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inspired air flow rate) are completely controlled by respirator, which supplies
all respiratory power. CV is classified into Volume Controlled Ventilation
(VCV) and Pressure Controlled Ventilation (PCV).
• AV
In AV (Assisted Ventilation), which is activated by decrease of airway
pressure (pressure trigger) or change in flow rate (flow rate trigger), the
respirator conveys air to the patient at preset tidal volume (or Inspiratory
pressure), frequency, inspiration duration and expiration duration.
Popularly speaking, in AV, ventilation of respirator is activated by the patient,
and ventilation will not be provided unless the patient inhales. Proper
parameters should be set for pressure activation or flow rate activation, in
the same way as with CV.
• A/CV
A/CV (Assisted/Controlled Ventilation) is a combination of CV and AV,
during which, when spontaneous breathing is sufficient and at a frequency
higher than the preset one, assisted ventilation is applied; when spontaneous
breathing is weak and at an actual respiration frequency equal to the preset
one, controlled ventilation is enabled. When the patient takes spontaneous
breath, mechanical ventilation is started. When spontaneous breathing is
unavailable at a time, mechanical ventilation is automatically switched from
assisted ventilation to controlled ventilation. A/CV is a type of IPPV.
• V-A/CV
V-A/CV (Volume Assisted/Controlled Ventilation) is based on VCV.
Synchronous activation is enabled in expiration stage. When the pressure
reaches activation pressure, respirator provides one push of VCV at fixed
tidal volume in advance.
A typical pressure waveform of V-A/CV is shown below：
FIGURE 28 V-A/C
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