Local Anesthetics

Front 1

Mechanism of LA actions

Back 1

Local anesthetics diminsh the amplitude of the action potential
Block peripheral nerve conduction

Front 2

On What Channel do LAs Act?
ON What Subunit, which domain?

Back 2

Major effect on Na+ Channels (Domain 4 of the alpha subunit)
Minor effect on Ca++ Channels

Front 3

DO LAs act on the intracellular or extracellular side of the lipid membrane?

Back 3

Intracellular (cytosolic), on domain 4

Front 4

How to LAs effect enzyme Kinetics?

Back 4

Normally:
Closed <--->Open<----> Inactivated

LA favors the closed and inactivated configurations over Open

Front 5

Where do LAs Lie on the pH scale?
Why is this Consequential?
How and when do we manipulate this situation?

Back 5

Weak Bsses
Cell is usually more acidic than the extracellular milieu. Thus, outside, the neutral, deprotonated form of the LA is favored. This is the from that can corss the Plasma membrane. When it arrives inside the cytosol is more acidic and B get protonate to BH+, trapping it in the cell.

Sometimes we co-administer LA with bicarb to as to be sure that the base gets deprotonated so it can enter the cell. This might be used at a infection site where extracellular pH is lowered.

Front 6

Determinants of Nerve Fiber Sensitivity:
Speed of firing
Myelination (Why?)
Anatomy?
Size?

Back 6

Rapidly firing> slowly firing
myelinated>unmyalinated (need only effect Nodes of Ranvier)
smaller> larger
Edge of nerve> fibers in center

Front 7

After all is said and done, which nerve fibers are most sensitive and least sensitve to LA?

Describe a physical manifestation of this fact

Back 7

C(sympathetic/touch)/Ad(pain) >
B (sympathetic preganglionic) >
Aalpha, Abeta, Agamma (motor, touch/pressure)

Pt. under LA may feel no pain, but still be able to move.

Front 8

Determinants of LA Potency (1)

Back 8

Lipophiliity

Front 9

Determinants of LA speed of onset (2)

Back 9

Lipophilicity
pKA [lower pKA (acidic) is quicker]


Lipophilicity is a bit counterintuituve because one would think that being abl to cross the PM would allow LA to leave as quick as it came. This is true, but high lipophilicity allows a pool of LA to get collected in the cell so increases duration

Front 10

Determinants of LA Duration of effect?


One of these can be pharmacologically modulated.... which one and how?

Back 10

Lipophilicty
Protein Binding
Washout (due to local bloodflow)

Washout can be prevented by Epi

Front 11

Two kinds of LAs


Which one is non-allergenic

Back 11

Aminoesters
Aminoamides(non-allergenic)

Front 12

Aminoesters are metabolized by_______ to what metabolite?


Why does this metabolite matter?

Back 12

Plasma cholinesterases

to PABA which matters because it can be an allergen

Front 13

Aminoamides are metabolized by

Back 13

Liver

Front 14

LAs are potentially toxic to all cells which have this property

Rank the relevant cells in terms of susceptibility to toxicity

Back 14

Cells with Na+ channels


Neurons> Cardiac>> Skeletal muscle

Front 15

Symptoms of CNS LA toxicity

Back 15

Circumoral numbness
Tinnitus
Drowsiness
LOC/seizures/respiratory depression

Front 16

Symptoms of Cardiac LA toxicity

Back 16

Prolonged PR
WIdened QRS
Bradycardia
Decreased Contractility--> hypotension
Arrythmias, asystole, or V-tach/V-Fib

Front 17

Why is it unsafe to neve block a patient who is not concious?

Back 17

They cannot report CNS toxicity symptoms of toxicity like circumoral numbness, tinnitus, drowsiness, LOC

Front 18

Treatment of LA toxicity SYMPTOMS:
For seizures:
FOr Asystole/V-fib
For bradycardia:

Back 18

Maintain Airway
Treat seizures (Benzodiazepines- Midazolam/versed)
Epinephrine for asystole/V-fib
Atropine for Bradycardia

Front 19

Treatment of LA toxicity meant to rapidly decrease effective dose

Back 19

20% lipid solution (Intralipid)
LAm partitions into intralipid and is carried away from sites of toxicity

Front 20

The only two things whih really cause TRUE LA allergy are:

Back 20

PABA mtabolite of aminoesters
preservtive within LA

Front 21

What do i adminster to patients with LA allergy?

What 2 precautions Might I take when doing so?

Back 21

It is OK to use aminoamide.

If it sounds like a real allergy, use preservative free and consider prophylactic anti-histamines.

