Pharmacology - Local Anaesthetic
Summary
TLDRThis video offers an insightful overview of local anesthetics, their use in minor surgeries, and their mechanism of action on nerve fibers. It explains how local anesthetics, like lidocaine and bupivacaine, penetrate the cell membrane to block sodium channels, preventing pain signals from reaching the brain. The video also touches on the history of anesthetics, mentioning cocaine as the first discovered, and discusses side effects and the unique properties of tetrodotoxin from pufferfish. It concludes with a look at different types of local anesthetics, their applications, and potential risks.
Takeaways
- đČ Local anesthetics are used to numb a small part of the body during minor surgery.
- đż Cocaine was one of the first local anesthetics discovered and is still used today.
- đ The effectiveness of local anesthetics depends on their form; in an ionized form, they cannot penetrate the cell membrane.
- đŹ Local anesthetics work by penetrating the cell membrane in an un-ionized form and then ionizing inside the neuron to block sodium channels, preventing nerve impulse propagation.
- đ« Local anesthetics are more effective on smaller nerve fibers and particularly on myelinated fibers.
- đĄ Tetrodotoxin (TTX), a natural toxin secreted by pufferfish, also blocks sodium channels but from the outside, unlike common local anesthetics.
- đĄ Lidocaine, also known as 'League no pain', is a commonly used local anesthetic with rapid induction and medium duration, often used in dentistry.
- đš Side effects of local anesthetics can include headache, dizziness, confusion, and potentially fatal CNS depression.
- đ Local anesthetics can also affect the heart, causing myocardial depression and vasodilation.
- đ Bupivacaine is used for long surgeries due to its long duration but requires caution due to high cardio toxicity.
- đ The video provides a brief but informative overview of local anesthetics, their mechanisms, and their clinical applications.
Q & A
What are local anesthetics used for in medical procedures?
-Local anesthetics are used to numb a small part of the body during minor surgery, preventing the sensation of pain in the area where they are administered.
Who discovered cocaine as an anesthetic and what is its significance?
-Cocaine was one of the first anesthetics discovered and was the first ester-type local anesthetic. It has historical significance as a milestone in the development of local anesthetics.
How does the form of a drug affect its ability to be absorbed by the body?
-A drug in its unionized form can penetrate the cell membrane and be absorbed by the body, whereas a drug in its ionized, polar form cannot penetrate the cell membrane and is less effective.
What is the pKa of a typical local anesthetic and how does it relate to its effectiveness?
-A typical local anesthetic has a pKa of about 8 and 9. In its unionized form, it can penetrate the cell membrane and is quite effective. However, at physiological pH, which is slightly acidic, it becomes ionized and less able to penetrate the cell membrane.
How do local anesthetics work to numb an area?
-Local anesthetics work by penetrating the cell membrane of nerve cells, becoming ionized inside, and binding to sodium channels, thus preventing the influx of sodium ions and blocking the propagation of nerve impulses, which numbs the area.
Why are local anesthetics more effective on smaller nerve fibers?
-Local anesthetics are more effective on smaller nerve fibers because they are more susceptible to the blocking action of the anesthetic compared to larger fibers.
What is the difference between tetrodotoxin (TTX) from pufferfish and local anesthetics used in hospitals?
-Tetrodotoxin (TTX) blocks the sodium channel from the outside, preventing sodium ions from entering the neuron and stopping the action potential. In contrast, local anesthetics used in hospitals typically block the sodium channel from the inside of the neuron.
What are some common side effects of using local anesthetics?
-Side effects of using local anesthetics can include headache, dizziness, confusion, and CNS depression, which can be fatal if it leads to respiratory depression.
How does cocaine differ from other local anesthetics in terms of side effects on the heart?
-Unlike other local anesthetics, cocaine does not cause myocardial depression but instead increases heart activity, which can lead to different cardiovascular effects.
What are some popular types of local anesthetics mentioned in the script?
-Some popular types of local anesthetics mentioned are lidocaine (known as 'League no pain' in some regions), which is used for its rapid induction and medium duration, and bupivacaine, which has a slow onset, long duration, and medium tissue penetration but is associated with high cardio toxicity.
Why is care needed when using bupivacaine as a local anesthetic?
