Does Roc rock? Does Sux suck?

aka Ruling the Resus Room 004

On the plus side, the patient who took the olanzepine overdose before being delivered to Resus bay 4 is no longer trying to kick and punch the nursing staff. On the minus side, he is descending into a deep coma and is no longer protecting his airway. You decide to perform rapid sequence intubation (RSI) and thus, with meticulous supportive care, ensure his survival… After all, you want to make sure he lives to fight another day.

But what neuromuscular blocker are you going to use? Rocuronium or suxamethonium (aka succinylcholine)?

Questions

Q1. How do roc and sux cause muscle relaxation/ paralysis?

Both roc and sux bind to nicotinic aceytlcholine receptors at the neuromuscular junction, thus preventing motor neurones from triggering action potentials in skeletal muscle.

Suxamethonium is really just two acetylcholine molecules stuck together. It acts as a depolarising muscle relaxant — hence fasciculations occur prior to muscle relaxation.

Rocuronium is an analogue of vecuronium, an aminosteroid. It acts as a non-depolarising muscle relaxant.

Q2. How are roc and sux metabolised?

Sux is rapidly hydrolysed thanks to the action of plasma and liver pseudocholinesterases (but not in patients susceptible to suxamethonium apnoea, which occurs in people with rare variations of the pseudocholinesterase gene).

Roc on the other hand, undergoes hepatic/ biliary and urinary excretion, so it is eliminated much more slowly than sux.

Q3. How are roc and sux administered, and in what doses?

Sux is typically given at a dose of 1 to 1.5mg/kg IV. In infants a higher dose of 1.5-2mg/kg is often used. It can also be given IM, but at a higher dose (e.g. double it). Sensitivity to suxamethonium is increased during pregnancy, and some advise decreasing the dose by about 25% (I doubt this is very significant clinically).

The dose of roc used in RSI varies from 0.6  to 1.2 mg/kg IV. I suggest using 1.2 mg/kg IV, as I’ll explain in Q4.

Q4. How rapid is the onset of paralysis with sux and roc?

Except in patients with poor perfusion states, good intubating conditions are typically achieved after 45 to 60 seconds with suxamethonium. Proponents of sux cite this as a major advantage over roc.

Traditionally roc is considered to have a slower onset of action than sux. Indeed, this is true if you use lower doses like 0.6 to 0.9 mg/kg IV. However, if a dose of 1.2 mg/kg IV is used there is no difference between roc and sux in the onset of good intubating conditions.

Q5. How long does paralysis last for with sux and roc?

There is no doubt that roc renders patients paralysed for much longer than sux. Optimal intubating conditions probably last about 5 minutes after giving an RSI dose of sux, although time to complete recovery is more like 10 minutes.

Like the onset, the duration of effect for rocuronium depends on the dose administered. Recovery may occur as early as 30 minutes following a dose of 0.6 mg/kg IV, but will be more like 90 minutes following a dose of 1.2 mg/kg.

Sux proponents typically highlight this difference as a major advantage of sux — you’d only have to bag for 10 minutes and then the patient can be woken up and allowed to breathe spontaneously. This isn’t quite how things work in the resus room though…

If you are performing RSI on a patient and it is feasible to wake them up if things go haywire, then you probably shouldn’t have been doing the RSI in the first place!

In the resus room, if you’re performing RSI and can’t get the tube in first try, then you better turn to Plans B, C, and D, etc. until you find a way to get some sort of airway — even if this means you need to cut the patient’s throat because you’re in a CICVBCO (can’t intubate, can’t ventilate, but can oxygenate) situation. In the resus room RSI, keeping the patient paralysed is an advantage: while you frantically work your way through your back up plans the last thing you need is the patient fighting your attempts at ventilation or pushing your scalpel-wielding hand away in the midst of a hypoxic spiral into the abyss…

Remember to use apneic oxygenation and the other tips shown in the videos featured in Own the Airway!

Anyway, roc can now be reversed in about 2.2 minutes. That’s how long it takes for a 16 mg/kg IV dose of sugammadex to achieve reversal of rocuronium-induced muscle relaxation.  However, like I just said, if you’ve planned things right you won’t want to do this….

Q6. What are the side effects of roc and sux?

Let’s start with roc as it’s easy — none!
(OK, I’m exaggerating… Allergy is always a risk, but there’s nothing else significant I can think of)

Suxamethonium, on the other hand, can cause:

  • bradycardia, potentially leading to cardiac arrest (especially in small children and following repeat doses)
  • hyperkalemia, which is potentially fatal (though K only rises about 0.4 mmol/L on average in normal individuals)
  • fasciculations which increase oxygen consumption and lead to muscle pain
  • increases in:
    • intra-gastric pressure, possibly offset by an increase in lower esophageal sphincter tone
    • intracranial pressure
    • intraocular pressure
  • malignant hyperthermia — rare, but very very bad
  • suxamethonium apnoea — rare, and not likely to be a major concern in the resus room.

