Maintaining a proper fluid balance in your lung tissue and its vasculature requires a dynamic combination of various opposing forces. Unopposed changes in any of these forces can result in a buildup of excess fluid — or edema — in your pulmonary tissue. The main variables involved in regulating this fluid balance are the following:
- Oncotic pressure (a form of pressure exerted by proteins) in the pulmonary capillaries, the tiniest vessels of the circulatory system
- Oncotic pressure in the pulmonary system's interstitial fluid (fluid in the cavities of your lung tissue)
- Permeability of the pulmonary capillaries
- Hydrostatic pressure (the pressure of a fluid at rest) in the pulmonary capillaries
- Hydraulic pressure (the pressure of a fluid that is being compressed or pumped) in the interstitial fluid
- Pressure in the alveoli, the tiny air sacs of the lungs.
Pulmonary edema is caused by changes in these forces — such as a drop in the levels of key proteins in the blood; leakage from the pulmonary capillaries due to sepsis (a life-threatening complication of infections); an increase in hydrostatic pressure in the pulmonary capillaries due to heart failure; and negative pressure in the alveoli due to resistance from breathing through a faulty regulator. Additional issues that can contribute to the development of pulmonary edema include side effects of some cardiovascular drugs; ARDS (acute respiratory distress syndrome, a life-threatening condition that prevents oxygen from getting to the lungs); reperfusion (a procedure that restores circulation after a heart attack or stroke); cardiomyopathy (a weakening of the heart muscle); high-altitude pulmonary edema; a pulmonary embolus (a blood clot lodged in a vessel in the lungs); re-expansion (the reinflation of a collapsed lung); pulmonary hypertension (elevated pressure in the arteries that carry blood from the heart to the lungs); lung cancer; hemorrhage (uncontrolled bleeding); and various disorders of the nervous system. Other factors can include overhydration by well-intentioned divers who have heard the conventional wisdom that dehydration is a risk factor for decompression sickness, as well as poor physical conditioning, which can result in increased negative pressure in the alveoli during deep inspiration.
The symptoms of IPE include chest pain; dyspnea (discomfort or difficulty breathing); wheezing; and pink, frothy sputum while submerged or shortly after emerging from the water. Most people who suffer an episode of IPE had no significant history or signs that would indicate a susceptibility to the condition; nevertheless, the risk of IPE does rise with age, obesity and elevated blood pressure.
Once pulmonary edema occurs, hypoxia (lack of an adequate supply of oxygen) leads to constriction of the pulmonary vasculature, which worsens the cascade of ill effects. The situation can be further aggravated by the accompanying dyspnea, which, when experienced underwater, can induce panic and uncontrolled ascent to the surface — leading to overinflation of the lungs and even near-drowning.
To help differentiate immersion pulmonary edema from other conditions with similar symptoms (such as near-drowning, pulmonary decompression sickness and pulmonary overinflation syndrome), it is important to keep in mind that IPE's onset can occur either at depth or upon reaching the surface. And it is not necessarily precipitated by aggressive diving, a rapid ascent or the aspiration of water.
Treatment for IPE should begin with removal of the affected individual from the water (to relieve the compression of the vessels in the lower extremities, allowing centrally pooled fluids to return to the extremities) and with administration of oxygen (beginning at 100 percent and later at a reduced concentration). A diuretic such as Lasix may help to reduce excess intravascular fluid, although diuresis — the body's natural excretion of fluid — may already be under way as a result of hormonal influences. The condition usually resolves quickly in a healthy diver. Prolonged hospitalization is rarely required; if it is necessary, it's usually due to contributing factors, such as an underlying cardiac problem.