Ineffective Efforts
Ineffective efforts by the simplest definition are efforts made by the patient that do not result in the machine delivering a breath. Visually, there is an upward deflection in the expiratory flow waveform, with downward deflection in pressure waveform. While severe flow limitation can result in dynamic hyperinflation and can result in difficult or the inability to triggering, it commonly occurs due to delayed cycling in pressure support when the ventilator breath lasts longer than the patient effort preceding the ineffective effort. This can happen due to excess volume delivered, or because the cycle criteria is no longer based on a controlled volume or iTime, rather the cycling is based the cycle % criteria (by default ~25% on most ventilators), which can take longer in patients with high resistance and/or compliance.
You can view our post on Ineffective Efforts here.
Reverse Triggering
Reverse triggering shares similarities with Ineffective efforts, but are not technically the same. They both can result in an effort by the patient that does not result in machine delivered (mandatory) breath. Visually, they also can have an upward deflection in the expiratory flow waveform, with downward deflection in pressure waveform. However, reverse triggering CAN result in a triggered breath causing breath-stacking, so it’s not always an ‘ineffective’ patient effort. By definition reverse triggering is a patient effort elicited by a machine delivered breath, so to be classified as such they must have a non-patient triggered breath to elicit the response. This means the patient is being managed in an assist-control mode of ventilation (it can occur in pressure support ventilation is the ventilator delivers an auto-cycled breath that was not initiated by the patient). Ineffective efforts do not require non-triggered breath to be classified as an ineffective effort, therefore can happen in any conventional mode of ventilation.
Finally, most definitions of reverse triggering used for detection algorithms use a strict criteria by which the patient effort must occur. An example of this criteria would be A) a machine delivered breath (not triggered by the patient) occurs first; B) a patient effort occurs within so many seconds from the start of the machine delivered breath (example: the patient effort starts at least 0.1 seconds but no later than 1.5 seconds after a machine breath is delivered). If an effort occurred more than 1.5 seconds after the machine breath started, it would be classified as an ineffective effort, as it is less likely to be a ‘reflex’ response to the machine delivered breath.
You can read more about Reverse Triggering here and here.
Summary Table
| Asynchrony | Simple Definition | Preceding Breath |
|---|---|---|
| Ineffective Efforts | Effort made by the patient that does not result in the machine delivering a breath. | Patient triggered or non-triggered breath. |
| Reverse Triggering | Effort that occurs within 1.5 seconds and at least 0.1 seconds AFTER a machine delivered (mandatory) breath* which may or may not result in a triggered (breath-stacked) breath | Non-triggered (mandatory or auto-cycled) breath only |
*Timing threshold used in a recent publication for automatic detection of reverse triggering. Pham T, Montanya J, Telias I, Piraino T, et al. Automated detection and quantification of reverse triggering effort under mechanical ventilation. Crit Care. 2021;25(1):60.
Thank you for the post. At my centre we do not have esophageal manometry.
Is it possible to differentiate ineffective efforts from reverse triggering by looking at the initial part of the expiratory flow waveform (i.e. the period from end-inspiration to start of negative deflection/”effort”). Specifically it seems that with ineffective efforts this initial part still shows exponential decay. Reverse triggering, on the other hand, typically show a more abnormal pattern/curve. I realize this would not be 100% specific but how else can these be differentiated without esophageal manometry (changing respiratory rate seems to be inconsistently helpful).
Reverse triggering can cause amputation of PEFR or reduced peak expiratory flow that is not seen with ineffective effort