Muscle Relaxants Flashcards
Dose of suxamethonium
75-100mg IV
Describe the action of suxamethonium
Depolarising agent
Double molecule of Ach
Binds with Ach receptors causing wave of depolarisation in muscles
Metabolised by plasma cholinesterase
However metabolised more slowly than Ach producing a prolonged period of depolarisation
Further depolarisation cannot occur until suxamethonium has been removed from Ach receptors
Causes a short period of paralysis
Duration of suxamethonium block
neuromuscular blockade produced in less than 1 minute
lasts for 3-5 minutes
Side effects of suxamethonium
Muscle pains due to fasciculation Increased intraocular, intracranial and intragastric pressure Hyperkalemia Bradycardia Anaphylaxis Malignant Hyperpyrexia Prolonged paralysis (dual block) Scoline Apnoea
What is dual block
Prolonged paralysis may occur following high or repeated doses by causing a non depolarising type block.
What is scoline apnoea
Absence of or abnormal plasma cholinesterase
leads to a prolonged effect from suxamethonium
risk of awareness as patient not breathing so not getting enough anaesthetic agent
patient needs to be sedated and ventilated until effects subside
differences between depolarising and non depolarsing muscle relaxants
Depolarising bind with ach receptors while non depolarising block ach receptors on neuromuscular junction
Depolarising works in less than a minute while non depolarising take 2-3 mins
Depolarising causes fasciculations non depolarising doesnt
Depolarising metabolised by plasma cholinesterase at neuromuscular junction while non depolarising not metabolised at neuromuscular junction. Instead when level of Ach becomes sufficient to displace agent from receptor sites the blocking effect is overcome
Non depolarising agents
Pancuronium Vecuronium Mivicurium Atracurium Rocuronium
How does neostigmine reverse non-depolarising muscle relaxants
Neostigmine is an anticholinesterase. It inhibits breakdown of acetycholine by competing with acetylcholine for attachment to acetylcholinesterase
Why is glycopyrolate given along with neostigmine
To counteract the muscarinic effects of neostigmine.
What are the muscarinic effects of acetylcholine
Acetylcholine is not only a neuromuscular transmitter at the NMJ causing nicotinic effects it also a major neurotransmitter of the autonomic nervous system where it exerts muscarinic effects so leads to bradycardia,increased salivation, blurred vision and increased bladder and bowel contractions
Methods of monitoring neuromuscular function
Clinical assessment
Peripheral nerve stimulator
How many twitches must be absent to obtain adequate conditions for abdominal surgery
3
How many twitches must be present for reversal of muscle relaxant
At least 2nd twitch must be visible
Following administration of muscle relaxant which twitch disappears first ?
Fourth disappears first followed by 3rd, 2nd and 1st
