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Flashcards in Local Anesthetics Deck (71)
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1

In general, the _______ the pKa of the LA, the ________ the proportion of LA in nonionized form at pH= 7.4, and the _______ the onset of the conduction block.

lower; greater; faster

2

What local anesthetic is the MOST nonionized at pH 7.4?

Mepivacaine b\c some sources say the pKa is 7.6.... some say 7.7.... which if that is the case, then lidocaine and etidocaine have the same

3

Why does chloroprocaine have a fast onset despite its high pKa?

d\t the high concentration of the drug injected

4

How do LA's block nerve conduction?

by blocking (impairing) propagation of the action potential along axons--> by directly acting on sodium channels and inhibiting sodium influx

5

What determines the SPEED of onset?

pKa
LA's with a lower pKa will have a faster onset

6

Remember is you take LSD you'll have to Pee Pee Pee.

P-----S (pKa=speed of onset)
L-----P (lipid solubility=potency)
P-----D (protein binding=duration of action)

7

What determines the POTENCY of LA's?

lipid solubility
a LA with a high lipid solubility is very potent

8

What determines the DURATION OF ACTION of LA's?

protein binding
LA's that are highly protein bound will have a prolonged DOA

9

The ______ the oil:water partition coefficient, the ______ the lipid solubility.

greater; greater

10

The _______ coefficient provides a measure of lipid solubility.

oil:water partition coefficient

11

Why do you need a higher concentration of lidocaine (ex: 2%) vs bupivacaine (ex: 0.25%)?

b\c bupivacaine has a higher oil:water partition coefficient (30 compared to 4)--> so it is more lipid soluble, therefore potent... so you need less of it to provide the effect

12

______ serve as storage depots for the LA's; as anesthetic diffuses, more become unbound maintaining the supply of anesthetic to nerve axons.

proteins (protein binding)---> directly correlated to the duration of action

13

What is responsible for the binding of weak bases?

alpha-1 acid glycoprotein

14

What is the second factor that determines the duration of action of local anesthetics?

lipid solubility
*when injected, the LA with higher lipid solubility will dissolve to a greater extent into surrounding lipids--> the lipids act as a reservoir for lipid soluble agents

15

What single change in a property of a LA will result in a more potent and longer acting agent?

increase lipid solubility will increase DOA and potency

16

Name two short acting LA's.

1) Procaine
2) Chloroprocaine

17

Name two moderate acting LA's.

1) Lidocaine
2) Mepivacaine

18

Name 4 long acting LA's.

1) tetracaine
2) etidocaine
3) bupivacaine
4) ropivacaine

19

Loss of an anesthetic from the injection site is primarily by ________.

vascular absorption

20

What 2 factors can influence the rate of absorption of LA from injection sites?

1) presence of vasoconstrictor--> EPI may increase the duration of spinal anesthesia by 75-100% (decreases BF and slows removal)
2) high blood flow to tissue where anesthetic is injected--> the greater the blood flow, the faster the agent is absorbed and washed away from the site

21

Is blood concentration higher after epidural anesthesia or a subarachnoid block?

epidural--> receives higher blood flow--> higher toxicity risk

22

Rank the tissues from highest to lowest blood flow.

1) IV
2) tracheal
3) intercostal
4) caudal
5) paracervical
6) epidural
7) brachial plexus
8) subarachnoid, sciatic, femoral
9) subcutaneous
*greatest to least for risk of LA toxicity
*I Think I Can Push Each Bolus SSlowly For Safety

23

What are 3 non-physiochemical properties that prolong conduction blocks?

1) presence of vasoconstrictor
2) concentration of LA injected (>concentration = > DOA)
3) blood flow--> lower blood flow in the tissues = > DOA

24

Is the ionized or nonionized form of the local anesthetic needed to block nerve conduction?

BOTH= nonionized LA diffuses into the nerve axon---> ionized form binds to receptors on the Na channel when the channel is in the inactivated state--> action potentials cannot be generated

25

For myelinated axons, ______ nodes of Ranvier must be blocked to stop nerve conduction.

2-3

26

Conduction block is _______ dependent.

frequency
*the > the frequency of action potentials, the faster the nerve is blocked by LA--> the LA must bind to the Na channel when it is in the inactivated state--> the faster the nerve is firing, the more opportunities the LA will have to catch the Na channel in the inactivated state

27

Voltage gated Na channels are found only in ______.

the nerve's axon

28

Sympathetic block is ____ to _____ dermatomes ______ than sensory block.

2-6 higher than sensory

29

Motor block is ______ dermatomes _______ than sensory block.

2 lower than sensory

30

Ester local anesthetics are metabolized by ________.

plasma pseudocholinesterase