What is Adult Respiratory Distress
Syndrome, commonly called simply: ARDS? What ARDS is not. What are the phases/stages of
ARDS?
Adult (or Acute) Respiratory Distress Syndrome (ARDS) is a medical
condition which prevents the normal breathing process from taking place. ARDS occurs
when there is severe inflammation in both lungs resulting in an inability of the lungs to
function properly. ARDS is a devastating, often fatal, inflammatory lung condition
that usually occurs in conjunction with catastrophic medical conditions, such as
pneumonia, shock, sepsis (or severe infection throughout the body, sometimes also referred
to as systemic infection, and may include or also be called a blood or blood-borne
infection), and trauma. It 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.
As will be seen, ARDS may result in a relatively short period of
battle to recover characterized by what seems to be a remarkably speedy recovery with
little if any damage to the lungs. More often, if death does not occur, there is a
very protracted period of battle with varying levels of lung damage sometimes but not
always leading to the need for extensive physical and pulmonary rehabilitation.
Thousands upon thousands of individuals suffer from ARDS (and the
less severe precusor medical condition known as Acute Lung Injury - ALI) each year in the
US alone. Worldwide, the cases of ARDS and ALI total in the hundreds of thousands.
Patients, family members and friends, survivors, medical personnel and facilities, are
severely tested emotionally, morally, financially, and significantly effected by the
devastating consequences of ARDS each year.
The pathogenesis of ARDS generally has been characterized into three
phases/stages. It is important to remember each individual is different and the path
through battling ARDS may vary widely. There may usually are many ups and downs
along the way.
1.) Exudative phase/stage.
Characterized by accumulation of excessive fluid in the lungs due to exudation
(leaking of fluids) and acute injury Characterized by accumulation of excessive fluid in
the lungs due to exudation (leaking of fluids) and acute injury (Acute Lung Injury
"ALI" often is a precusor injury medical condition to the more severe
development of ARDS, although ALI is more prevalent and not all ALI cases develop into
ARDS). Arterial oxygention is usually most severe during this phase of actute
injury, including injury to the endothelium (lining membrane) and epithelium (surface
layer of cells). Some individuals quickly recover from this first phase; many others
progress after about a week into the second phase/stage.
2.) Fibroproliferative (or sometimes
shortened to proliferative) phase/stage. Connective tissue and other structural
elements in the lungs proliferate in response to the initial injury, including development
of fibroblasts (cells giving rise to connective tissue). Under a microscope, lung
tissue appears densely cellular. Terms "stiff lung" and "shock lung"
have been known to characterize this phase/stage. Two to four weeks after the onset
of lung injury, abnormally enlarged air spaces and fibrotic tissue (scarring) are
increasingly apparent. There is ongoing danger of barotrauma or volutrauma causing a
pneumothorax - a rupture allowing leakage of air from the damaged lung into surrounding
spaces, driven by the high pressure (barotrauma) or the volume of air used (volutrauma) in
mechanically assisted breathing. There is also danger of pneumonia and blood-born
infection (sepsis) developing, or difficulty in resolving one or both of these conditions
if they were the precipitating conditions leading to the ARDS. Many people die during this
phase/stage because of Multiple Organ Failure (MOF) or infectious complications. The
second phase/stage typically lasts 3-10 weeks. The first two phases/stages generally are
the most critically severe stages from a life or death consequence standpoint.
3.) Fibrosis (or fibrotic) phase/stage-Repair and
recovery (or the healing stage). The lung reorganizes and recovers during
this phase/stage. Resolution of inflammation, excess cellularity, and fibrosis
settles. Oxygenation improves to the point of liberation from mechanical ventilation
becomes possible. Lung function may continue to improve for as long as 6 to 12
months after onset of respiratory failure, depending on the precipitating condition and
severity of the initial injury. It is important to remember that there may be and
often are different levels of pulmonary fibrotic changes between individuals who suffer
from ARDS. |
