The Pulmonary and Critical Care
Division of Harborview Medical Center, University of Washington School
of Medicine, Seattle, Washington has granted permission to include
this article in the ARDS Support Center website.
"WHAT IS ARDS,
"Four of the most frightening
letters I have ever had to deal with."
That was how a mother, whose son
eventually recovered from ARDS, once described this disease. Adult
Respiratory Distress Syndrome, or ARDS (also referred to as acute
respiratory distress syndrome), is a form of sudden and often severe
lung failure. Lung failure means that the lungs can no longer carry
out their normal function of getting oxygen into the blood and
removing carbon dioxide from the body. In order to understand how ARDS
can cause this, it is important first to review how the lung works.
Air, which contains oxygen, is inhaled
through the nose and mouth. It then passes into the windpipe
(trachea). From the trachea the air flows through tubes called
bronchi. These bronchia tubes go to the microscopic air sacs called
alveoli. Very small blood vessels (capillaries) sit next to these air
sacs. Oxygen passes out of the air sacs into the bloodstream and
carbon dioxide passes from the bloodstream into the air sacs. The
carbon dioxide is then exhaled. Unfortunately, ARDS prevents this
normal process from taking place.
ARDS causes the lungs to become
inflamed. Sometimes the inflammation can be mild but is often very
severe. ARDS usually involves both lungs; in the early stages of the
illness the inflammation can start in one lung, but often spreads to
involve the other lung as well. When this inflammation occurs, it
causes a great deal of lung damage, specifically to the alveoli and
When alveoli are damaged, they can
collapse and lose the ability to receive oxygen. When capillaries are
damaged, they leak fluid (edema) into the lungs and alveoli. With some
alveoli collapsed and others filled with fluid, it becomes very
difficult for the lungs to absorb oxygen and get rid of carbon
dioxide. If this inflammation continues, the lung, like any other part
of the body, can become scarred as it tries to heal itself. When that
happens, much of the fluid in the lungs becomes replaced by scar
tissue (fibrosis). If too much fibrosis occurs, it will also interfere
with the exchange of oxygen and carbon dioxide.
ARDS often comes on very quickly, but
it is not always easy to diagnose. It can be easily confused with
pneumonia (or "double pneumonia" if both lungs are involved)
and with congestive heart failure, two other conditions that can lead
to inflammation and edema collection in the lungs. However, pneumonia
results from an infection in the lung whereas ARDS is inflammation
without direct infection. Congestive heart failure causes fluid to
back up into the lungs because the heart is weak and loses its ability
to pump normally, but there is no actual damage to the lungs. A chest
X-ray would be abnormal in all three of these situations and sometimes
it is very difficult to tell them apart. When that happens, other
tests and procedures are sometimes necessary to properly diagnose ARDS.
To summarize, ARDS occurs when there is
severe inflammation in both lungs resulting in an inability of the
lungs to function properly. The following questions and answers
discuss the causes, prognosis, and treatment of ARDS.
WHAT CAUSES ARDS?
HOW DO YOU GET ARDS?
"He was sick enough already and
now this had to happen!"
What causes this widespread lung
inflammation called ARDS? Although this sounds like a simple question,
the answer is not well known. There is a large amount of scientific
information that supports many different theories about how ARDS
develops, but the truth is that no one knows the precise reason why
What is known, however, is that ARDS
can be caused by two basic mechanisms. The first is a direct physical
or toxic injury to the lungs. Examples of this include the inhalation
of vomited stomach contents (aspiration), smoke or other toxic fumes,
and a severe "bruising" of the lungs that usually occurs
after a severe blow to the chest.
The other mechanism that causes ARDS is
more common but is more difficult to understand. When a person is very
sick or the body severely injured, some chemical signals are released
into the bloodstream. These signals reach the lung, and the lung
reacts to these messages by becoming inflamed, thus causing lung
failure. Examples of this type of indirect lung injury include the
presence of a severe infection somewhere in the body (sepsis), a
severe injury (trauma) to some part of the body, severe bleeding that
requires many units of blood (massive transfusion), and some types of
drug overdoses. There are several other rare causes of ARDS, but the
two most common causes are sepsis and severe trauma.
