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Board Review CRNA (Sweat Book) > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

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.

A

lower; greater; faster

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2
Q

What local anesthetic is the MOST nonionized at pH 7.4?

A

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

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3
Q

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

A

d\t the high concentration of the drug injected

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4
Q

How do LA’s block nerve conduction?

A

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

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5
Q

What determines the SPEED of onset?

A

pKa

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

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6
Q

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

A

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

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7
Q

What determines the POTENCY of LA’s?

A

lipid solubility

a LA with a high lipid solubility is very potent

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8
Q

What determines the DURATION OF ACTION of LA’s?

A

protein binding

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

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9
Q

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

A

greater; greater

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10
Q

The _______ coefficient provides a measure of lipid solubility.

A

oil:water partition coefficient

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11
Q

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

A

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

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12
Q

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

A

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

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13
Q

What is responsible for the binding of weak bases?

A

alpha-1 acid glycoprotein

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14
Q

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

A

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

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15
Q

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

A

increase lipid solubility will increase DOA and potency

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16
Q

Name two short acting LA’s.

A

1) Procaine

2) Chloroprocaine

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17
Q

Name two moderate acting LA’s.

A

1) Lidocaine

2) Mepivacaine

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18
Q

Name 4 long acting LA’s.

A

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

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19
Q

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

A

vascular absorption

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20
Q

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

A

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

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21
Q

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

A

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

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22
Q

Rank the tissues from highest to lowest blood flow.

A

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

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23
Q

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

A

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

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24
Q

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

A

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

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25
Q

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

A

2-3

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26
Q

Conduction block is _______ dependent.

A

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

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27
Q

Voltage gated Na channels are found only in ______.

A

the nerve’s axon

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28
Q

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

A

2-6 higher than sensory

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29
Q

Motor block is ______ dermatomes _______ than sensory block.

A

2 lower than sensory

30
Q

Ester local anesthetics are metabolized by ________.

A

plasma pseudocholinesterase

31
Q

Amides are metabolized by the _______.

A

LIVER

am”I”de–>l”I”ver

32
Q

What is the MAX dose for chloroprocaine?

A

12mg/kg (duration 0.5-1hr)

33
Q

What is the MAX dose for cocaine?

A

3mg/kg (duration 0.5-1hr)

34
Q

What is the MAX dose for procaine?

A

12mg/kg (duration 0.5-1hr)

35
Q

What is the MAX dose for tetracaine?

A

3mg/kg (duration 1.5-6hr)

36
Q

What is the MAX dose for bupivacaine and ropivacaine?

A

3mg/kg (duration 1.5-8hr)

37
Q

What is the MAX dose for lidocaine and mepivacaine?

A

4.5mg/kg without EPI
7mg/kg with EPI
lidocaine duration= 0.75-2hr
mepivacaine duration= 1-2hr

38
Q

What is the MAX dose for prilocaine?

A

8mg/kg

duration= 0.5-1hr

39
Q

What is the treatment for local anesthetic toxicity?

A

1) airway
2) breathing
3) circulation
* Drugs:
- lipid emulsion (20% Intralipid) 1.5mL/kg, followed by continuous infusion of 0.25ml/kg/min
- benzo’s to treat seizures, small amount of propofol in benzo are not available, but no propofol in the context of cardiovascular instability
- AVOID vasopressin, CCB’s, beta blockers, and local anesthetics
- muscle relaxants to secure airway

40
Q

What is the initial dosing of _____% lipid emulsion (Intralipid) in the case of LA toxicity?

A

20%; 1.5ml/kg

41
Q

With methemoglobin, Fe2 (ferrous) becomes ________. What is the treatment?

A

Fe3 (ferric); Tx= methylene blue 1-2 mg/kg
normal Hgb has iron in the ferrous (Fe++) state, oxygen carried by normal Hb is excellent–> Met-Hb has iron in the ferric (Fe+++) state, oxygen carrying capacity Met-Hb is poor

42
Q

What is the normal (“therapeutic”) plasma concentration of lidocaine?

A

1-5 mcg/mL= analgesia, therapeutic

43
Q

What is the plasma concentration of lidocaine where you will begin to see early s/s of toxicity?

A

x2 of normal, so 5-10 mcg/ml

44
Q

What are the early s/s of lidocaine toxicity?

