Understanding the Link Between Air Leaks and Delayed Cycling

In pressure support mode, cycling to expiration occurs when the inspiratory flow decreases to a preset percentage of the peak inspiratory flow. However, in the presence of an air leak, the flow may fail to drop to the preset threshold, as the ventilator continues to deliver additional flow to maintain the target pressure and compensate for the leak. This results in a prolonged inspiratory phase and delayed cycling.

In this example, the pressure–time scalar shows a notch during inspiration caused by the leak. The ventilator responds by delivering additional flow to stabilize airway pressure, producing a boot-shaped waveform in the latter part of inspiration. The failure of flow to decay normally further contributes to inspiratory prolongation.

To prevent excessively long inspiratory times, the ventilator’s backup time-cycling mechanism is automatically activated, ensuring timely transition to expiration.