Front 22

Prilocaine specific toxicity

Back 22

Methemoglobinemia

O2 doesnt unload well--> tissue hypoxia

Front 23

2 LAs causes cardiac arrythmias?

Back 23

Bupivicaine and Etidocaine

Front 24

Which 3 LAs are metabolized to PABA?

Back 24

Benzocaine, tetracaine and Procaine

Front 25

EMLA topical anesthetic cream?
1) contains what?
2)Used for what?
3) specific toxicity

Back 25

1) lidocaine and prilocaine
2) putting IV's in ids
3)Prilocaine causes Methemoglobinemia--> tissue hypoxia

Front 26

Topical anesthetic for mucous membranes includes these three drugs

Back 26

Lidocaine
Cocaine
Tetracaine

Front 27

SubQ Anesthetic
1)most common
2) for longer duration (2)
3) What is the maor problem with SubQ and how is it solved?

Back 27

1) lidocaine
2) Bupivicaine and Ropivicaine
3) Burning on injection due to acidic medium. Solved by adding NaHCO3 which will alo help deprotonate the weak base and make it more absorbable.

Front 28

IV Regional (BIER block)
1) describe procedure
2) how long ca nthis be done?
2) Why doesn’t it give toxicity when releases systemically at end of procedure when cuff is removed?

Back 28

1)Exsanguinate a limb with an elastic bandage
Inflate a tourniquet above systolic BP
Inject 30 – 50 ml of LA into a cather in the limb
2)It is ok to do this for a couple of hours
3)LA gets protein bound in the limb and therefore leeches out slowly. Do not remove cuff too soon.

Front 29

Nerve/Plexus block
1)use?
2)4 sites of use
3) some common LAs

Back 29

1) Anesthetize the sensory innervation of a nerve or plexus
2) axillary, femoral/popliteal, Intercostal, Digit
3) Lidocaine, bupivicaine, etidocaine, ropivicaine

Front 30

Spinal Neuraxial block
1) site of injection
2) agents
3) block of what funtions?
4) distribution
5) Relative speed and dose

Back 30

1) Intrathecal
2) Lidocaine, bupvicaine, tetracaine
3) Sensory and motor
4) Dermatomal
5) quicker and need smaller dose than epidural

Front 31

Epidural Neuraxial Block
1) Injection site
2) Onset time/relative dose needed
3)Distribution

Back 31

1)Placed in epidural space
2)Slower in onset than spinal, Requires much more drug
3)Sometimes “patchy” anesthesia – less predictable

Front 32

Local Anesthetic Adjuvants:
Epinephrine
1) Direct effect
2) Indirect use
3) avoid these sites

Back 32

1) vasoconstriction, reduces peak blood levels and increases duration by decreasing washout
2)Indicator of intravascular injection by loking for rapid onset tachycardia
3) Penis, nose, fingers, toes

Front 33

Local Anesthetic Adjuvants:
NaHCo3

1) purpose

Back 33

1) speeds onset and reduces pain on injection

Front 34

PT needs LA for finger lac but has "allergy" and is prone to arrythmias. What to give?

Back 34

Any aminoamide except bupivicaine or etiocaine (arrhythmias). Dont Give epi

Front 35

4 Aminoesters

Back 35

Procaine
2-Chloroprocaine
Tetracaine
Benzocaine

Front 36

5 Aminoamides

Back 36

Bupvicaine
Etidocaine
Lidocaine
Mepivicaine
Prilocaine

Front 37

aminoester or aminoamide?
Lidocaine

Back 37

Aminoamide

Front 38

aminoester or aminoamide?
Procaine

Back 38

Aminoester

Front 39

aminoester or aminoamide?
Tetracaine

Back 39

Aminoester

Front 40

aminoester or aminoamide?
Etidocaine

Back 40

Aminoamide

Front 41

aminoester or aminoamide?
Bupivicaine

Back 41

Aminoamide

Front 42

aminoester or aminoamide?
Benzocaine

Back 42

Aminoester

Front 43

aminoester or aminoamide?
Procaine

Back 43

Aminoester

Front 44

aminoester or aminoamide?
Prilocaine

Back 44

aminoamide

Front 45

aminoester or aminoamide?
mepivicaine

Back 45

aminoamide

Front 46

Name the three groups in an LA

Back 46

Aromatic group
Amino group
Intermediate chain

Front 47

What group on an LA most determines lipophilicty?

Back 47

Aromatic Group

Front 48

What group on an LA most determines seum protein binding?

Back 48

Amino group

Front 49

Which group on an LA determines how the LA is metabolized and how it is used clinically?

Back 49

Intermediate chain
(determines ester vs. amide)

Front 50

Potency of an LA is primarlily determined by?

Back 50

Lipophilicity