Volume-Controlled ventilation delivers a breath at a clinician defined flow rate. Spontaneously breathing patients periodically desire additional flow during a breath which by definition, is not possible VC in mode. This results in patient synchrony problems and discomfort.
Demand Flow is an intra-breath synchrony tool that detects when a patient wants additional flow during a breath and instantly transition to pressure support allowing the patient to inhale the desired flowrate and volume.
As illustrated in the image below, the demand flow breath then cycles based on the set exhalation sensitivity like any other pressure support breath.