Propofol is a great anaesthetic – but it can cause pain on injection. This is one of the tricks of the trade: mix in some lidocaine in your propofol syringe, and the patient is pain free. Sounds like magic. Especially as there’s no way lidocaine can work its usual local anaesthetic effect that quickly. But it works. There’s been a lot of studies on the subject, and now there’s a Cochrane review too.
Propofol induction pain
Most people experience some light discomfort at the injection site on injection of propofol, as it is irritating to the vessel wall. According to Cochrane, 64% of people experience pain on injection, and 38% report strong pain on injection, but most are able to tolerate it. The biggest problem is for the kids.
We can usually avoid the problem by using a larger vein for induction, or another induction drug, like Thiopental, or a lower strenght propofol like the 5mg/ml solution available. This also usually avoids any pain.
But often, we use the old trick of mixing in some lidocaine with the propofol. Our usual practice is to add 1 ml of 1% or 2% lidocaine to a 10 ml syringe of propofol. And like magic, the incidence of pain on injection is almost gone.
Lidocaine intravasal effect
So, how does this work? Truth is, we don’t know. We’ll start with the lidocain pretreatment method that’s easier to explain: Pretreatment with intravenous lidocain and venous occlusion, sort of like a low dose and local Bier block. I can understand how this can work, with a direct local anaesthetic effect on the vessel wall.
Then we’ll move to the next level: just pretreating with intravenous lidocain without any venous occlusion. One would think lidocain would pass through the injection site and up the vessel much to quickly to be able to affect the local vessel wall at the injection site, but this works well too.
Now, for the magical one: mix some lidocaine to your propofol syringe, and inject that mix. There is no way lidocaine can invoke its usual anaesthetic effect this quickly. It sounds like an urban legend. But it works. And now, Cochrane is here to prove it.
The Cochrane review
For once, the Cochrane review found a big effect of this intervention, and with a high level of evidence! Here are the review findings:
Interestingly, the Cochrane review didn’t find any significant difference between admixing lidocaine or pretreating. Previous reviews have found both pretreating and admixing to give the best result. So it’s probably a toss. For kiddies, you usually can’t play around with too many syringes before you start losing their trust. So admix is my preferred choice. I also like the magic of it.
Lidocaine against propofol induction pain works. For us, the main uses are: Kids. Or patients with previous experience of intense pain on propofol induction. It’s long been a handy magic trick of anaesthesia, although we have no real idea of how it works. At least now there’s also a Cochrane review on it, documenting the effect.