6.4 ARDS

Question 1

Q4 — Acute respiratory distress syndrome

a) List the criteria for a diagnosis of acute respiratory distress
syndrome (ARDS).

Answer 1

1 Timing — within 1 week of a known clinical insult or new/worsening respiratory symptoms.

● Chest imaging (CXR or CT) —
bilateral opacities not fully explained by
effusions/lung collapse.

● Origin of oedema —
respiratory failure not fully explained by cardiac
failure or fluid overload (objective assessment [echocardiography] is
needed if there is no risk factor present).

Question 2

b) How would you classify ARDS?

Answer 2

ARDS is diagnosed according to the Berlin definition and is characterised as mild, moderate and severe depending on the paO2/FiO2 ratio:

● Mild — paO2/FiO2 26.6kPa to <39.9kPa with PEEP or CPAP>5cm H2O.
● Moderate — paO2/FiO2 13.3kPa to 26.6kPa with PEEP or CPAP 5cm H2O.
● Severe — paO2/FiO2 <13.3kPa with PEEP >5cm H2O

Question 3

c) List any four clinical indices to quantify oxygenation in ARDS.

Answer 3

● Partial pressure of arterial oxygen (paO2).

● Fraction of inspired oxygen (FiO2).

● PaO2/FiO2 ratio.

● Oxygen saturation (SpO2).

● Oxygenation index — lower is better.

● Alveolar partial pressure of oxygen.

● Alveolar — arterial oxygen tension gradient.

Question 4

d) What are the ventilatory strategies in managing a patient with
ARDS?

Answer 4

● Lung protective ventilation (6ml/kg of IBW tidal volume; plateau
pressure <30cm H2O [ARDSnet protocol]).

● Optimal PEEP.

● Prone ventilation.

● Lung recruitment manoeuvres.

● Inverse ratio ventilation.

● High-frequency oscillation ventilation (HFOV).

● Extracorporeal membrane oxygenation (ECMO).

● Weaning protocols with spontaneous breathing trials
(when ready to wean).

Question 5

e) What are the non-ventilatory strategies in managing a patient
with ARDS?

Answer 5

● Conservative fluid management.

● Neuromuscular blockade in the early phase of severe ARDS.

● Steroids (not recommended for routine use).

● Ensure adequate nutrition.

● Prevent complications of critical illness.

● Stress ulcer prophylaxis.

● VTE prophylaxis.

● Glucose control.

● Statins, inhaled NO, ketoconazole —
the existing evidence does not
support these therapies.