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Chapter 3 Modes, Features, and Alarms
37
Auto-Trak Sensitivity
An essential feature of the device while operating in all modes is
its ability to eectively sense spontaneous breathing eorts, which
causes the ventilator to trigger to inspiration and cycle to expiration.
Because no preset sensitivity threshold can assure patient and
machine synchrony with changing breathing eorts and circuit
leaks, the device continuously tracks patient breathing patterns
and automatically adjusts sensitivity thresholds to ensure optimum
sensitivity as breathing patterns change or as circuit leaks change.
The algorithms used to ensure optimum sensitivity are the Volume
Trigger, Shape Signal, Spontaneous Expiratory Threshold (SET), Flow
Reversal, Maximum IPAP Time, and Volume Control Cycle.
Volume Trigger (Expiration to Inspiration):
The volume trigger is one method used to trigger inspiration during
spontaneous breathing in all modes except T and CV. The volume
trigger threshold is 6 ml of accumulated patient inspiratory volume.
When patient eort generates inspiratory flow causing 6 ml of
volume, inspiration is triggered.
Shape Trigger/Shape Cycle (Expiration to Inspiration) (Inspiration to
Expiration):
The shape trigger/cycle is another method used to trigger inspiration
and/or cycle from inspiration to expiration during spontaneous
breathing in all modes except T and CV. This method continuously
tracks patient inspiratory and expiratory flow and adjusts the
spontaneous trigger and cycle thresholds for optimum sensitivity.
The Shape Signal appears as a shadow image of the patient’s actual
flow. The shape signal functions as a sensitivity threshold at either
inspiration or expiration. When the patient’s flow rate crosses the
shape signal the unit changes pressure levels. The following gure
illustrates how the shape signal is super-imposed onto the actual
waveform to trigger and cycle o IPAP. The shape signal is created
by osetting the signal from the actual patient flow by 15 l/min and
delaying it for a 300 msec period. This intentional delay causes the
shape signal to be slightly behind the patient’s flow rate.
Note: Auto-Trak is only
available if you are using a
passive circuit.