Local Anesthetics Flashcards Preview

Anesthesiology > Local Anesthetics > Flashcards

Flashcards in Local Anesthetics Deck (63):
1

What was the first local anesthetic and when was it introduced?

Cocaine- 1884

2

What is unique to cocaine as a LA?

It causes profound vasoconstriction

(others will cause vasodilation)

3

Is cocaine still in use today? If yes, what is it typically used for?

Yes! It is a schedule II drug typically used for nasal surgery in humans (or other highly vascular surgeries)

4

What are the two classifications of LAs?

Ester-CO-

Amide -NHC-

5

What is the general structure of LAs?

Aromatic ring and hydrophilic portion joined by a hydrocarbon chain

They are classified by the hydrocarbon chain

6

What are the esters?

Cocaine, procaine, chloroprocaine, tetracaine

7

What are the amides?

Lidocaine, mepivicaine, bupivicaine, etodicaine, prilocaine, ropivacaine

8

What is the general MOA of LAs?

Bind to sodium channels in nerve membranes slowing rate of depolarization

Threshold potential cannot be reached and action potentials are not propagated

9

T/F: LAs are weak acids.

False- all LAs are weak bases

pK ~7.7-9

10

What kind of tissues will increase ionization of LAs?

Acidic tissues (ie infection esp) which makes them inactive

11

What three things affect potency, onset, and duration?

- pK
- protein binding
- lipid solubility

12

Will a higher or lower pK increase onset time?

Lower- closer to tissue pH

13

Will a greater or lesser affinity to protein binding increase duration of action?

High protein binding affinity

14

Will a higher or lower lipid solubility increase potency?

Higher the lipid solubility, higher the potency

15

What is the only LA that can be given IV or for IVRA?

Lidocaine

16

What is lidocaine onset/duration?

Fast onset, short duration

17

Is lidocaine absorbed transcutaneously?

Yes

18

What are the systemic/IV effects of lidocaine?

1. Antiarrhythmic
2. Decrease MAC
3. Analgesic
4. Free radical scavenger
5. Improves GI motility

19

What is the onset/duration of bupivicaine?

Immediate onset, moderate duration (3-8hr)

20

T/F: Bupivicaine has the lowest cardiovascular toxicity.

FALSE- highest toxicity, do not give IV

21

What is mepivacaine used for?

Nerve blocks, intra-articular analgesia (large animals)

22

What is the onset/duration of mepivacaine?

Fast onset, short duration (1.5-3)

23

What is the onset/duration of ropicacaine?

Intermediate onset, moderate duration (3-8hr)

24

T/F: Ropivacaine is less cardiotoxic than bupivacaine.

True

25

What is procaine commonly used for?

Procaine penicillin G suspensions (PPG)

26

What are tetracaine and proparacaine commonly used for?

Ophthalmic preparations

27

What is benzocaine commonly used for?

Historically used as a laryngeal spray for intubation

28

What does systemic absorption depend on?

1. Site of injection
2. Dosage
3. Drug Characteristics
4. If epinephrine is used

29

What site of injection has the fastest absorption?

Intercostal blocks

30

How are esters metabolized?

Hydrolysis of plasma cholinesterases

31

How are amides metabolized?

Microsomal liver enzymes

32

Are amides or esters more likely to accumulate?

Amides

33

Do amides or esters have a metabolite that may cause allergic reactions?

Esters

PABA may cause subsequent allergic reactions

34

Why is epinephrine used with LAs?

To prolong duration of block via vasoconstriction

35

Why is bicarbonate used with LAs?

Shorten onset and prolong duration, decrease sting on injection

36

Why would LAs be combined?

Shorter onset and longer duration combining lidocaine and bupivicaine?

Not really useful overall and may increase toxicity

37

What drugs cause methemoglobinemia?

Benzocaine and prilocaine

Benzocaine + tetracaine (cetacaine) laryngeal spray especially in cats (discontinued used in vet med)

38

T/F: Neurotoxicity is concentration dependent and can cause permanent damage.

True, although permanent damage is rare with normal clinical use

39

What drugs are the most neurotoxic?

Spinal lidocaine most, bupivacaine

40

What kinds of LAs should be used for spinal anesthesia/epidurals to avoid neurotoxiticy?

Preservative free

41

T/F: Chondrotoxicity is concentration and time dependent.

True

42

What is the most chondrotoxic LA?

Bupivicaine, no longer administered IA

43

What is the least chondrotoxic LA?

Mepivacaine (carbocaine)- most often used for equine lameness dx

44

What is systemic toxicity caused by?

Excessive plasma concentrations due to inadvertent IV infection or excessive doses/intolerant patient

45

What are the signs of systemic toxicity with lidocaine?

Depression/sedation, twitching, CV signs

46

What are the signs of systemic toxicity with bupicavaine?

Cardiovascular collapse and death

47

If epinephrine is used, what is the first sign of accidental IV injection?

Increased HR

48

What are the goals of local anesthesia?

1. Provide analgesia before, during, and after a procedure
2. May allow decreased dosage of systemic drugs
3. Prevents central sensitization
4. Important for multimodal anesthesia

49

What is the order of the nerve blockade?

Smaller, less myelinated fibers first

1. B fibers- pre-gang. sympathetic
2. A-delta and C fibers- pain
3. A-gamma fibers- prorioception
4. A-beta fibers- touch/pressure
5. A-alpha fibers- motor

50

What is the exception to the order of nerve blockade?

Brachial plexus- motor neurons blocked fist

(motor nearer to periphery)

51

What are the three types of local anesthesia?

1. Topical
2. Subcutaneous
3. Line block

52

What are the three types of regional anesthesia?

1. IVRA
2. Peripheral- individual nerves or areas
3. Central (neuraxial)- epidural or spinal

53

What type of anesthesia is a bier block?

Intravenous regional anesthesia

54

What is the procedure for a bier block?

Tourniquet is placed and anesthetic is injected to a peripheral vein and allowed to diffuse into target tissues

55

What LA is used for bier blocks and why?

Lidocaine only- it will be released into systemic circulation after procedure is finished

56

What is the difference between epidural and spinal anesthesia?

Epidural- injection into the space between the dura and vertebrae

Spinal- injection into the space between the dura and spinal cord, into CSF

57

Where are epidurals used?

Tail/perineum, hindlimb, and abdominal/thoracic pain/procedures

58

Where does the spinal cord end?

Dogs- L6-L7
Cats- L7-S3
Horses, ruminants, pigs- mid sacrum

59

How should the doses be adjusted if CSF is encountered?

Decreased by 50%

60

What are contraindications to epidurals?

CHINAS

- Coagulopathy
- Hypovolemia
- Infection at site
- Neoplasia at site
- Anatomy- Inability to palpate landmarks
- Sepsis

61

What are adverse effects of epidurals?

- Hypotension
- Motor block/paralysis (concerning for LA)
- Hematoma
- Infection
- Neurotoxicity

62

What is a nerve locator?

Electrostim unit with an insulated needle that produces a motor response when needle is close to a nerve

63

Can ultrasound be used to locate nerves?

Yes