Canis ISSN: 2398-2942

Muscle relaxant: overview

Contributor(s): Sheilah Robertson, Marieke de Vries

Significance

Introduction

  • General anesthesia is a triad consisting of narcosis (drug induced sleep), analgesia and muscle relaxation.
  • Muscle relaxation allows: precision surgery to be performed (eg intra-ocular surgery); prevents unexpected reflex movement; reduces traction needed to expose deep structures and therefore reduces tissue damage and post-operative discomfort; facilitates mechanical ventilation of lungs.
  • Movement during anesthesia is usually of 3 types:
    • Involuntary movement resulting from local (spinal) reflexes in response to noxious stimuli;
    • Tonus resulting from slow asynchronous discharge from ventral horn in spinal cord;
    • Muscular contraction as a myogenic response to direct traction (largely beyond pharmacological control).
If the movement is purposeful or in response to a painful stimulus, reassess the level of anesthesia.
  • Surgical muscle relaxation can be produced in 5 ways:
  1. General anesthetics General anesthesia: overview.
  2. Centrally acting muscle relaxants - drugs acting in spinal cord to block impulse transmission.
  3. Local anesthetics Local anesthesia: overview.
  4. Peripherally acting muscle relaxants, or neuromuscular blocking agents Anesthesia: non-depolarizing neuromuscular blockade.
  5. A combination of these.

1. General anesthesia

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2. Drugs acting within spinal cord

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3. Local anesthetics

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Neuromuscular blocking agents

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Pharmacology non-depolarizing NMBAs

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Pharmacology - depolarizing NMBA

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Further Reading

Publications

Referred papers

  • Recent references from VetMed Resource and PubMed.
  • Leece E A, Clark L (2017) Diabetes mellitus does not affect the neuromuscular blocking action of atracurium in dogs. Vet Anaesth Analg doi: 10.1016/j.vaa.2016.07.011 PubMed.
  • Clark L et al (2012) Diabetes mellitus affects the duration of action of vecuronium in dogs. Vet Anaesth Analg 39 (5), 472-479 PubMed.
  • Sarrafzadeh-Rezaei F, Clutton R E (2009) The effect of volatile anaesthetics on the relative sensitivity of facial and distal thoracic limb muscles to vecuronium in dogs. Vet Anaesth Analg 36(1), 55-62 PubMed.
  • Kastrup M R et al (2005) Neurmuscular blocking properties of atracurium during sevoflurane or propofol anaesthesia in dogs. Vet Anaesth Analg 32 (4), 222-227 PubMed.
  • Appiah-Ankam J, Hunter J M (2004) Pharmacology of neuromuscular blocking drugs. Contin Educ Anaesth Crit Care & Pain 4(1), 2-7.
  • Dugdale A H et al (2002) The clinical use of the neuromuscular blocking agent rocuronium in dogs. Vet Anaesth Analg 29 (1), 49-53 PubMed.
  • Adam W A et al (2001) The use of the nondepolarizing neuromuscular blocking drug cis-atracurium in dogs. Vet Anaesth Analg 28 (3), 156-160.

Other sources of information

  • Flaherty D & Auckburally A (2016) Neuromuscular blocking agents. In: BSAVA Manual of Canine and Feline Anaesthesia and Analgesia. 3rd edn. Eds. Duke-Novakovski T, de Vries M, Seymour CJ BSAVA, Quedgeley (UK). Chapter 16.
  • Martinez E A (1999) Newer neuromuscular blockers, is the practitioner ready for muscle relaxants? Vet Clin North Am Small Anim Pract 29(3), 811-817 PubMed.


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