In cases where a patient exerts minimal inspiratory effort, the flow-time scalar usually displays an exponential decay, while the pressure remains constant throughout the inspiratory phase in pressure support mode. A similar appearance can also be observed during false triggering when the patient is in a passive state.  In the second breath, the waveform exhibits typical characteristics of pressure support waveforms, indicating the possibility of either a patient-triggered br

A notch on the pressure waveform (1) accompanied by a sudden rise in inspiratory flow (2) signifies a neural diaphragmatic contraction induced by passive mechanical inflation, a phenomenon termed reverse triggering. Since mechanical inflation precedes neural inspiration, it is also referred to as early triggering.

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.

These breaths are initiated by the ventilator (time-triggered). An observable change in the pressure-time curve occurs during late inspiration, where the pressure waveform returns towards the baseline without maintaining a plateau. This suggests that neural inspiration begins after passive mechanical inflation, a phenomenon known as reverse triggering. Neural inspiration extends into the expiratory phase, causing an upward distortion of the expiratory flow-time curve (where i

These are machine-triggered mandatory breaths. During mid-inspiration, a pressure drop appears on the pressure-time scalar along with a corresponding spike on the inspiratory flow-time scalar. This indicates the onset of neural inspiration induced by passive mechanical inflation - a phenomenon known as reverse triggering. The patient's neural effort persists beyond the set inspiratory time, triggering another breath during the expiratory phase and resulting in a double trigge

Early cycling and early trigger can produce similar waveform patterns during the expiratory phase, making them challenging to distinguish. The following example highlights the key differences between the two. In early cycling, the breath is initiated by the patient, but the neural inspiratory effort continues beyond the ventilator’s inspiratory phase, resulting in an upward deflection in the expiratory flow–time scalar. In contrast, during early trigger, the breath is initiat

An upward deflection in the expiratory flow–time scalar, accompanied by deformation of the plateau phase in a machine-triggered breath during volume control ventilation, should raise clinical suspicion for reverse triggering

When two breaths occur in succession without allowing full expiration, it is termed double triggering. In this example, the first breath is machine-triggered, indicated by the absence of a pressure drop prior to inspiration. This is immediately followed by a patient-triggered breath, and the pattern continues consistently. The predictable relationship—where the ventilator-delivered breath initiates a subsequent patient effort—indicates reverse triggering, meaning the machine-

The second and fourth breaths are machine initiated mandatory breaths (No pressure drop before inspiration) The first and third breaths are considered mandatory breaths, but there is noticeable evidence of inspiratory muscle activity (P insp mus) during the second half of the inspiratory phase and early expiratory phase. This occurrence is referred to as reverse triggering, which involves the passive inflation of the lungs leading to neural activation of the diaphragm. This p

In mechanical ventilation, there is typically a delay of a few milliseconds between the onset of a patient's neural inspiration and the ventilator's delivery of flow. When this delay exceeds 100 milliseconds, it is referred to as late triggering. Late triggering increases the patient's work of breathing because the ventilator does not assist during the initial phase of inspiration. Conversely, in early triggering, the ventilator delivers a breath before the patient initiates

The following image illustrates four types of patient-ventilator interactions that can occur while triggering a breath 1) Early trigger: A mechanical breath is initiated before the onset of neural inspiration. Revere trigger is an example of early trigger where passive mechanical inflation triggers diaphragm contraction. 2) Late trigger: Mechanical inflation begins more than 100 milliseconds after the start of the patient's inspiration. 3) Failed Trigger:  Also known as an in

All these breaths appear to be patient-triggered, as indicated by the pressure drop before each inspiration. However, this pressure drop is actually caused by a large leak from the mask, leading to a breath being delivered—this is known as a false trigger or auto-trigger. The expiratory limb of the volume- time scalar fails to reach the baseline before the next breath because of a significant leak. Additionally, the area under the expiratory flow-time scalar is much smaller c

You can observe three pairs of breaths (double trigger) in this image. The first breath in double trigger is triggered by the machine, characterized by a rapid increase in pressure that reaches the pressure alarm limit, causing pressure cycling. The subsequent breath is a patient triggered mandatory breath. The pressure-time scalar deviates below the baseline due to strong inspiratory effort, known as work shifting. As the inspiratory muscles relax, the pressure-time scalar r

These breaths appear to be patient-triggered, as indicated by the purple color on the ascending limb of the inspiratory flow-time scalar (with flow trigger setting). During mid-inspiration, a notch is visible in the pressure-time scalar, suggesting inspiratory muscle contraction leading to a pressure drop. Correspondingly, an increase in inspiratory flow can be observed, indicating the patient's inspiratory effort. This pattern suggests that each breath is patient-triggered,