What is SIPE?

To start, let's define what pulmonary edema is. Pulmonary edema is the accumulation of fluid in the lungs, which hinders the body's ability to exchange oxygen and carbon dioxide. Normally, the lungs facilitate the exchange of gases that are essential for breathing, but when fluid fills the air sacs, this process becomes impaired.

In the case of Swimming-Induced Pulmonary Edema (SIPE), this fluid buildup happens specifically during swimming. Swimmers may not realize they’re suffering from this condition until symptoms manifest, such as shortness of breath, which is why it’s so important to be aware of the signs. It is important to understand that this is not the same as swallowing water or breathing in water (aspiration of water).

SIPE was first described in scuba divers in 1981 and later reported in open water swimmers. There are more and more reports as time goes on and people are more educated. This occurs in all populations and predominantly in otherwise healthy individuals. Among the most fit may be the Navy SEALs who are also affected by SIPE. In the United States, we call people who swim in natural bodies of water “open water” swimmers, while in the UK and Europe and other parts of the world they are known as “Wild” swimmers.  Clearly, wild swimmer sounds more fun! 

Anyone can potentially develop SIPE, however certain groups of swimmers may be more at risk:

1. Cold-water Swimmers: Athletes who regularly swim in open water, where the temperature is low, are at a higher risk. For example, triathletes who swim in cold open-water environments are more likely to experience SIPE.

2. Competitive Swimmers and Endurance Athletes: Some believe swimmers involved in high-intensity or endurance events, like long-distance swimming or competitive triathlons, are more likely to experience SIPE due to the extreme physical demands placed on the body. Others believe recreational swimmers are more at risk due to the lack of training.

3. Pre-existing Health Conditions: Swimmers with cardiovascular issues, respiratory illnesses, obesity, or asthma may be at higher risk because their lungs and/or circulatory systems are already compromised. Their bodies may struggle to handle the additional stress of intense swimming.

A Swedish study by Hageman et al showed that SIPE occurrence was 8.59 times higher for women compared with men, and 12.74 times higher for the older age groups compared to the younger. However, there is a higher number of young men having SIPE just because more young men are active in triathlons and open water swims.

So, what does SIPE look like in a swimmer? The symptoms usually occur during swimming or very shortly after. They can range from mild to severe and may include:

• Shortness of Breath (Dyspnea): The most common symptom, where swimmers feel they cannot catch their breath, even after moderate exertion.

• Coughing: Some swimmers may develop a dry cough. In severe cases, the cough may produce pink, frothy sputum.

• Chest Pain or Tightness: A swimmer might feel discomfort or tightness in their chest as the fluid builds up in the lungs.

• Fatigue: A swimmer might feel unusually tired and weak, even after finishing a relatively short swim.

• Cyanosis (Bluish Skin): In severe cases, the skin around the lips and fingertips may turn blue due to low oxygen levels.

• Other less traditional symptoms not always included in studies are anxiety or a feeling that a wetsuit is too tight

Diagnosing SIPE involves considering the swimmer’s recent activity and symptoms.  A medical professional will likely take a history of the swimmer’s physical exertion, water temperature, and any pre-existing health conditions. 

• Vital signs are easily checked at the side of the water. Respiratory rate may be high, but we would also suspect that in anyone who is exerting themselves. Respiratory rate itself has not been found to be a consistent diagnostic criterion for SIPE. In studies at low altitude, SO2 was found to be useful; however, in our studies at moderate and high altitude, it is less accurate as a diagnostic criterion given this value is already lower at baseline. 

• SIPE is usually diagnosed at the site of the swim, so more advanced imaging is not available, but this can easily be diagnosed by portable ultrasound. This will show fluid within the lung. The study used for this is often the Blue protocol. This is an evaluation of 3 different areas on each side of the lungs.  3 or more B lines are a sign of pulmonary edema. These are hyperechoic lines (or white lines) that are vertical on the ultrasound. It is normal to have up to 2 B lines in a lung field- remember the lungs are not completely dry to start.  

• If someone doesn’t have rapid resolution of their symptoms and needs to go to the hospital, X-rays or CT imaging may be performed. Also, remember that a swimmer can have SIPE, that is 3+ B lines on ultrasound, without having symptoms.

The treatment of SIPE focuses on reducing symptoms and managing fluid buildup in the lungs. 

The vast majority of people will have their symptoms resolve very quickly simply by exiting the water and resting. Their wetsuit should be removed to decrease the constriction. Place them in a warm environment. If their oxygen saturation is in a normal range, there is nothing else to do other than allow rest.

Oxygen therapy can be used if the oxygen saturation is low. Sitting upright or a partially reclined position may also help. We generally monitor patients until they have stable normal vital signs and no shortness of breath for 15 minutes.

If not improving or their oxygen saturations are low, they need to go to the hospital by ambulance. Pharmacologic intervention diuretics, beta agonists, and steroids have been shown to potentially help in more severe cases. Extreme cases may need CPAP or other respiratory treatments.

While SIPE can be treated, preventing it from happening is even better. Here are some prevention strategies:

• Warm-Up Properly: Properly warming up before swimming helps prepare the body for physical exertion, reducing the risk of extreme stress on the cardiovascular system.

• Gradual Acclimatization to Cold Water & Wet Suit: Swimmers who are planning to swim in cold water or race in a wet suit should gradually acclimatize themselves to lower temperatures over time and/or the feeling of swimming in a wet suit as this adds external compression. This helps the body adapt and minimizes the risk of SIPE.

• Avoid Overexertion: Swimmers should listen to their bodies and avoid pushing themselves too hard, particularly in extreme environmental conditions like cold water or at high altitudes.

• Breathing Techniques: Proper breathing techniques can help improve oxygenation during swimming, thus reducing the risk of lung stress and fluid buildup.

• Some studies show that Sildenafil (brand names Revatio or Liqrev), which relaxes blood vessels and lowers blood pressure in the lungs, may be helpful in preventing recurrences of SIPE

Where are we going with this? If you are thinking it seems like we have more questions than answers, you may be correct. We feel that way ourselves many times! Such is the life of research. There are several areas of research we are further investigating. One area is looking into how altitude affects the risks. Another is looking at exact mechanisms, wondering which may be more of a factor- cold water? Chest constriction? Cardiac involvement? Exertion or other factors. Some studies are looking deeper at pre-existing conditions. Another area of study is the use of cold- water acclimatization techniques to understand their effectiveness or lack thereof. A deeper look at medications is also an area of research, although many of the cases do not need medications.  This is a growing area of research, and answers will benefit recreational swimmers, athletes, and the military.