Muscle Relaxants Flashcards
What is the difference between a neuromuscular blocker and a centrally acting muscle relaxant?
Neuromuscular blockers act at the NMJ paralysing all striated muscle. Centrally acting muscle relaxants act on interneurones in the spine and weaken postural muscles
Dantrolene MOA.
Interupts excitation-contraction coupling by preventing release of Ca2+ from the sarcoplasmic reticulum (antagonises ryanodine receptors)
Botulinum toxin
MOA
Interferes with ACh release
Why would we want to use muscle relaxants?
- Help surgical access
- Facilitate IPPV
- Balanced anaesthesia
- Endotracheal intubation
What are the problems with muscle relaxant use during anaesthesia?
Unable to judge anaesthetic depth
Unable to fully ventilate patients lungs
What is the order of paralysis in dogs?
- Facial expression
- Tail
- Distal limb/neck
- Proximal limbs
- Throat
- Abdominal wall
- Intercostals
- Diaphragm (fairly resistant)
What is the MOA of peripherally acting nm blocking agents?
Compete with normal NMJ transmitter ACh at post-synaptic nicotinic ACh receptors
Name the categories of Non-depolarising agents.
What is their MOA?
- Amino-steroids
- Vecuronium
- Rocuronium
- Benzylisoquinoliniums
- Atracurium
- Cis-atracurium
Block post-synaptics NACh recepts and prevent ACh from activating them
Name the two depolarising agents.
Outline their MOA.
- Succinylcholine
- Suxamethonium
Firstly stimulate post-synaptic NACh receptors and then block them once the membrane becomes refractory
Which parameters are used to assess degree of block?
- Diaphragmatic movements - cleft in the capnograph
- Jaw tone
- Eye position
- Eye reflexes and movement
What is the gold standard for assessing degree of muscular block?
How can the twitch response be measured? (x4)
Apply electrical stimulus to a superficial nerve suppling a muscle where the twitch can be observed.
- Mechanomyography - m tension
- Acceleromyography - acceleration
- Electromyography - electrical response of muscle
- Phonomyography - sound of moving muscle
Outline the different patterns of electrical stimulation often used during twitch response measurment.
- Single stimuli
- Train of four stimuli - TOF
- Two bursts of stimulation - DBS
- Tetanic
Name three anticholinesterases and outline their mechanism of action.
Which are appropriate for reversal of muscle relaxants?
- Edrophonium - reversible
- Neostigmine - reversible carbamylation of enzyme
- Organophosphates - irreversible phosphorylation of enzyme
Why do anticholinesterases have side effects?
What are the potential side effects of their use?
They increase ACh at muscarinic receptors as well as nicotinic receptors (autonomic ganglia, parasympathetic terminals)
- Bradycardia
- Bronchoconstriction
- Salivation
- Defecation/urination
- Moisis
How are the side effects associated with Anticholinesterases combatted?
Add an anticholinergic such as atropine (edrophonium) or glycopyrrolate (neostigmine)
