Succinylcholine in EMS: What to Check Before and After RSI

Succinylcholine can produce the muscle relaxation needed for rapid sequence intubation within a short period of time. Using it safely requires understanding how the patient's history changes its risks and what to watch for after administration.

For paramedics, the important questions extend beyond onset and duration: Could this patient release a dangerous amount of potassium? Could paralysis last much longer than expected? Is a change in the monitor showing an airway problem, a medication reaction, or both?

Plan for unconsciousness, pain control, and ventilation

Succinylcholine causes paralysis without providing sedation or pain relief. A patient who cannot move may still be aware of what is happening.

When a neuromuscular blocker is used for RSI, an appropriate induction agent is part of the procedure. The team also needs a plan for continued sedation and analgesia after intubation. Lack of movement cannot establish that a paralyzed patient is comfortable or unconscious.

Prepare oxygenation, suction, ventilation equipment, and backup airway options before administering the medications. Drug selection and dosing should follow the agency's RSI protocol and medical direction.

Why muscle twitching comes before paralysis

At the neuromuscular junction, acetylcholine normally activates nicotinic receptors on the muscle membrane. These receptors are ion channels. Their activation allows an electrical change that initiates muscle contraction.

Succinylcholine activates these receptors as well. The initial stimulation can cause brief, visible muscle twitches called fasciculations.

The problem for further muscle activity is sustained depolarization. Nearby voltage-gated sodium channels remain inactivated, preventing normal repetitive signaling. The muscle becomes unable to respond effectively to additional nerve impulses, producing the initial depolarizing, or phase I, block.

This mechanism also explains why potassium matters: activating these channels allows potassium to leave muscle cells.

Screen for the patient who cannot tolerate potassium release

In patients without predisposing conditions, succinylcholine typically raises serum potassium by approximately 0.5 mEq/L. Certain patients can experience a much larger increase.

After denervation, significant burns, prolonged immobilization, and some other illnesses or injuries, acetylcholine receptors can increase in number and spread beyond their usual location. Succinylcholine can activate this expanded receptor population, producing extensive potassium release and potentially fatal dysrhythmias.

A focused history should identify:

Known or suspected hyperkalemia.
Major burns or multiple trauma beyond the acute phase.
Spinal cord injury or other conditions causing significant denervation.
Upper motor neuron injury with persistent motor deficits.
Skeletal muscle myopathies.
Prolonged immobilization or critical illness that raises concern for receptor changes.

These findings require careful contraindication screening and selection of an appropriate alternative when indicated. A normal potassium result does not eliminate the risk of an excessive potassium release in a patient with receptor upregulation.

Avoid treating a particular number of hours after injury as a universal safety boundary. Prescribing information states that the precise onset and duration of the increased risk are uncertain.

Ask about previous problems with anesthesia

Succinylcholine is normally cleared rapidly through metabolism by butyrylcholinesterase, also called pseudocholinesterase. This enzyme is produced in the liver and circulates in blood.

Unlike acetylcholine, succinylcholine is not rapidly broken down by acetylcholinesterase at the neuromuscular junction. Its effect ends as it diffuses away and is metabolized.

Some patients have inherited or acquired reductions in butyrylcholinesterase activity. In these patients, paralysis and apnea may persist for hours. The condition may remain unknown until a patient receives an affected medication.

A history of needing unexpected ventilatory support after surgery is therefore useful. Ask whether the patient or a relative has had prolonged paralysis or a serious anesthesia reaction, and communicate any findings to medical control.

If paralysis lasts unexpectedly, maintain ventilation, appropriate sedation, and monitoring while evaluating other causes. Where available, neuromuscular monitoring can help assess residual blockade. Do not assume continued paralysis means the induction medication is still providing adequate unconsciousness.

Recognize malignant hyperthermia as a metabolic emergency

Succinylcholine can trigger malignant hyperthermia in susceptible patients. Abnormal calcium regulation within skeletal muscle drives excessive metabolic activity, increasing oxygen demand, carbon dioxide production, and heat generation.

Susceptibility may be unrecognized. Previous uneventful anesthesia does not reliably exclude it, and a personal or family history of malignant hyperthermia is a critical part of medication screening. Known or suspected genetic susceptibility is a contraindication to succinylcholine.

Concerning changes after exposure include:

An unexplained rise in end-tidal carbon dioxide despite adequate ventilation.
Unexpected tachycardia.
Generalized rigidity or marked jaw muscle rigidity.
A rapidly rising core temperature.
Developing dysrhythmias or cardiovascular instability.

Do not wait for a dramatic fever before investigating a concerning pattern. Reassess tube position, ventilation, and equipment immediately while considering the medication exposure and associated findings.

When malignant hyperthermia is suspected, stop triggering agents, notify medical control and the receiving hospital, and initiate the applicable emergency pathway. Treatment includes ventilation with 100% oxygen, prompt IV dantrolene, management of hyperkalemia and other metabolic complications, and cooling when indicated. If dantrolene is unavailable in the field, coordinate urgent access without delaying supportive care or transport.

Keep other medication complications in view

Succinylcholine can also cause profound bradycardia, particularly in children and after repeat dosing. Severe allergic reactions are another possibility when hypotension or bronchospasm develops after administration.

The pediatric boxed warning addresses hyperkalemic rhabdomyolysis and cardiac arrest in children with previously unrecognized muscle disease. Pediatric use is reserved for emergency intubation and other specified urgent airway circumstances.

Short duration does not replace an airway rescue plan

A patient can become critically hypoxemic before spontaneous breathing returns. An anticipated short block therefore cannot serve as the backup plan for failed intubation.

Maintain oxygenation and move through the agency's rescue airway sequence when needed. After successful placement, use continuous waveform capnography with clinical assessment, pulse oximetry, ECG, and blood pressure monitoring. Reassess after patient movement and throughout transport.

The responsibility continues after the tube is placed. Document medication names, doses, administration times, airway confirmation, ongoing sedation, and any unexpected physiologic changes. Those details help the receiving team continue airway care and investigate unexpected responses.

Clinical references

Disclaimer: This article is for educational purposes only. Always follow your agency’s current local protocols and medical direction.