Module 4 Muscle relaxants Flashcards
Where does Ach bind on the post junctional membrane
It binds on the Nicotinic cholinergic receptors
What is the enzyme that breaks down the Ach
Acetylcholinesterase
What are the 3 compounds that block ACh binding
- Mg
- Aminoglycosides
- Botox
What are the 3 locations at which you can block a motor impulse and give an example for each
- Motor nerve: Local anesthetics
2.NMJ: IV muscle relaxants - Receptors inside the cells: Dantrolene
What is the mode of action of a depolarising agents
They act as non competitive inhibitors binding to the nicotinic receptors and so causing depolarisation
What is the mechanism of nondepolarizing agents
They bind to the nicotinic receptors but do not activate the receptors and so do not cause depolarisation of the membrane
What is the effective dose 95
This is the dose that would cause muscle relaxation in 95% of people
What are the 5 factors that make muscle relaxants more potent
- Inhaled agents and aminoglycosides
- Low K and Ca
- Acidosis
- Cold for depolarising and heat for non depolarising
- Myasthenia gravis in nondepolarizing
What are the surgical indications for muscle relaxants
- Facilitate surgical access
- If immobilisation of the field is required
What are the anaesthetic factors that indicate muscle relaxants
- Intubation
- Controlled ventilation is required
- Prone
What are the patient factors that indicate for muscle relaxants
Critically ill patients
What is the structure of sux
2 Ach molecules that are stuck together
What is the most short acting muscle relaxant
Sux
What is the enzyme that metabolises sux
Pseudocholineesteases
What is a complication that can occur from sux and what causes it
Scoline apneoa: This is caused by a lack of the pseudocholinesterase
What are some of the complications of sux
- Histamine release
- Anaphylaxis
- Bradycardia
- Muscle pain
- Hyperkalemia
What are the 2 main classes of non depolarising MR
Benylisoquilines: Curare based [All end in curium]
Aminosterids: [All end in ronuim]
What is the dose of nondepolarizing agents based on
Lean body mass
How are non depolarising agents metabolised
- Hoffman degredation
- Hepatic
What patients can get Vecuronium and which cant
Can:
Cardiovascular
Renal
Asthma
Cant:
Liver
Which patients can get Roc
Cardiovascular
WHich patients can get Atracurium and which cant
Can
Renal and liver patients
Cant
Asthma
What is the MOA of non depolarising reversal agents
They work by increasing the conc. of Ach this is because the non depolarising agents are competitive inhibitors and so the reversal agents inhibit acetylcholinesterase
What is the MOA of neostigmine
Acetylcholinesterase inhibitor
What is the side effect of neostigmine
It also inhibits the acetylcholinesterases at the muscarinic receptors
What can be done to counter the effects of neostigmine
Give and anticholinergic for the muscurinic reseptors e.g. glycopyrralate or atropine
What is needed to check the readiness for reversal
Peripheral nerve stimulator, it should have atleast 3 twitch present in a train of 4
What are some of the signs of an inadequate reversal
Looks like a fish out of water
Jerky respiration
Tracheal tug
Restlessness
Inability to lift the head from the pillow
Poor ability to cough
What is the order of steps taken if the dose of reversal was inadequate
- Exclude other causes e.g.hyper or hypocarbia and CVS
- Maintain the ventilation
- Reverse any specific causes
- Check PNS
- Give additional doses of neostigmine
What is the MOA of sugammadex
It works by binding to rocuronium
What are the 2 main benifits of sugammadex
- It can be used at any time and there is no need to to wait until the patient is reversible
- It does not affect the muscarinic receptors
What does the binding of Ach cause on the postsynaptic neuron
It causes the influx of Na
How is acetylcholine stored
As vesicles in the presynaptic motor axon
Which is the most rapidly acting muscle relaxant
Sux
How should suxamethonium be reversed
Waiting for pseudocholinesterase to break it down
In which situation is suxamethonium contraindicated?
- Drug allergies
- Scoline apnoea
- MH
- Areas of hyperkalcemia e.g. renal failure, paralysis, crush and burns
Which is the only non-depolariser that can be used for rapid sequence induction?
Rocuronium
