ARDS Flashcards
Berlin definition of ARDS
Onset of symptoms and signs are within 1 week of insinuating event
Hypoxemia is present
Chest xray shows bilateral opacities that are non-cardiogenic in etiology (not caused by heart failure)
PaO2/FiO2 < 300 mmHg
Pathophysiology of ARDS
Some sort of insult causes damage to capillary endothelium and alveolar epithelium
Results in diffuse alveolar disease/ hyaline membrane disease
- hyaline cartilage develops to alveoli damage
Possible causes for ARDS
Alveoli can be direct (pneumonia, lung contusion, near drowning, smoke inhalation) or indirect (sepsis, burns, emboli from fractures, TRALI, pancreatitis, OD).
- if direct, release of pro-inflammatory cytokines are induced and includes TNF and ILs
- cytokines recruit neutrophils and release toxic mediators and ROS
- causes tissue destruction
What is the most common cause of ARDS?
Sepsis, usually secondary to pneumonia
3 phases of ARDS
Exudative (1-7 days)
- hyaline membrane production begins and edema is present (exudate)
- diffuse alveolar damage is present
- shows bilateral opacities
- lungs are stiff w/ VQ mismatch and increased dead space
- respiratory failure may occur here
Proliferative (7-21st day)
- often cured here*
- removed from ventilators sometimes
- reparative processes begin here with type 2 pneumocystis proliferating along alveolar basement membranes
- new surfactant and type 1 pneumocystis production begins
Fibrotic (21st day+)
- require long-term ventilators
- resembles emphysema
- interstital fibrosis is widespread
- pulmonary hypertension begins
- high rate of death if at this stage (53%)
Non-cardiogenic pulmonary edema
Looks similar to cardiogenic pulmonary edema except:
1) Normal hydrostatic pressure with loss of oncotic pressure (no pulmonary hypertension < 25mmHg)
2) heart size is normal
3) if you can get fluid, exudate is rich in
proteins
4) BNP will not be elevated
5) ECG shows nothing abnormal
6) no JVD present
Cardiac ultrasound with heart failure vs ARDS
HF:
- low ejection fraction
- dilated left ventricle/atrium
- overall structure looks different
ARDS:
- none of the above present
Severity of ARDS
Measured by ratio of paO2/FiO2
- partial pressure of oxygen/ fraction of inspired O2 (in decimal form)
Mild = ratio is >200 but less than 300mmHg
Moderate = ratio is >100 but less than 200 mmHg
Severe = ratio is <100 mmHg
Treatment of ARDS
Require ventilator (but try to limit use) - also patient must be prone
Fluid management without excess IV fluids
DONT use glucocorticoids or surfactant replacement
Can use PEEP to prevent persistent alveoli collapse (usually 5mmHg)