Local Anaesthetics Flashcards
What is the function of local anesthetics
Their job is to prevent sensation and also stop pain, they have a local action and don’t cause any loss of consciousness. They block the conduction of action potentials.
What is the general chemical structure of a local anesthetic
Aromatic—Ester or Amide—Basic side chain 2/3 Amine
What is Preferred and Ester or an amide link within the structure of a local anesthetic
Ester links tend to be hydrolyzed quite quickly therefore there have a shorter duration of action for these anesthetics whereas Amides are a bit more hardy they need to go through the liver to be metabolized and thus tend to last longer and are not so prone to hydrolysis
At physiological PH Will most of the molecule be negatively or positively charged
At physiological pH when these agents are injected most of the molecules will be positively charged by the protonation of the nitrogen in the side chain and positively charged molecules will have difficulty diffusing into some cellular components
What is the site of action of a local anesthetic
Usually it is the sodium channels but for a local anesthetic to work it Has to penetrate inside the cell to gain access to it’s binding site
LA + H+= LA+
A)Most of the equilibrium will lie on the right hand side (PK8 or nine) LA+ Will not penetrate through the hydrophobic environment of a connective tissue sheath a.k.a. Schwan cell
B) LA Will diffuse through the lipid medium establishing a new equilibrium with in the lipid medium and axon
C) once inside the axon LA+ Will block the sodium channels preventing the influx of sodium into the sodium channels and hence action potential will fail losing sensation/pain
What are the twomechanism of action of a local anesthetic
A)Hydrophilic pathway
B)hydrophobic pathway
What Events take place during a hydrophilic pathway mechanism
A) LA goes through membrane
B) LA + H+= LA+
C) LA+ in the cell will block the open sodium channel by binding inside the ion channel and presenting a physical plug to the free movement of sodium ions.
Note; here the sodium channel is open
What events take place during a hydrophobic pathway
La diffuses through to the middle of the membrane
LA moved up to the side of the channel, and travels through the porous channel
Once inside the ion it is protonated and blocks the sodium channel that has not yet opened
Note: in the hydrophobic pathway the sodium channel has not yet opened
What are the four ways of administrating local anesthetics
A) Topical administration
B) infiltration administration
C) peripheral nerve block administration
D) Central nerve block administration
what is the principle of topical administration
It is mostly used on skin, cornea (opthalmogical investigations), in the cavity
Note that these days not so much used on the skin because they can cause some side effects/side reactions
What is the principle of infiltration administration
It is an injection around nerve endings (in the dermis/intradermal layer) mostly used in dentistry, note that there is a time to delay before you feel the effects of anesthesia 5 to 10 minutes
What is the principle of peripheral nerve block administration
It is an injection close to major sensory nerve trunks a.k.a. used to anesthetize the a limb where general anesthesia might not work. Hence The injection site is either topical, inradermal or in the subcutaneous layer
What is the principle of Central nerve block administration
It is an injection into either the subcutaneous space to produce spinal anaesthesia or epidural anesthesia to anesthetize specific nerve roots in the spinal cord a.k.a. the lumbar region of the vertibral column
Epidural injection
Won’t penetrate all the way through the arachnoid membrane and dura matter and is injected between lumbar three and four. It will stop short just into the fatty tissue between the two vertebrae to anesthetize only those nerve fibers that flow out of the spinal cord at this particular level therefore more local versus intrathecal is more widespread
