Can muscle relaxants be safely used in patients with rhabdomyolysis?

Muscle Relaxants in Rhabdomyolysis: Safety and Contraindications

Muscle relaxants should NOT be used in patients with active rhabdomyolysis, particularly succinylcholine which is absolutely contraindicated due to the risk of life-threatening hyperkalemia from muscle membrane damage. Non-depolarizing agents can be used with extreme caution if absolutely necessary for anesthesia, but require dose reduction and intensive neuromuscular monitoring. 1

Critical Contraindications

Succinylcholine (Absolute Contraindication)

• Succinylcholine is contraindicated in all cases of primary muscle damage, including rhabdomyolysis, as it induces generalized muscle contraction that can worsen rhabdomyolysis and cause life-threatening hyperkalemia. 1
• The mechanism involves depolarization of already-damaged muscle membranes with massive potassium efflux from injured myocytes. 2
• This contraindication applies to any condition causing muscle membrane damage or receptor upregulation, which is present in rhabdomyolysis. 1

Non-Anesthetic Muscle Relaxants

• Cyclobenzaprine has been directly associated with causing rhabdomyolysis in overdose situations and should be avoided in patients with existing muscle damage. 3
• The combination of muscle relaxants with high-dose corticosteroids has been implicated in precipitating rhabdomyolysis in critically ill patients. 4

If Neuromuscular Blockade is Absolutely Required

Agent Selection

• If anesthesia is unavoidable, use benzylisoquinoline muscle relaxants (atracurium or cisatracurium) as they have organ-independent elimination and are safer in the setting of muscle damage. 1
• Rocuronium shows significantly increased sensitivity in patients with primary muscle damage, with prolonged onset and recovery times. 1
• Patients with muscle damage demonstrate very significant increases in sensitivity to all non-depolarizing agents, requiring substantial dose reductions of 50-75%. 1

Essential Monitoring

• Neuromuscular blockade monitoring is mandatory when any muscle relaxant is used in patients with muscle disease or damage. 1
• Train-of-four (TOF) ratio monitoring by EMG should be performed to guide dosing and prevent overdosing. 1
• If TOF ratio is less than 0.9 before neuromuscular blockade, sensitivity to muscle relaxants is greater and doses must be substantially reduced. 1

Reversal Strategy

• Sugammadex is the preferred reversal agent for steroidal muscle relaxants in patients with muscle disease, as neostigmine can cause additional complications including effects on muscle action potential and rhythm disturbances. 1
• Neostigmine and atropine are difficult to manage in primary muscle damage due to drying of secretions, potential cardiac conduction disorders, and central effects. 1

Clinical Context and Pitfalls

Key Considerations

• The primary concern in rhabdomyolysis is preventing acute renal failure through aggressive fluid resuscitation, not administering muscle relaxants. 5
• Any medication that could worsen muscle membrane damage or precipitate further myocyte injury should be avoided. 6
• The risk-benefit calculation heavily favors avoiding muscle relaxants entirely unless the patient requires emergency surgery or intubation where alternatives are not feasible. 1

Common Pitfall

• Do not assume that "muscle relaxants" for spasm management (like cyclobenzaprine, methocarbamol) are safe in rhabdomyolysis—these are contraindicated and can worsen the condition. 3
• The combination of neuromuscular blocking agents with high-dose steroids in critically ill patients has been specifically associated with precipitating severe rhabdomyolysis. 4