When the Ventilator Responds to Strong Patient Efforts

A major limitation of volume control ventilation is that it delivers a fixed inspiratory flow, regardless of the patient’s effort. This can increase the patient’s work of breathing, a phenomenon known as work shifting.

To improve patient comfort, some ventilator manufacturers have introduced a feature called flow adaptation, which allows the ventilator to sense strong inspiratory efforts and provide additional flow as needed. This feature can significantly modify the waveform morphology.

In the waveforms shown, there is severe work shifting during volume control ventilation. The pressure–time scalar demonstrates a marked pressure drop during the trigger phase and a downward deformation of the inspiratory pressure, reflecting substantial patient effort. The flow–time scalar displays a rounded inspiratory contour, indicating that the ventilator has switched to a pressure support–like pattern in response to the strong inspiratory demand.

Without the flow adaptation feature, a more pronounced negative pressure deflection and a constant flow pattern would be expected in volume control mode. Because flow adaptation alters the appearance of ventilator waveforms, operators should be aware of this feature to ensure accurate waveform interpretation.