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| Image 1: The Settings of VC-CMV. The settings highlighted in yellow are associated with patient-ventilator asynchrony. |
VC-CMV is likely the most utilized mode of mechanical ventilation. This is due to a few a reasons:
1. VC-CMV is a standard mode on almost every intensive care ventilator (table 1).
2. VC-CMV is one of the first modes of mechanical ventilation.
3. VC-CMV is easy to understand in both theory and operation.
Table 1: MANUFACTURER
NAMES for VC-CMV
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Manufacture
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Ventilator
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Name
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Cardinal
|
AVEA
|
Volume
A/C
|
Bear
1000
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Assist
CMV
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|
VELA
|
Volume
A/C
|
|
Draeger
|
Evita 4
|
CMV
|
Evita XL
|
CMV
|
|
Hamilton
|
Galileo
|
CMV
|
Raphael
|
n/a
|
|
G5
|
CMV
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|
Maquet
|
Servo-i
|
VC
|
Servo-s
|
VC
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|
Puritan Bennett
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PB 840
|
Assist/Control
Volume
|
Philips/Respironics
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Esprit
|
VCV-A/C
|
VC-CMV has one main advantage, that
it can deliver a preset tidal volume (Vt) and minute ventilation (VE).
The
advantages of this include:
1. Providing a precise Vt that is lung
protective, to meet ARDSnet guidelines (e.g. 4-6 ml/kg/IDBW).
2. Providing a Vt that will prevent or decrease
the incidence of atelectasis. Conversely, this can also be accomplished with
Positive End-Expiratory Pressure (PEEP).
3. Providing a minimum VE that allows for optimal
alveolar ventilation.
4. Since
VE and PaCO2 are mathematical inverses one can predict changes in PaCO2 and pH
with changes in minute ventilation.
Problem
VC-CMV may be an easy to use mode that has advantages during the acute phase of mechanical ventilation; however I believe it has no utility for the spontaneous breathing patient.
VC-CMV is associated with eight out of the ten patient ventilator asynchronies (Table 2) and shifts additional work to the patient during periods of high inspiratory demand.
VC-CMV may be an easy to use mode that has advantages during the acute phase of mechanical ventilation; however I believe it has no utility for the spontaneous breathing patient.
VC-CMV is associated with eight out of the ten patient ventilator asynchronies (Table 2) and shifts additional work to the patient during periods of high inspiratory demand.
Table 2 : PATIENT-VENTILATOR
ASYCHRONIES ASSOCIATED with VC-CMV
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Breath
Phase
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Asynchrony
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Yes (Y) or n/a
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Trigger Phase
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Auto-Triggering
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Y
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Trigger
Delay
|
Y
|
|
Ineffective
Efforts
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Y
|
|
Double
Triggering
|
Y
|
|
Inspiratory Phase
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Flow Mismatch
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Y
|
Low
Driving Pressure
|
n/a
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|
Pressurization
Rate
|
n/a
|
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Cycling Phase
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Premature
Cycling
|
Y
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Delayed
Cycling
|
Y
|
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Expiratory Phase
|
Intrinsic
PEEP (PEEPi)
|
Y
|
Just switching to a pressure control mode can decrease dyspnea in the spontaneous breathing patient [1].
So how does one switch to Pressure-Control Continuous Mandatory Ventilation?
First, Evaluate the current settings on VC-CMV, I'm sure you want to keep the same respiratory rate, FiO2, & PEEP.
Second, if you want to generate the same tidal volume, evaluate the measured plateau pressure. You are going to use the plateau pressure measurement as a starting point for your pressure control setting (see video below).
Third, switch to pressure control and enter all the parameters similar with your previous settings on VC-CMV. Set the pressure control level the same as the previously measured plateau (e.g. plateau pressure 20, then set PC to 20).
Note- some ventilators when changing modes will match the previous settings for you.
Fourth, evaluate measured tidal volumes and titrate pressure control setting for appropriate target tidal volume.
Fifth, assess the flow waveform to see if inspiratory time or I:E ratio is set appropriately (see link).
Sixth, evaluate the pressure waveform to determine if pressurization rate is set appropriately (see links)
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