🫁 Chapter 39: Acute Respiratory Distress Syndrome (ARDS)

Berlin definition · Pathophysiology (exudative, proliferative, fibrotic) · Lung protective ventilation (low tidal volume 6 mL/kg, Pplat <30) · Optimal PEEP · Prone positioning · HFOV · Neuromuscular blockers · Inhaled nitric oxide · ECMO · Conservative fluid management

🔍 Core Concepts: Acute Respiratory Distress Syndrome

📌 Berlin Definition
Acute onset within 1 week of insult. PaO2/FiO2 ≤300 with PEEP ≥5. Bilateral opacities not fully explained by effusion or atelectasis. Not fully explained by cardiac failure.
📊 Severity (PaO2/FiO2)
Mild: 200-300 · Moderate: 100-200 · Severe: <100 with PEEP ≥5. Associated with increased mortality.
🫁 Lung Protective Ventilation
Low tidal volume 6 mL/kg IBW. Limit Pplat <30 cmH2O. Permissive hypercapnia (pH ≥7.2). Optimal PEEP (recruitment without overdistension).
💊 Adjunctive Therapies
Prone positioning (16-20h/day) reduces mortality in severe ARDS. Neuromuscular blockers (early, 48h) may improve outcomes. Conservative fluid management after shock resolves.
🔄 Rescue Therapies
Inhaled nitric oxide (iNO) for refractory hypoxaemia (temporary). HFOV if severe and failing conventional ventilation. ECMO (VV-ECMO) as salvage if OI >30 or refractory.
⚠️ VILI types
Barotrauma (high pressure), Volutrauma (high volume), Atelectrauma (cyclic collapse), Biotrauma (inflammation). Low tidal volume reduces volutrauma and biotrauma.

🩺 Stepwise Approach: ARDS Management

1
Diagnose & classify severity (Berlin criteria)
PaO2/FiO2 ratio with PEEP ≥5, bilateral opacities, acute onset (<7 days), not cardiac failure. Mild: 200-300, Moderate: 100-200, Severe: <100.
2
Initiating lung protective ventilation
Tidal volume 6 mL/kg ideal body weight. Measure Pplat (≤30 cmH2O). Permissive hypercapnia (target pH ≥7.20-7.30). Use pressure control or volume control with decelerating flow.
3
Optimise PEEP (recruitment vs overdistension)
Use PEEP/FiO2 table (ARDSnet). Higher PEEP for moderate-severe ARDS if no haemodynamic compromise. PV loop: set PEEP above lower inflection point, avoid upper inflection point.
4
Prone positioning (severe ARDS, PaO2/FiO2 <100)
Prone for 16-20h/day improves V/Q matching and reduces mortality. Requires skilled team, monitor ETT, lines, pressure points.
5
Adjunctive & rescue therapies
Neuromuscular blockers (cisatracurium) for 48h if severe asynchrony. Conservative fluid management after shock. Inhaled nitric oxide for refractory hypoxaemia (temporary). HFOV if severe and failing. ECMO (VV-ECMO) as salvage.
6
Weaning & recovery
Wean FiO2 first, then PEEP. Transition to pressure support. Avoid fluid overload. Monitor for VAP, barotrauma, MODS. Long-term rehab for survivors.