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# Flow-Triggered Ventilation This document describes a flow-triggered ventilation strategy used in mechanical ventilators. ## Figure 3-9: Pressure-Trigger Mechanism **A)** Before inspiratory effort, pressure in the airway and ventilator tubing is 0 cm H₂O. A mechanical breath is not initiated be...

# Flow-Triggered Ventilation This document describes a flow-triggered ventilation strategy used in mechanical ventilators. ## Figure 3-9: Pressure-Trigger Mechanism **A)** Before inspiratory effort, pressure in the airway and ventilator tubing is 0 cm H₂O. A mechanical breath is not initiated because there is no pressure drop to trigger the ventilator sensitivity. **B)** At beginning inspiration, the pressure in the airway and ventilator tubing is -3 cm H₂O. A mechanical breath is initiated because the pressure drop is sufficient to trigger the ventilator's sensitivity setting. ## Flow-Triggered Ventilation Strategy Some ventilators can measure inspiratory and expiratory flows. When the patient's inspiratory flow reaches a specific value, the ventilator delivers a breath. Flow triggering is more responsive to patient effort than pressure triggering. The strategy combines continuous and demand flow. * It reduces the patient's inspiratory effort. * It usually requires less inspiratory work than pressure triggering. In flow triggering, continuous flow passes through the ventilator circuit and returns to the ventilator. As the patient initiates a breath, a portion of the flow goes to the patient and the return flow to the ventilator reduces ( *delivered flow > returned flow*). The ventilator detects this flow differential and instantaneously supplies enough flow to meet the patient's mechanical or spontaneous tidal volume. This feature applies to CMV, SIMV, and PSV modes (Refer to Figure 3-10 for illustrations). ## Ventilator Sensitivity The effort required by the patient to initiate a breath is the ventilator sensitivity. A more sensitive ventilator (higher sensitivity, in terms of pressure, flow, or volume) will be easier for the patient to trigger. The opposite is also true. ## Limit Variable During flow-triggered ventilation, volume, pressure, and inspiratory flow all increase above their baseline values. The inspiratory time is the time interval during which these values rise.