ResMed Elisee 350 Clinical Manual page 29

Synchronized Intermittent Mandatory Ventilation (SIMV and
PSIMV)
These ventilation modes allow you to alternate between:
•
Assisted ventilation cycles that are either flow-controlled (SIMV) or pressure-controlled
(PSIMV)
•
Cycles that allow the patient to produce spontaneous breaths with pressure support (PS).
They are generally used to wean patients off ventilation and help them regain respiratory
independence.
Principle
A respiratory rate F is set on the device. This allows you to define a mechanical period, Tmech,
in seconds, whereby:
60
= ----- -
Tmech serves as a basis for triggering controlled cycles (CC). One minute of ventilation is
segmented into set mechanical periods, and the respiratory rate remains unchanged.
To synchronise the ventilator with the patient, a trigger window called Wsync (
controlled cycles (ACC), is defined before the start of a controlled ventilation cycle. This window is
5 s long for adults and 1.5 s long for paediatric patients.
After each Wsync window (whether assisted or controlled), there is a Wvs window (
during which the patient can trigger a spontaneous breath with adjustable pressure support (see
page 52 for instructions on setting the parameters). The patient is consequently relieved of part
of the respiratory effort required to overcome the resistance of his/her respiratory system as well
as the combined resistance of the ventilator, circuit, filter and water traps.
Note: Make sure the respiratory rate is set below 10 bpm and an appropriate I:E ratio is set, so
that the patient can make the most of this window for triggering a spontaneous breath with
pressure support. For example:
•
If F = 10 bpm, the respiratory cycle lasts 6 seconds (60/10). If Ti = 1.2 s, then Te = 4.8 s.
Te < the 5 s minimum limit of the Wsync window. Therefore, Wsync extends throughout
the entire expiratory phase and does not allow the patient to trigger any spontaneous
breaths with pressure support between the controlled cycles.
•
If F = 8 bpm, the cycle is 7 .5 s. If Ti = 1.2 s, then Te = 6.3 s, which leaves 6.3–5, or 1.3 s for
the Wvs window.
How SIMV mode works:
Scenario 1: Patient effort in the
Wsync window triggers an assisted
controlled cycle (ACC)
P
CC
Wvs: Trigger window for spontaneous pressure support cycles
Wsync: Trigger window for assisted controlled cycles (5 s or 1.5 s)
Tmech: Set mechanical period defined by the respiratory rate (F)
Δ
: Duration of the inspiratory phase
Te: Expiratory time
NOT013281-8
Scenario 2: An absence of patient effort in the Wsync window
triggers a cycle controlled by the ventilator (CC)
(Controlled cycle if
there was no patient
ACC CC
effort)
ΔT Te ΔT
Scenario 3: Patient effort in the Wvs window triggers
a spontaneous cycle with pressure support
CC
), for assisted
)
CC
t (s)
t (s)
Ventilation 23/102