Local Anaesthetic Agents Flashcards
LA agents refers to drugs which (reversibly or irreversibly ?) block the transmission of __________ nerve impulses.
Some others also ß-blockers, antihistamines.
reversibly
peripheral
A reversible block may also be produced by __________ factors; __________, _______.
physical
pressure, cold.
All LA originates from __________ , an __________ found in Erythroxylum coca in 1860.
Its fisrt LA action was demonstrated by Koller ,1864. limited use owing to __________.
In 1904, __________ synthesized
cocaine ; alkaloid
allergic reactions.
procaine
In North America, the __________ {A,C,P} are popularly used but its use is limited by potential __________
esters{A,C,P}
allergic reactions
Classification/structure
Based on the physical structure: ________ and ________.
The ________ chain allows either an ________ OR ________ linkage.
esters and amides.
intermediate chain
ester[ESTER LA}
amide {AMIDE LA}
Esters; examples???
Amide ; list 6.
Esters; cocaine,procaine,amethocaine, chloroprocaine.
Amide ; lidocaine,mepivacaine, prilocaine, bupivacaine, ropivacaine, levobupivacaine.
Classification of LA
Based on potency/duration of action
Short duration of action +low anaesthetic potency; _______,__________
Intermediate duration of action/anaesthetic potency;
__________, __________, __________, __________.
Long duration of action and high potency;
__________, __________, __________
procaine, chloroprocaine.
lidocaine, mepivacaine, prilocaine, cocaine.
bupivacaine, tetracaine, etidocaine
Classification of LA
Esters tend to _________ spontaneously in storage and should only be _________ once.
Amides are (more or less?) stable in solution. H/v the heavy preparations is (more or less?) stable with heat changes, it is allowed to be heat sterilized once.
hydrolyse ; heat sterilized
more ;less
Pharmacology of LA
Duration of action; increases with ______ solubility, affinity for ____________ , type of ____________ fibre.
Potency; related to __________
Rate of onset; _______ of the LA , this will increase the proportion of the drug in the non-ionised form.
The __________ the pka, the faster the the onset of action of the LA.
__________ of the LA to a lesser extent also affect the rate of onset.
lipid
binding to protein
peripheral nerve fibre.
lipid solubility
pka ; lower
Lipid solubility
Pharmacokinetics of LA
Site of injection is influenced by _____________
rate of blood flow
Pharmacokinetics of LA
IVRA; ___________ release will result in ————————————- directly into the circulation if released within _______ of application.
premature tourniquet
rapid entry of large dose
20 mins
Pharmacokinetics of LA
LA gets into the systemic circulation
____________ {no effect}
Lungs{some _________ and ____________ }
Tissues depending on blood flow{ brain, heart, liver, spleen, muscle, fat}
Right heart
sequestered and metabolized
Pharmacokinetics of LA
Metabolism of LA; generally the ester LA undergo __________ by __________. This is a very (slow or rapid?) process hence the blood concentration difficult to measure in blood after RA. Hence _____________ with them is very rare.
Amide LA are metabolised in the _______. __________ however undergo some extra-hepatic metabolism. Severe ___________ damage will affect metabolism of amide LA
hydrolysis by plasma cholinesterase
Rapid; systemic toxicity
liver; Prilocaine
hepatocellular
Pharmacokinetics of LA
Protein binding; LA bind to plasma protein to some degree. 2 plasma proteins; ——————- and _______________ .
Placental transfer; LA present in maternal blood will equilibrate through the ______________ and then________________ {α1-acid}. .
α1- acid glycoprotein and albumin
placental membrane
fetal circulation
Pharmacokinetics of LA
α1-acid glycoprotein has ________ capacity but binds ______ while albumin has ____ affinity but _______ capacity.
___________ is least bound and yet the least toxic amide LA.
lesser; avidly
low; large
Prilocaine
Pharmacodynamics of LA
During the resting phase, the interior of a peripheral nerve axon has a potential difference of about -70mV relative to the outside. With nerve stimulation, it rises to +20mV then repolarization until resting potential is restored. {Na/K}
The ___________ portion of LA that enters and ________ the __________ channels, and prevents _________ of _______ ions. As a result, no action potential is generated or transmitted, and ______________ occurs.
re-ionized
blocks ; sodium; influx; sodium
conduction blockade
Additives to LA
List 8
AIM: To adjust the pH, tonicity, baricity, preservative, pharmacologic reasons
Adrenaline
Dextran
Clonidine
Sodium bicarbonate
Felypressin
Neostigmine
Hyaluronidase
EMLA
EMLA {__________________________________}
Eutectic Mixture of Local Anaesthetics
LA Toxicity
If significant amounts of LA reach the tissues, heart and brain, they exert the same membrane-stabilizing effect
as on peripheral nerve, resulting in ________________________.
