Local Anesthetics Flashcards Preview

Anesthesia Pharmacology > Local Anesthetics > Flashcards

Flashcards in Local Anesthetics Deck (68)
1

What is the mechanism of local anesthetics?

LA block voltage gated sodium channels preventing the influx of sodium ions, thus preventing an action potential

2

Local anesthetics bind Na channels in the _______ state

activated

3

How do local anesthetics affect resting and threshold potentials?

not altered

4

Which nerves are more easily blocked?
Myelinated or unmyelinated?
small or large fibers?
resting or rapidly firing channels?
proximal or distal?

Easier:
Myelinated
Small
rapidly firing
proximal

5

What are the three groups in the LA molecule?

Lipophilic group (benzene ring) and hdyrophilic group (tertiary amine) linked together with either an ester or amide

6

Name the amide LAs

Lidocaine
mepivacaine
Prilocaine
Bupivacaine
Ropivacaine
Etidocaine
i before the caine

7

Name the ester linked LAs

Procaine
Chloroprocaine
tetrocaine
cocaine
benzocaine

8

Where are the amides metabolized?

liver

9

Where are esters metabolized? Exception?

esters are metabolized by plasma cholinesterases, except cocaine which is met in liver

10

Which are more potent, esters or amides? What determines potency?

Esters are more potent. Potency determind by lipid solubility

11

what properties determine onset?

lipid solubility and pKa

12

What is the measure of local potency for LA that is similar to MAC?

Cm

13

What factors determine the absorption of LA?

Dosage
Site of injection
Drug-tissue binding
Local blood flow
vasoconstrictors

14

What side effect can metabolites of prilocaine and benzocaine have?

methemoglobinemia (ortholuidine)

15

What is the metabolite of esters that may cause an allergic rxn?

para aminobenzoic acid (PABA)

16

What is the physiologic effect of methemoglobinemia?

decreases O2 and CO2 carrying capacity of hemoglobin

17

Which group of pts have a higher risk for methemoglobinemia?

neonates due to fetal hemoglobin

18

What is normal methemoglobinemia?

<1%

19

What are the S & S of methemoglobinemia?

SOB
cyanosis
chocolatey-brown arterial blood
pulse ox that always reads 85%

20

What is the treatment for methemoglobinemia?

1-2 mg/kg methylene blue

21

Does addition of vasoconstrictors affect onset of LA?

no

22

Vasoconstrictors _________ duration of LA by limiting systemic _________ and maintaining the drug concentration at the _______.

increases
absorption
nerve

23

Addition of epi (increases/decreases) the chance of systemic toxicity?

decreases

24

What is concentration of epi used with LA?

1:200,000 or 5 mcg/ml

25

How much does epi prolong the effect of bupivicaine?

epi has very little effect with bupivicaine

26

what factors influence the possibility of absorption leading to systemic toxicity?

Dose
Vascularity of site
presence of epi
properties of the drug

27

Subcutaneous, intravenous, sciatic, tracheal, intercostal, brachial plexus, caudal, epidural paracervical. Arrange from most to least vascular

intravenous>tracheal>intercostal>caudal>paracervical>epidural>brachial plexus>sciatic>subcutaneous

28

What effects does systemic toxicity have on CNS?

Circumoral numbness
Restlessness
slurred speech
siezure

29

What effects does systemic toxicity have on the cv system?

Hypotension
Decreased cardiac conduction
Ventricular arrythmias

30

Which has worse effects on the CV system? lidocaine or bupivicaine?

bupivicaine

31

What is the limit for dosages for lidocaine?

5mg/kg/ without epi
7mg/kg with epi

32

What is the limit of the dose of bupivicaine?

2.5 mg/kg

33

What is the method of action of cocaine?

aside from its local effect cocaine also blocks reuptake of dopamine and norepi

34

How is cocaine used clinically?

mostly in ENT surgery for the nose due to its vasoconstrictive and local effects

35

What is the peak time of intranasal cocaine?

30-45 minutes

36

What are the adverse effects of cocaine?

increased HR, ventricular arrhythmias, and coronary vasoconstriction

37

How do you treat the toxicity of cocaine?

Supportive treatment
nitroglycerine

38

Is ephedrine a good choice for a chronic cocaine user?

No. Norepi stores will be depleted so ephedrine won't work

39

How long does lidocaine last in a spinal?

<1.5 hours

40

What is the side effect of lidocaine in a spinal?

transient neurological symptoms

41

What is a usual concentration of lidocaine for a spinal?

5% with 7.5% dextrose

42

How long does bupivicaine last in a spinal?

2-2.5 hours

43

What is a usual concentration of bupivicaine used for a spinal?

0.5% and 0.75% with or without dextrose

44

How long does tetracaine last in a spinal?

2-3 hours up to 5 with epi

45

What is the usual concentration of tetracaine used for a spinal?

1% solution, can be mixed with 10% dextrose

46

When and how does epidural anesthesia during deliveray become a problem for the neonate?

When the baby is in distress, it will become acidotic which traps the drug. toxicity may become a problem, esp with lido

47

What is the differences in volume used for epidural vs spinal?

Spinal usually uses 1-2 ml (up to 3-4 with bupivicaine according to the chart in the notes) while epidurals require 15-30ml

48

How is the duration of a bier block determined?

tourniquet time

49

How much 5% lidocaine or prilocaine would you use for a bier block?

50 cc

50

Which has a lower plasma concentration in a bier block at the same dose, prilocaine or lidocaine?

prilocaine

51

How much bupivicaine do you use for a bier block?

don't use bupivicaine for a bier block, more likely to cause cardiac effects when tourniquet is deflated

52

The _______ of the drug determines the amount of local anesthetic that exists in the nonionized form in the tissue

pKa

53

Which drugs are used for topical anesthesia?

prilocaine,cocaine, lidocaine (w/ oxymetazoline

54

What is local infiltration?

Extravascular placement of local anesthetic in the area to be anesthetized

55

What anesthetic is in hurricane spray?

benzocaine

56

Name a procedure where nebulized lidocaine may be used?

awake bronchoscopy

57

What is emla?

eutectic mixture of local anesthetic (a cream that is put on the skin and held there with a tegaderm)

58

What is the impediment that makes it difficult for local anesthesia to cross skin

keratin in the skin

59

How long is the onset and duration of emla?

1 hour, duration ~ 2 hrs

60

What is the dose for emla?

1-2 gram/10cm2 area of skin

61

Which patient is contraindicated for emla?

<1mo

62

Can a patient use an emla if they are susceptible to methemoglobin?

yes, just don't use prilocaine or benzocaine in the preparation

63

How much EMLA do you use for broken skin?

Don't use on broken skin

64

Which drugs are considered short acting for infiltration anesthesia?

procaine-20-30 min
Chloroprocaine 15-30 min

65

Which drugs are considered moderate duration for infiltration anesthesia?

Lidocaine-30-60 min
Mepivacaine 45-90 min
prilocaine 30-90

66

Which drugs are long acting for infiltration anesthesia?

Bupivacaine 120-240 min
Endocaine 120-180 min

67

What are the first 4 symptoms of local anesthetic toxicity?

circumoral numbness
tinnitius
lightheadedness
visual disturbances

68

What are the last 5 symptoms of LA toxicity?

Muscle twitching
Unconsciousness
convulsions
Respiratory depression
cardiovascular collapse