So, no contest here…

Q7. What are the contra-indications to roc and sux?

Again, it’s easier to start with roc — contra-indications… roc allergy, anything else?

The use of sux should be avoided if the following conditions are present:

  • hyperkalemia
  • risk of hyperkalemia(occurs in many of these conditions because of proliferation of acetylecholine receptors beyond the normal neuromuscular junctions)
    • renal failure (a relative CI)
    • severe sepsis
    • congenital myopathies
    • neuromuscular disorders such as tetanus and botulism
    • upper motor neuron disorders: stroke >72h, motor neuron disease, mutliple sclerosis, spinal cord injury >72h
    • burns > 72h
    • crush injury
  • malignant hyperthermia
  • suxamethonium apnoea

Most of these conditions are seen rarely in the resus room, so widespread use of sux is rarely going to cause problems. However, it will happen to someone… It is not always possible to exclude all of these conditions prior to rapid sequence intubation in the resus setting.

Q8. How do sux and roc compare in terms of ‘safe apnoea times’?

The ‘safe apnoea time‘ is how long a patient can remain apnoeic for before developing hypoxemia.

Rocuronium appears to have longer safe apnoea times than suxamethonium. For instance, in ASA grade 1 or 2 patients with BMIs of 25 to 30 receiving general anesthetic, patients who were given rocuronium took 40 seconds longer to fall to an SO2 of 93% when apneic than those who received suxamethonium. This might be a result of increased oxygen consumption from the fasciculations caused by depolarising neuromuscular blockade.

Q9. How do roc and sux compare in terms of cost and storage time?

A 50mg/5mL amp of roc costs about 1o times as much as a 100mg/2 mL amp of sux. However, this is a difference of about 20 bucks… Absolute peanuts in the context of a critically ill patient.

Roc can be stored safely at room temperature for about 12 weeks, six times longer than sux (stable at room temperature for 14 days).

Well, you answered all the hard questions… So, do you think roc rocks and sux sucks, or vice versa? Which are you going to use next time you perform rapid sequence intubation?

I’m with Reuben Strayer on this one (in case you haven’t seen it yet):

Rocuronium vs. Succinylcholine from reuben strayer on Vimeo.

 

References

Print Friendly

Comments

  1. Torferson the Brave says

    Interesting Chris.
    We had a case illustrating your point just the other day. An unexpected difficult airway, where the use of roc would have bought us more time to establish a secure airway.
    I also take your point that RSI should be an all or nothing decision. As Robin Williams once said “…it’s like talking about partial circumcision.. you either go all the way or forget it”. Sux’s short duration of action in a patient whom you can’t intubate and can’t ventilate, may more likely serve as a disadvantage in the ED setting. Unlike in the elective or semi-elective setting, critical airways in ED rarely get better by themselves.
    You also highlight the negligible difference between the cost of sux and roc. $20 is hardly going to be noticed when the ICU invoice is drawn up. However, in the unlikely event of having to reverse the effects of roc quickly, there is a considerable expense in the use of sugammadex, which “can cost more than $1350 per case” (Statewide Anaesthesia and Perioperative Care Clinical Network, sugammadex Guideline v1.0, 2009).
    Whilst the expenses incurred reversing roc are unlikely to be frequent, other hidden costs would need to be considered; the availability of the reversal agent in ED, the shelf life of that agent as well as education in the use of roc, and the knowledge of when and how to use its reversal agent.

  2. says

    Thanks for the good info. I think the textbooks are still a bit behind on this issue, at least when we briefly covered this as an MSIII. Curious to hear what are going to be taught this year as a PG1.

  3. says

    This is a nice little series of questions. There are either Sux shops or Roc shops. They both seem to get the job done, but it certainly seems to me that the way of the future is Roc. I wonder why Billy seems so unconvinced by the obvious logic.

    Anyway, we put together a little online airway course with a short little online lecture on the topic. I’ve tried to translate it into Kiwi and I’d love to hear if I’ve succeeded. Check it out at http://www.thesharpend.org/eeacc-5-airway-pharmacology

Trackbacks

  1. [...] Heard the cry “Sux Sucks! Rock Rocks!”? People have varied opinions about whether or not to use any paralytic agent, and those that use them argue about which is the right one.As to whether or not you should paralyse your obese patient prior to intubation, Scott Weingart has a great debate with Paul Mayo about use of paralytics in critical care intubations here. [...]

Comments