Mandatory Volume Control Breath - GE iVent 201 Series User's Reference Manual

MANDATORY VOLUME CONTROL BREATH

The speed of change for peak flows and inspiratory times is based upon the
difference between the current flow/ time and the required flow/ time. The
greater the difference, the greater the step changes in peak flow or inspiratory
time during the next breath. Most changes are gradual and may take 8 to 10
breaths to make a full change to the new patient condition. The iVent
turbine delivers peak inspiratory flow rates to a maximum of 120 liters per
minute. Factors limiting the delivery of gas flow are patient lung compliance,
airway resistance and ventilator circuit compliance and resistance. Inspiratory
time is limited to 3 seconds or a 1.2 :1 I:E ratio based upon the set rate.
Another feature of Adaptive Flow is its ability to track and match the mandatory
breath inspiratory flow rate to the patient's spontaneous inspiratory flow demand
during SIMV. The ventilator constantly monitors the patient's spontaneous breath
flow rate. If the mandatory breath inspiratory flow is less than the patient's
average spontaneous inspiratory flow demand, the mandatory inspiratory flow is
increased to the same value to minimize the feeling of "air hunger" experienced
by some patients during mandatory breath delivery.
The Adaptive Flow value is shown on the display at all times and is depicted by a
circled A symbol next to the peak inspiratory flow value.
Adaptive Flow can be disabled at any time by manually changing the peak
inspiratory flow control setting. The flow value for the manually set flow rate that
the ventilator uses, is depicted by a circled M symbol next to the peak inspiratory
flow value.
NOTE:

When setting a manual inspiratory flow during low flow conditions, this flow
target may briefly over shoot as the ventilator controls the flow to the
patient. However, the average flow is maintained at the set value.

If the target flow is set higher than the ventilator is able to provide, due to
high resistance and/or low compliance of the patient/ventilator circuit, then
the ventilator attempts to deliver as high a flow as possible during the
inspiratory phase. Under these conditions, inspiratory time increases in order
to deliver the set tidal volume and the set peak flow reading flashes.

During SIMV, Adaptive FlowTM is always operational, even if a manual peak
flow is set. If the patient's average spontaneous flow exceeds the set manual
peak flow, the Adaptive Flow drives the delivered mandatory breath flow to
approximately 80% of the spontaneous inspiratory flow.
Mandatory volume control breath is pressure limited mandatory breath in which
the ventilator delivers a set tidal volume at an Adaptive FlowTM or manually set
value. The flow is controlled by the ventilator in a way that the flow at the end of
the inspiratory phase is half of the peak inspiratory flow. This breath type can be
initiated by the ventilator (time-triggering – a in the figure below), or by the
patient (pressure or flow triggering – b in the figure below). Once initiated, it is
always controlled and terminated by the ventilator. The tidal volume, breath rate,
inspiratory time (adaptive or manual) and pressure limit are set by the operator
using the front panel controls and display.
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