Acute respiratory distress syndrome (ARDS) is an acute inflammatory lung injury causing hypoxemia. It is diagnosed using Berlin criteria including onset within 1 week, bilateral opacities on imaging, and low PaO2/FiO2 ratio. Radiographically, ARDS presents as diffuse opacities resembling pulmonary edema that emerge 12-24 hours after injury. Management involves mechanical ventilation with low tidal volumes, conservative fluid management, treating the underlying cause, and considering strategies like prone positioning to improve oxygenation. ARDS has various causes including direct lung injury from pneumonia, inhalation, or indirect injury from sepsis, shock, or pancreatitis.

1. Acute Respiratory Distress Syndrome – ARDS
- Clinical Cheat Sheet
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Overview
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● An acute diffuse, inflammatory lung
injury, leading to increased pulmonary
vascular permeability, lung congestion
with hypoxemia and bilateral radigraphic
opacities, associated with decreased
lung compliance.
Berlin criteria (2013)
● Acute onset over 1 week or less
● Bilateral opacities consistent with
pulmonary edema must be present;
they may be detected on CT or CXR
● PaO2/FiO2 ratio <300mmHg with a
minimum of 5 cmH20 PEEP
● Volume overload with heart failure
should be ruled out either subjectively
or an “objective assessment“ (e.g. echo
cardiogram) should be performed in most
cases if there is no clear cause such as
trauma or sepsis.
Radiographic assessment
Acute pulmonary edema Pulmonary hemorrhage
● CXR findings of ARDS are non-specific
and resemble those of typical pulmnary
edema or pulmonary hemorrhage.
● Develop 12-24 hours after initial lung insult
as a result of proteinaceous interstitial edema.
● In contrast to cardiogenic pulmonary edema,
which responds to diuretic therapy, ARDS
persists for days to weeks.
● Clues to ARDS: normal heart size, absent
pleural effusions, absent Kerley B lines, and
the presence of air bronchograms (relatively
uncommon in cardiogenic pulmonary edema).
Severity categories
ARDS
severity PaO2/FiO2 Mortality
Mild
Moderate
Severe
200 – 300
100 – 200
< 100
27%
32%
45%
Early-phase CT scan features
● Pulmonary opacification: anteroposterior
density gradient within the lung, with dense
consolidation in the most dependent regions,
merging into a background of widespread
ground-glass attenuation and then normal or
hyperexpanded lung in the non-dependent
region.
● Ground-glass opacification: a non-specific
sign that reflects an overall reduction in the air
content of the affected lung. In acute ARDS
likely represent edema and protein within the
interstitial and alveolar spaces.
● Bronchial dilatation within areas of
ground-glass opacification
Causes
Management
Dense dependant consolidation
● Calculate predicted body weight
● Select any ventilator mode
● Set ventilator settings to achieve
initial VT = 8 ml/kg PBW
● ↓ VT by 1 ml/kg at intervals ≤ 2
hours until VT = 6ml/kg PBW.
● Set initial rate to ~ baseline min
ventilation (not > 35 bpm).
● Adjust VT and RR to achieve pH
and plateau pressure goals as
shown in table:
Oxygenation
goal
Plateau
pressure goal
pH goal
Inspiration:
expiration goal
PaO2 55-80 or
SpO2 88-95%
7.30-7.45
≤ 30 cm H2O
I:E < 1
Mechanical Ventilation
Weaning
● Conduct spontaneous breathing
trial daily when FiO2 ≤ 0.40 and
PEEP ≤ 8 OR FiO2 < 0.50 and
PEEP < 5, patient has acceptable
spontaneous breathing efforts,
SBP ≥ 90 mmHg without pressors,
No neuromuscular blocking agents.
● Assess for tolerance as below of
SBT for up to two hours:
a. SpO2 ≥ 90: and/or
PaO2 ≥ 60 mmHg
b. Spontaneous
VT ≥ 4 ml/kg PBW
c. RR ≤ 35/min
d. pH ≥ 7.3
e. No respiratory distress
● Extubate if tolerate for > 30 min
● Use a minimum PEEP of 5 cm H2O.
Consider use of incremental
FiO2/PEEP combinations.
Other techniques
● Prone posture: ↓ mortality,
improves oxygenation
● inhaled iNO, inhaled prostacycline
● VV-ECMO
● Early resuscitation, appropriate
antibiotic agents, and source
control if sepsis-associated ARDS.
● Conservative fluid-management
● Supportive management with
early enteral nutrition
● Treat the underlying cause
● Glucortecoids may improve
oxygenation in pneumonia and
are harmful if started >14 days
after dx of ARDS
Direct lung
injury
Indirect lung
injury
pneumonia, bacterial, viral including
COVID19!, fungal, aspiration,
contusion, inhalational, near drowning
Sepsis, hemorrhagic shock, pancreatitis,
major burn, drug overdose, transfusion
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