Dräger Babylog 8000 plus Operating Instructions Manual page 134

Theory of Operation
Ventilation Modes
Synchronized Intermittent Mandatory
Ventilation
(SIMV)
SIMV combines synchronized ventilation with spontane-
ous breathing. Different from A/C, not each and every
spontaneous inspiration is supported, but only as many
as needed to ventilate a patient with the set ventilator
rate. The patient is allowed to breathe between manda-
tory breaths, however without receiving support.
During a time interval of length T +T the first spon-
in ex
taneous inspiration will trigger a mandatory breath of
length T . Any further spontaneous breathing until the
in
end of the time interval is ignored. Ventilator breaths will
thus exhibit the irregularity of spontaneous breathing,
however, with a time average that corresponds to the
set ventilation rate.
The same rules as in A/C mode apply for triggering.
The shape of the mandatory breaths is set in the same
fashion as in CMV.
During SIMV, the ventilator rate may be set as during
CMV. Triggered, mandatory breaths will alternate with
spontaneous breathing without support, during which the
patient will have to perform the total work of breathing.
Therefore, by extending T a successively increasing
ex
portion of the total work of breathing can be shifted from
the ventilator to the patient.
If the patient fails to trigger breaths, ventilation will be
peformed as in CMV.
SIMV is suitable for patients with sufficient spontaneous
breathing. Weaning is performed by slowly extending T
ex
and decreasing inspiratory pressure.
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