Pressure Regulated Volume Control
Delivers a target tidal volume but continually adjusts the amount of pressure needed to use the lowest amount of pressure to reach that set tidal volume. Inspiratory flow is variable and changes with patient effort and lung mechanics (airway resistance, lung compliance).
The vent initially delivers a volume test breath upon starting PRVC. From there, it will calculate the needed pressure to deliver that set tidal volume, and then switch to a pressure breath with continual adjustments from that point. The vent will not make adjustments of more than 3 cmH2O of pressure with each breath. The vent will also deliver volume test breaths at other times as well such as after the rate is changed or after high pressure alarm.
PRVC breaths can be more comfortable for the patient and are beneficial as they respond to changes in compliance to ensure the desired tidal volume.
Volume Limited Alarm
One alarm that we can run into specifically when set to a PRVC breath type is a Volume Limited alarm.
The Volume Limited alarm is based off of our High Pressure Limit. If airway pressure raises to within 5 cmH20 of that high pressure limit to deliver our tidal volume goal, the vent will cut the breath short, thus limiting the volume.
Example: Our high pressure limit is currently 35 cmH20 and our tidal volume is set to 450 mL. If the airway pressure increases to at least 30 cmH20 at any point during inhalation, the vent stops the breath. So the patient may only get a tidal volume of 300 mL instead of our desired 450 mL.
When we get the volume limited alarm, something to consider, especially if we haven’t had any problems previously, is why are we now running into higher pressures? Maybe it was a one time alarm due to road bumps or something similar, but if it continues, troubleshoot as you would any other high pressure alarm. Assuming there is nothing else causing higher pressures, there are two simple adjustments that we can make.
We can start by simply increasing our High Pressure Limit. Perhaps we haven’t finely tuned this yet and we can bump it up a little. Remember we generally set the high pressure limit to 10-15 cmH20 above our PIP.
If appropriate, we can also make a small decrease to our tidal volume. Maybe we are at the high end of normal at 8 mL/kg, giving us some room to decrease it to 7 mL/kg. If the vent cant deliver 450 mL, maybe it can deliver 400 mL.