What is the recommended muscle relaxant injection for treating respiratory intercostal muscle spasm?

Recommended Muscle Relaxant Injection for Respiratory Intercostal Muscle Spasm

For respiratory intercostal muscle spasm, suxamethonium (succinylcholine) at a dose of 1.0 mg/kg intravenously is the recommended first-line muscle relaxant injection due to its fast onset, high efficacy, and particular sensitivity of laryngeal and respiratory muscles to this agent. 1

Mechanism and Clinical Approach

Intercostal muscle spasm can cause significant respiratory compromise through:

• Restriction of chest wall movement
• Impaired ventilation
• Potential airway obstruction if laryngeal muscles are involved

First-line Treatment:

• Suxamethonium (Succinylcholine):
  • Dosing: 1.0 mg/kg IV 1
  • Onset: 30-60 seconds
  • Duration: 5-10 minutes
  • Particularly effective for respiratory muscle spasm due to high sensitivity of laryngeal muscles 1
  • Alternative routes if IV access is difficult:
    • Intramuscular: 4.0 mg/kg
    • Sublingual administration possible in emergencies 1

Important Precautions:

• In children under 3 years, add atropine 0.02 mg/kg to prevent bradycardia or cardiac arrest 1
• Be aware of contraindications to suxamethonium:
  • Primary muscle damage (myopathies)
  • Upregulation of nicotinic acetylcholine receptors 2
  • History of malignant hyperthermia

Alternative Options

If suxamethonium is contraindicated, non-depolarizing muscle relaxants can be effective:

• Rocuronium or Atracurium:

  • Dosing: 0.1 to 0.2 mg/kg IV 1
  • Lower doses are often sufficient for respiratory muscle relaxation
  • Requires adequate depth of anesthesia 1
  • Consider rocuronium at higher doses (>0.9 mg/kg) for rapid sequence situations 2

• Cisatracurium:

  • Preferred in patients with renal or hepatic impairment 2
  • More predictable pharmacokinetics in special populations

Adjunctive Treatments

• Propofol: Can be used as an adjunct (0.25 to 0.8 mg/kg) and is effective in approximately 77% of cases of laryngospasm 1, 3
• Inhalational anesthetics: Sevoflurane may help relieve tetany and muscle spasm 3

Monitoring and Safety

• Intraoperative monitoring of neuromuscular blockade is strongly recommended 1
• If using instrumental monitoring, the corrugator supercilii muscle is recommended as the monitoring site due to its sensitivity to muscle relaxants and kinetics comparable to laryngeal muscles 1
• Always have reversal agents readily available:
  • Sugammadex for rocuronium-induced blockade
  • Neostigmine with anticholinergic for other non-depolarizing agents

Special Considerations

• In severe cases of respiratory muscle spasm (such as in tetanus), a combination approach may be required
• Ensure immediate availability of suxamethonium and atropine, especially in emergency settings, as this reduces the incidence of severe airway obstruction accidents by nearly half 1
• Always have facilities for adequate artificial respiration available when administering any muscle relaxant 4

Remember that the choice of muscle relaxant should be guided by the clinical scenario, contraindications, and the need for rapid onset versus duration of action, with suxamethonium being the first choice for most acute respiratory muscle spasm situations.