Topic Progress:

Most commonly used are

  • Assist Control (AC)
  • Volume Controlled Synchronized intermittent mandatory ventilation (VC-SIMV)
  • Continuous Mandatory Ventilation (CMV)

Breath Characteristics

  • A set volume of gas delivered at a set flow rate
    • Flow is constant throughout inspiration (square waveform)

These are settings you decide and set, so nothing new here!

  • Resultant pressure generated will depend on patients lung mechanics and ventilator circuit

This gives you new information about your patient!!

  • 3 different values are important in the pressure waveform of a VC-AC mode

  • Peak inspiratory pressure (PIP)
    • The highest pressure reached during inspiration
    • Affected by the resistance of the tube to flow
    • Increasing flow or volume will result in a higher peak pressure
  • Plateau pressure (Pplat)
    • The pressure within the lungs and circuit once inspiratory flow has stopped (inspiratory hold maneuver)
    • Equates to alveolar pressure
  • Inspiratory pause time
    • The time between reaching the preset TV and cycling into expiration during which there is no gas flow
    • Dependent on the set inspiratory time (Ti) and flow rate
    • Pause lengthens with increasing Ti and flow rates


[az_accordion_section] [accordion title=”Volume Control Assist Control” id=”acc-1″]• What ventilator setting won’t you have to set?

o FiO2

o Tidal Volume

o Respiratory Rate [you will have to set a RR, but it might be higher if patient triggers additional ones]

o Flow

o Inspiratory time (Ti)

o Pressure [this depends on your other settings and the patient’s respiratory unit mechanics]


Hover over your screen to understand it better!

[az_toggle_section] [toggle title=”You decided to try AC-VC on your patient. Can you tell what was set for every phase of a breath by looking at the ventilator screen above?” id=”tgl-1″]Trigger

In this case, there is no negative deflection at the beginning of flow or pressure curves, so it is time-triggered. Makes sense since your patient just got paralyzed during intubation! RR was set at 12/min, so a breath is triggered every 5s.


Tidal volume was set at 500cc


Ti was set at 1.7s


PEEP of 5cmH2O [/toggle] [/az_toggle_section]

[/accordion] [accordion title=”Volume Controlled Synchronized intermittent mandatory ventilation (VC-SIMV)” id=”acc-2″]• Equivalent of VC-AC interspersed with Pressure Support (PS)

• What ventilator setting won’t you have to set?

o FiO2

o Tidal Volume

o Respiratory Rate

o Flow

o Inspiratory time (Ti)

o Pressure (you’ll have to set all of them, even Pressure for the PS breaths)


Hover over your screen to understand it better!

[az_toggle_section] [toggle title=”If you chose this mode for your patient, what would it look like?” id=”tgl-1″] It would look exactly like an VC-AC screen. Since your patient is paralyzed, he wouldn’t trigger any breath during the SIMV or the PS ‘trigger window’ and would let himself be ventilated at the RR and Ti that you would have set for the SIMV component of it. [/toggle] [/az_toggle_section]

[/accordion] [accordion title=”Continuous Mandatory Ventilation” id=”acc-3″]

• Same as VC-AC, except that patient can’t initiate any breath.

o RR and MV are always the same as what is set

• Not used in ICU but more common in anaesthetics

[az_toggle_section] [toggle title=”• Would you put your patient on CMV?” id=”tgl-1″] Hopefully, your patient will eventually start getting better and wanting to breathe on his own when paralysis will have weaned. Nothing is more unconfortable and counterproductive than trying to initiate a breath against a closed valve and only getting air when the ventilator says so! [/toggle] [/az_toggle_section]

[/accordion] [/az_accordion_section]

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