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acute respiratory distress syndrome (ARDS) Correct Answers a sudden
and progressive form of acute respiratory failure (ARF) in which the
alveolar-capillary membrane becomes damaged and more permeable to
intravascular fluid
- one of the most common conditions seen in the adult ICU
- mortality rate is 35%
etiology of ARDS Correct Answers - most common cause is sepsis
- may also develop because of multisystem organ dysfunction syndrome
(MODS). Patients with multiple risk factors are 3 or 4 times more likely
to develop ARDS.
- caused by direct or indirect lung injury
direct lung injury Correct Answers pathogen comes into contact with the
lung tissue
example: aspiration of gastric contents into the lung immediately
initiates the inflammatory response
indirect lung injury Correct Answers ARDS develops due to a problem
somewhere else in the body
example: necrotizing pancreatitis or bowel obstruction with perforation
causes widespread inflammation and infection. As a result, septic
mediators gain entrance to the bloodstream and often move toward the
,lungs, which provide a favorable, dark, moist environment for their
proliferation
common causes of direct lung injury Correct Answers • Aspiration
(gastric contents or other substances)
• Bacterial or viral pneumonia
• Sepsis
less common causes of direct lung injury Correct Answers • Chest
trauma (blunt or penetrating)
• Embolism: fat, air, amniotic fluid, thrombus
• Inhalation of toxic substances
• Near-drowning
• O2 toxicity
• Radiation pneumonitis
common causes of indirect lung injury Correct Answers • Massive
trauma
• Sepsis and septic shock (especially gram-negative infection)
• Severe TBI
• Shock states (hypovolemic, cardiogenic)
less common causes of indirect lung injury Correct Answers • Acute
pancreatitis
• Cardiopulmonary bypass
,• Disseminated intravascular coagulation
• Opioid drug overdose
• Transfusion-related acute lung injury (e.g., multiple blood
transfusions)
• Urosepsis
3 phases of pathophysiologic changes in ARDS Correct Answers (1)
injury or exudative phase
(2) reparative or proliferative phase
(3) fibrotic or fibroproliferative phase
injury (exudative) phase of ARDS Correct Answers - usually occurs 24
to 72 hours after the initial insult (direct or indirect)
- generally lasts 7 to 10 days
major pathologic events in injury phase of ARDS Correct Answers
damage to alveolar-capillary membrane leads to:
(1) damage to type I and II alveolar cells
(2) the release of inflammatory mediators
damage to alveolar-capillary membrane leads to damage to type I and II
alveolar cells: Correct Answers decreased surfactant production ->
decreased alveolar compliance and recoil -> atelectasis (hyaline
, membrane formation and decreased lung compliance) -> impairment in
gas exchange -> ARDS
damage to alveolar-capillary membrane leads to the release of
inflammatory mediators Correct Answers 2a: release of inflammatory
mediators -> bronchoconstriction -> impairment in gas exchange ->
ARDS
2b: release of inflammatory mediators -> increased alveolar-capillary
membrane permeability -> outward migration of blood cells and fluids
from capillaries -> pulmonary edema -> decreased lung compliance and
impairment in gas exchange -> ARDS
2c: release of inflammatory mediators -> vascular narrowing and
obstruction -> pulmonary hypertension -> ARDS
alveolar-capillary membrane damage occurs in the injury (exudative)
phase Correct Answers - Engorgement of the peribronchial and
perivascular interstitial space causes interstitial edema.
- Fluid in the parenchyma of the lung surrounding the alveoli crosses the
alveolar membrane and enters the alveolar space.
- V/Q mismatch and shunt develop because the alveoli fill with fluid.
- Blood in the capillary network cannot be oxygenated.
what causes the alveolar-capillary membrane damage? Correct Answers
We do not know the exact cause, some think it is caused by stimulation
of the inflammatory and immune systems
- This stimulation attracts neutrophils to the pulmonary interstitium.