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23 spring anesthesia > Test 3: 34 local > Flashcards

Test 3: 34 local Flashcards

1
Q

what is a local anesthetic

A

drug that causes reversible loss of sensory perception and motor function, in a localized area of the body

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2
Q

lidocaine is used because

A

antiarrhythmic
prokinetic
MAC reduction
analgesia

systemic administration

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3
Q

local anesthetics work on what type of channels

A

periphery: Na channels

dorsal horn spinal cord: LAs inhibit K+ or Ca2+ channels, inhibit substance P binding and reduce glutamatergic transmission by reducing N-methyl-D-aspartate (NMDA) postsynaptic depolarization. Work on serotoninergic and AcH receptors

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4
Q

how does lidocaine effect Na channels

A

lidocaine either ionized or uncharged

uncharged version will cross lipid membrane, become ionized and bind to inside of Na Channel from the intracellular side

this will prevent Na channel from opening and prevents Na from entering the cell → can can not depolarize and send signal

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5
Q

if the local has an ester group it will be broken down by

A

hydrolyzed by plasma esterases

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6
Q

if local has an amide group it will be broken down in

A

metabolized in the liver

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7
Q

All clinically useful local anesthetics are —, and as such they exist in equilibrium between the neutral, non‐ionized, lipid soluble form (B) and the ionized (charged), water‐soluble form (BH+).

A

weak bases

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8
Q

The neutral/uncharged form is — and easily crosses the cell membrane. The — form is more water soluble and can cross only through the open channel.

A

lipid soluble

ionized

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9
Q

what three physiochemical properties control the effect of Local

A

The pKa of a LA determines the onset of the pharmacological effect

The lipid solubility of a LA determines its potency

The protein binding (of a LA with serum proteins) determines the duration of the pharmacological action

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10
Q

what is the pKa for most LA

A

ph>7.4

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11
Q

The — the pKa, the greater the degree of ionization or proportion of local anesthetic in the ionized, charged, hydrophilic form at physiologic pH (7.4), and the — the onset of action.

A

higher

slower

(if LA is in ionized form it can not cross through membrane, takes longer for effect to happen)

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12
Q

a local anesthetic with a — pKa will have a greater proportion of the non-ionized lipid-soluble form at physiologic pH and a more — onset of action.

A

low

rapid

(at a pka< 7.4, the LA will be in the nonionized, neutral form, it can easily move across membranes and attach to NA channels on the intercellular side → rapid onset)

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13
Q

Increasing lipid solubility facilitates the penetration through lipid membranes, potentially — onset of action.

A

hastening

the more lipid soluble the greater the potency of a drug

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14
Q

the lower the lipid solubility, the — the potency

A

lower

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15
Q

Higher protein binding is associated with — duration of action

A

increased

only free, unbound drug is active, if most of the drug is bound to protein, it will take a long time to use up the drug

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16
Q

lidocaine, procaine, and tetracaine have what chirality?

A

achiral

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17
Q

what are some S-enantiomer LA

A

Left: leviosomers
levobupivacaine and ropivacaine

they are less toxic then their Right versions (bupivicane)

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18
Q

what is differential blockade

A

Some LA can produce vasodilation →loss of sensory → motor loss based on dose of med given

Ropivacaine > Bupivacaine > Lidocaine = Mepivacaine

Local anesthetics with an amide group, high pKa, and lower lipid solubility show greater differential blockade

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19
Q

if you give low dose ropivacaine what will happen

A

differential blockade

at low does will have vasodilation and some sensory loss, but motor still intact

if you increase dose will lose all three

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20
Q

what length exposed to drug is important for differential pattern

A

three or more nodes of Ranvier

Therefore, larger fibers with greater internodal distances are less susceptible to local anesthetic blockade

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21
Q

decremental conduction

A

usually need 3 nodes of ranvier for effect

DC: describes the diminished ability of successive nodes of Ranvier to propagate the impulse in the presence of a local anesthetic. This principle explains why the propagation of an impulse can be stopped even if none of the nodes has been rendered completely unexcitable, as occurs for example with low concentrations of local anesthetics.

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22
Q

which type of nerve fiber is blocked first with LA

A

B > C = A-δ > A𝛄 > Aβ > A⍺

23
Q

Systemic absorption depends on several factors including

A

site vascularity: ↑ vessels= ↑ absorption

intrinsic vasocativity: vasodilators ↑ absorption, constrictors (ropivacaine and levobupivacaine) ↓ absorption

lipid solubility, protin binding, dose

the lower the systemic absorption the safer the med, increased systemic absorption can be toxic

24
Q

which LA injection site has increased vascularity

A

intercostal > epidural > brachial plexus > sciatic/femoral

25
Q

which LA are vasoconstrictive

A

ropivacaine and levobupivacaine

constriction will lead to slower systemic absorption →less toxicity

26
Q

if you add epi to lidocaine will it dilate or constrict vessels

A

lidocaine- dilate
epi- constrict

constriction wins= less systemic absorption of LA

27
Q

what type of LA is widely distributed throughout body

A

amino-amides

amino-ester LA are rapidly hydrolyzed = ↓ distribution

28
Q

explain 1st pass pulmonary uptake

A

amino-amides LA are widely distributed throughout the body

amino-amides will go through 1st pass pulmonary uptake = lung will absorb a lot of the lipid-soluable, ↓pKa drugs (bupivacaine> lidocaine)

increased risk of toxicity if R-L cardiac shunt (drug doesn’t get to lungs to be cleaned out)

increased risk if ↓ blood pH, cause that will ↑ ionized form of meds and lungs abdorb the unionized version

