Critical illness, lung injuries and severe infections are examples of problems that can cause an inflammatory response within the lungs. Inflammation makes the blood vessels "leaky". When the blood vessels in the lung bcome leaking, fluid gets into the surrounding lung tissues and makes it hard for the air sacs of the lung to remain open leak. Fluid in the lung tissue is called "Pulmonary Edema".

The small air sacs at the end of the breathing passages are called "alveoli". These alveoli are surrounded by tiny s blood vessels, called capillaries. The word "pulmonary" means lung, therefore, these small vessels are called pulmonary capillaries. In order for oxygen to enter the pulmonary capillaries, the air must be able to reach the alveoli.

When the lung tissue becomes flooded with fluid, the alveoli have trouble staying open. As more and more alveoli begin to close down, it becomes harder and harder to breathe. In addition, the amount of oxygen that can enter the blood stream can also fall.

When a patient develops pulmonary edema (lung water) that is due to lung inflammation and the patient's blood oxygen level becomes very low, the disorder is called Acute Respiratory Distress Syndrome (ARDS). If the oxygen level becomes too low, the patient may need the help of a breathing machine (ventilator). A ventilator can help the lungs to rest and recover.

Patients with ARDS usually require treatment with a mechanical ventilator and PEEP.  PEEP adds positive pressure into the breathing passages to help diseased alveoli to reexpand. If the disease is very severe, patients may need to be deeply sedated with medications. We may even need to turn the patient onto their stomach and ventilate them in the prone (chest down) position. This can help the lungs to work better.

Patients can survive ARDS. Like many critical conditions, early treatment and preexisting medical problems can make an important difference to recovery.

There are other diseases that can cause fluid to collect in the lung, such as heart failure (called congestive heart failure or cardiac pulmonary edema). These problems can also become severe enough that the patient requires the support of a breathing machine, but the treatments will be different.

ABOVE: Normal air sacs or "alveoli", surrounded by pulmonary capillaries.


ABOVE: Acute Respiratory Distress Syndrome (ARDS) cause large areas of alveoli (air sacs) to collapse. This makes it more difficult to breathe, and causes the level of oxygen in the blood to drop. Positive pressure is used to hlep reopen the lungs. 




Last Revision: October 23, 2014



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Last Updated October 23, 2014 | © 2007, LHSC, London Ontario Canada