November 18, 2022

Dear Colleagues,

Welcome back to EMS-I’s Pharmacy Phriday.  In the last edition, the focus was on the use of Etomidate in Rapid Sequence Intubation (RSI).  This week’s focus is on Succinylcholine, the neuromuscular blocking agent used within UH protocols RSI algorithm. 

In RSI, two types of neuromuscular blocking agents can be used.  One is a depolarizing agent, and the other is a non-depolarizing agent.  The depolarizing agent Succinylcholine (the only one in this class presently) causes a neuromuscular block by depolarizing the membrane and then does not allow repolarization.  As the depolarization persists, this mechanism causes a common side effect of the medication, fasciculations, or uncoordinated contractions of the muscle fibers.  The effect quickly results in skeletal muscle paralysis that is typically short-lived, allowing the intubation.  A non-depolarizing agent, such as Rocuronium, is effective by competing with and blocking acetylcholine’s neurotransmitter action, preventing the fibers from depolarizing.  These medications are known to cause muscle relaxation for longer periods than the depolarizing agent. 

Both agents have pros and cons to their use.  UH protocols currently allow the use of Succinylcholine for the RSI procedure.  Due to its rapid onset and short duration of action, it is often recommended as the drug of choice in emergencies where immediate airway management is required. The drug's rapid onset allows for quick intervention and control of the airway, and its short duration is advantageous when endotracheal intubation is not possible.

Succinylcholine has no known effect on consciousness or pain perception and, therefore, should only be used after the use of an anesthetic such as Etomidate.  The medication should only be administered once the provider and team are prepared with a plan and available equipment to manage the patient’s airway, as apnea is sure to follow.  Once administered, the provider can expect to witness the fasciculations as mentioned above, with progressive paralysis beginning with the eyelids and jaw, progressing to the limbs and abdomen, and finally to the diaphragm and intercostal muscles.  The time of onset is typically less than 60 seconds and will last up to approximately 6 minutes.

Succinylcholine has numerous contraindications that the provider should consider before use. 

• Hyperkalemia is the most common adverse effect of succinylcholine administration, attributed to the drug's stimulatory effect on skeletal muscles. The healthy patient may be able to manage this increase in potassium, but the resulting electrolyte imbalance can cause serious side effects such as heart palpitations, dysrhythmias, or cardiac arrest in the compromised patient.  The concern of hyperkalemia is also the reason Succinylcholine is contraindicated in the patient with renal failure, recent trauma, crush injury, burns, a history of Muscle Dystrophy, Multiple Sclerosis, Lou Gehrig’s disease (ALS), or other skeletal muscle myopathies. 

• Succinylcholine administration has been associated with the onset of malignant hyperthermia (MH), a potentially fatal hypermetabolic state of skeletal muscle (recall the constant state of depolarization that occurs with the medication).  Therefore, a history of MH in the patient or the patient’s family is considered a contraindication.  Malignant hyperthermia could present after the administration of the medication as intractable spasms of the jaw muscles (trismus or lockjaw), which may progress to generalized rigidity, increased oxygen demand, tachycardia, tachypnea, and profound rise in body temperature.  Continuous monitoring of temperature and expired CO2 is recommended as an aid to early recognition of malignant hyperthermia.



• A “Blackbox” warning, the strictest and most serious type of warning that the FDA gives a medication, exists for the use of Succinylcholine for infants and children.  The use of Succinylcholine in this age group is not approved within the UH protocols and another contraindication.

The dosage for Succinylcholine is a single dose of 1-2mg/kg IV/IO. The medication is predominantly supplied as 200mg in 10ml. Though the medication does not have a direct effect on the myocardium, continuous cardiac monitoring is recommended due to the concern of possible hyperkalemia.  The provider should also be sure to perform end-tidal carbon dioxide and pulse oximetry monitoring. 

Once again, know that UH protocol allows only those fire departments and EMS agencies approved by their medical director to perform RSI.  Agencies that are interested in receiving permission to use the skill would need to contact their medical director for approval and additional training.

Have a wonderful Thanksgiving! Stay safe!

Sincerely,

The UH EMS-I Team

University Hospitals