Episode 85- “It Takes 1 to Roc”: Part Two: Is 1 enough?

Hello and welcome to Episode 85 of ER-Rx, a podcast tailored to your clinical needs. I’m your host, Adis Keric, and this is Part Two of our Mini Grand Rounds series discussing dosing of rocuronium (roc). In Part One of the series, I talked about how to dose roc and other RSI meds in obese patients. I sent out a poll on the IG page and everyone was evenly split on how they dose roc- with some using an Actual Body Weight, others using Ideal Body Weights, and some just giving 100 mg to everyone. Hopefully, through some discussion of volume of distribution and lipophilicity, I was able to change your practice a bit and get you to dose roc based off of an Ideal Body Weight (IBW) for all patients- especially the obese. This week in Part Two of the series, I’m gonna talk about the 1 mg/kg dosing of roc that we all know about and discuss why a slightly higher dose could be better.

When it comes to the debate of using succinylcholine or roc, we have a ton of data showing that first-pass success rates and adverse events are equal between the two. Unfortunately, the studies that looked at first-pass success rates didn’t take into consideration the dose of roc used. And I know that some of you think that doses higher than 1 mg/kg are better- and you have some data that would back you up.

For example, there’s this recent retrospective review published in April of 2021 in the Canadian Journal of Emergency Medicine that included data from over 8,000 intubations using roc. After controlling for confounding variables like hemodynamics, induction meds used, and intubation and intubator characteristics, the authors found that odds of first-pass success were highest in the patients who got >/= 1.4 mg/kg of roc compared to patients who received the standard 1 mg/kg dose (1.5; 95% CI 1.1-2). [Strangely, there was no difference between patients who got 1.4 mg/kg and < 1 mg/kg (1.1; 95% CI 1-1.4) or those who got an intermediate dose of 1.2-1.3 mg/kg (1.2; 95% CI 0.9-1.5)]

And as a quick side-note, when they stratified patients who were intubated with direct versus video laryngoscopy (about a 50/50 split), they found that the higher doses of >/= 1.4 mg/kg were only significantly better relative to using the standard 1 mg/kg dose if direct laryngoscopy was used (1.9; 95% CI 1.3-2.7) – when video was used it didn’t matter what dose of roc you gave- which seems like more of a plug to use video than to give higher doses of roc. But, still, they also found that these higher doses worked better in hypotensive patients, which makes sense since these patients have reduced cardiac outputs and therefore less drug delivery to the site of action.

When we want to avoid using succinylcholine, the biggest drawback to using roc is the idea that succ has a much quicker onset time- which is usually, but not always, the case. There are a handful of older studies that show using roc doses slightly higher than 1 mg/kg- somewhere around 1.2 -1.4 mg/kg- leads to onset times that are comparable to using succinylcholine. In one study, those times were 50 seconds for succ, and 55 seconds for roc.

For those who jokingly, or maybe seriously, said they just give 100 mg to all patients– you’re not really too far off- especially in male patients. For example, given the average male height in the US of 5’9”, most males will have an IBW of roughly 70-80 kg. Giving 1 mg/kg means you’d give 70-80 mg, but if you rounded up to 100 mg you’d be giving about 1.2-1.4 mg/kg- which according to the studies I talked about should be perfect for both first-pass success and onset times.

For females, it gets a little trickier and you do have to do a bit of math. With an average height of 5’4”, their IBWs are roughly 60-70 kg. Rounding up to 100 mg means you’re giving about 1.4-1.7 mg/kg which is kind of high- but probably not harmful as long as you realize the duration of roc is prolonged with these higher doses. Or, you could round to 80ish mg to hit that 1.2-1.4 mg/kg dosing range for females.

Lastly, I want to touch on max dosing. Like I said in the previous episode, I personally max out at 100 mg- even in obesity- for all of the reasons mentioned in this episode and the last one. But I have maxed out at higher doses- like 150 mg- in the morbidly obese, hypotensive patient who looks like they’re going to have a difficult airway and I’m worried about their cardiac output delivering the roc where it needs to go.

Some may say, what’s the harm in giving higher doses of roc? The thing that I worry about is the duration of paralysis- which again, can be prolonged, and even doubled- with higher doses of roc. So you’re looking at up to 2 hours of ensuring adequate, deep, amnestic sedation for your patient once the induction agent wears off. And if you’ve been around this show for a while- you know how much I hate deep, amnestic sedation for our intubated patients. But if there’s one thing I hate more—it’s the idea of being awake and paralyzed.

To wrap up the series- keep in mind that there are a couple of nuances to the saying “it takes 1 to roc.” First, we should be dosing roc off of an IBW- especially in obesity. Second, there is a good amount of data showing that we should use slightly higher doses- like 1.2-1.4 mg/kg- to make sure we have quicker onset times and to make sure the drug is delivered to the site of action in hypotensive, low-cardiac output patients. So, in conclusion, let’s change the saying to “it takes (slightly more than) 1 (based on IBW) to roc.” That’s really smooth.

As always, thank you so much for your time, and thank you for wanting to learn more about pharmacotherapy. If you have any comments or anything you’d like to add to this episode, please give me a shout out on the @errxpodcast Instagram page, or reach out to me on errxpodcast.com- I’d love to respond to all comments and criticisms.

I also want to take a second to shout out friend-of-the pod Elsa for their generous donation on BuyMeACoffee.com- donations like this help keep the podcast running and free for everyone. If you’d like to sponsor an episode, the link to donate is super easy to get to. It’s linked in the bottom of the episode description wherever you get your podcasts, on YouTube, and on the website.