A

lightheaded, tinnitus, visual disturbances, numbness of tongue, muscle twitching
*almost like being drunk and then getting tazed

45
Q

List the s/s of lidocaine toxicity from early to late.

A

lightheaded, ears ringing, vision disturbed, numb tongue, muscles twitching, seizures and convulsions–> unconsciousness into coma into respiratory arrest into cardiovascular depression

46
Q

What plasma concentration of lidocaine is required to reach cardiovascular depression?

A

> 25 mcg/ml

47
Q

What plasma concentration of lidocaine is required to reach seizures and convulsions?

A

10-15 mcg/ml

48
Q

What plasma concentration of lidocaine is required to reach unconsciousness to coma to respiratory arrest?

A

15-25 mcg/ml

49
Q

What plasma concentration of lidocaine is required to reach lightheadedness, tinnitus, visual disturbances, numbness of the tongue, and muscle twitching?

A

5-10 mcg/ml

50
Q

_______ is the LA to which all others are compared.

A

lidocaine

51
Q

The action of _______ local anesthetics would be prolonged in the patient with atypical pseudocholinesterase.

A

ester

52
Q

Chronic therapy with acetylcholinesterase inhibitors (edrophonium, physostigmine, echothiophate) prolongs the action of ______ LA’s b\c these agents depress _________ function.

A

ester; pseudocholinesterase

53
Q

What is the end product of ester metabolism?

A

PABA–> para-aminobenzoic acid

this metabolite may mediate the hypersensitivity reactions to ester LA’s

54
Q

How does cocaine differ from other local anesthetics?

A

1) vasoconstrictor

2) naturally occurring

55
Q

Why is Chloroprocaine a suitable anesthetic for obstetric practice?

A

1) rapidly metabolized by plasma cholinesterase
this means plasma levels are kept low (important b\c LA’s cross the placenta)–> in order to protect fetus from toxic levels of LA, an agent that has its blood levels kept low is advantageous

56
Q

______ is hydrolyzed by plasma cholinesterase much more slowly than procaine or chloroprocaine.

A

tetracaine

57
Q

Dibucaine is about ____ times more toxic than procaine.

A

15

58
Q

If pseudocholinesterase is normal, dibucaine will depress the activity of pseudocholinesterase by _____%.

A

70-85%= dibucaine number

59
Q

If the dibucaine # is _____, the individual is a homozygote for the abnormal (atypical) pseudocholinesterase.

A

20

60
Q

If the dibucaine # is _____, the individual is a heterozygote for the abnormal (atypical) pseudocholinesterase.

A

30-70

61
Q

What is the clinical concern for patients with atypical pseudocholinesterase?

A

1) the lower the dibucaine number, the slower the hydrolysis of Sux
2) toxicity of ester local anesthetics is MORE likely

62
Q

Which local anesthetic can lead to methemoglobinemia and why?

A

prilocaine–> metabolite is O-toluidine which may lead to methemoglobinemia

63
Q

The dose of local anesthetic administered epidurally should be reduced by _____% in the parturient.

A

25-50%

64
Q

What is the cause of hypotension following spinal and epidural anesthesia?

A

blockage of sympathetic preganglionic nerves–> relaxation of arterial and venous vascular smooth muscle–> decreases SVR and reduced venous return–> decreases arterial BP (the decrease in preload is the biggest factor of hypotension)

65
Q

If beta effects are not desirable, what can be given instead of EPI with a local anesthetic?

A

1:20,000 phenylephrine

66
Q

The risk of aspiration pneumonitis is increased when gastric pH and gastric volume are:_____ and _______.

A

25mL

67
Q

What agent consistently reduces gastric volume and the acidity of gastric contents?

A

ranitidine

68
Q

Alfentanil is eliminated faster than sufentanil b\c alfentanil has a _______ volume of distribution than sufentanil.

A

smaller

69
Q

A drug will be eliminated slowly if its clearance is ______ and volume of distribution is ______.

A

small; large

70
Q

What segment of the neuron does local anesthetics work on?

A

the axon only

71
Q

Duration of action of local anesthetics is determined by?? (2 things)

A

BOTH lipid solubility and protein binding

Board Review CRNA (Sweat Book) (38 decks)

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