Page 143 - Clinical Application of Mechanical Ventilation

Operating Modes of Mechanical Ventilation 109

Volume Control Plus (VC1)

Volume control plus (VC1) is used to deliver mandatory breaths during AC and
SIMV modes of ventilation. VC1 is intended to provide a higher level of synchrony
than standard volume control ventilation.
In VC1, the clinician sets the target tidal volume and inspiratory time. The ven-
Following a test breath, tilator delivers a single test breath using standard volume and decelerating flow and
the target pressures for sub-
sequent breaths are adjusted plateau to determine the relative compliance. The target pressures for subsequent
accordingly to compensate for breaths are adjusted accordingly to compensate for any tidal volume differences
any tidal volume differences
(Set V T 2 Delivered V T ). (Set V 2 Delivered V ). Flow is adjusted automatically to reduce the likelihood of
T
T
inadequate flow or aggressive flow demand.
Active spontaneous breaths are allowed during the inspiratory phase of a man-
In VC1, active spontane- datory breath by way of a pressure control style of breath and the use of an active
ous breaths are allowed
during the inspiratory phase exhalation valve. Excessive pressure caused by breathing or coughing is vented, thus
of a mandatory breath. maintaining synchrony.

Volume Support (VS)

Volume support (VS) is intended to provide a control tidal volume and increased
patient comfort. Weaning from anesthesia is a common application for VS.
In VS, the clinician sets the target tidal volume but not the inspiratory time or
In VS, the clinician sets mandatory frequency. The ventilator delivers a single spontaneous pressure sup-
the target tidal volume and
the ventilator uses variable port type of breath and uses variable pressure support levels to provide the target
pressure support levels to pro- tidal volume. During weaning or awakening from anesthesia, the patient assumes
vide the target tidal volume.
a higher spontaneous tidal volume and the ventilator decreases the pressure sup-
port level accordingly. When the spontaneously tidal volume decreases, the ven-
tilator increases the pressure support level automatically to maintain the target
tidal volume.
During VS, the ventilator frequency and minute ventilation are determined by
the triggering effort of the patient. The inspiratory time is determined by the patient
respiratory demand.

PRESSURE-CONTROLLED VENTILATION (PCV)

pressure-controlled ventila- In pressure-controlled ventilation (PCV), the pressure-controlled breaths are
tion (PCV): A pressure plateau time-triggered by a preset frequency. Once inspiration begins, a pressure plateau
is created at the beginning of
inspiration and the pressure is is created and maintained for a preset inspiratory time. Pressure-controlled breaths
maintained for a preset inspiratory
time. PCV can minimize the airway are therefore time-triggered, pressure-limited, and time-cycled.
pressures while providing support PCV has some functional similarities to pressure support ventilation, but they
to oxygenation and ventilation.
have very different indications. Pressure-controlled breaths are time-triggered by
a preset frequency, and, as in the control mode, the patient should be sedated.
Once a pressure-controlled breath has been time-triggered, a pressure plateau is
created and maintained by servo-controlled inspiratory flow in a manner simi-
lar to pressure support. Recall that the pressure plateau in pressure support is

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