local anaesthetics Flashcards
reasons why you might use local anaesthetics
- diagnostic purposes
- permit minor injury
- antiarrhythmic treatment
two chemical types of local anaesthetics
- esters
- amides
ester local anaesthetics
procaine, chloroprocaine, oxybuprocaine, tetracaine, benzocaine, cocaine
amide local anaesthetics
lidocaine, prilocaine, mepivacaine, bupivacaine, ropivacaine, articaine
local anaesthetics mechanism of action
- blocks action potential generation by blocking Na+ channels
- act in cationic form
in which order do LAs block conduction
- non myelinated axons
- small myelinated axons
- large myelinated axons
order of disappearance of nervous function
pain>warmth>touch>deep pressure>motor function
return of nerve function is in reverse order
side effects of LAs
- slow heart conduction
- CNS-inhibitiory effect
- peripheral blood vessels dilated
what does cocaine do to the blood vessels
constricts them
does lidocaine cause vaosdilation
no
effect of LAs on inflammed or hypocix tissue
no effect
what does the concomitant application of vasoconstrictor medicines do to the effects of LAs
increases duration and decreases toxicity
factors determining absorption of LAs
- site of application
- dose
- vasoconstrictive drugs
- features of LAs
ester LAs are metabolised where
hydrolysed primarily by the plasma esterase and degraded by hepatic metabolism -> safer LAs
where are amide LAs mostly metabolised
largely degraded by hepatic inactivation and some plasma hydrolysis
order of clearance of amides
prilocaine>lidocaine>mepi>ropi>bupivacaine
toxicity of LAs in increasing order
mepivacaine
side effects of LAs
- allergy
- asthmatic seizure
- local tissure irritation
- systemic effects - CNS, cardiovascular
- effect of adjuvant
systemic side effects of LAs in CNS
first mild sensory inhibiton, agitation, confusion, tremors progressing to convulsions and resp depression
systemic side effects of LAs in cardiovascular system
namely myocardial depression and vasodilation, leading to fall in blood pressure
uses of local anaesthetics
- topical anaesthesia
- local infiltration
- perineural injection
- intra-articular use
- intravenous regional anaesthesia
- epidurl and spinal block
places of application of topical anaesthesia
cornea, mucous membranes or skin
topical anaesthesia indications
GI-ulcers, pharngeal painful diseases, opthalmology, rectal, before examinations, burnings, sun irritation, inflammation of outer or inner ear
local infiltration method
numerous SC/IM inj of small volumes 0.5-2ml
local infiltration indications
minor surgery, dentistry, castration of males, subcutaneous regional anaesthesia
local infiltration theory
LA injected along a line, blocking conduction in the nerves that pass through the tissue. all regions supplied by the distal section of these are blocked
perineural injection indications
dentistry, minor surgery
perineural injection what is it
injection of anaesthetic in the immediate vicinity of peripheral nerves
intra-articular use therapeutic indication
operation of the affected joint
intra-articular use diagnostic goal
to facilitate the diagnosis of lameness
intravenous regional anaesthesia what is it
local anaesthetic injected IV distal to a tourniquet
extreme isolation from the rest of ciruclation, only less toxic agents allowed
intravenous regional anaesthesia usage
for operations of the digit in cattle
whats TIVA
total intravenous anaesthesia
epidural and spinal block disadvantages
spinal cord injury
what is epidural spinal anaesthesia
injecting LAs into the epidural or subarachnoid space
large areas of the body can be anaesthesied with small amounts of drug
epidural spinal anaesthesia indications
surgery of perineal region, anal, peri-anal region, obstetric operations, urology
epidrual anaesthesia place of injection horses, cattle
first or second intercoccigeal spaces - higher application producing limb paralysis
epidural anaesthesia place of injection sheep, dog, pig
lumbosacral space
epidural anaesthesia dose large animals
lidocaine 1% 60-80ml
epidural anaesthesia dose dogs, pigs
according to body size eg 40cm 2ml
can epinephrine be injected into the spinal cord or IV
no, with systemic use its a lot more harmful
