Contents
What Is ARDS?
- Acute Respiratory Distress Syndrome: diffuse alveolar damage causing refractory hypoxemia
- Non-cardiogenic pulmonary edema from increased alveolar-capillary permeability
- Hallmark: hypoxemia that does NOT improve well with supplemental oxygen (shunt)
- Common triggers: sepsis (most common), pneumonia, aspiration, trauma, pancreatitis
Berlin Definition
- Timing: within 1 week of a known insult or new/worsening symptoms
- Imaging: bilateral opacities not fully explained by effusions/collapse
- Origin: respiratory failure not fully explained by cardiac failure/fluid overload
- Oxygenation: defined by the PaO₂/FiO₂ (P/F) ratio with PEEP ≥5
P/F Ratio Severity
- Mild: P/F 200–300
- Moderate: P/F 100–200
- Severe: P/F ≤100
- Example: PaO₂ 80 on FiO₂ 0.8 → 80/0.8 = 100 (severe ARDS)
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Start Free Practice →Lung-Protective Ventilation (the cornerstone)
- Low tidal volume: 6 mL/kg ideal body weight (reduces volutrauma)
- Plateau pressure ≤30 cm H₂O
- Permissive hypercapnia: allow PaCOâ‚‚ to rise / pH ~7.25+ to protect lungs
- ARDSNet low-Vt strategy improves survival — a high-yield testable fact
PEEP Strategy
- Higher PEEP recruits collapsed alveoli and improves oxygenation in moderate–severe ARDS
- Titrate PEEP to oxygenation while watching for hypotension and barotrauma
- Goal: keep alveoli open through the respiratory cycle (prevent atelectrauma)
- Balance recruitment against overdistension of healthy lung units
Prone Positioning
- Proning for ≥12–16 hours/day improves oxygenation and survival in severe ARDS (P/F <150)
- Recruits dependent dorsal lung and improves V/Q matching
- Nursing risks: pressure injuries, tube/line dislodgement, facial edema
- Requires a trained team and meticulous airway/line protection during turns
Adjunct Therapies
- Neuromuscular blockade: short-course paralysis in early severe ARDS to improve synchrony
- ECMO: rescue for refractory hypoxemia when lung-protective vent fails
- Inhaled pulmonary vasodilators may transiently improve oxygenation
- Treat the underlying cause (e.g., antibiotics for sepsis/pneumonia)
Fluid Management
- Conservative fluid strategy reduces ventilator days in ARDS
- Avoid fluid overload, which worsens pulmonary edema
- Balance perfusion needs (especially in septic shock) against lung water
- Monitor daily weights, I&Os, and CXR trends
Complications
- Barotrauma/pneumothorax from high pressures
- Multi-organ dysfunction (ARDS often part of sepsis/MODS)
- VAP, delirium, ICU-acquired weakness, and pulmonary fibrosis (late phase)
- Right heart strain from high PEEP and pulmonary hypertension
Nursing Priorities
- Maintain lung-protective settings; do not increase Vt to normalize COâ‚‚
- Optimize sedation/analgesia; minimize ventilator dyssynchrony
- Prevent VAP (bundle), provide skin care (especially when prone)
- Monitor oxygenation trends, hemodynamics, and end-organ perfusion
Can you answer these 3 CCRN questions?
Here are 3 questions in the style of our premium bank. The full rationale explains exactly why the right answer is right — and why the distractors trap most test-takers.
Premium Practice Question
A patient has PaOâ‚‚ 90 on FiOâ‚‚ 1.0 with PEEP 10 and bilateral infiltrates not explained by heart failure. How is the ARDS classified?
- Mild (P/F 200–300)
- Moderate (P/F 100–200)
- Severe (P/F ≤100)
- Does not meet ARDS criteria
Rationale: P/F = 90/1.0 = 90, which is ≤100 with PEEP ≥5 and bilateral non-cardiogenic infiltrates — severe ARDS by the Berlin definition....
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Premium Practice Question
To follow lung-protective ventilation in ARDS, the nurse anticipates which tidal volume target?
- 10–12 mL/kg actual body weight
- 6 mL/kg ideal body weight
- 8–10 mL/kg actual body weight
- Whatever keeps PaCOâ‚‚ normal
Rationale: ARDSNet lung-protective ventilation uses 6 mL/kg of IDEAL body weight with plateau pressure <30, accepting permissive hypercapnia to protect the lungs....
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Premium Practice Question
A patient with severe ARDS (P/F 95) remains hypoxemic despite optimized PEEP and FiOâ‚‚. Which intervention is most appropriate next?
- Increase tidal volume to 10 mL/kg
- Initiate prone positioning
- Begin aggressive diuresis to a negative 3 L
- Switch to a normal PaCOâ‚‚ goal
Rationale: Prone positioning for 12–16 hours/day improves oxygenation and survival in severe ARDS with P/F <150 and is the appropriate next step....
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Related CCRN Guides
Frequently Asked Questions
What is the Berlin definition of ARDS?
ARDS is defined by four criteria: onset within 1 week of an insult, bilateral opacities on imaging not explained by effusion or collapse, respiratory failure not fully explained by cardiac failure or fluid overload, and impaired oxygenation measured by the PaOâ‚‚/FiOâ‚‚ ratio with PEEP at least 5.
How is ARDS severity graded?
By the P/F ratio: mild is 200–300, moderate is 100–200, and severe is 100 or less. For example, a PaO₂ of 80 on an FiO₂ of 0.8 gives a P/F of 100 (severe).
Why is low tidal volume used in ARDS?
Low tidal volume (6 mL/kg ideal body weight) with a plateau pressure below 30 cm Hâ‚‚O limits volutrauma and barotrauma to the injured lung. This ARDSNet strategy improves survival, even if it means permitting a higher PaCOâ‚‚ (permissive hypercapnia).
When is prone positioning used in ARDS?
Prone positioning for at least 12–16 hours per day is used in severe ARDS (P/F below 150) to recruit dependent lung, improve V/Q matching and oxygenation, and reduce mortality.
What is the most common cause of ARDS?
Sepsis is the most common cause, followed by pneumonia, aspiration, severe trauma, and pancreatitis.
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