Dräger Evita 4 - Simv

Description
Ventilation Modes
164
SIMV
Synchronised Intermittent Mandatory Ventilation
Combination of machine ventilation and spontaneous
breathing.
SIMV enables the patient to breathe spontaneously in
regular prescribed cycles, with the mechanical mandatory
ventilation strokes providing a minimum ventilation during
the remaining cycles.
The minimum ventilation is controlled by the two set
values tidal volume (VT) and ventilation frequency (f) and
is determined from the product of VT x f.
The ventilation pattern results from the set values VT,
Insp. Flow, frequency f and inspiration time Tinsp.
To prevent the mandatory ventilation stroke being applied
during spontaneous expiration, the Flowtrigger of the
machine ensures that the ventilation stroke is triggered in
synchrony with the patient's spontaneous inspiratory
effort within a "trigger window".
The "trigger window" is 5 seconds long in adult mode
and 1.5 seconds long in paediatric mode. If the expiration
times are less than 5 seconds or 1.5 seconds, the
"trigger window" covers the entire expiration time.
Since the synchronisation of the mandatory ventilation
stroke reduces the effective SIMV time, which would
result in an undesirable increase in effective IMV
frequency, Evita 4 prolongs the subsequent breathing
time by the missing time difference ∆T – thus preventing
an increase in SIMV frequency. The frequency para-
meter f remains constant. This parameter, in combination
with the tidal volume VT, sets the minimum ventilation.
If the inspiratory volume of the patient is considerable at
the beginning of the "trigger window", the machine
reduces the subsequent mandatory ventilation stroke by
shortening the time for the inspiratory flow phase and the
inspiration time. In this way, the tidal volume VT remains
constant, and overinflation of the lungs is avoided.
During the spontaneous breathing phases, the patient
can be assisted with pressure by ASB pressure support.
In the further weaning process, the frequency f on the
ventilation unit is further reduced, thereby prolonging the
spontaneous breathing time, until finally the required
minute volume is entirely covered by spontaneous
breathing.
Paw
PEEP
t
spontaneous
breathing time
spontaneous
breathing time + T
set IMV time set IMV time
trigger
window
spontaneous
breathing
mandatory
ventilation
synchronised
mandatory stroke
Tinsp
f
1
f
1