-Care must be taken when using bupivacaine because it has high cardio toxicity, making it necessary to monitor patients, especially those with heart conditions, to avoid complications.
Outlines
đ©ș Overview of Local Anesthetics
In this video, we explore the basics of local anesthetics, which are used in minor surgeries to numb specific body parts. We discuss the importance of the drug's ionization state for effectiveness, the use of cocaine as the first anesthetic, and how local anesthetics work by blocking nerve signals to the brain. The video covers the concept of local anesthetics being weak bases with a pKa of about 8-9, which penetrate cell membranes in their un-ionized form but become ineffective in acidic environments.
âïž How Local Anesthetics Work
This section explains the mechanism of local anesthetics, detailing how they numb specific body parts by targeting nerve fibers, particularly pain fibers. Local anesthetics block sodium channels inside neurons, preventing the transmission of pain signals to the brain. The video also highlights the susceptibility of different nerve fibers to local anesthetics, noting that smaller, myelinated fibers are more affected than larger ones. The segment concludes with a brief mention of tetrodotoxin (TTX) from pufferfish, which blocks sodium channels from the outside.
Mindmap
Keywords
đĄLocal Anesthetics
đĄCocaine
đĄpKa
đĄCell Membrane
đĄNerves
đĄAction Potential
đĄSodium Channels
đĄTetrodotoxin (TTX)
đĄLidocaine
đĄBupivacaine
đĄSide Effects
Highlights
Local anesthetics are used to numb a small part of the body for minor surgery.
Cocaine was one of the first local anesthetics discovered.
Local anesthetics can be administered through various methods including intra-dermal, subcutaneous, or in the spine.
The effectiveness of a drug depends on its form; non-ionized forms can penetrate the cell membrane.
Local anesthetics are weak bases with a pKa of about 8 and 9, becoming ionized in physiological pH.
Local anesthetics work by blocking sodium channels, preventing the generation and conduction of nerve action potential.
Tetrodotoxin (TTX), a natural local anesthetic from pufferfish, blocks sodium channels from the outside.
Side effects of local anesthetics include headache, dizziness, confusion, and CNS depression.
Cocaine does not cause CNS depression but instead causes excitement.
Local anesthetics can also affect the heart, leading to myocardial depression and vasodilation.
Lidocaine, also known as 'League no pain', is commonly used in dentistry and has anti-arrhythmic properties.
Propofol, another local anesthetic, has many side effects and is not very useful.
Bupivacaine has a slow onset, long duration, and medium tissue penetration, making it suitable for long surgeries.
Bupivacaine has high cardio toxicity and requires caution in patients with heart conditions.
Local anesthetics generally work more on smaller nerve fibers due to their susceptibility.
Local anesthetics are more effective on myelinated nerve fibers than unmyelinated ones.
The video provides a brief but comprehensive overview of local anesthetics and their applications.
Transcripts
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graphics in this video we're going to
look at local and aesthetics and this is
sort of an overview on local
anaesthetics to do with pharmacology now
local anesthetics are used in minor
surgery to numb a small part of the body
so here you can see some doctor in
injecting some local anesthetics into
the body to numb the area so we can't
feel anything
interestingly cocaine was one of the
first anesthetics actually it was the
first itis type to be discovered we can
administer at aesthetics through intra
dermal subcutaneous or in tropical in
the spine before we continue on please
remember the basics of pharmacology if a
drug is an onion eyes form it can
penetrate the cell membrane it is
effective for example it can be absorbed
by the body however if a drug is in an
ionized form if it's polar it cannot
penetrate the cell membrane it's not
very effective and for example it cannot
be absorbed by the body now a local
anesthetic is a weak base with a pKa of
about 8 and 9 and in an unannounced form
it can penetrate the cell membrane it is
quite effective however if when it
enters a physiological pH which is
slightly acidic below 7 it will become
ionized and so it cannot penetrate the
cell membrane so for example if we were
to administer a local anesthetic to a
person suffering from high levels of
acids in their body the local anesthetic
will be ionized very quickly and so is
not
very effective so this is an important
concept to know and will I will learn
more about it during this video so how
do local anesthetic works will they numb
a small part of the body by particularly
working on the nerves especially the
African air fibers the pain fibers by
preventing the pain fibers to send pain
signals to the brain let's have a closer
look here is the cell membrane of the
neuron with channels here is the outside
of the neuron and here is the inside the
insides not going to be here it's meant
to be in the inside I hope you
