Dosing a PCA with OpenEvidence

Hey there 👋🏻

I have a million dollar question: How do we go about dosing a patient controlled analgesia (PCA)?

And don’t be confused about setting up a PCA. There are YouTube videos for that kinda walkthrough. Because really, I’ve asked many clinicians and residents by now, and I seem to get a similar answer:

You ask nursing and see if the patient is “pushing the button” a lot, and you go from there.

Sounds a bit vague, doesn’t it?

So this week, I’m going to research this topic with OpenEvidence, a trendy AI tool, and see whether you and I will accept the guidance it provides.

There are a few good points it pointed out. Initial PCA dosing often has to take into account the patient’s baseline opioid use. When I refer to baseline, it doesn’t just mean chronic opioid use. Think of a patient who’s been in pain for two days. The patient likely received some level of opioids. You have to factor that in as the baseline, or you risk underdosing.

The second paragraph starts off with something in bold:

The routine use of basal infusion is recommended against.

Here’s the logic behind that. If you ask yourself whether you’d start anybody on long acting morphine or oxycodone right away, you’d likely say no. That’s because you don’t quite know how much opioid the patient needs to get their pain under control. That’s why you often see PRN opioid dosing when you first start gauging opioid needs. The same logic applies here.

So far the answer is pretty good. It gives me a decent background. But if a patient is on chronic opioids, I need more guidance. So here we go.

The first paragraph starts to explain why chronic opioid use needs special attention. We have to factor that into our dose calculation. Oh, and they use the 1:1.5 ratio when converting oxycodone to morphine, and 1:3 when converting IV to PO morphine.

I like what I see so far.

But here’s where it could do a better job.

If we take the second paragraph’s recommendation at face value, it basically calculates the breakthrough doses...and just the breakthrough doses. But how are we addressing the chronic oxycodone the patient has been on? Should we start an infusion? And if so, what rate are we starting?

As a preceptor in opioid management, I often refer my learners to the opioid conversion book by Dr. Lynn McPherson. It has a dedicated chapter that walks through how to go about PCA dosing. So if we take a look at the references OpenEvidence provides...

Well, now I know why the answer to the second question seems off.

P.S. I love using AI. This just happens to be one very niche question where our opinions differ. And it falls outside what current AI tools are built to handle well.

See you next time.

SP