Local Anaesthesia Flashcards
what is the MOA of local anaesthetics?
block the voltage-dependant sodium channels that depolarise the neuron
name 4 factors that influence local anaesthetic action
- local concentration of the LA
- the size of the nerve fibre
- nerve myelination
- length of nerve exposed to the LA
out of pain, sensory and motor fibres, whcih fibres do LAs block first?
pain fibres (myelinated A-delta and non-myelinataed C fibres)
what effect does hypokalaemia and hypercalcaemia have on LA?
it antagonizes the blockade.
what is the potency of a LA related to?
Its lipid solubility.
a lipophilic aromatic group is what enables the molecule to cross the nerve membrane.
what are the implications of a LA having a high pKa in practice?
it means it will be more ionised at physiological pH so its speed of onset will be slower but it will also re-ionise to a greater extent within the cell and produce mroe effective blockade.
what does the term use-dependence mean
the more channels are open, the greater the block becomes
name 5 clinical uses for local anaesthetics
- local infiltration e.g. for suturing
- topical
- nerve blocks (local and regional)
- epidural
- spinal
what is the most commonly used LA?
lidocaine
is an epidural given inside or outside of the dura mater?
outside
what is an epidural anaesthetic often used in combination with?
opiate
what space is a spinal aneasthesia given and between which vertebrae usually?
the subarachnoid space.
between L3 and L4 usually
what does the spread of the LA within the subarachnoid space depend on in a spinal anaesthetic?
- the density of the solution
2. the posture of the person during the first 10-15 mins while the solution flows up or down the subarachnoid space.
what does IV regional anaesthesia involve?
injection of a dilute solution of LA into a limb after application of a tourniquet
what is IV regional anaesthesia used for?
reduction of fractures or removal of ganglia etc.