Greetings, dear readers. Let’s talk analgesia.
A couple of months ago I was on a hospital gurney, and my attending, Dr. Blackburn—whom I had waved goodbye to a few hours previously—told me that by the time my liter bolus finished running, the Reglan would kick in, and I could sleep the rest of it off. During the worst headache of my life, it was a great kindness to envision relief on a finite horizon.
Transformed (as most are) by my ED experience as a patient, I decided to become more comfortable with the numbers of analgesia; I wanted to effortlessly switch between different medications, IV, and PO, and—like Dr. Blackburn—be able to look someone in the eye and give them reasonable expectations for relief.
It took a bit of reading, and I’ve forgotten much of it multiple times, but I’ll share the take-homes.
The rule of 5’s
… is a method of simplifying equianalgesic opioid dosing, which I’m pretty sure I invented just now. For background, most people work off a standard equianalgesic opioid dosing chart:
It’s a good primer, great for giving homework to medical students, perfect for palliative care, but for EM residents, you might try the rule of 5’s, which is as follows:
For a 50 kg patient (multiply as necessary, depending on patient size), the following are equivalent and adequate weight-based opioid doses per Tintinalli’s (caveat below):
= 5 Morphine
= 10 Oxycodone
= 15 Hydrocodone
= 50 Fentanyl
= 0.5 Dilaudid
Pretty simple, right? (These are for PO oxy/hydrocodone, and IV everything else, per usual.)
The only one here that isn’t a true weight-based dose is Dilaudid (hydromorphone), the dose of which is technically 0.015mg/kg, or 0.75mg for a 50-kg patient. But it comes in 1mg/mL concentrations, and in 1mg and 5mg vials, so I might round to the nearest 0.5mg for the love of nursing. You can round up to 1mg (for a 50 kg patient) to ensure efficacy, or down to 0.5mg like me, to control the most euphoric opioid we have. Either is fair.
When you know the numbers, it usually becomes easier to feel comfortable giving increased doses. I had a great nurse who not infrequently gave 300 ug boluses of fentanyl in the burn unit ask, “I’ve never given 15mg of oxycodone before—is it safe?” I think it was reassuring to relate that dose to 7.5mg of morphine, or 75 of fentanyl. We often don’t take full advantage of PO weight-based dosing, and it’s easy to think of oxycodone and Norco as either 5mg or 10mg, period.
The rule of 5’s can also help when treating patients with chronic pain. For example, a hospice patient with metastatic cancer who takes 30mg MS Contin tid (btw, the conversion from IV: PO morphine is 3:1)—takes the equivalent of 10mg of IV morphine over 8 hours at baseline. If they take 10mg oxy PRN, that’s another 5mg IV morphine you know they can tolerate—and all this is in addition to the unadjusted dose an opioid-naïve person could tolerate.
When you’re *appropriately* comfortable giving higher doses, and it’s satisfying to control someone’s pain more quickly.
I had a 70-kg burn patient recently—an IV heroine user—who was pretty uncomfortable. As soon as we could, we pushed 100 ug of Fentanyl, waited 5 minutes, then gave another 100. Then 50, 50, and 50—each with ~5 minutes between doses.
Why 5? Is that a Corey Slovis thing?
It’s 5 minutes because that’s our margin of safety; that’s how long the textbook says to wait to ensure the peak effect has occurred before re-dosing. The textbook says 2-5 minutes to peak for fentanyl, and 3-5 minutes to peak for morphine, but since we’re trying to be conservative and not unwittingly dose-stack, I would just remember “5 minutes” for both of them.
That’s the second rule of 5’s: it takes at most conservative estimates 5 minutes for fentanyl and morphine to peak, so definitely administer more if they’re still in pain 5 minutes after the last dose.
Oxy vs Hydrocodone
Ok, this one’s embarrassing (except it’s not, because most people don’t know this either): for approximately 100% of intern year, I didn’t realize there was a potency difference between oxycodone and hydrocodone, and I thought the only difference between Percocet and Norco was that Norco was less emetogenic. Feeling clever, I started giving Norco to almost all of my ED patients who needed something PO. That’s probably when I started thinking everyone was drug-seeking because no one was reporting great pain relief anymore. It turns out there’s a huge difference in not only potency but time to action as well.
So which one is harder, better, faster, stronger? I’ll let you figure it out:
|Onset (minutes)||Peak effect (minutes)||Duration (hours)|
|Fentanyl||now||5||0.5 – 1|
Yeah, so… I now use Norco for outpatient prescriptions only, and if I want a PO opioid to result in noticeable relief during the visit, I use oxycodone.
Another interesting observation is that Dilaudid– despite being the most euphoric—has a longer time to onset (5 minutes) than morphine and fentanyl, took longer to peak (10 minutes), but also lasts way longer (2-4 hours; twice as long as morphine). It also has less associated histamine release, so it’s not surprising why patients might ask for the magic di-la-la…
What are your practice pearls for opioid analgesia in the ED?
- Ducharme J. Acute Pain Management. In: Tintinalli JE, Stapczynski J, Ma O, Yealy DM, Meckler GD, Cline DM. eds. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 8e New York, NY: McGraw-Hill; 2016. http://accessmedicine.mhmedical.com/content.aspx?bookid=1658§ionid=109405019. Accessed November 14, 2017.