Dräger Evita 2 Dura - Simv

Description
118
Ventilation Modes
SIMV
Synchronised Intermittent Mandatory Ventilation
Combination of machine ventilation and spontaneous
breathing.
SIMV enables the patient to breathe spontaneously in regular
prescribed intervals between mandatory mechanical
ventilation strokes that ensure a minimum ventilation.
This minimum ventilation is defined by two set values,
tidal volume (V
T) and ventilation frequency (f). The minimum
ventilation is the product of V
T x f.
The ventilation pattern is programmed by the following set
values: tidal volume V
T, Insp. Flow, frequency f and inspiration
time T
insp. To prevent the mandatory ventilation stroke being
applied during spontaneous expiration, the Flowtrigger of the
machine ensures that the ventilation stroke is triggered within
a "trigger window" and synchronised with the patient's
spontaneous inspiration.
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 respectively, the
trigger window covers the entire expiration time.
Since the synchronisation of the mandatory ventilation stroke
reduces the effective SIMV time and therefore would normally
result in an undesirable increase in the effective SIMV
frequency, Evita 2 dura adds back the reduced SIMV time by
prolonging the subsequent spontaneous breathing phase by
the SIMV time difference Δ T – thus preventing an increase in
SIMV frequency. The frequency parameter f remains constant.
This parameter, in combination with the tidal volume V
T, sets
the minimum ventilation. If the patient has breathed in a
considerable inspiratory volume 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 V
T
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.
During the weaning process, the frequency f/breath rate on
the ventilator is gradually reduced, the clinician thereby
reduces the mandatory minute volume. The increase in
expiratory time allows for a longer spontaneous breathing
window, eventually the required minute volume level should be
met by the patients’ spontaneous breath rate.
009
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