Neuromuscular Blocking Flashcards
what may be an effect of ketamine being given alone as an anaesthetic drug?
muscle ridgidity
what methods can be used to provide muscle relaxation under anaesthesia?
local anaesthetics
benzodiazipines
alpha-2 adrenoreceptor agonists
guaiphenesin (GGE)
neuromuscular blocking drugs
what is often sufficient to provide muscle relaxation for most procedures?
GA
what type of drug is guaiphenesin (GGE)?
centrally acting muscle relaxant
what areas of the body does guaiphenesin (GGE) work at?
internuncial neurones of the spinal cord, brainstem and subcortical areas of the brain
does guaiphenesin (GGE) have analgesic or anaesthetic properties?
no
when is guaiphenesin (GGE) most commonly used?
infusion during induction
part of a triple for GA maintenance
what species is guaiphenesin (GGE) used in?
horses
why is guaiphenesin (GGE) useful in equine anaesthesia?
counteracts ketamine muscle rigidity
what are the main considerations for guaiphenesin (GGE)?
can cause haemolysis at higher concentrations
can cause tissue damage if given perivascularly
when can guaiphenesin (GGE) cause haemolysis?
at concentrations greater than 10%
what can happen at guaiphenesin (GGE) concentrations greater than 10%?
haemolysis
how can tissue necrosis from perivascular guaiphenesin (GGE) administration be prevented?
clean stick IVC
patency confirmed
what are the clinical indications for the use of NMBAs?
relax skeletal muscles for surgical access
facilitate control of ventilation
facilitate tracheal intubation in cats and pigs
ophthalmic surgery
assist reduction of dislocated joints and fractures
reduction of anaesthetic needed to relax muscles
how can relaxation of skeletal muscles by NMBAs increase surgical access?
aids retraction
how can relaxation of skeletal muscles by NMBAs facilitate control of ventilation?
prevents patients bucking the vent which can cause physiological disturbance
how can administration of NMBAs aid ophthalmic surgery?
creation of a central and stable eye to aid surgery
how does administration of NMBAs aid reduction of dislocated joints and fractures?
can aid closed reduction as muscles will relax and so traction easier to perform
when may administration of NMBAs not be of use for fracture or dislocation reduction?
if the injury is older and scar tissue has formed
why may NMBAs not be useful in the reduction of old fractures or dislocations?
fibrosis will be present which will not be responsive to NMBAs
how can NMBAs reduce the amount of anaesthetic drug needed?
MAC sparing as less volatile needed to produce muscle relaxation
fewer analgesic drugs needed to produce muscle relaxation so fewer side effects
what must you ensure about your patient when they are anaesthetised and have a NMBA on board?
anaesthetic depth is adequate
what is the anaesthetic triad?
narcosis
analgesia
muscle relaxation
why were NMBAs initially unsuccessfully used in dogs?
patients weren’t ventilated
describe the process of an impulse passing through the neuromuscular junction
acytylcholine (ACh) released from presynaptic neurone due to change in charge of cell
acytylcholine (ACh) passes across synapse and binds to post-synaptic nicotinic receptor
once two acytylcholine (ACh) subunits are bound there is a resulting muscle contraction
acytylcholine (ACh) is then rapidly hydrolysed within the synaptic cleft by acytylcholineesterase
what is the neuromuscular junction formed of?
motor neurone
muscle cell
seperated by synaptic cleft
what is the role of acytylcholine (ACh)?
passes across synapse and binds to muscle cell to instigate muscle contraction
what receptor on the post synaptic cell does acytylcholine (ACh) bind to?
nicotinic receptor
how may subunits of the post synaptic nicotinic receptor must be bound to acytylcholine (ACh) in order to stimulate muscle contraction?
two
how is muscle contraction kept brief?
acytylcholine (ACh) is broken down rapidly in synaptic cleft by acytylcholinesterase
what enzyme breaks down acytylcholine (ACh)?
acytylcholinesterase
what is the role of acytylcholinesterase?
break down of acytylcholine (ACh) remaining in the synaptic cleft to keep muscle contraction short
what must be available before neuromuscular blocking drugs are given?
facilities for ET intubation
IPPV
robust analgesic and anaesthetic protocol
appropriate anaesthetic depth
why is a robust analgesic and anaesthetic plan vital when NMBAs are used?
they have no anaesthetic or analgesic effects
what muscles are most sensitive to the action of NMBAs?
peripheral
what muscles are least sensitive to NMBAs?
central - diaphragm and intercostals
are all muscle groups equally sensitive to NMBAs?
no - peripheral much more sensitive and central (e.g. diaphragm and intercostals) much less so
what are the 2 main groups of NMBAs?
depolarizing
non-depolarizing
what is an example of a depolarising NMBA?
Suxamethonium
what is Suxamethonium formed from?
2 ACh molecules
how does Suxamethonium exert its action at the NMJ?
administered IV, moves into synaptic cleft down concentration gradient
binds to post synaptic receptors
how is Suxamethonium broken down by the body?
cannot be broken down by acytylcholineesterase in the synapse so moves out of synapse and is broken down in the plasma
what is Suxamethonium broken down by?
pseudocholinesterase / plasma cholinesterase
can Suxamethonium be broken down within the synapse?
no - must diffuse out into the plasma and be broken down by pseudocholinesterase / plasma cholinesterase
what is the speed of onset of Suxamethonium?
2-3 minutes
how many doses of Suxamethonium can be given?
only one
what is seen in the patient on initial administration of Suxamethonium?
muscle fasiculation
why is muscle fasiculation seen in the patient on initial administration of Suxamethonium?
due to the binding of the molecule to the post synaptic cell
what can occur if multiple doses of Suxamethonium are given?
accumulation leading to phase II block
how long is the duration of action of Suxamethonium in cats?
5 minutes
how long is the duration of action of Suxamethonium in dogs?
20 minutes
how may Suxamethonium be used in cats and pigs?
aid intubation