VIII THEORY OF OPERATION- cont’d.
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- SIMV (Synchronized Intermittent Mandatory Ventilation) MODE
SIMV (Synchronized Intermittent Mandatory Ventilation) MODE SIMV (Synchronized Intermittent Mandatory Ventilation) MODE
SIMV (Synchronized Intermittent Mandatory Ventilation) MODE
In the SIMV mode, the CROSSVENT-3+ delivers two main types of breaths: ASSISTED and
SPONTANEOUS. Both are initiated by the patient’s inspiratory effort, which is sensed by the ventilator.
The assisted breaths are the same as assisted breaths in the Assist Control mode. The rate of administration
of assisted breaths is set using the SIMV RATE key and entering the desired value.
In between the assisted breaths, patient inspiratory efforts initiate spontaneous breaths. When the ventilator
detects an effort to breathe, it initiates inspiration and delivers gas to the patient at a rate determined by the
FLOW control and for a period of time equal to the inspiratory time of a normal assisted breath.
The difference between a spontaneous and assisted breath is that during a spontaneous breath, Maximum
Pressure is not applied, only the PEEP pressure signal is applied to the exhalation valve, thus delivering gas
to the patient at zero or PEEP pressure, if PEEP is on.
The full tidal volume is made available at the proximal airway. Whatever gas is not inspired by the patient is
vented to atmosphere. At the end of the inspiratory time, should the patient desire a greater tidal volume
than that which is set, he need only continue to inhale. As long as pressure below baseline (zero or PEEP)
is detected, the ventilator will continue to deliver boluses of gas as determined by the TV setting. The
patient is free to trigger as many spontaneous breaths as needed between assisted breaths. At the end of the
time interval established by the SIMV RATE control, the ventilator administers an assisted breath,
synchronized to the patient’s breathing effort.
Pressure Support: When pressure support is turned on, the patient circuit pressure is allowed to increase
above baseline (zero or PEEP) by the number of cmH
2
O as set by PRESSURE SUPPORT. This occurs only
during spontaneous breaths. When the airway pressure reaches the pressure support level, the baseline
pressure is restored, allowing the exhalation valve to open, but the patient gas continues to flow for the
duration of a normal assisted breath as set by the RATE and TIDAL VOLUME controls.
WARNINGS: It is extremely important that the Pressure Trigger control be carefully
adjusted to assure proper operation in the SIMV mode. Also, under certain
conditions in SIMV with PEEP, even though the low peak pressure alarm is set
correctly for assisted breaths, there may be no low peak pressure alarm following a
patient disconnect until the next assisted breath. This period may be up to 2
minutes. As an added precaution, set the low PEEP/CPAP and low exhaled tidal
volume (if installed) alarms so that they are operative.
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