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?

Answer and interpretation

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.

suxamethonium
suxamethonium

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

rocuronium
rocuronium

Q2. How are roc and sux metabolised?

Answer and interpretation

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?

Answer and interpretation

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 (or more), as I’ll explain in Q4.


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

Answer and interpretation

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?

Answer and interpretation

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?

Answer and interpretation

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?

Answer and interpretation

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’?

Answer and interpretation

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?

Answer and interpretation

A 50mg/5mL amp of roc costs about 10 times as much as a 100mg/2 mL amp of sux. A difference of about $20… 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


References

Ruling the Resus Room 700

CLINICAL CASES

Resus Room Reflection

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health and Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of two amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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