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Succinylcholine: vital drug or dinosaur? Succinylcholine (sux) has the wonderful advantage of rendering a patient paralyzed in less than a minute, and the discouraging disadvantage of a long list of side effects that make the drug problematic.
I would never begin an anesthetic without succinylcholine being immediately available. No other muscle relaxant supplies as rapid an onset of action and as short a duration of action. An intravenous dose of 1 mg/kg of succinylcholine brings complete paralysis of the neuromuscular junction at 60 seconds, and recovery to 90% of muscle strength in 9 – 13 minutes. (Miller’s Anesthesia, 7th Edition, 2009, Chapter 29, Pharmacology of Muscle Relaxants and Their Antagonists). If a patient has an acute airway disaster on induction such as laryngospasm or pulmonary aspiration, no drug enables emergency endotracheal intubation as quickly as succinylcholine. That said, I never use succinylcholine unless I have to. The drug has too many side effects and rocuronium is often a better choice. For an elective anesthetic on a patient who has fasted and has an empty stomach, one almost never needs to use succinylcholine. If you do use sux, you are exposing your patient to the following side effects:
1. Myalgias. Your patient complains to you the following day, “Doc, I feel like I was run over by a truck.” Because the majority of anesthetics are currently done on outpatients, and because you do not personally interview these patients the following day, you won’t be aware of the degree of muscle pain you’ve induced by using the depolarizing relaxant succinylcholine. Published data quantitates the incidence of post-succinylcholine myalgia as varying from 0.2 % to 89% (Brodsky JB, Anesthesiology 1979; 51:259-61), but my clinical impression is that the number is closer to 89% than it is to 0.2%. Myalgias aren’t life-threatening, but if you ever converse with your patient one day after succinylcholine and they complain of severe muscle aches, you’ll wish you’d chosen another muscle relaxant if possible.
2. Risk of cardiac arrest in children. Succinylcholine carries a black box warning for use in children. Rare hyperkalemia and ventricular arrhythmias followed by cardiac arrest may occur in apparently healthy children who have an occult muscular dystrophy. The black box warning on succinylcholine recommends to “reserve use in children for emergency intubation or need to immediately secure the airway.”
3. Hyperkalemia, with an average increase of 0.5 mEq in potassium concentration after intravenous succinylcholine injection.
4. Cardiac arrest in patients with a history of severe trauma, neurologic disease or burns. There’s a risk of cardiac arrest with succinylcholine use in patients with severe burns, major trauma, stroke, prolonged immobility, multiple sclerosis, or Guillian-Barré syndrome, due to an up-regulation of acetylcholine. The increase in serum potassium normally seen with succinylcholine can be greatly increased in these populations, leading to ventricular arrhythmia and cardiac arrest. There is typically no risk using succinylcholine in the first 24 hours after the acute injury.
5. Cardiac arrhythmias. Both tachy and bradycardias can be seen following the injection of succinylcholine.
6. Increase in intraocular pressure, a hazard when the eye is open or traumatized.
7. Increase in intragastric pressure, a hazard if gastric motility is abnormal or the stomach is full.
8. Increase in intracranial pressure, a hazard with head injuries or intracerebral bleeds or tumors.
9. Malignant Hyperthermia (MH) risk. The incidence of MH is low. A Danish study reported one case per 4500 anesthetics when triggering agents are in use (Ording H, Dan Med Bull, 43:111-125), but succinylcholine is the only injectable drug which is a trigger for MH, and this is a disincentive to use the drug routinely.
10. Prolonged phase II blockade. Patients who have genetically abnormal plasma butyrylcholinesterase activity have the risk of a prolonged phase II succinylcholine block lasting up to six hours instead of the expected 9 – 13 minutes. If you’ve ever had to stay in the operating room or post-anesthesia recovery room for hours with a ventilated patient after their surgery ended because your patient incurred prolonged blockade from succinylcholine, you won’t forget it, and you’ll hope it never happens again.
What does a practicing anesthesiologist use instead of succinylcholine? Rocuronium.
A 0.6 mg/kg intubating dose of the non-depolarizing relaxant rocuronium has an onset time to maximum block of 1.7 minutes and a duration of 36 minutes. The onset time can be shortened by increasing the dose to a 1.2 mg/kg, a dose which has an onset time to maximum block of 0.9 minutes and a duration of 73 minutes. These durations can be shortened by reversing the rocuronium blockade as soon as one twitch is measured with a neuromuscular blockade monitor. Thus by using a larger dose of rocuronium, practitioners can have an onset of acceptable intubation conditions at 0.9 X 60 seconds = 54 seconds, compared to the 30 seconds noted with succinylcholine, without any of the 10 above-listed succinylcholine side effects. The duration of rocuronium when reversed by neostigmine/glycopyrrolate can be as short as 20 – 25 minutes, a time short enough to accommodate most brief surgical procedures.
Now that sugammadex is commercially available, we can reverse rocuronium blockade in seconds, making rocuronium shorter in duration than succinylcholine.
Here is a list of surgical cases once thought to be indications for using succinylcholine, which I would argue are now better served by using a dose of rocuronium followed by early reversal with sugammadex:
1) Brief procedures requiring intubation, such as bronchoscopy or tonsillectomy.
2) Procedures which require intubation plus intraoperative nerve monitoring, such as middle ear surgery.
3) Procedures requiring intubation of obese and morbidly obese patients who appear to have no risk factors for mask ventilation.
4) Procedures requiring full stomach precautions and cricoid pressure, in which the patient’s oxygenation status can tolerate 54 seconds of apnea prior to intubation. This includes emergency surgery and trauma patients. Miller’s Anesthesia (Chapter 72, Anesthesia for Trauma) discusses the induction of anesthesia and endotracheal intubation for emergency patients who are not NPO and may have full stomachs. Either succinylcholine or rocuronium can be used, with succinylcholine having the advantage of a quicker onset and the 1.2 mg/kg of rocuronium having the advantage of lacking the 10 side effects listed above. The fact that succinylcholine takes 9 – 13 minutes to wear off makes it riskier than rocuronium, which can be reversed in seconds by sugammadex. Waiting for 9 minutes for a return to spontaneous respirations after succinycholine would be associated with severe hypoxia.
On the other hand, succinylcholine is the sole recommended muscle relaxant for:
1) Cesarean sections. Miller’s Anesthesia (Chapter 69, Anesthesia for Obstetrics) still recommends thiopental and succinylcholine for Cesarean sections that require general anesthesia, and I would be loath to disagree with our specialty’s Bible.
2) Electroconvulsive therapy (ECT) for depression. Miller’s Anesthesia (Chapter 79, Anesthesia at Remote Locations) recommends partial muscle relaxation during ECT, and recommends small doses of succinylcholine (0.5 mg/kg) to reduce the peripheral manifestations of the seizure and to prevent musculoskeletal trauma to the patient.
3) Urgent intubation or re-intubation in a patient when every second counts, e.g. a patient who is already hypoxic. A subset of this indication is the patient who is being mask-induced and becomes hypoxic and requires intramuscular succinylcholine injection.
4) Laryngospasm either during mask induction or post-extubation, in which the patient requires urgent paralysis to relax the vocal cords.
In conclusion, most indications for muscle relaxation are better handled by using the non-depolarizing drug rocuronium rather than succinylcholine. However, because of the four recommended uses for succinylcholine listed in the previous paragraph, none of us would ever practice anesthesia without a vial of succinylcholine in our drawer for immediate availability.
I try very, very hard to minimize my use of succinylcholine, and so should you. But to answer our original question… succinylcholine is still a vital drug and not a dinosaur at all.
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