Specifications

8
Maximum IPAP Time (IPAP to EPAP)
A maximum IPAP time of 3.0 seconds acts as a safety mechanism to limit the time spent at the IPAP level
during spontaneous breathing in the S and S/T modes. Once the time limit is reached, the unit
automatically cycles off IPAP to the EPAP level.
Flow Reversal
As flow begins to decrease during IPAP, a flow reversal can occur due to a large leak around the mask or
because the patient's mouth is open. When the BIPAP S/T unit senses this flow reversal, the unit
automatically cycles to the EPAP level.
Summary
The sensitivity criteria for spontaneous breathing in the S and S/T modes can be summarized as follows:
Spontaneous Trigger to IPAP
A transition from EPAP to IPAP will occur when one of the following conditions is met:
• patient flow exceeds the shape signal
• 6 cc inspired volume accumulates above baseline flow (V
leak
)
Cycle to EPAP
The transition from IPAP to EPAP will occur when one of the following conditions is met:
• patient flow is less than the shape signal
• Spontaneous Expiratory Threshold (SET) is achieved
• a 3.0 second maximum IPAP time has occurred (safety feature)
• flow reversal occurs during IPAP (safety feature)
•
Principles of Operation
Shape
Signal
IPAP
EPAP
Crossover
Point
Cycle to
EPAP
Crossover
Point
Trigger to
IPAP
Estimated
Patient
Flow
PRESSURE
FLOW
Figure 5: Shape Signal
Tracking the patient's flow pattern with the shape signal provides a sensitive mechanism to trigger to
IPAP or cycle to EPAP in response to changing breathing patterns and circuit leaks.
Spontaneous Expiratory Threshold (IPAP to EPAP)
A second method used to cycle off IPAP during spontaneous breathing in the S and S/T modes is called
Spontaneous Expiratory Threshold (SET). The SET is an electronic signal that rises in proportion to the
inspiratory flow rate on each breath. When the Spontaneous Expiratory Threshold (SET) and actual
patient flow value are equal, the unit cycles to EPAP.
Spontaneous
Expiratory
Threshold
PRESSURE
FLOW
EPAP
IPAP
Figure 6: Spontaneous Expiratory Threshold