How is controlled ventilation characterized?

Controlled ventilation is characterized by the ventilator taking full responsibility for the patient's breathing, which includes determining both the frequency and tidal volume of each breath delivered. This mode of ventilation is typically used for patients who are unable to initiate their own breaths or when it is essential to ensure a consistent and adequate level of ventilation, such as in cases of severe respiratory failure or during sedation.

In this mode, the ventilator operates independently of any patient effort. This means that regardless of the patient's ability to breathe spontaneously or any effort they may make, the ventilator will deliver a set number of breaths with a predetermined volume. This emphasis on the ventilator’s control over the details of breathing is what fundamentally defines controlled ventilation, making it a crucial aspect of ventilatory management in critical care scenarios.

The other options describe aspects of other ventilation strategies, where either patient control or spontaneous breathing plays a significant role, but these do not align with the characteristics of controlled ventilation.