Local Anaesthesia Flashcards
Why use local anaesthetics?
Targeted analgesia – e.g. nerve blocks
Suitable for high risk patients where GA not apt
Part of multi-modal analgesia approach
intra-op – reduce dose of other drugs
Pre-emptive analgesia
Widely used in equine and farm animal practice
How do local anaesthetics work?
Block sodium channels at nerve endings»_space;> block nerve impulse conduction
Sensory neurons more sensitive (some motor block)
Technically they produce local ANALGESIA
Clinical use of local anaesthetics (10)
Topical e.g.. Intubeze, EMLA, minims Amethocaine
Subcutaneous infiltration – ring/line block
Nerve blocks e.g.. Intercostal, dental,
Intra-articular (joint)
Epidural
Intra-pleural – via chest drain (cf. pain) eg. bupivicaine
Intra-spinal – rarely used
Intravenous – with care (cardiac effects at high dose)
Splash blocks
Anti –arrhythmic – eg. lidocaine for Vtach i/v
Local anaesthetic drugs examples (7)
Lignocaine (+/- adrenaline)
Bupivacaine
Amethocaine
Lidocaine – anti arrhythmic
Benzocaine
Mepivicaine
Benefits of local
Little sedative effects (minimal depression of CNS)
Few effects on the CVS and respiratory systems
Local analgesics are redistributed to the liver where they are inactivated.
Local Infiltration
Can be intradermal, subcutaneous or between muscles
Superficial tissues – lumpectomy, minor stitch ups
Procedure for local infiltration;
Clip area to be treated
Aseptic prep
Use small gauge needle (23-25G) to prevent tissue damage
Inject small amount (0.5-1ml usually)
Onset of action usually within 3-5 mins
Test effectiveness of block – prick skin
Local anaesthetic duration
Duration of effect depends on;
Drug used
Rate of absorption – affected by route given, proximity to local blood vessels
Adrenaline may be added to lignocaine in some circumstances…
Why may epinephrine be added to local analgesics?
causes VASOCONSTRICTION which…
Constrics blood vessels which decreases the rate of drug absorption (prolonging effect)
Reduces the concentration of drug entering the circulation»_space;> reduced toxicity
Regional analgesia
Injection into a major nerve plexus /close to spinal cord
Cause blockage of a relatively large area eg. limb, caudal area of body
Require anatomical knowledge to ID nerve +/- nerve stimulator to locate nerve accurately
Regional anaesthetic types
Epidural
Spinal Anaesthesia
Splash blocks
Topical Anaesthetics
Eyes – corneal eg. proxymetacaine, amethocaine
Skin – EMLA – lidocaine and prilocaine
Larynx – lignocaine spray
Lignocaine gel – urinary catheterisation
Risks of local anaesthetics
May cause nerve damage or permanent loss of function when injected into nerve fibres
Some local anaesthetics can cause tissue irritation – Mepivicaine is least irritant
Animals may chew the area following recovery – paraesthesia
Occasional allergic reactions
Hypotension may occur especially after epidural anaesthesia
SYSTEMIC TOXICITY OF LOCAL ANAESTHETICS
Depends on rate of uptake/metabolism of drugs
CNS ; stimulation may lead to seizures, higher doses may lead to depression»_space; respiratory failure
Heart; decrease contraction force»_space; myocardial depression
Methods of local anaesthetic administration
Local infiltration – injection
Regional anaesthesia – injected into nerve that supplies a specific region eg. brachial plexus block, spinal
Trans –mucosal – absorbed across mucous membranes
Trans-cutaneous – due to poor absorption a carrier compound is often combined with the local anaesthetic drug.
Local Infiltration
Local anaesthetics may be infiltrated in close proximity to the nerve that is to be affected.
Can be given intradermally, subcutaneously or between muscles
Used most commonly for surgery involving superficial tissues e.g. removal of small skin tumours/ stitch up
