Patient-ventilator asynchrony

Double and Reverse Triggering

Reverse Triggering

Reverse triggering is a type of dyssynchrony that occurs when a patient's effort occurs after (i.e. is triggered by) the initiation of a ventilatory breath.

Diagnosis of Reverse Triggering

The recognition begins with the fact that the ventilator breath was not triggered by the patient. Typically this is easiest on a PCV mode, as the flow will change when the effort occurs early enough in the inspiratory phase,

  1. Detecting effort during ventilator insufflation - late insufflation phase increase in flow?
  2. Detecting effort during ventilator exhalation - positive deflection in flow which leads to alteration of the peak expiratory flow at the onset of exhalation

Image Volume, flow, and pressure waveforms, respectively, illustrating two simulations of asynchrony. The first three waveforms (panel A) represent a case in which the first breath is always triggered by the patient during volume-controlled ventilation. The dots indicate stacked tidal volume caused by double triggering. The bottom three waveforms (panel B) represent a case of reverse triggering due to respiratory muscle effort triggered by reflex mechanisms resulting from a ventilator-delivered breath, during pressure-controlled ventilation. Note, in both cases, stacked tidal volume and increased airway pressure during asynchrony. The dots indicate reverse triggering.

When Does Reverse Triggering Occur?

Occurs in heavily sedated patients +/- lung injury. More common in those transitioning from sedated to awakened states. Can also occur in patients with brain death...

Correction of Reverse Triggering

Because it normally occurs in patients heavily sedated, the decision must be made whether sedation is still necessary (plan to liberate the patient from the ventilation), or whether the patient is still in the acute phase combined with the breath profile (ex. presence of breath-stacking).  It should be noted that increasing sedation will often not resolve reverse triggering, and paralysis may be necessary if lung injury is of concern.

References

  1. Pham T, Telias I, Piraino T, Yoshida T, Brochard LJ. Asynchrony Consequences and Management. Critical Care Clinics. 2018;34(3):325-341. doi:10.1016/j.ccc.2018.03.008
  2. Double triggering and reverse triggering - UpToDate