Not everyone who has these problems,
however, develops ARDS. This is fortunate since all of the above
problems are relatively common. So why should some patients with
sepsis or trauma develop ARDS and not others? There are not any good
answers to this question. It does not appear that cigarette smoking,
or the presence of other lung diseases such as asthma, emphysema,
chronic bronchitis of lung cancer, makes one more susceptible to ARDS.
It seems that only a small percentage of the patients who are at risk
for ARDS because of their other illnesses or injuries actually develop
ARDS. We cannot predict with any certainty who will get ARDS and who
will escape it. This unpredictable nature makes ARDS a very
frustrating complication of other illnesses that may be serious enough
HOW COMMON IS ARDS?
"I had never even heard of ARDS
until my son John was in a car crash."
This is an all too common statement
from people affected by ARDS. Almost everyone knows about cancer,
strokes, and heart attacks, but most people have never even heard of
ARDS until someone they know develops the disease. Yet the statistics
are surprising. It is estimated that there are approximately 150,000
cases of ARDS each year in the U.S. alone.
HOW SERIOUS IS ARDS?
ARDS is not only more common than most
people think, it is also a very serious problem. Since ARDS was first
described in 1967, the prognosis has improved only slightly despite
rapid advancements in medical science and technology. Statistics
reveal that approximately one half of the 150,000 people who develop
ARDS each year (in the United States) will survive.
Younger people and those who have fewer
chronic health problems are more likely to recover. It is known that
people with a milder form of ARDS tend to have a better chance of
recovering than those with a more severe form of the illness.
It is also known that the cause of a
patient's ARDS helps predict that patient's chances for survival. For
example, patients who develop ARDS due to sepsis usually do not do as
well as patients whose ARDS is related to trauma. Finally, those
patients who do survive after developing ARDS usually improve over
several months with a return to normal or near normal lung function.
As suggested above, very few cases of
ARDS are alike. Some people get better quickly within a matter of
several days and others take weeks or months to improve. Some people
have no complications and others seem to develop every possible
complication of ARDS. Finally, some will die quickly while others die
after a long and trying illness.
Dealing with the seriousness and the
unpredictability of ARDS is extremely frustrating and can be
emotionally devastating for patients, family, friends, and for doctors
and nurses as well. Hopefully, current and future research will make
ARDS a more treatable and hence much less serious and more predictable
illness than it is now.
HOW IS ARDS TREATED?
At this time there is no specific
treatment for ARDS although several therapies are now being tested.
Patients with ARDS are supported on a breathing machine (ventilator)
to maintain enough oxygen in the bloodstream while they recover from
ARDS and their other injuries or illness. When a person is on a
ventilator there is an artificial airway or endotracheal tube, a tube
that goes into the windpipe through the mouth or nose or a surgical
incision in the neck. This tube is connected to the ventilator. While
in place, the tube temporarily interferes with the patient's ability
to speak since it passes between the vocal cords. Positive
end-expiratory pressure (PEEP), is a special setting on the ventilator
that keeps the lungs expanded to help get oxygen from the lungs into
the bloodstream. Patients may be placed on a special bed, such as an
"air bed" or a rotating bed to position them properly to
help prevent complications such a bed sores and pneumonia.
Medications are used to treat the
original injury or illness as well as complications that may occur.
Some general categories of medications are listed below:
ANTIBIOTICS -drugs that fight infection
ANALGESICS - pain-relieving drugs
SEDATIVES -anti-anxiety drugs
CARDIOVASCULAR -raise blood pressure or stimulate heart
MUSCLE RELAXANTS -that prevent voluntary muscle movement and reduce
the body's demand for oxygen.
WHAT IS A VENTILATOR
HOW IS IT USED TO SUPPORT ARDS PATIENTS?
WHAT DOES IT FEEL LIKE TO HAVE IT BREATHE FOR YOU?
A ventilator is a breathing machine
that is connected to a tube in the patient's windpipe, an endotracheal
tube or tracheostomy tube. It can breathe completely for a patient or
assist a patient's own breathing. There are a number of controls or
settings on the ventilator that are ordered by the doctor. The amount
of oxygen that the patient receives can be adjusted. The air we
normally breathe contains 21% oxygen. It is possible to give a patient
as much as 100% oxygen through a ventilator but this, too, can cause
damage to the lung so an effort is made to give the lowest amount of
oxygen necessary. PEEP is one way to avoid giving the patient high
levels of oxygen.
