How do VCV and PCV differ in breath delivery?

• A. VCV delivers a fixed pressure with variable tidal volume; PCV delivers a fixed tidal volume with variable pressure
• B. VCV uses spontaneous breathing; PCV requires full mechanical support
• C. VCV delivers a set tidal volume with airway pressure varying; PCV delivers a set pressure with tidal volume varying
• D. Both modes deliver identical breath mechanics

Answer: (C)

The key distinction is whether the breath is volume-targeted or pressure-targeted. In volume-controlled ventilation, you set a specific tidal volume, and the machine delivers the breath to reach that volume—usually with a relatively constant flow. The pressure required to achieve that volume can vary from breath to breath depending on lung compliance and airway resistance. In pressure-controlled ventilation, you set a specific inspiratory pressure, and the breath will reach that pressure; the resulting tidal volume depends on the current lung mechanics, so it can vary if compliance or resistance changes. So a set tidal volume with airway pressure that varies, versus a set airway pressure with tidal volume that varies, are the defining differences. The idea that one mode uses spontaneous breathing, or that both modes deliver identical breath mechanics, isn’t correct.