Swimming-induced pulmonary edema

Swimming induced pulmonary edema (SIPE), also known as immersion pulmonary edema, occurs when fluids from the blood leak abnormally from the small vessels of the lung (pulmonary capillaries) into the airspaces (alveoli).
SIPE usually occurs during exertion in conditions of water immersion, such as swimming and diving. With the recent surge in popularity of triathlons and swimming in open water events there has been an increasing incidence of SIPE. It has been reported in scuba divers, apnea (breath hold) free-diving competitors combat swimmers, and triathletes. The causes are incompletely understood as of 2010.
Signs and symptoms.
As with other forms of pulmonary edema, the hallmark of SIPE is a cough which may lead to frothy or blood-tinged sputum. Symptoms include:
The wetsuit may feel as though it is hindering breathing ability.
Risk factors.
It has been described in scuba divers, long distance swimmers, and breath-hold diving.
Mechanism.
The mechanisms by which SIPE occurs are controversial, and likely multiple factors are required for the phenomenon to manifest.
SIPE is believed to arise from a "perfect storm" of some combination of these factors, which overwhelms the ability of the body to compensate, and leads to alveolar flooding.
Management.
Management has generally been reported to be conservative, though deaths have been reported.
Epidemiology.
SIPE is estimated to occur in 1-2% of competitive open-water swimmers, with 1.4% of triathletes, 1.8% of combat swimmers and 1.1% of divers and swimmers reported in the literature.
Research.
Most of the medical literature on the topic comes from case series in military populations and divers, and an epidemiological study in triathletes. A recent experimental study showed increased pulmonary artery pressure with cold water immersion, but this was done in normal subjects rather than in people with a history of SIPE. A study in SIPE-susceptible individuals during submersion in cold water showed that pulmonary artery and pulmonary artery wedge pressures were higher than in non-susceptible people. These pressures were reduced by Sildenafil. SIPE may also be a cause of death during triathlons.