PEEP, which is positive end expiratory
pressure, is adjusted through the ventilator. It keeps some pressure
in the lungs at the end alveoli, the tiny air sacs where oxygen passes
into the bloodstream, from collapsing. The pressure is measured and
carefully adjusted because there can be complications with high levels
of PEEP. The amount of PEEP is often increased and decreased gradually
but occasionally it is important to change the level of PEEP more
Other adjustments on the ventilator
include the size of each breath (tidal volume) the patient receives
and the number of breaths (respiratory rate) the patient receives each
minute. The ventilator can be adjusted so that it does all of the
breathing or so that the patient breathes partially on his or her own.
These settings are adjusted depending on the amount of oxygen and
carbon dioxide in the blood as well as other tests of lung function.
The ventilator can sense when the
patient takes a breath of his or her own, timing the set number of
breaths to the patient's own rhythm. Often the amount of breathing
needed by the body is much more than the patient is able to do on his
or her own. The patient may require sedatives or relaxing drugs to
help them breathe with the ventilator. PEEP is an odd sensation
because it feels like the lungs do not empty at the end of each
breath. However, the patient may also feel better because it can make
breathing easier and gets more oxygen into the bloodstream.
NOW THAT YOU HAVE
WHAT HAPPENS NEXT?
The course of events after ARDS has
developed is determined, in part, by the degree of abnormality in lung
function and in part by the illness or injury that led to the
development of ARDS. Most patients need to be on the ventilator for
several days. If the underlying medical condition has stabilized and
no new complications develop, then it is likely that the lungs will
begin to heal, allowing the patient to do more and more of the
breathing on his or her own, and the ventilator may be removed within
a week. This happens in about a third of the patients with ARDS.
In another third of the patients, the
underlying condition is so severe that even intensive therapy is not
able to reverse the abnormalities. Such patients may have, or develop,
progressive or irreversible damage to other vital organs. Sometimes
the healing process is further compromised by chronic illnesses or
advanced age. Although intensive medical care is sometimes able to
prolong survival by a few days, such patients often die within the
Those who survive the first week but
whose ARDS has not yet improved enter what might be termed the
"chronic phase" of ARDS. These patients need to be on the
ventilator for up to three or four weeks and sometimes longer.
Sometimes this happens because of the original injury or illness, but
often it occurs because of other complications. Even when there is a
satisfactory response to treatment of the underlying condition, a
small number of patients have persistent inflammation in the lung and
seem unable to begin the healing process. The outcome in patients who
enter this chronic phase is dependent on reversing the inflammation
and preventing or treating complications, especially infection.
Sometimes unusual or experimental treatments may be considered. About
half of the patients with "chronic" ARDS will get better and
leave the hospital, but recovery is slow and may be incomplete.
WHAT ARE THE COMMON
COMPLICATIONS THAT OCCUR WITH ARDS?
Barotrauma is one complication that may
occur with ARDS. The word means injury caused by pressure. In ARDS,
the lung is weakened and, combined with the high pressures of the
ventilator, there is a risk of lung rupture. This is called a
pneumothorax and leads to an accumulation of air in the pleural
cavity. The pleura form a smooth, moist lining around the lungs.
Normally, there is no air in the small space between the pleura and
the lungs. When a pneumothorax develops, a chest tube is inserted by a
physician through the patient's chest wall, into the pleural cavity
outside the partially collapsed lung to remove the air. The tube is
connected to a suction machine to help the lung reinflate. The suction
machine or wall suction is used until the patient's lung is healed
enough to stay inflated on its own. A pneumothorax may also be related
to trauma or to other procedures used in treating the patient.
Bacterial infections are a common
complication of ARDS and contribute to continued lung injury. The lung
is the most common site of infection. Lung infection or pneumonia may
be difficult to diagnose in a patient with ARDS because, as we've
said, the patient's chest X-ray is already very abnormal. The nurse or
respiratory therapist will obtain a specimen of phlegm or sputum from
the lungs by suctioning through the patient's endotracheal tube when
the patient has a fever. The specimen is sent to the laboratory for a
culture, a method that allows any bacteria that are present to grow.