29
Q

what happens when LA amino-amides get into placenta

A

ion trapping

maternal pH is higher then the baby, the lower pH makes more ionized form of LA, that can not cross back out of baby

30
Q

use — LA in pregnant pts to prevent ion trapping

A

lidocaine > bupivacaine

31
Q

breakdown of benzocaine and procaine can produce —

A

PABA → rare allergic reaction

amino-ester LA that are hydrolyzed by plasma pseudocholinesterases

32
Q

Prilocaine is broken down by — and forms —

A

prilocaine is an amino-amide
metabolized in liver by CYP450
makes toxic metabolite methemoglobin

33
Q

lidocaine is broken down by — and makes —

A

Lidocaine= amino-amide LA
broken down in liver by CYP450
produce MGEX toxic

34
Q

The dose of a local anesthetic causing systemic toxicity will depend on the —

A

route and speed of administration (rapid intravenous administration will be more likely to cause high plasma levels),

the species involved

patient factors (such as acid–base balance, serum potassium levels)

more lipid soluble drugs will be more potent

R-enantiomers more toxic

35
Q

what are signs of LA toxicity

A

CNS: excitation, seizure, depression and coma

cardiac: ↓Na into a cell= prolonged PR and QRS intervals = bradycardia, ↓BP, ↓ contractility, asystole

↑potassium = toxic

36
Q

how does increased PaCO2 lead to ↑ risk of seizures with LA

A

↑PaCO2= vasodilation in the brain= more LA into the brain = ↑ toxicity → seizures

37
Q

how does increased PaO2 protect from seizures from LA

A

hypoxemia increases the CNS and cardiovascular toxicity of local anesthetics

high O2 vasoconstrictive?

38
Q

how to treat LA overdose

A

supportive care: oxygen, ventilation

may need to do CPR, epi and difibrillate

DO NOT USE LIDOCAINE to treat arrhythmias: use amiodarone or IV lipid emulsion

39
Q

local LA can be neurotoxic to — cells and is — dependent

A

schwann cells
time and concentration

mepivacaine < lidocaine < ropivacaine < bupivacaine.

40
Q

local LA can be myotoxic to —- and is — dependent

A

skeletal muscle: mess up intracellular Ca and mitochondria

concentration dependent

bupivacaine is worse

41
Q

LA can be chondrotoxic if — and are — dependent

A

intra-articular injection

time and concentration dependent

mepivacaine < ropivacaine < bupivacaine= lidocaine

42
Q

which LA can produce methemoglobin when broken down

A

ester type: benzocaine and amide type prilocaine

chocolate brown colored blood- not responsive to O2 therapy- need to treat with methylene blue or blood transfusions in severe cases

43
Q

it is recommended that animals known to be allergic to ester‐type local anesthetics be treated with a —

A

preservative‐free amide‐type agent

procaine: ester: forms PABA when metabolized, can be allergic

44
Q

procaine

A

amino ester LA
fast onset
30-60 min duration
CNS stimulant in horse if given IV
metabolism → PABA→allergic reactions

45
Q

benzocaine

A

fast acting
topical only
amino ester LA → PABA → allergic reaction
Can also cause Methemoglobinemia in small animal
used for fish

46
Q

Tetracaine

A

amino ester LA
rarely used due to very slow onset when administered in the periphery and potential for systemic toxicity

excelent topical anesthetic

47
Q

lidocaine

A

amino-amide LA

  • fast onset, 1 hrs duration
  • inflitration, nerve blocks, epidural and intrathecal blocks, and intravenous regional anesthesia
  • EMLA cream, patches

analgesia from action at Na+, Ca2+, and K+ channels and the NMDA receptors.

Class Ib antiarrhythmic drug

some anti‐inflammatory effects

prokinetic in horses: prevent post op ileus by improving GI motility

48
Q

mepivacaine

A

amino-amide LA
* fast onset, 1-2 hrs
* infiltration, nerve block
* poor topical
* low neurotoxicity- use for horses
* very slow metabilism in fetus and newborns

49
Q

bupivacaine

A

amino-amides LA
* highly lipophilic= 4 x more potent then lidocaine
* slow onset (20-30 mins), long duration 3-10 hrs
* infiltrative, peripheral nerve, epidural, and intrathecal blocks
* poor topical
* NO IV → cardiotoxic

Levobupivacaine: levoisomer or S‐enantiomer of bupivacaine →less cardiotoxic

50
Q

Ropivacaine

A

amino-amide LA
* S- enatiomer = ↓ CV toxic
* similar onset to bupivacaine (20-30 mins), duration (6 hrs)
* infiltrative, peripheral nerve, epidural, and intrathecal blocks
* Biphasic effect of vasculature
* > 1% vasodilation
* < 0.5% vasoconstriction

51
Q

why add epinephrine to local

A

it causes vasoconstriction → Decreased systemic absorption and longer duration

  • decreases local blood flow to nerves and spinal cord → can cause ischemia
  • systemic absoprtion will cause CV effects

1: 200,000 (5 mcg/ml)

52
Q

what will bicarb do to LA

A

↑pH= ↑ unionized form = shorter onset
* efficacy depends on LA and location
* decreases pain of injection

1 mEq/10ml

53
Q

what will adding an ⍺2 agonist do to LA

A

enhances sensory and motor blockade
* receptors not involved- hyperpolarized C fibers

shorter onset, longer duration of sensory and motor block, enhanced block quality, lower pain scores, and decreased systemic opioid requirements

54
Q

nocita

A

72 hr analgesia

multivesicular liposomes, that encapsulate aqueous bupivacaine

23 spring anesthesia (40 decks)

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