Acute Respiratory Distress Syndrome
last authored:
last reviewed:
Introduction
Acute Respiratory Distress Syndrome (ARDS) is also known as shock lung, diffuse alveolar damage, or acute lung injury.
Severe acute lung injury is caused by toxic insults.
The Case of...
a simple case introducing clincial presentation and calling for a differential diagnosis to get students thinking.
Causes and Risk Factors
ARDS has many causes:
infection
trauma and injury: fractures and fat emboli, burns, radiation
gas and chemical injury
- oxygen toxicity
- smoke
- heroin/methodone overdose
- ASA
- barabiturates
- paraquat
multiple transfusions
disseminated intravascular coagulation
pancreatitis
uremia
cardiopulmonary bypass
hypersensitivitry reactions
idiopathic ARDS is referred to as acute interstitial pneumonia
Pathophysiology
ARDS results from diffuse alveolar capillary damage. Alveolar flooding leads to loss of diffusion capacity, and type II pneumocytes become damaged.
During the acute phase, epithelial and endothelial injury lead to edema and hyaline membranes form.
During the organizing phase, alveolar collapse, fibroblast proliferation, and fibrosis occurs. Diffuse tissue destruction is not easily repaired, and scarring results.
IL-1 and TNF recruit neutrophils, and NF-kB-mediated genes are transcribed. Histologically, hyaline membranes are present.
Signs and Symptoms
ARDS is characterized by the rapid onset of severe, life-threatening respiratory insufficiency (dyspnea and tachypnea), cyanosis, and..
- history
- physical exam
History
Physical Exam
Investigations
- lab investigations
- diagnostic imaging
Lab Investigations
Severe arterial hypoxemia and decreased PaO2, with a PaO2/FiO2 ratio less than 200, refractory to oxygen therapy.
Diagnostic Imaging
Chest radiographs are intially normal but soon show diffuse alveolar infiltration and bilateral opacities. As this can mimic heart failure, clinical correlates are also required for diagnosis.
on chest X ray:
- small lung volumes
- hazy allover (ground glass appearance)
- air bronchograms: bronchi are visible outside the heart shadow due to consolidation
Pulmonary arterial wedge pressure (surrogate for left atrial pressure) is <18 mmHg, suggesting no clinical evidence of left heart failure.
Differential Diagnosis
Treatments
Positive expiratory pressure (PEP) keeps the airways open and keeps them from filling with fluids.
Consequences and Course
Respiratory acidosis can develop.
Mortality rate is about 60%.
Resources and References
Topic Development
created:
authors:
editors:
reviewers:
 |