False Trigger & Early Trigger

The following waveform illustrates three consecutive breaths, each with distinct morphologies. On this ventilator (Maquet, Getinge), patient-triggered breaths are marked in pink at the initial rise in pressure and flow, corresponding to pressure or flow triggering. In this case, flow triggering was used. The breaths appear to be patient-triggered, as suggested by a small negative deflection in airway pressure preceding inspiration and the pink marking on the flow–time scalar.

However, ventilators can not reliably distinguish between true patient efforts and non-patient signals (e.g., cardiac pulsations, leaks, or secretions). As a result, they may incorrectly label false triggers as patient-triggered breaths, potentially leading to misinterpretation of ventilator waveforms. Identifying Pmus (the negative pressure generated by respiratory muscles) is essential in differentiating true patient efforts from false triggers.

First breath: Although labeled as patient-triggered, its passive morphology suggests it is likely a false trigger.

Second breath: Here, Pmus is evident, producing higher tidal volumes and an altered flow–time morphology, confirming a true patient effort.

Third breath: This breath also appears patient-triggered, but closer inspection reveals a notch in the pressure–time scalar with a concomitant rise in inspiratory flow. This indicates that neural inspiration occurred shortly after a false trigger, initially caused by cardiac oscillations.

In this example, the underlying mechanism of false triggering is cardiac oscillations, visible as smooth oscillations in the expiratory flow–time scalar. These oscillations initiated the first and third breaths, with the third breath being followed by a true inspiratory effort.

Key message: Ventilators may incorrectly label false triggers as patient-initiated breaths. Differentiation requires careful recognition of Pmus and identification of the underlying cause of the false trigger—most commonly cardiac oscillations, secretions, or air leaks.