What is the recommended intravenous (IV) muscle relaxer for immediate muscle relaxation?

Recommended Intravenous Muscle Relaxers for Immediate Muscle Relaxation

For rapid-sequence intubation requiring immediate muscle relaxation, succinylcholine 1 mg/kg IV is the first-line agent in adults, with rocuronium 0.6-1.2 mg/kg IV as the alternative when succinylcholine is contraindicated. 1

Primary Agent: Succinylcholine

Dosing

• Adults: 0.6 mg/kg IV (range 0.3-1.1 mg/kg) 2
• Pediatric dosing (age-specific): 1
  • <1 month: 1.8 mg/kg
  • 1 month to 1 year: 2.0 mg/kg
  • 1-10 years: 1.2 mg/kg

  • 10 years: 1.0 mg/kg

Onset and Duration

• Onset: Neuromuscular blockade develops in approximately 1 minute, with satisfactory intubation conditions at 30-45 seconds IV 1, 2
• Duration: Maximum blockade persists for 2 minutes, with recovery within 4-6 minutes (5-10 minutes total) 1, 2
• Intramuscular administration (when IV access unavailable): 3-4 mg/kg IM, onset 2-3 minutes 2

Critical Contraindications

Succinylcholine is absolutely contraindicated in: 1

• Primary muscle damage (myopathies)
• Chronic motor deficit with upregulation of nicotinic receptors
• History of malignant hyperthermia
• Severe burns/crush injury
• Spinal cord injury
• Neuromuscular disease

Important Caveats

• Pretreatment with atropine (0.02 mg/kg, minimum 0.1 mg, maximum 1 mg) is recommended to prevent bradycardia or asystole, particularly in children <3 years 1
• Risk of hyperkalemia-induced cardiac arrest, especially in undiagnosed myopathy in boys <9 years old 1
• Increased serum potassium is life-threatening in contraindicated conditions 1

Alternative Agent: Rocuronium

When to Use

Rocuronium is the recommended alternative when succinylcholine is contraindicated 1

Dosing

• Rapid-sequence intubation: 0.9-1.2 mg/kg IV 1
• Standard intubation: 0.6 mg/kg IV 1, 2
• Lower doses (0.1-0.2 mg/kg) sufficient for airway obstruction with adequate anesthesia depth 1, 3

Onset and Duration

• Onset: Satisfactory intubation conditions at approximately 60-90 seconds 1
• Duration: 30-45 minutes (dose-dependent) 1
• Significantly longer than succinylcholine, requiring reversal planning 1

Reversal Considerations

• Sugammadex allows rapid reversal of rocuronium 1
• Dose: 2 mg/kg for partial blockade (two TOF responses), 4 mg/kg for deep blockade 1
• Sugammadex availability makes rocuronium increasingly viable as primary agent 4

Alternative Non-Depolarizing Agent: Atracurium

Clinical Applications

• Dosing for airway obstruction: 0.1-0.2 mg/kg IV (when adequate anesthesia depth achieved) 1, 3
• Standard intubation: 0.1 mg/kg IV 1
• Onset: Approximately 2 minutes to satisfactory intubation conditions 1
• Duration: 45-90 minutes (dose-dependent) 1

Specific Advantages

• Preferred in renal or hepatic failure due to organ-independent elimination (Hofmann elimination and ester hydrolysis) 3, 5
• No dose modification required in organ dysfunction 3
• Lower anaphylaxis risk compared to succinylcholine 1

Monitoring Requirement

• Peripheral nerve stimulator monitoring of corrugator supercilii muscle recommended for optimal dosing 3

Clinical Decision Algorithm

For emergency rapid-sequence intubation:

1. First choice: Succinylcholine 1 mg/kg IV (if no contraindications) 1
2. If contraindicated: Rocuronium 0.9-1.2 mg/kg IV 1
3. If renal/hepatic failure: Consider atracurium 0.1 mg/kg IV 3, 5

For non-emergency intubation:

• Rocuronium 0.6 mg/kg IV or atracurium 0.1 mg/kg IV are appropriate 1, 3

For airway obstruction/laryngospasm:

• Succinylcholine remains most effective 1
• Low-dose rocuronium or atracurium (0.1-0.2 mg/kg) acceptable if adequate anesthesia depth 1, 3

Essential Safety Measures

• Ventilatory support must be immediately available with all muscle relaxants 1
• Personnel skilled in airway management must be present 1
• Age-appropriate equipment for suctioning, oxygenation, intubation, and ventilation required 1
• Never administer without ability to provide positive pressure ventilation 1, 2