Flashcards in Katzung 12th ed - Chapter 27 - General Anaesthetics - Muscle Relaxants (1) Deck (19):
Review the mechanism of neuromuscular transmission at the motor end plate.
Acetylcholine is released from the motor nerve terminal, diffuses across the synaptic cleft, and binds to nicotinic receptors on the motor end plate. The nicotinic receptor (an ion channel) then opens, and there is sodium influx, causing depolarization.
Structurally, all skeletal muscle relaxants are similar to _________.
What is the basic mechanism of action of non-depolarizing muscle relaxants?
They inhibit the opening of the nicotinic ACh receptor ion channel, preventing sodium influx, and thus preventing depolarization.
What is the basic mechanism of action of depolarizing muscle relaxants?
They function just as ACh, causing motor end plate depolarization by opening sodium channels. However, they are not metabolized effectively at the synapse (not like ACh, which is rapidly broken down by AChE), and so the membrane does not repolarize, and so no further action potentials can be propagated.
Name one commonly used depolarizing muscle relaxant.
Name one commonly used non-depolarizing muscle relaxant that is NOT a steroid.
Atracurium (it is an isoquinolone).
Name three commonly used non-depolarizing muscle relaxants that are steroids.
What is the dose of suxamethonium given for use in intubating?
What is the dose of vecuronium given for use in intubating?
Describe some of the adverse effects of depolarizing muscle relaxants.
Muscle pain (the most common AE)
Bradycardia (can be prevented by premedicating with atropine).
Hyperkalaemia (particularly in burns and renal failure)
Raised IOP, raised ICP, raised intragastric pressure.
Malignant hyperthermia (rare)
Describe the metabolism, and thus the duration of action, of suxamethonium.
Onset of action: 30 seconds.
Duration of action 5-10 minutes, due to rapid breakdown by pseudo-cholinesterase.
What are the onsets of action of the non-depolarizing muscle relaxants?
Rocuronium - very fast
Vecuronium - 2-3 minutes
Pancuronium - 2-3 minutes
What is the (most significant) route of elimination for pancuronium, vecuronium and rocuronium?
Pancuronium - kidney
Vecuronium - liver
Rocuronium - liver
What is the difference in duration of action of pancuronium, vecuronium and rocuronium? Explain a mechanism behind this difference.
Pancuronium has a longer duration of action than the others, because it is eliminated by the kidney (occurs more slowly), whilst the others are eliminated more quickly by the liver.
Pancuronium - 35-60 minutes
Vecuronium - 20-35 minutes
Rocuronium - 20-35 minutes
What is dantrolene used for?
To treat malignant hyperthermia.
Describe an adverse effect of suxamethonium encountered by less than 1% of the population.
Prolonged apnoea, up to several hours, due to their extreme deficiency of pseudo-cholinesterase.
Which muscle relaxant is associated with histamine release?
How is atracurium eliminated?
Hofmann elimination (non-liver, non-renal)