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Chapter 7
Operating Theory
REF 1057983 A Respironics V200 Ventilator Operator’s Manual 7-3
Ventilation Modes
Common to VCV and
PCV
In Volume Control Ventilation and Pressure Control Ventilation, the operator
can select between ventilation modes of Assist/Control, SIMV, and CPAP.
Assist Control Ventilation (A/C)
With the Assist/Control mode (refer to Figure 7-1 or Figure 7-2), a minimal rate
and tidal volume (or inspiratory pressure) are set by the operator. The patient
can trigger the ventilator at a more rapid rate, but the operator set tidal volume
(or inspiratory pressure) is delivered during each breath. The ventilator delivers
only mandatory breaths. Assisted breaths may be either pressure or flow
triggered. If the trigger setting is adjusted so that the patient cannot trigger the
ventilator, all breaths will be delivered by the ventilator at the operator set rate
and tidal volume (or pressure).
Synchronized Intermittent Mandatory Ventilation (SIMV)
SIMV is a ventilation mode where the patient is allowed to breathe
spontaneously and the machine attempts to deliver volume (VCV) or pressure
(PCV) mandatory breaths in synchrony with the patient’s effort at the operator
set rate and volume (or pressure). This is accomplished by a combination of
spontaneous and mandatory windows that open and close. The type of breath
delivered depends upon whether the event during the window is patient
initiated, operator initiated or time initiated. This logic is illustrated in Table 7-
1: “SIMV Logic”.
SIMV Logic
Current
SIMV State Inputs Ventilator Response
Next
SIMV State
Mand
Window
Time Trigger
(breath period
timer expires)
Deliver mandatory breath using operator
settings for mandatory breath type; Restart
breath period
Mand
Window
Mand
Window
Patient Trigger;
Operator Trigger
Deliver mandatory breath using operator
settings for mandatory breath type
Spont
Window
Spont
Window
Patient Trigger Deliver a spontaneous breath using
operator settings for spontaneous breath
type
Spont
Window
Spont
Window
Operator Trigger Deliver a mandatory breath using operator
settings for mandatory breath type
Spont
Window
Spont
Window
Time Trigger
(breath period
elapses)
Restart breath period timer Mand
Window
Table 7-1: SIMV Logic