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,
