I’m not sure when PRVC started being so widely used but it definitely snuck up on me and our unit. Perhaps it’s an old friend from COVID days (but I remember using tons of PC during that time). 4/5 intubated patients on my floor are usually on PRVC but why? When did we start navigating away from our old friend VC, an almost standard of care ventilator mode?#nonewfriends. Most of my colleagues also choose PRVC nowadays. Well, this is the perfect topic to go over on this post.
What is my practice now? When I see PRVC, I’ll switch back to VC (because of my traditional style and stubbornness). When I see an ARDS patient on PRVC, I definitely switch back to VC and aim for 4-6cc/kg per IBW. After my reading today, let’s see if I can be persuaded that most people could be on PRVC.
What is PRVC? It stands for Pressure Regulated Volume Control. To go over the basics, assist control is our standard mode of delivering a set breath to a patient, whether that means delivering a set amount of volume (VC) or pressure (PC) at a set respiratory rate (unless there is overbreathing) and minute ventilation (MV).
PRVC is an adaptive form of mechanical ventilation that is pretty sophisticated: the ventilator uses a feedback mechanism based on the TV set vs the TV delivered based on the patient’s lung compliance or resistance (as seen in TVe). Another way to say it is that it ventilator responds to changes based on changes in patient respiratory drive. I think clinicians misinterpret PRVC as a volume control mode; to my understanding, it is not. It’s a pressure control mode that responds to volume. The ventilator will change the inspiratory pressure based on the volume or flow time of the preceding breath. So if a patient takes a big breath, flow increases, and the patient generates a large TVe (greater than the set TV). On the next breath, the machine will not apply that much inspiratory pressure in order to achieve the set TV. However, if the patient takes a very tiny breath (decreased inspiratory flow and TV), the next breath will generate a larger inspiratory assist from the ventilator.
It’s a bit confusing but I recommend understanding the basics of ventilators and modes like VC and PC, terms like TV and flow time, inspiratory effort, etc. (not that I am the expert on these things; talk to your friendly neighborhood/hospital pulm crit intensivist).
Will this information change my clinical practice? A bit, but probably not really. If I have a critically ill patient whom I worry about his or her respiratory effort, I would likely avoid PRVC. I fear that using that mode would worsen their work of breathing (WOB) and tire them out. Might as well use a “real” assist control mode. If a patient is super agitated, having pain or anxiety, I would avoid PRVC as well given the same reason that his or her respiratory drive will be everywhere and WOB will increase. Their desired inspiratory flow would go up and the ventilator would generate very minimal assisted pressures. I would choose PC given that I expect their peak pressure to rise and sedate them.
If I have a patient who is compliant, comfortable, not critically ill, cooperative with compliant lungs, I would probably be OK with PRVC. Otherwise, probably would stick to VC.
Clinical Pearl: Don’t forget to check your P0.1 as well (this is your inspiratory occlusion pressure; it tells you a lot about what the patient’s respiratory effort is like (effort generated by the diaphragm for normal physiologic negative pressure ventilation). Normal/average levels are 3–5. May write a post about this later…
Let me know what you guys think.