Stephan EVETR, Instructions For Use Manual, Page: 152 / 254

7 Ventilation modes
152 GA-070T-0518V2.7-HAO-EN

Fritz Stephan GmbH
Pressure-controlled synchronized intermittent mandatory 7.3.2.3
ventilation (PC-SIMV)
Controlled ventilation may result in asynchrony between the spontaneous
breathing efforts of the patient and the fixed ventilation cycles of the
ventilator. In this case, the mandatory breaths randomly coincide with
different phases of spontaneous breathing. Due to the possible resulting
adverse effects, syncing between a spontaneously breathing patient and
the ventilator is especially important.
The
EVE
TR
uses the flow sensor's patient gas flow signal as a
synchronization trigger. The flow sensor enables the EVE
TR
to measure
the patient’s inspiratory flow. If the inspiratory flow exceeds the value set
by the user, a mandatory breath is triggered. This "trigger threshold" is
set in the »Trigger« field as flow in l/min. The trigger threshold appears
as a light blue line in the respiratory gas flow signal window. The higher
the setting for this trigger threshold above the respiratory gas flow signal
in the expiratory pause, the more the patient has to breathe in to activate
the trigger. In turn, too little distance to the respiratory gas flow signal
can cause unintended triggering due to artifacts or leakage flows.
For PC-SIMV, the
EVE
TR
delivers a mandatory breath once an
inspiratory flow reaches the preset trigger threshold. The trigger is only
active within a so-called trigger expectation window. The length of this
expectation window and the time gap between the windows vary
depending on the set expiration time.
The expiration time is divided into two phases.
In the first phase (Texp
spon
= 50% of Texp), the patient can only breathe
spontaneously. Even when the trigger threshold is crossed, there is no
mandatory support from the ventilator. If the patient breathes
spontaneously during the second phase of the expiration time, the
EVE
TR
now delivers a mandatory breath.
Selecting the inspiration and expiration time or frequency lets the user
specify a mandatory base frequency that does not change. It applies even
if the patient exhibits active spontaneous breathing that could
theoretically trigger a lot more mandatory breaths. As a result, the time
by which the expiration time was reduced is added to the next following
expiration times after each trigger event. This means that the average
matches the mandatory base frequency set by the user.