Hence the features; ___________ or __________
of the tongue and circumoral area; ____________, anxious, drowsy and/or complain of ________. ___________ is lost, convulsions.
progressive depression of function
numbness or tingling
light-headed; tinnitus
consciousness
Mgt of LA Toxicity
No matter how careful the anaesthetist is with regard to prevention, facilities for treatment must always be available.
The _________ is maintained and _______ administered by _________ , using ______________ , if apnoea occurs.
Convulsions ; small increments of either ___________ (___ mg) , _________ or __________ (____ mg).
airway; oxygen
face mask; artificial ventilation
Midazolam;2
diazepam or thiopental; 50
Mgt of LA Toxicity
Excessive doses should not be given to control convulsions, as ____________ may be exacerbated. If cardiovascular collapse occurs despite ________________ (and this is (common or rare?)), it should be treated with an __________ drug with α and β effects e.g. __________ in ______ mg increments.
cardiorespiratory depression
adequate oxygenation; rare
adrenergic; ephedrine
3-5
Choice of LA
___________ of the solution
______ of injection/ _____of absorption
Expected _________ of surgery
___________ of the drug
Strength
Site; rate
duration; Availability
Site of injection and rate of absorption when choosing an LA
Lidocaine ____% for infiltration/IVRA, ____% for minor nerve block, _____ % brachial plexus and sciatic /femoral nerves, _____% for epidural, _____% for spinal.
0.5
1
1-1.5
1.5-2
2.5
Role of Cocaine in modern anaesthetic practice?
Cocaine has no role in modern anaesthetic practice,
Cocaine
used in _______________ surgery for its vaso__________ action.
Because of its use as a drug of __________, it is increasingly difficult to obtain cocaine legitimately at a reasonable price.
Causes systemic ________ and _______ reactions
ear, nose and throat
constrictor; addiction
toxicity; allergic
Benzocaine
An ester LA, does not ionize easily hence readily form _____________ and can only be used ___________.
It is hydrolysed very rapidly to ______________ , hence _____ toxicity but may cause _______ reactions.
Mode of mech is the classical effect on the Na/K but thought to diffuse directly into the cell membrane.
water soluble salts
topically; ρ- aminobenzoic acid
Low ; allergic
Procaine & Chloroprocaine
Ester LA, ______ shelf life, ______ duration of action, relatively ______ incidence of allergic reactions .
_______________ is hydrolysed faster than _________ and more potent.
short; brief; high
Chloroprocaine
procaine
Most potent and longest acting ester LA in clinical use ???
Amethocaine/tetracaine
Amethocaine/tetracaine
Hydrolysed by ________________, (slowly or rapidly?) hence quite _______
In small doses, used for ______ anaesthetic
plasma cholinesterase
Slowly ; toxic
spinal
Lidocaine
Lidocaine (previously ___________ )
Having been used safely and effectively for ___________ type of local anaesthetic procedure
lignocaine
every possible
Local Anaesthethic
__________ is currently the standardagent. It has no unusual features and is also a standard __________.
lidocaine
Lidocaine is used commonly for _________ , for peripheral nerve blocks if __________ duration is required. It can be used for intravenous regional anaesthesia, although ___________ is preferred.
infiltration
an intermediate
Prilocaine
Lidocaine can be used for intravenous regional anaesthesia
T/F
T
although prilocaine is preferred.
lidocaine
Lidocaine 5% has been used for _______ anaesthesia, although the ___________ is unpredictable, the duration of action is relatively ________. However there are relatively new concerns about its __________ in such high concentrations.
subarachnoid
degree of spread
short; neurotoxicity
1-2%, lidocaine produces _______ anaesthesia with a ______ onset time.
Lidocaine 2—4% is used by many anaesthetists as a _______ solution for anaesthesia of the ____________ before awake fibreoptic intubation.
epidural
Short
topical
upper airway
Bupivacaine
The introduction represented a significant advance in anaesthesia.
Relative to potency, its acute central nervous system toxicity is __________ than that of lidocaine, but its (shorter or longer ?) duration of action reduces the need for ___________ , and thus the risks of ____________ .
only slightly lower
longer
repeated doses
cumulative toxicity
Several deaths have occurred after accidental intravenous administrationof large doses of bupivacaine
T/F
T
Uses of bupivacaine
Bupivacaine, for _________ , frequently for ______________ blockade and for __________ and _________ anaesthesia because of its ____________________.
infiltration; peripheral nerve
subarachnoid and epidural
prolonged duration of action
Uses of bupivacaine
________ —-% is the most commonly used drug for subarachnoid anaesthesia in the UK.
It may be used in a _____ solution or in a ________ formulation
Bupivacaine 0.5
plain; hyperbaric