understand that in the inside of the
neuron it's more negatively charged in
respect to the outside in the inside we
have more potassium ions and in the
outside we have more sodium ions when an
action potential or impulse travels
through along the neuron the inside will
become more positive like so because of
the influx of sodium ions from the
outside to the inside what happens when
a local anesthetic comes along a local
anesthetic will come along in an onion
eyes form meaning that it can penetrate
the cell membrane so here the local
anesthetic will penetrate the cell
membrane and come inside the neuron the
inside of the neuron is slightly acidic
in the physiological pH and so when this
local anesthetic goes inside the neuron
it will become ionized and so will not
leave this the neuron and this is what
we want because then the local
anesthetic in an onion and I announced
form can bind on the sodium channels
here and essentially prevent the sodium
ions from coming inside the neuron and
so prevent the impulse or action
potential from propagating down along
the neuron so in summary a local
anesthetic
essentially prevents both the generation
and conduction of the nerve action
potential it blocks the sodium channels
by physically plugging the transmembrane
port from the inside and so when we
prevent the conduction of this action
potential from this pain fiber that
means that the brain will not receive
this pain signal and so we would we
would feel no pain when we use local
anesthetics however local anesthetics
actually work on every type of nerve not
only these afferent nerve fibers the
pain fibers but as a general rule they
work more on smaller fibers because
small fibers are more susceptible than
large fibers and local anesthetics also
work particularly on myelinated more
than unmyelinated nerve fibers so if we
draw this up from the most susceptible
to the least susceptible is that
nociceptors the pain fibers are more
susceptible to local anesthetics and
then we have the sympathetic fibers the
temprature fibers and and so on and so
on
until finally on motor fibers but we
would need a massive dose of local
anesthetic to paralyze a person as a
side note let's look at another type of
local anesthetic a natural one which is
secreted by pufferfish and it's a toxin
so here again I'm drawing a membrane of
a neuron and with the channel the inside
is more negative and respect to the
outside but when an action potential
comes along the inside will become more
positive the pufferfish as we know is
pretty toxic for humans and that is why
we stay away from it the pufferfish this
is because the pufferfish secretes a
toxin known as tetrodotoxin or TTX TTX
unlike our local anesthetic that we use
in hospital TTX blocked the sodium
channel from the outside like so and so
this will not allow sodium ions to come
inside and so will not allow the
action potential to pass through the
side effects of using local anesthetic
include headache dizziness confusion and
CNS depression which may be fatal if it
leads to respiratory depression
however cocaine actually doesn't cause
CNS depression but causes excitement
instead so that's cocaine
side effects of local anesthetic also
affect the heart it can lead to
myocardial depression vasodilation as
well and so care must be taken we have
to check the blood pressure before
giving local anesthetic cocaine again on
the other hand doesn't cause myocardial
depression but increases like the
activity now let's look at some types of
local anesthetics some popular ones
League no pain also called lidocaine in
America is as a rapid induction has a
medium duration so you won't feel pain
for medium duration has good tissue
penetration and it's very commonly used
especially in dentistry I think but
lignin can also works as an
anti-arrhythmic drug a class 1 B so this
league no pain can be a local anesthetic
as well as anti-arrhythmic drug as an
anti-arrhythmic drug it tries to are fix
not fixed but tries to help in
arrhythmias so it works on the
depolarization phase rapid
depolarization phase of the ventricles
so if this was the normal action
potential of a ventricle myocyte where
we in the zero phase we have a rapid
depolarization caused by an increase in
sodium influx lignum cane will cause
this type of shift which will
essentially deep slow down the
depolarization phase but we don't really
need to know that leg McCain is a
antiarrhythmic drug because this is a
local anesthetic video but that's just a
good concept
to understand another type of local
anesthetic is propane which is I wrote
here crap because it has many side
effects and it's not very useful and the
last look like I said I will talk about
is bupivacaine it has a slow onset a
long duration and medium tissue
penetration so it's pretty good and that
is why it is commonly used in long
surgeries because of this long duration
however it has high cardio toxicity so
care must be taken when using this with
people suffering from my heart failure
or something like that I hope you
enjoyed this video on local anaesthetic
it was very brief but please like share
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