Local Anesthetics Flashcards
What is the axolemma?
cell membrane of
What do schwann cells do in unmyelinated nerves?
one single schwann cell will cover multiple axons.
What do schwann cells do in myelinated nerves?
in larger nerves, one schwann cell covers only one axon and has several concentric layers of myelin
What are the breaks in the myelin sheath called?
Nodes of Ravier
What level of nerves/neurons do we block?
primarily first order
Will unmyelinated or myelinated nerves be blocked faster?
unmyelinated
Where are VG Na channels located along the axon?
at/in the Nodes of Ranvier
To block a myelinated axon, how much must be blocked?
At least 3 nodes of ranvier in a row
What is a fasciculi?
bundle of axons
How many layers cover a fasciculi?
3;
Endoneurium
Perineurium
Epineurium
What is the endoneurium?
thin delicate collagen that embeds the axon in the fascicule
What is the perineurium?
layers of flattened cells that binds groups of fascicles together
- bundles of fascicles
What is the epineurium?
surrounds the perineurium and is composed of connective tissue that holds fascicles together to perform a peripheral nerve
Injecting into the perineurium does what?
separates the nerves
injecting into the perineurium injecting into he endoneurium will be good or bad?
direct nerve injury
- needle trauma
- local anesthetic volume will cause pressure
injecting into the perineurium injecting into he endoneurium will be good or bad?
direct nerve injury
- needle trauma
- local anesthetic volume will cause pressure
What is the normal neuron RMP?
-70 to -90mV
What is the most important pump in the axolemma?
Na+/K+ ATPase pump?
2K in
3Na out
What is the intracellular K:Na concentration?
30:1
What does the Nernst equation express?
the charge created by the K concentration gradient
In the axoplasm, is there excess anions or cations?
anions
negatively charged ions
What causes a nerve cell depolarization (what ion movement?)
VG na channels open, Na rushes INTO the cell
[overrides the K that is maintaining the potential]
When do the VG Na channels reach an inactive state?
+20mV
What phases of the Na channel opening do LA act on?
open and inactive
NOT closed
What phases of the Na channel opening do LA act on [preferentially]?
open and inactive
NOT closed
What confirmation is the Na channel in during repolarization?
inactive
Will LA bind to the VG Na channels when in the closed state?
open state?
inactive state?
closed- no
open- yes
inactive- yes
Will LA bind to the VG Na channels when in the closed state?
open state?
inactive state?
closed- no
open- yes
inactive- yes
LA act on which channels?
Na (preferentially)
K
Ca
G-protein coupled receptors
LA prevents movement of what ion and in which direction?
binds to VG Na channel;
Na cannot rush in, no action potential
How to LA affect the action potential?
LA block the transmission of the AP;
do not change the RMP
How do LA affect the RMP?
they don’t alter the RMP, only AP transmission
What is “frequency-dependent blockade”?
resting nerve is less sensitive to LA
a stimulated nerve will be affected more by the LA
What is “use-dependent” block?
resting nerve is less sensitive to LA
a stimulated nerve will be affected more by the LA
What is “phasic block”?
resting nerve is less sensitive to LA
a stimulated nerve will be affected more by the LA
What is the LA MOA?
- UNionized drug crosses nerve sheath & cell membrane
- Re-equilibrium drug binds with H+ ion inside the cell (inside the bi-phospholipid layer)
- drugH binds to open or inactive Na channel producing BLOCK
ALL local anesthetics are acids or bases?
WEAK BASE
Are big or small nerves easier to block?
small, unmyelinated
What will be seen first, before loss of sensation or movement? Why?
vasodilation d/t blockage of small preganglionic (controls SNS) fibers first
What type of nerves are harder to block?
big, myelinated
What will you see first when a nerve is blocked?
vasodilation/flushing d/t blocking of small preganglionic neurons (SNS)
Why do pregnant women complain of nausea after getting a spinal?
vasodilation distal to the block resulting in hypotension =
is sensation or motor lost first?
sensation - smaller block = loss of sensation not motor
Be careful d/t unintended injury
If motor is blocked, what does that tell us?
preganglionic & sensory nerves should be blocked
Who is Karl Koller?
introduced cocaine in 1884
Who first began using a drug as a local anesthetic?
Karl Koller
When was a drug first used as a local anesthetic?
1884
What are the 3 specific portion of the chemical structure of local anesthetics?
aromatic ring (makes it lipophilic) tertiary ring (hydorphilic) ester OR amide linkage
Why can local anesthetics get through the axon?
aromatic ring
What are 3 characteristics that differentiate ester vs amide local anesthetics?
- metabolism
- duration of action
- allergic potential
How to know what kind a local anesthetic is?
ester (one i)
amide (two i)
How are amides metabolized?
by the liver
Which type of local anesthetics will have more allergies?
esters
What is a metabolite that increases the risk of an allergic reaction?
PABA
para-amino benzoic acid
is made from ester local anesthetics
What is a metabolite that increases the risk of an allergic reaction?
PABA
para-amino benzoic acid
is made from ester local anesthetics
When does the affect of the LA wear off?
when it goes somewhere else in the body
more volume can last longer b/c it takes longer to go elsewhere in the body
What is C(m)
minimum concentration of LA necessary to produce conduction blockade of a nerve impulse
How does the C(m) of sensory fibers differ from the C(m) of motor fibers?
C(m) of motor fibers is approximately TWICE that of sensory fibers
Does intrathecal or spinal anesthesia require more local anesthetic?
epidural
When injecting an epidural (labor) what is the concentration/volume like?
lower concentration, higher volume
NEVER entering into the dura; hoping to get the nerve roots as they exit
large volume will spread
To allow sensation of contraction & assist
Spinal is where?
intrathecal; compromising the dura
injecting onto the nerve
FANTASTIC BLOCK
Where does the spinal cord end?
L1-L2?
Where does the dural sac end?
sacrum
After L1 what is present in the spinal cord?
3 nerves (sacral roots)
What is the ligament that attaches the spinal cord to the sacrum?
Coccygeal ligament
How will increasing the concentration affect the onset?
increased concentration = faster onset
How will increasing the concentration affect the onset?
increased concentration = faster onset
Never inject more than __ mL of a drug
5mL