Effect of Cardiogenic Oscillations on Trigger Delay During Pressure Support Ventilation

Sensitive flow or pressure triggers are usually applied to improve ventilator response time. Conversely, too sensitive triggers can incur risk of auto-triggering, a type of asynchrony in which a breath is triggered without inspiratory muscle activity. A frequent cause of auto-triggering is cardiogenic oscillations, characterized by cyclical variations in pressure and flow waveforms caused by cardiac contractions. Our goal was to test trigger performance and capacity to abolish auto-triggering in 5 different ICU ventilators using different simulated levels of cardiogenic oscillations.

A mechanical breathing simulator was used to test 5 different ICU ventilators' trigger response time and capacity to minimize auto-triggering in conditions with 0, 0.25, 0.5, and 1 cm H₂O cardiogenic oscillation. Each ventilator was evaluated until an ideal trigger was found (the most sensitive that abolished auto-triggering). When the least sensitive flow trigger was unable to avoid auto-triggering, a pressure trigger was used. We compared time delay, airway pressure drop until triggering, and work of breathing before each trigger, all at the ideal trigger level for each cardiogenic oscillation amplitude. We also assessed the proportion of auto-triggered breaths in the whole range of trigger levels tested.

Larger cardiogenic oscillations were associated with more frequent auto-triggering. To avoid auto-triggering, less sensitive triggers were required (+2.51 L/min per 1 cm H₂O increase in cardiogenic oscillation; 95% CI 2.26-2.76, P < .001). Time delay increased with larger cardiogenic oscillations, because less sensitive trigger levels were required to abolish auto-triggering (4.79-ms increase per 1 L/min increment on flow trigger).

More sensitive triggers led to faster ventilator response, but also to more frequent auto-triggering. To avoid auto-triggering, less sensitive triggers were required, with consequent slower trigger response. To compare trigger performance in a scenario that more closely represents clinical practice, evaluation of the tradeoff between time delay and frequency of auto-triggering should be considered.