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An Easy Way to Remember if Sux is Safe for Your Patient

Succinylcholine (Sux) is a depolarizing skeletal muscle relaxant. It combines with the cholinergic receptors of the motor end plate to produce sustained depolarization and paralysis, and it’s rapid onset makes it an effective agent for use in rapid sequence intubation (RSI).

This mechanism of action however, also makes it a potentially dangerous drug in a subset of patients who need RSI because it can cause significant hyperkalemia, and subsequent cardiac arrhythmia.

For this reason, succinylcholine has fallen out of favor over the last few years, and its use has been overshadowed by Rocuronium. For many, remembering the long list of relative contraindications for sux seems like the perfect motivation to just always use Roc and be done with it. I think this is a mistake. In some instances Sux is still the best choice for RSI. It has the most rapid onset of any paralytic and its shorter duration can be a benefit.

But if remembering that long list of specific contraindications to Sux seems intimidating and inclines you to avoid it as your go to RSI paralytic, don’t give up. Sux remains one of the safest, most useful, and reliable agents for RSI. And with only a few exceptions, most of the contraindictions on the list are related in some way to hyperkalemia. So instead of trying to memorize (and then worrying about if you will be able to recall) that long list of contraindications during critical moments, you can organize that list into two main categories:

  1. Those with conditions that intrinsically cause hyperkalemia
  2. Those with a conditions that cause an exaggerated response to succinylcholine.

Placing the contraindications within these two catogories makes it easier to remember (and thus recall) under the stress of managing a rapidly evolving airway. Let’s get into it.

Those with a disease that causes hyperkalemia.

Typically Sux administration will raise a person’s potasium about 0.5–1.0 mEq/L. This isn’t serious for someone with a potassium of 4.0 mEq/L, but it could be enough to kill someone if their potassium is already twice that. So in general, avoid giving Sux to anyone with a disease process that you know causes intrinsic hyperkalemia unless you already know that there potassium is in a safe range. This includes diseases such as renal failure, some malignancies, massive cellular injury from a crush injury, or toxicity from some drugs such as digitalis.

Those with a disease that cause an exaggerated response to Succinylcholine.

This category is a little hard to conceptualize. Because Sux acts on acetycholine receptors at the neuromuscular junction (NMJ), any disease process that effects the NMJ can cause an exaggerated response to Sux that may increase serum potassium far above the typical 0.5 -1.0 mEq/L after administration. This includes any upper neuron disease or process that causes extensive denervation of the skeletal muscle (such as in stroke patients, spinal cord injury), and any disease that specifically effects the NMJ such as severe burns. This includes some autoimmune disorders, muscular dystrophies and related myopathies.

The major distinction of diseases in this category is that since it is related to a physiologic response to a disease Sux is usually safe in the acute phase. This is why patients with an acute stroke, spinal cord injury or burn can still be safely intubated using Sux: because the up regulation of cholinergic receptors takes time; typically there is a short window of a few days before this occurs.

The other difference is that in the first category if you know your patient with renal failure has a normal potassium, then sux is going to be safe. In a patient with a burn injury you can’t know how the patient is going to respond and so sux in this group is usually a more absolute contraindication.

A patient with Guillan Barre Syndrome

We recently took care of a patient with Guillain-Barre Syndrome (GBS) who needed intubation for airway protection and ventilatory support, and it was a great moment to review why Sux is contraindicated in these patients.

GBS is an acute autoimmune disorder that effects peripheral netve function, and the body responds to the disease by increased Ach receptor production at the neuromuscular junction, so it falls into the category of a disease that causes an exaggerated response to Sux.

It’s also why these patients have an increased sensitivity to non-depolarizing neuromuscular (NdNM) blocking agents such as Rocuronium, and while these agents are safer than Sux, in this situation many give a reduced dose of an NdNM agent to avoid prolonged adverse effects.

GBS patients have a number of other specific airway related issues like autonomic instability that make them perilous to intubate, and there are some great FOAM resources available on how to safely manage these patients, including when to intubate them, but we were also fortunate enough to have doctor Mahendra Samaru with us that day to give us some quick pearls on this topic after the intubation. Here he is:

Bottom Line

Don’t give up on succinylcholine. It still has its uses in the right clinical scenario, and expands your RSI options.

If you’ve made the decision to intubate your GBS patient for airway protection or ventilatory support, RSI is appropriate but avoid the use of Succinylcholine.

For the same reason, GBS patients also have a sensitivity to non-depolarizing neuromuscular blockade (NdNM) so a reduced dose is also wise when using Rocuronium.

This article is part of the Protected Airway Series where we focus on the knowledge needed to safely navigate the intersection of critically ill physiology and endotracheal intubation.

The information presented here is based on my own personal views, opinions, and experience and do not represent those of my employer. I do not have any relevant financial disclosures to make. Any mention of drugs or medical products is done only in the setting of clinical and educational discussion, and does not represent my endorsement of those drugs or products. Do not use this website for medical advice. The information here is intended only for qualified medical personnel.

Succinylcholine Is Safe in Renal Failure RM Walls, reviewing Thapa S and Brull SJ. Anesth Analg 2000 Jul

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