How does flow behave in pressure-controlled ventilation?

In pressure-controlled ventilation, the key principle is that the ventilator delivers a set pressure during each breath, which directly influences how flow behaves. When a pressure is set, the ventilator tries to achieve that pressure as rapidly as possible, resulting in a high initial flow at the beginning of the breath.

However, as the lung volume increases and the compliance and resistance factors come into play, the flow of gas does not remain constant. Instead, the flow decreases over the course of the breath; this is referred to as decelerating flow. This means that the initial high flow rate slows down as pressure is maintained at the set level.

In contrast, in volume-controlled ventilation, the flow can often be constant throughout the inspiratory phase. The deceleration of flow in pressure-controlled ventilation allows for more gentle pressure delivery into the lungs, which can help to prevent barotrauma and is often better tolerated by patients with certain lung pathologies. This behavior is essential in optimizing oxygen delivery and reducing the work of breathing for the patient.