Duke University published a report entitled, “Immersion Pulmonary Edema and Comorbidities: Case Series and Updated Review” in a recent edition of the sports medicine journal, Medicine & Science in Sports & Exercise (1).
SIPE is known to occur not only in recreational or competitive swimmers, but also in divers. In fact, the condition was first recognized because of breathing difficulties encountered by military divers. As triathlete and swimmer readers here will know, there are many reasons why an athlete might develop shortness of breath during an open water swim. Water conditions, water and air temperature, exertion, and anxiety all play a role. SIPE is something different, altogether, though. This is a condition that develops because of immersion in the water, in which fluid builds up in the lungs and makes breathing difficult. The condition is believed to be self-limiting; if a swimmer gets out of the water, the condition will resolve. The underlying mechanisms and risk factors are not completely understood.
The newly published report is important because it reviews the medical literature and gathers all of the pertinent information about pre-existing medical conditions, or so-called comorbidities, in victims of SIPE. Dr. Moon is probably the world’s foremost authority on the topic of SIPE, so this new report deserves our attention.
There are 2 parts to the study: 1) a look at the Duke University experience with recreational swimmers who’ve had a SIPE episode and 2) a review of the medical literature on SIPE cases, both in military and recreational divers and swimmers.
In the first part, the investigators collated information on 41 swimmers who, over the past several years, had been studied at Duke University after reporting a SIPE episode. The mean age was 50.1 +/- 10.8 years (range, 25-71 years). Complete medical history data was available for 36 of the 41 swimmers.
In the second part, the investigators collected 45 previously published articles in the medical literature that reported on 292 cases of SIPE. There were 156 recreational swimmers or divers (89 men and 67 women), with a mean age of approximately 47.8 +/- 11.3 years. There were also 136 military swimmers or divers (135 men and 1 woman), with a mean age of approximately 23.3 years (range, 18-47 years).
For each of these groups, the investigators gathered information about pre-existing medical conditions in order to determine potential risk factors for the development of SIPE, focusing on: hypertension (high blood pressure), lung disease, overweight/obesity, sleep apnea, hypothyroidism, and cardiac abnormalities).
Among the Duke University group, 9 (25%) of the 36 swimmers with available health history were completely healthy. The remaining 27 (75%) had 1 or more medical/health conditions, including:
- overweight/obesity in 12
- hypertension in 7
- cardiac arrhythmias in 4
- heart valve problem (mitral valve prolapse) in 1
- reduced heart function in 2
- repaired congenital heart conditions in 2
- asthma in 3
- COPD in 1
- reactive airways disease in 1
- hypothyroidism in 3
- diabetes in 2
- polycystic ovary syndrome in 1
- obstructive sleep apnea in 2
Twelve subjects had more than one of these conditions.
In the literature review, all of the 136 military swimmers and divers were healthy; they had none of the pre-existing medical/health conditions that were surveyed. In contrast, 70 (45%) of the 156 recreational swimmers or divers had one or more significant pre-existing risk factors:
- asthma in 4
- enlarged heart in 2
- arrhythmias in 2
- coronary artery disease in 3
- diabetes in 4
- exercise-induced cough in 1
- Elevated serum lipids in 22
- hypertension (high blood pressure) in 25
- thickening of the left ventricle in 9
- peripheral vascular disease in 1
- sleep apnea in 6
As a side note, approximately 17% of cases in the literature review reported similar previous episodes or follow-up episodes that were suggestive of SIPE, giving an important look at the potential recurrence rate. And in total, 6 fatal cases of SIPE were identified in the literature review.
How can all of this collated information be useful to us?
First, it’s important to note that all of the military swimmers and divers included in the literature review were healthy. We shouldn’t overlook the possibility that even completely healthy swimmers may experience SIPE.
Second, the recurrence rate of ~17% in the literature review is probably an underestimate. No doubt, some swimmers who experienced a worrisome episode of SIPE might avoid future swimming altogether. It’s very important to remember that this condition may recur.
Third, it’s very apparent that, among recreational swimmers who experience SIPE, the prevalence of important pre-existing medical conditions is rather high, at 75% in the Duke group and 45% in the recreational swimmers in the literature review. I suspect that the Duke investigators were more thorough in their history-taking and the 75% is probably more reflective of the reality.
The investigators’ aim was to identify risk factors for SIPE. Sadly, there’s obviously no single, unifying thread here. Hypertension (high blood pressure) was the most commonly identified condition among the cases, but this accounted for only ~15% of the cases. As I mentioned at the top, the physiologic underpinnings of SIPE are not completely understood and indeed there may be more than one responsible mechanism leading to some common final pathway by which fluid accumulates in the lungs. All of the various cardiovascular abnormalities identified in the cases might conceivably play a role. There’s more to learn.
It’s worth noting that the long list of medical conditions that were identified deserve careful medical attention before participating in recreational swimming events.
I’ll reprint here my best advice to athletes and event organizers regarding SIPE. I originally included this in another blog post, but this is still my best advice!
- Triathletes and open water swimmers should be aware of SIPE and the possibility that this condition can be lethal.
- Symptoms of SIPE can manifest for the first time even in experienced swimmers. Symptoms may develop rapidly, be unexpected, and confuse the athlete about the cause.
- The development of SIPE does not appear to be confined to cold water swims or only to victims who are wearing a wetsuit at the time.
- SIPE appears to be self-limiting–that is, the symptoms will subside if the victim stops exercising and gets out of the water.
- Because of #2, #3, and #4, athletes who experience breathing difficulties in the open water should treat the problem like a medical emergency and STOP swimming and SEEK immediate assistance. Because of the challenges of rescue in the open water, your life could depend on recognizing a problem early and getting out of the water. I would encourage affected athletes to get complete medical evaluation as soon as possible after an episode.
- There appear to be no effects on lung function after an episode of SIPE, but repeat episodes of SIPE may occur.
- Affected athletes have described a variety of strategies for preventing repeat episodes of SIPE. From athlete accounts, no single strategy appears to be universally successful.
- Affected athletes should use EXTREME CAUTION in subsequent open water training and races, being hypervigilant for warning signs.
- Event organizers and on-water rescue personnel should be familiar with SIPE. The safety plan should allow for athletes with breathing difficulties to be removed from the water as quickly as possible.
1. Peacher DF, Martina S, Otteni C, et al. Immersion pulmonary edema and comorbidities: Case series and updated review. Med Sci Sports Exerc 2015;47(6):1128-1134.