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.
The absence of Pmus (pressure drop below the baseline or negative pressure deflections in the pressure-time scalar) during an expiratory hold maneuver indicates a lack of spontaneous efforts.
An expiratory hold is used to differentiate between patient-triggered breaths and those initiated by non-patient signals. When an expiratory pause is applied, the patient's inspiratory efforts will cause negative deflections in the pressure-time scalar. The absence of these negative deflections indicates that the breaths are triggered by non-patient signals. In such cases, cardiogenic oscillations may be observed during the expiratory hold maneuver.
False or auto-trigger occurs when flow or pressure oscillations in the circuit, unrelated to the patient's inspiratory efforts, reaches the trigger sensitivity threshold, resulting in the delivery of a breath. These breaths are labeled as patient-triggered because the ventilator cannot distinguish between pressure or flow changes caused by the patient's efforts and those from other sources.
Auto-triggering can be caused by leaks, secretions in the circuit, or cardiac pulsations. Additionally, a highly sensitive trigger setting may contribute to this issue. To prevent auto-triggering, a less sensitive trigger setting can be selected.
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