Which statement about pressure-cycled ventilators is true?

• A. They deliver a fixed tidal volume during inspiration.
• B. They require a time-based inspiratory duration.
• C. They use active expiratory flow to help ventilate.
• D. They deliver a predetermined maximum pressure during respiration, and the inspiratory phase ends when that pressure is reached.

Answer: (D)

In pressure-cycled ventilation, inspiration ends when a preset maximum airway pressure is reached. The ventilator delivers flow to raise airway pressure to that limit, and once reached, the inspiratory phase ends. Because the pressure target is fixed, the amount of air delivered (tidal volume) varies with the patient’s lung compliance and airway resistance. This is why the same pressure limit can produce different volumes on different breaths or in different patients.

This differs from a mode that delivers a fixed tidal volume, which ends after a set volume is delivered regardless of pressure. It also differs from time-cycled modes, where inspiration ends after a predetermined time interval. Expiration in pressure-limited modes is typically passive, relying on the chest wall and elastic recoil, rather than requiring active expiratory flow.