Based on the ventilator flow sheet in VC-CMV mode, which adjustment is most appropriate?

• A. Increase extrinsic PEEP
• B. Decrease FiO2
• C. Increase tidal volume
• D. Increase respiratory rate

Answer: (A)

In VC-CMV, the tidal volume and rate are fixed, so when the flow sheet shows inadequate oxygenation despite the current settings, the most effective adjustment is to increase extrinsic PEEP. PEEP keeps airways open at the end of expiration, which helps recruit collapsed alveoli and maintains them open between breaths. This increases the surface area for gas exchange, raises the oxygenation at the same FiO2, and often improves overall lung compliance once recruitable units are opened. By raising the end-expiratory lung volume, mean airway pressure goes up, helping oxygen transfer without needing to raise the tidal volume or RR.

Decreasing FiO2 would worsen oxygenation if it’s already insufficient. Increasing tidal volume can improve ventilation but risks pressure-related lung injury in patients with fragile lungs. Increasing respiratory rate tackles ventilation and CO2 removal, not primarily oxygenation, and can cause air-trapping in certain lung conditions.