Lung-protective ventilation in ARDS: plateau pressure and volume
30 kg (ideal weight) Labrador with acute respiratory distress syndrome after aspiration pneumonia, on volume-controlled mechanical ventilation. Settings and arterial blood gas at 2 hours:
| Parameter | Result | Reference |
|---|---|---|
| Tidal volume | 360 mL (12 mL/kg) | — |
| PEEP | 2 cmH₂O | — |
| Plateau pressure | 34 cmH₂O | < 30 |
| FiO₂ | 0.8 | — |
| PaO₂ | 72 mmHg | — |
| PaCO₂ | 48 mmHg | 32–43 |
| pH | 7.31 | 7.35–7.45 |
Which change is most appropriate?
chevron_right Show answer and explanation
A. Increase the tidal volume to normalise PaCO₂ and pH
Plateau pressure already exceeds 30 cmH₂O: increasing volume would worsen alveolar overdistension (volutrauma) in pursuit of a moderate hypercapnia that is tolerable.
B. FiO₂ of 1.0 and PEEP of 0 to reduce the risk of barotrauma
A sustained very high FiO₂ causes oxygen toxicity and absorption atelectasis, and without PEEP the alveoli collapse and reopen with every breath (atelectrauma), worsening oxygenation.
C. Lower the tidal volume to 6–8 mL/kg, raise PEEP and tolerate some hypercapnia
Correct. The protective strategy aims for a plateau pressure below 30 cmH₂O with low tidal volumes, and PEEP that recruits alveoli and allows FiO₂ to be lowered. Permissive hypercapnia is accepted if pH does not fall excessively and there is no intracranial hypertension; the rate can be increased to compensate.
D. Raise PEEP to 15 cmH₂O while keeping the current tidal volume
Raising PEEP without reducing volume increases the already excessive plateau pressure further, and raises the risk of volutrauma, pneumothorax and hypotension.
lightbulb Key takeaway
In ARDS the functional lung is small (the 'baby lung'): calculate tidal volume on ideal weight, monitor plateau and driving pressures, and prioritise reducing FiO₂ below 0.6 as soon as possible. Moderate hypercapnia is preferable to ventilator-induced lung injury.
Test yourself with 10 random questions
VET PRO · 100 questions, a different test every time
Related questions
Updated: November 1, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.