In this way, bacteria that may be causing an infection can be
identified and the sensitivity of the bacteria to antibiotics can be
determined. Sometimes the doctor may want to obtain a sputum specimen
from deeper in the lung. In that case a bronchoscopy may be performed
by a physician. The bronchoscope is a flexible tube like instrument
that contains a light and an eyepiece. It is inserted through the
patient's endotracheal tube and the doctor can see inside the
patient's airways. A special small brush is passed through the
bronchoscope and into an area of the lung that appears infected. This
brush is then sent to the laboratory for culture and sensitivity
tests. Sedative medications are used to keep the patient comfortable
and the ventilator is adjusted during this procedure so the patient's
breathing continues without a problem.
Bacterial infections may also occur in
other parts of the body such as the bloodstream, the urinary tract,
sinuses, skin or muscle, the abdomen or the spinal fluid.
All of these areas are tested for
infection in various ways. Antibiotics are used when an infection is
present or suspected. Antibiotics are powerful drugs and must be used
carefully. Bacteria may become resistant, especially if the
antibiotics are used when they are not needed. When a patient has been
treated with many antibiotics for a long period of time they are at
risk of developing a fungal or yeast infection, which may cause
Abnormal organ function in addition to
the lung failure caused by ARDS can develop and may involve the liver,
kidney, brain, blood or immune system. These organ dysfunctions may be
related to the underlying illness, to treatment or may occur through
the same inflammatory process which injured the lungs. If kidney
failure occurs, the patient may be maintained with dialysis, which is
treatment that removes waste products from the patient's blood by
circulating the blood through a special machine.
Liver failure is a difficult problem to
treat because there is no replacement for the many functions that the
liver performs in our bodies. Ongoing infections, despite appropriate
antibiotic therapy, may be due to dysfunction of the immune system.
Patients may become unconscious or confused when they previously have
been alert and oriented due to dysfunction of the brain or central
nervous system. Blood transfusions or replacement of certain elements
of the blood, such as platelets, which are needed for clotting of the
blood, may be required.
IF YOU SURVIVE ARDS,
WHAT HAPPENS TO YOUR LUNG FUNCTION,
AND HOW LONG DOES IT TAKE FOR YOUR LUNGS TO RECOVER?
Most patients who survive ARDS have a
remarkable degree of recovery of lung function, given the severity of
the initial injury. Recovery time for each patient is variable.
Patients recover at different rates and have different end points.
However, most patients recover the great majority of lung function in
the first three to six months and then recovery levels of up to a year
and beyond. Only a few patients have decreased lung function forever.
Recovery is defined as how well the
patient is able to take a deep breath and how well oxygen is able to
go from the lungs into the bloodstream. We measure these in tests
called pulmonary function tests. Patients may receive these tests at
discharge from the hospital and at three to six months after hospital
During the first three months after
discharge from the hospital, some patients may feel short of breath,
have a cough, produce phlegm, and feel fatigued. Some may be required
to use supplemental oxygen for a period of time when they go home.
Many patients experience hoarseness, which is due to irritation from
the endotracheal tube used while they were on a ventilator. As the
months go by, however, patients may feel like they can take a deep
breath more easily, walk farther distances, or get tired less easily.
Again all of these symptoms usually get better, usually within the
first six months after leaving the hospital.
WHAT RESEARCH IS
BEING DONE ON ARDS?
Research is being conducted all over
the world in attempts to better understand the causes of ARDS, why
some people get it and others do not, and on ways to improve the
treatment of ARDS. Unfortunately, no magic cure for this illness has
been found, but there are many new exciting possibilities being
The major areas of ARDS research have
revolved around four topics:
- treatments to reduce the risk of
- therapy to reduce or reverse the
inflammation in the lungs that is ARDS;
- improvements in the supportive
therapy for ARDS, such as better ventilators, and ways to minimize
the risk of complications; and
- therapy to improve the abnormal lung
function that exists once ARDS occurs.
This article was written by the staff
of Harborview Medical Center, including ARDS Support medical advisor,
Dr. Ken Steinberg, taken from a brochure developed by them. Harborview
Medical Center is a national center for ARDS research and involved in
many of the above mentioned studies. It is supported by the
Respiratory Distress Syndrome Foundation in Montgomeryville,
Pennsylvania, directed by Frank Cannon. The scientific research
contained in the brochure and in this article is supported by a
Specialized Center of Research grant from the National Heart, Lung,
and Blood Institute.