Chapter 3
Theory of Operation
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BiPAP Vision Service Manual © Respironics, Inc.
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3.7 Ventilator Modes
The BiPAP Vision comes standard with continuous positive airway pressure
(CPAP) and spontaneous/timed (S/T) modes. A third optional mode,
proportional assist ventilation/timed (PAV/T), is also available internationally.
3.7.1
CPAP
CPAP delivers a constant level of positive over the entire patient spontaneous
breath cycle. Pressure is controlled and maintained, and flow varies as needed
to meet patient demand and compensate for leaks. The mode delivers the set
CPAP pressure from 4 to 20 cmH
2
O).
3.7.2
Spontaneous/Timed (S/T)
S/T mode provides pressure support during spontaneous breaths, and time-
triggered, pressure-limited, time-cycled machine breaths.
Spontaneous breaths
:
Spontaneous breaths have two pressure level settings:
•
Expiratory positive airway pressure (
EPAP
) establishes the baseline
pressure (range: 4 to 20 cmH
2
O).
•
Inspiratory positive airway pressure (
IPAP
) determines the level of
pressure support delivered during inspiration (range: 4 to 40 cmH
2
O).
Pressure support = IPAP – EPAP).
During the inspiratory phase, the device responds as necessary to satisfy the
patient’s flow requirements while maintaining the preset IPAP level. Patient
demand determines inspiratory time and tidal volume. The delivered tidal
volume depends on the difference between IPAP and EPAP levels, patient
effort, and the combined resistance and compliance of the circuit and the
patient. If the patient does not actively participate, the device delivers a timed
breath.
Timed breaths
:
S/T mode delivers timed breaths when the spontaneous respiratory rate drops
below the Rate setting.
If the device does not detect a spontaneous trigger within the interval
determined by the Rate setting, it delivers a time-triggered machine breath at
the IPAP level. Machine breaths are not synchronized with patient effort, and
the length of inspiration is determined by the Timed Inspiratory setting (up to a
maximum 3.0 seconds, as long as the I:E ratio does not exceed 1:1, as
determined by the Rate setting).
For example (Figure 3-9), if the Rate setting is 10 breaths per minute (BPM),
the total respiratory cycle is 6 seconds. If a spontaneous trigger occurs before
the inspiratory cycle is complete, the BiPAP Vision delivers a spontaneous
