False trigger/ Auto triggering due to cardiac pulsations
A patient with neuromuscular disease, Day 5 on the ventilator, appeared quite comfortable when the ventilator mode changed to pressure support from volume assist control. False triggering (auto triggering) was suspected as he did not appear trying to trigger the ventilator (spontaneous respiratory efforts were absent). The set RR (RR back up) and observed RR were 16 and 24, respectively. The flow trigger sensitivity setting was 1.0. The trigger sensitivity setting was changed (selected a less sensitive trigger setting) to avoid auto triggering. Auto triggering persisted with a flow trigger setting of 3.0 but it disappeared when the flow trigger setting was changed to 10. The underlying cardiogenic oscillations appeared on the flow-time scalar with the disappearance of auto triggering.
The initial flow trigger setting was 1.0
Flow trigger setting 10.0 was selected as auto triggering persisted with a trigger setting of 3.0
Auto triggering disappeared and all breaths are mandatory breaths. The observed RR is equal to the backup RR. Cardiogenic oscillations can be seen on the flow-time scalar.
Pmus was absent during an expiratory hold maneuver indicating the absence of spontaneous efforts.
False trigger/ Auto triggering occurs due to flow or pressure oscillations in the circuit not caused by patient inspiratory efforts. The ventilator identifies these oscillations as the patient's inspiratory efforts and delivers breath.
These breaths are labeled as patient-triggered breaths since the ventilator can not differentiate the pressure/flow changes caused by patient inspiratory efforts from other causes.
Leaks, secretions in the circuit, and cardiac pulsations can cause auto triggering. A highly sensitive trigger setting can also lead to auto triggering.
It can be avoided by selecting a less sensitive trigger setting.