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Auto-Trak Sensitivity
An essential feature of the device while operating in all modes is its ability to effectively sense spontaneous breathing efforts, 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 efforts 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 effort 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 figure illustrates how the shape signal is
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Chapter 3 Modes, Features, and Alarms
