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).

• 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

2. Drugs acting within spinal cord

3. Local anesthetics

Neuromuscular blocking agents

Pharmacology non-depolarizing NMBAs

Pharmacology - depolarizing NMBA

Further Reading

Publications

Refereed papers

• Recent references from PubMed and VetMedResource.
• Leece E A, Clark L (2017) Diabetes mellitus does not affect the neuromuscular blocking action of atracurium in dogs. Vet Anaesth Analg 44 (4), 697-702 PubMed.
• Clark L, Leece E A, Brearley J C 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, Marsico F F, Ascoli F O et al (2005) Neuromuscular 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 BJA Education.
• Dugdale A H, Adams W A, Jones R S (2002) The clinical use of the neuromuscular blocking agent rocuronium in dogs. Vet Anaesth Analg 29 (1), 49-53 PubMed.
• Adam W A, Robinson K J, Mark Senior J et al (2001) The use of the nondepolarizing neuromuscular blocking drug cis-atracurium in dogs. Vet Anaesth Analg 28 (3), 156-160 PubMed.

Other sources of information

• Flaherty D & Auckburally A (2016) Neuromuscular blocking agents. In: BSAVA Manual of Canine and Feline Anaesthesia and Analgesia. 3^rd 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.