Muscle Relaxant Flashcards
What are muscle relaxant and what are the different types
Depolarising
Non-depolarising
They act on the post-synaptic receptor at the NMJ prevents muscle firing
What are depolarising agents and what do they do
Suxamenthonium succycholine is the only one commonly used
It is a partial agonist for the Ach rectors
And causes initial fasciculation though depolarising the of the post synaptic membrane and the paralysis by inhibiting the restoration of normal membrane polarity
What is suxamethonium rapidly deactivated by
Plasma cholinesterases
Why has it been most popular analytic agent in rapid sequence induction
Rapid onset
Short duration
Rapid onset lessens the time lessons the time between induction and intubation
Dec risk of aspiration and potential hypoxia
The short duration men that if intubation isn’t possible
THe patient regains muscle tone
And starts protecting there own airway again - quickly
Side effects of sux
Inc K+
Enough to raise the plasma K+ by 0.5-1mmol/l so avoid in burns and paraplegia
Beware k+ liberation is inc with MS, GBS, stroke and crush injury
Inc IOP - risk of vitreous extrusion
30% post op muscle pains
Repeated doses of sux at lead to bradycardia -more common in children - tx atropine
Beware sux apnoea
What are non-depolarising agents
Competitive antagonists of Ach - they compete with Ach at the NMJ
But without reproducing depolarisation -no fasciculations
How can non -depolarising agent be reversed
anticholinesterases
(Neostigmine)which lead to an inc amount of Ach available at the NMJ
Wen are non-depol agents used
Balanced anaesthesia
To facilitate IPPV and surgery
Example no depol agents
Rocuronium lasts 20mins
Can non-depol agent rocuronium be used for RSI
Yes it can the induction dose has been increased from 0.6 Ideal body weight kg to 0.9-1.2 this has reduced the induction time to 60 seconds
It lasts 20 mins so initially could not be used for RSI but now due to sugammadex a reversal agent for rocuronium
It can be reversed faster than the time sux takes to wear off
SE rocuronim
Known to cause anaphylaxis
Excretion via liver
Which non -depol agent is used if cardio vascular stability is important
Vecuronium
Lasts 30-40 mins
Sugammadex also reverses it
What non depol is the drug of choice in renal and liver failure
Atracurium
Lasts 25 min
Metabolism spontaneous Hoffman elimination
What do do with neuromuscular blockers in MG
Myasthenia patients are resistant to sux
And v sensitive to non depol
So effect may be longer and lower doses needed
Need to work with senior anaesthetist
