Phase variables with trigger, limit, and cycle criteria can be used to characterize breath types during mechanical ventilation, four different breath types can be generated based on different phase variables; spontaneous, supported, assisted and controlled breaths.
Spontaneous breath is completely regulated by the patient with no contribution of the ventilator. The breath is triggered and cycled by the patient with no set target on the ventilator. The baseline variable can be set with positive pressure (Continuous Positive Airway Pressure: CPAP) (A)
Supported breath is triggered by the patient (pressure or flow trigger), the target (limit) is set as pressure and the cycle variable being a percentage of the peak inspiratory flow (patient-triggered, pressure-limited and flow-cycled breath) (B)
Assisted breath is initiated by the patient, but all other aspects of the breath are controlled by the ventilator. The breath is triggered by the patient (pressure or flow trigger), the target is set as pressure or volume, and the cycle variable is a volume or a set time (patient-triggered, pressure- or volume-targeted and time-cycled breath). (C)
A breath that is time triggered, with a set target being a pressure or volume and the cycle variable is a set volume or time (time-triggered, pressure- or volume-targeted and time-cycled breath) (D)