How do VCV and PCV differ in breath delivery?

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.

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.