On most modern mechanical ventilators, the gas delivery algorithm is generally one of two types: flow/volume targeting (volume assist-control ventilation [VACV]) or pressure targeting with time or flow cycling (pressure assist-control ventilation [PACV] or pressure support ventilation). With flow/volume targeting, the clinician sets an inspiratory flow along with a volume cycling criteria. Airway pressure is, thus, the dependent variable (ie, varying according to lung mechanics and effort). With pressure targeting, the clinician sets an inspiratory pressure target along with either time or flow cycling criteria. Flow and volume are now the dependent variables (ie, varying with lung mechanics and effort). Changes in compliance, resistance, or patient effort will change airway pressure (but not flow) with flow/volume targeting. In contrast, similar changes in compliance, resistance, or effort will cause a change of flow and tidal volume (Vt) (but not airway pressure) with pressure targeting.