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6 Specifications and Theory of Operation
At the specified time interval, the ventilator will wait for the next inspiratory
effort from the patient. The sensitivity of this effort is adjusted using the flow
trigger level. When the ventilator senses the beginning of inspiration it
synchronously delivers a volume breath using the set tidal volume, and
inspiratory time that is set on the ventilator. If the patient fails to make an
inspiratory effort during the trigger window time interval, the ventilator will
deliver a machine breath to the patient. The ventilator will always deliver the
specific number of breaths per minute that the clinician has set.
In SIMV, the spontaneous breaths can be pressure supported to assist the
patient in overcoming the resistance of the patient circuit and the artificial
airway. When the Psupport level is set, the ventilator will deliver the pressure
support level to the patient during inspiration. PEEP can also be used in
combination with this mode.
SIMV mode settings
• VT
• Rate
• Tinspired • Psupport • PEEP
PSVPro mode
P
aw
PEEP
T
I
Time
Figure 6-8 • PSVPro diagram
PSVPro is pressure supported ventilation with apnea backup.
PSVPro is a spontaneous mode of ventilation that provides a constant
pressure once the ventilator senses that the patient has made an inspiratory
effort. The ventilator identifies an inspiratory effort using a flow trigger that is
user adjustable. In this mode, the user sets the Pressure Support (Psupport)
and PEEP levels. The patient establishes the frequency, inspiratory flow and
inspiratory time. The tidal volume is determined by the pressure, lung
characteristics and patient effort.
PSVPro uses an inspiration termination level that establishes when the
ventilator will stop the pressure supported breath and cycle to the expiratory
phase. The inspiration termination level is user adjustable from 5% - 50%.
This parameter sets the percent of the peak inspiratory flow that the ventilator
uses to end the inspiratory phase of the breath and to cycle into the expiratory
phase. If the inspiration termination is set to 30% then the ventilator will stop
inspiration when the flow decelerates to a level equal to 30% of the measured
peak inspiratory flow. The lower the setting the longer the inspiratory time and
conversely, the higher the setting the shorter the inspiratory phase.
6-21
1009-0633-000
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