Pulmonary

ARDS: definition, lung-protective ventilation and prone positioning

The Berlin criteria and severity bands, the ventilator settings that reduce mortality, and when to use prone positioning and neuromuscular blockade.

10 min read·advanced·

Reviewed by a licensed nurse · 25 October 2026

Severity (Berlin definition, on PEEP of 5 cmH2O or more)

01
Calculate predicted body weight
Use height and sex, not actual weight. Male: 50 + 0.91 x (height in cm minus 152.4). Female: 45.5 + 0.91 x (height in cm minus 152.4).
02
Set the tidal volume
6 mL/kg of predicted body weight to start, within 4 to 8 mL/kg.
03
Check the plateau pressure
Keep it at or below 30 cmH2O. Lower the tidal volume further if it is higher.
04
Set PEEP and FiO2
Use a PEEP and FiO2 table to reach an oxygen saturation of about 88 to 95 percent (PaO2 55 to 80 mmHg). Higher PEEP is favored in moderate-to-severe disease.
05
Accept some hypercapnia
Permissive hypercapnia is acceptable if the pH stays at or above about 7.20 to 7.25.

·Prone positioning for at least 12 to 16 hours a day when PaO2/FiO2 stays below 150 despite optimized ventilation.
·Neuromuscular blockade for a short period in severe early ARDS when ventilator synchrony is a problem.
·Extracorporeal membrane oxygenation in selected severe cases at experienced centers.
·Conservative fluid management once the patient is out of shock, with the aim of reducing ventilator days.
·Corticosteroids are suggested by some guidelines for moderate-to-severe ARDS.

Check yourself

1. A 175 cm man (predicted body weight about 70.6 kg) has ARDS. What initial tidal volume is closest to guideline-based lung-protective ventilation?
2. Which plateau pressure is the usual upper limit in ARDS?
3. A patient with moderate ARDS has PaO2/FiO2 of 120 after optimizing ventilation. Which intervention has mortality benefit?