ARDS

Question 1

Berlin definition of ARDS

Answer 1

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

Question 2

Pathophysiology of ARDS

Answer 2

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

Question 3

Possible causes for ARDS

Answer 3

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

Question 4

What is the most common cause of ARDS?

Answer 4

Sepsis, usually secondary to pneumonia

Question 5

3 phases of ARDS

Answer 5

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%)

Question 6

Non-cardiogenic pulmonary edema

Answer 6

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

Question 7

Cardiac ultrasound with heart failure vs ARDS

Answer 7

HF:

• low ejection fraction
• dilated left ventricle/atrium
• overall structure looks different

ARDS:
- none of the above present

Question 8

Severity of ARDS

Answer 8

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

Question 9

Treatment of ARDS

Answer 9

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)