I am a 1st year student and I am trying to understand pressure control. If someone is on pressure control can they have a plateau pressure or since pressure is supposed to be constant and volume will vary; the plateau should be equal to the set pressure right? Im not sure. Is someone out there that actually knows there stuff that could clarify this for me.

Thanks,
Simon

Hello Simon,

Pressure control is setting a constant pressure over a period of time. Volume control is constant flow over time.

If you think back to graphing functions, put time on the x axis and pressure on the y axis. You get a square waveform or "plateau" because you keep pressure constant while time increases. The same is true in volume control when flow is kept constant over time.

So when you look at a ventilator you can look at the waveform and know how the ventilator is controlling the breath. In volume control the flow waveform is square/a rectangle. In pressure control the pressure waveform is square. Some may argue that this is not the case in dual modes (PRVC, Autoflow) but in my humble opinion the ventilator is still in pressure control for these modes.

To clarify, tidal volume is flow over time. When you set a tidal volume and flow rate, you don't actually need to set a time. The time knob is used to control pause time, or any additional time added after flow has ceased. In a leak free system this will create a plateau pressure.

In pressure control, tidal volume is a dependent variable. It is dependant on the following: lung mechanics (compliance, resistance), delta pressure (PIP-PEEP), and patient interaction. In volume control, pressure is the dependent variable. When the ventilator is delivering flow, pressure is dependent on resistance and compliance, patient interaction, and the specific flow rate (the higher the flow rate the higher the peak pressure...I think). If the breath is held after flow has ceased (insp. hold/pause), this pressure is dependent on just compliance and patient interaction.