ARDS Flashcards
What is ARDS?
Acute resp distress syndrome
Non cardiac pulmonary edema and disruption of alveolar capillary membranes as a result of injury to the pulmonary vasculature and alveoli
What are the 2 types of ARDS?
1) Direct injury ARDS (direct injury to pulmonary system causes inflammation which activates mediators)
2) Indirect injury ARDS (Insult occurs somewhere else and mediators transported via blood to lungs)
What are causes of direct injury ARDS?
Aspiration, near drowning, toxic inhalation, pneumonia, O2 toxicity
What are causes of indirect injury ARDS?
Sepsis, shock, cardiopulmonary bypass, trauma, burns, pancreatitis, pulmonary embolus
What are the phases of ARDS?
1) Exudative
2) Fibro-proliferative
3) Recovery
What happens in the exudative phase of ARDS?
48-72 hrs after initial injury, mediators cause injury to pulmonary capillary membrane
Fluid moves into lungs with mediator activation results in:
1) Non cardiogenic pulmonary edema
2) Damage to alveolar capillary membrane
3) Compression of small airways increases air resistance
4) Inflammatory mediators cause bronchoconstriction
5) Protein + cellular debris form hyaline membrane over damaged alveoli cells
What are the systemic consequences of the exudative phase of ARDS?
Intrapulmonary shunting (blood shunts from R to L heart without participating in gas exchange at lungs d/t decreased ventilation)
Hypoxemia
Pulmonary HTN (from leakage of fluid into interstitium forming micro-emboli in capillary membranes) increase alveolar deadspace, possible silent units
Increase RV afterload decreases overall CO
What are the causes for pulmonary HTN in ARDS?
Micro-emboli in capillary membranes
Pulmonary vasoconstriction due to hypoxemia
What causes RV failure in ARDS?
Increase in RV afterload as a consequence of pulmonary HTN
What happens in the fibro-proliferative phase of ARDS?
New cells replace damaged cells in alveoli and capillaries, but are laid down in a disordered manner causing:
Fibrotic alveoli
Scarred capillaries
Pulmonary edema and inflammation begin to subside but cells still damaged
What are the systemic consequences of the fibro-proliferative phase?
Further pulmonary HTN resulting:
- Stiffening of lungs
- Decreased lung compliance
- Continued hypoxemia
What happens in the recovery phase of ARDS?
Over several weeks, alveolar-capillary membrane re-establishes itself
Type I and II cells recover, III cells remove hyaline membrane and clear out debris
How is ARDS diagnosed?
Occurs within 1 week of known insult
CXR showing bilateral infiltrates
Non cardiogenic pulmonary edema
P/F ratio classification
What are the P/F ratio classifications for ARDS?
P/F 201-300 mmHg –> MILD ARDS
P/F 101-200 mmHg –> MODERATE ARDS
P/F < 100 mmHg –> SEVERE AARDS
How are ABGs affected by ARDS?
Low PaO2 despite increased FiO2 (refractory hypoxemia)
Initially low PaCO2, then high as pt fatigues and retains. Later metabolic and mixed acidosis