Local Anesthestics Flashcards
Conduction - Myelinated vs. Unmyelinated Fibers:
-Propogation of impulses is ___ in both.
\_\_\_ = impulses travel along the length of the fiber in a continuous fashion (spans entire length) \_\_\_ = conduction is "\_\_" so fast (50x) that it appears as if impulses leap from one node of Ranvier (no myelin) to the next
-similar
Unmyelinated fibers
Myelinated fibers
“saltatory”
*Both rely on movement of ___ but a little differently.
myelinated - “jumping” from node to node
unmyelinated - spans entire length
Local can’t get to the nerve at the ___. In order for a local to really block a nerve it has to block at least ___ if not ___ or will not be effective.
ions
myelinated section
2 nodes, 3
Nerve Fibers:
- The velocity an impulse travels is proportional to the ___.
- The ___ the ___, the higher the conduction velocity.
- Fibers classified according to ___.
- 3 Types???
diameter of the fiber
larger the diameter
diameter
A, B and C fibers
Receptors fluctuating btw active and inactive states, agonist or antagonist will hold it in a certain conformation. Locals keep the ion channel in the ___.
Cell or neuronal membrane important - allows us to develop an ___ across the 2 sides of the membrane (___ more permeable in a resting neuron). ___ can not really move until channels open. Electric charge (negative charge inside becomes too strong) and ___ will no longer leak out.
inactivated-closed state electrochemical gradient potassium sodium potassium
Nerve Fibers that sense pain, temperature and touch and their differences?
What nerve fiber is associated with the preganglionic autonomic?
A delta fibers - fast pain
C fibers - dull pain, POSTganglionic autonomic, no myelin
B-fibers
Differential Blockade:
- Clinically, the sensitivity of a peripheral nerve to local anesthetic is ___ related to size. Why you see __-first, __-second, __-last.
- HOWEVER THIS IS NOT A CAUSE AND EFFECT!
- In a lab, larger fibers __ and __ are actually more sensitive to local anesthetics than the __ fibers which are unmyelinated and small.
inversely autonomic blockade sensory motor A delta A gamma C fibers
Differential Blockade continued:
- Difference btw clinical observation and research theories =
- anatomic issues (__ found deeper in nerve bundles - harder for the LA to reach)
- variable activity in different nerves - __ fire at higher frequency)
(ex: frequency dependent blockade) - variable ___ mechanisms
- larger nerves
- pain fibers
- variable ion channel mechanisms
Differential Blockade:
___ are the easiest fibers to block, then sensory, then motor. Will see ___ first.
But in lab this is the opposite - easier to block ___.
***Leading theory is the ?
Autonomic
BP change
large A fibers
***anatomy and the location of the nerves
Spread of Local Anesthetic-LOCATION, LOCATION, LOCATION:
- Outer surface of a peripheral nerve is known as the ___ (usually more ___ structures)
- Inner surface known as ___ (these fibers usually serve more ___ structures)
- THE SEQUENCE OF ONSET AND RECOVERY FROM A LA BLOCK IN A MIXED PERIPHERAL NERVE RELIES HEAVILY ON ???
- This factor is much more important than the ___ of the nerve fiber to local anesthetics.
-mantle proximal -core distal -WHERE IT IS LOCATED -inherent sensitivity
Local anesthetic has the most access to the ___ nerves, LA hits the nerves on the outer surface aka the mantle of the bundle and then need more LA to penetrate into core where you have the ___.
peripheral
larger fibers
Achieve deeper block (loss of touch and pressure and then finally motor blockade) by giving more, but going for a ___.
higher concentration (Ex: lidocaine sensory go for 1%, even deeper block go for 2%)
The difference in the concentration of positive and negative ions when the cell is at rest? Approximately?
Resting Membrane Potential
-70 to -90 millivolts
The Action Potential:
- ___ state = ___ space has a relatively ___ compared to the ___ space.
- __ = result of impermeability of the resting cell membrane to ___ outside the cell.
*Polarized state intracellular negative charge extraceullular *Polarity sodium
Action Potential:
- Membrane is more permeable to ___, BUT as ___ exits the cell, a higher proportion of negative ions remain.
- ___ becomes more positive (___ ions) and the electrical gradient favors movement of ___ back into the cell.
- IT IS THIS MOVEMENT OF ___ THAT ESTABLISHES AND MAINTAINS ???
-Potassium potassium -Extracellular fluid potassium ions potassium potassium Resting membrane potential (RMP)
Action Potential:
An action potential is a ___ of the membrane, lasting ___.
- Occurs when a specific physiologic stimulus is received by the ___.
- Stimuli nerve receptors respond to = ????
rapid depolarization
1-2 milliseconds
nerve receptor
mechanical, chemical, thermal and pressure
Action Potential:
- Stimulus causes ___ of the nerve membrane to open, ___ rushes into the cell, causing the ___ of the membrane.
- Influx of sodium causes membrane potential to increase to __ to __.
- As permeability of ___ decreases, ___ permeability increases –> efflux of ___ from the cell and return to ___.
sodium channels sodium rapid depolarization \+20 to +40 millivolts sodium potassium, potassium RMP
___ = a schwann cell wraps itself around the axon several times, enveloping the axon in a myelin sheath. (speeds conduction)
___ = a single schwann cell surrounds several axons
Myelinated nerve fiber
Unmyelinated nerve fiber - not entirely unmyelinated, but not enough to the degree to provide fast conduction
Blockade of Nerve Conduction by Local Anesthetics:
Bind the ___, binds when it is in the ___ (no AP will occur, sodium channel blocked no longer able to conduct ions).
-This blocks impulse conduction during the ___ of the action potential.
sodium channel on the alpha subunit
inactivated closed state
depolarization phase
Locals only change the ___, they do not change the resting membrane potential or the threshold itself - JUST THE ??? With local do not reach threshold, will see it rise up just under threshold line.
ability to reach threshold
ABILITY TO REACH IT
Good strong binding in ___. An ___ is much easier to block than a ___ not firing at a fast rate. ___ and ___ firing at a more frequent rate normally compared to a ___, possibly why they are blocked first.
-___ does play a part.
- inactivated closed state
- active nerve
- resting nerve
- Autonomic and sensory
- motor
- Lipid solubility
Aminoamides vs. Aminoesters:
Distinction is important because they are ___ - with ___ have much more of an issue with allergies!!!
metabolized differently
esters
___ = has only been approved for bunionectomy and hemorrhoidectomy, no other dosing available for any application because it has not been approved! Lots of concern about toxicity because safe doses have not been established for other surgeries.
- This is a bupivacaine extended release ___ injection. FDA approved.
- Dose depends on?
- Max dose?
Exparel
- liposome injection
- surgical site
- 266 mg or 20 mL
