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Flashcards in Local Anesthetics Deck (51):
1

MOA of local ansthetics

site- Sodium ion channels

Block conduction of neural transmission by decreasing rate of depolarization in response to excitation (prevent reaching threshold potential)

Does NOT change resting potential, or actual threshold potential value



2

Describe normal nerve conduction:
resting potential
impulse propogation/excitation

Resting potential of neural membrane = -90mV (via Na out, K+ in)

Excitation = increase in permeability to Na = depolarization (more +) = hit threshold = self sustaining influx of Na (massive depolarization)

3

Form of local anesthetic most helpful for causing activity

neutral form = can cross lipophillic membrane to Na channel receptor (ie site of action)

Ionized form inside nerve causes activity

4

Describe conformations of Na channel, and conformations most helpful for local anesthetic activity

Resting-closed : NO ACTIVITY
Activated - Open: ACTIVITY
Inactivated - Closed: ACTIVITY

Repeated depolarization (which cauases activated/inactivated states vs resting) more effective anesthetic binding = enhancement of conduction blockade

USE DEPENDENT / FREQUENCY DEPENDENT BLOCK

5

Role of pH on LA activity

pKa of LA determines proporation of neutral to ionized forms

lower pKa= greater % of unionized (active) drug

6

Why would you add bicarbonate to LA?

Increase pH of environment = more neutral/ionized form (for any given pH)

7

Why may infected tissue be difficult to anesthetize?

infection = low pH

less proportion of neural/ionized form for given pKa of LA

8

What does the lipid solubility of a LA confer?

describes uptake into neural membrane

lipid solubility generally correlates to POTENCY, DURATION OF EFFECT, and sometimes INVERSELY WITH LATENCY/TIME TO ONSET

9

ETIDOCAINE OR BUPIVUCAINE

more motor blockade?

etidocaine

10

Describe relationship between location of nerve fibers in nerve bundle, and onset of effect.

Mantle (external) = 1st = effects proximal structures

Core (internal) = 2nd = effects distal structures

11

How do lipophilicity and protein binding effect LA uptake into blood stream?

higher lipo/PB = slower uptake

12

LA effect on vasoactivity

Vasodilators at clinically relevant concentrations

13

Why add vasoconstrictors to LA?

prolongation of anesthesia by decreased uptake into blood stream

less likelihood of toxicity (uptake is slower than metabolism)

14

Adding epi to which of the following LA will have greater effect on activity?
Bupivicaine, Tetracaine, Lidocaine

TEtracaine

Has vasodilation (greater), so epi will have greater effect on general activity

15

Esters

Cocaine, Procaine, chlorproacaine

16

Amides

lidocaine, bupivicaine, mepivicaine, ropivicaine

17

Metabolism of esters

hydrolysis in plasma

18

metabolism of amides

metabolism by hepatic microsomal enzymes, and lung extraction

19

Site with highest systemic absorption of LA

Intercostal blocks
( > caudal >epidural > brachial plexus) for the most part

20

LA w/ highest potency (greatest to least)

Bupivacaine/Tetracaine > ropivacaine > prilocaine/mepivacaine/lidocaine/chlorprocaine > procaine

21

Max dose of lidocaine for infiltration (in mg)

300 mg

22

Max dose of Mepivacaine for infiltration

300 mg

23

Max dose of prilocaine for infiltration

400 mg

24

Max dose of Bupivacaine for infiltration

150 mg

25

Max dose of Ropivacaine for infiltration

200 mg

26

Max dose of Procaine for infiltration

500 mg

27

Max dose of Chlorprocaine for infiltration

600 mg

28

Major LA for IV anesthesia

Chlorprocaine, Lidocaine, Prilocaine

29

Major LA for local anesthesia

All

30

Major LA for peripheral nerve block

Procaine, Chlorprocaine, All amides

31

Major LA for epidural anesthesia

Chlorprocaine, all amides

32

Major LA for spinal anesthesia

Procaine, tetracaine, Bupfivacaine, ropivacaine

33

CNS toxicity symptoms

circumoral numbness, facial tingling, restlessness, vertigo, tinnitus, slurred speech, TC seizures

34

How do LA cause seizures?

depression fo cortical inhibitory neurons, letting excitatory pathways rule

35

How can LA seizures propogate LA toxicity?

hypoxemia/metabolic acidosis

acidosis propogates LA toxicity

36

Tx for CNS toxicity of LA

-Benzos vs Propofol

37

Cardiovasular toxicity of LA effects

profound hypotension (relax arteriolar SM relaxation)
direct myocardial depression
impaired cardiac automaticiy/conduction = prolonged PR, wide QRS

38

LA with highest cardiac toxicity?

bupivacaine

39

How do interlipids help reduce toxic events?

provide lipid sink that binds to LA and pulls it out of active circulation = diminish toxicity

40

Esters vs amides; more allergic reactions

esters = produce PABA metabolites = hypersensitivity

41

Does cross sensitivity between esters and amides for hypersensitivity exist?

Esters make PABA (allergen)

some amides contain methylparaben as preservative (cross reacts w/ PABA); it is not the amide itself but the preservative

42

Major use of Tetracaine

spinal anesthesia (high risk of TNS)

RARELY used for epidural/PNB (slow onset, profound motor blockade, high toxicity at high conc)

43

Major uses of lidocaine

topical, local, IV, PNB, epidural/spinal (restricted 2/2 side effects)

44

What form of lidocaine infusion has highest risk of neurotoxicyt and neural injury?

spinal anesthesia (via continuous spinal) = cauda equina syndrome

maldistribution and high does through small gauge catheter

45

What is TNS?

transient neurologic syndrome =

pain and dysesthesia following intrathecal doses of lidocaine

occurs in up to 1/3 of patients, lasts up to 3 days

46

Factors increasing risk of TNS?

lithotomy position

knee arthroscopy positioning

outpatient procedures

47

1st line treatment for TNS

NSAIDS

48

How does mepivacaine vary from lidocaine?

piperdine ring = less vasodilation = longer duration of action

49

Major limitation of mepivacaine?

ineffective as topical anesthetic

50

Major limitation of prilocaine

At high doses may result in clinically significant of ortho-toluidine = can convert hgb to methemoglobin

antidote = methylene blue

51

most comonly used LA for epidural anesthesia and post op pain management

bupivacaine (long duration, very low motor blockade)