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Summer Pharm (2016) ** > Local Anesthetics - concepts > Flashcards

Local Anesthetics - concepts Flashcards

1
Q

What is anterior spinal artery syndrome?

A

LE paralysis with/ without sensory deficit

is a clinical subset of spinal cord injury syndromes, due to ischemia/infarction of the anterior two-thirds of the spinal cord, typically sparing posterior third of the spine

Unknown cause, maybe vasoconstrictors (epi)?, PVD, advanced age ↑ the risk

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2
Q

What is the general difference between A, B, and C fibers?

(which are myelinated, speed, and size)

A

A fibers: myelinated, large, size 1-22 micrometers, FAST

  • important for afferent and efferent somatic (they have motor and sensory)

B fibers: myelinated, size 1-3 micrometers, slower than A, but faster than C

  • important for autonomic function (Motor only)

C fibers: unmyelinated fibers, small, size 0.1-2.5 micrometers, SLOW

  • motor only
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3
Q

The ionized form is favored when?

The non-ionized form is favored when?

(acid/base drug in acid/case environment)

A

Ionized favored when

  • acidic drug in basic environment
  • basic drug in acidic environment

Nonionized favored when

  • acidic drug in acidic environment
  • basic drug in basic environment
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4
Q

when do you redose lidocaine (epidural)?

A

lidocaine lasts about 1.5-2 hours etc

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5
Q

Potency is most influenced by _____

DOA is most influenced by _____

Onset is most influenced by ______

A

Potency - Lipid solubility

DOA - protein binding

Onset - pKa

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6
Q

What is caudal equina syndrome?

causes?

A

Diffuse lumbosacral injury, numbness in LE, loss of bowel and bladder control, paraplegia

this is PERMANENT

Causes: lidocaine 5%, tetracaine, chloroprocaine

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7
Q

what impact does the terminal group have on potency and toxicity

A

↑ length of terminal groups located on the tertiary amine (tail) & aromatic ring = ↑ potency & ↑ toxicity

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8
Q

What influences DOA of LAs

A

Duration proportional to amount of time LA is in contact with the nerve fiber

  1. protein binding - most important
  2. tissues blood flow
  3. addition of vasoconstriction
  4. lipid solubility
  5. intrinsic vasodilator activity (ex: lidocaine can vasodilate)
  6. Uptake by the lungs
  7. Metabolism
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9
Q

How many nodes of ranvier must be blocked by LA to stop the propagation of action potentials?

A

3

≈ 1 cm

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10
Q

what influences Cm (concentration minimum)

A
  1. Nerve fiber diameter (the farther the nodes of Ranvier the harder to block)
  2. Tissue pH (determines how much remains non-ionized)
  3. Frequency of nerve stimulation
  4. Potency of particular LA (determines how many molecules you need)
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11
Q

Epidurals are dosed based on what?

A

VOLUME

1.25-1.6 mL/segment

Choose concentration to use based on MAXIMUM DOSE, density of block required and toxicity profil

The dose really depends on the level that you want to achieve (for example, T4 vs T10 sensory level)

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12
Q

How can the name of a LA identify it as an amide vs ester?

A

One eyed ester (procaine)

Two i’s amide (lidocaine)

or amide has an “i” in from of “caine”

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13
Q

Local anesthetic uses?

A
  1. Infiltrated around the nerve
  2. Applied topically to the skin & mucous membranes
  3. Injected into blood vessels that are first exsanguinated
  4. Injected into the subarachnoid or epidural spaces
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14
Q

What are the pros/cons of ionized LAs vs. non-ionized?

A

Ionized binds to the receptor easier

Nonionized gets through the barrier easier

The ideal LA drug would be 50/50 (half ionized, half nonionized)

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15
Q

Why are vasoconstrictors added to LAs

A
  1. Inhibition of systemic absorption of LA
  2. Prolongation DOA of the LA effect → ↓ chance of toxicity d/t slowing systemic absorption
  3. Detection of intravascular injection
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16
Q

pH - effects on onset

A

pH of the local anesthetic solution & the pKa of the drug determine proportion of drug in the non-ionized state

high/normal pH values, the rate & amount of absorption is higher

lower pH, the rate & amount of absorption are lower

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17
Q

Do locals change the threshold potential, the ability to reach threshold, or both?

A

NO

they ONLY change the ability to reach threshold

(they inhibit reaching the threshold)

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18
Q

Between sensory, motor, and autonomic, which is blocked first when given an LA?

A

Autonomic blocked first, more on the outside/mantle of the nerve (C fibers)

Sensory blocked next

Motor blocked last because it is at the core/inner surface and hardest for the LA to reach

onset relies on location of nerve fibers

autonomic and smaller fibers go first

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19
Q

Cm (concentration minimum)

A

the min number of molecules needed to block a certain nerve

analogous to MAC

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20
Q

Peripheral nerve blocks are dosed based on what?

A

VOLUME

Choose concentration based on limits of max dose

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21
Q

Are local anesthetics triggers for MH?

A

Nope

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22
Q

which nerve roots has the sensory nerves

A

dorsal roots = sensory = afferent neurons

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23
Q

Adding vasoconstricor to LA has what three effects?

A
  1. Inhibits systemic absorption
  2. Prolongs DOA
  3. Detects intravascular injection
24
Q

What treats LA toxicity CV collapse?

A
  • CPR
  • Modified ACLS
    • limit medications to epinephrine 10-100 mcg
    • use amiodarone
      • avoid CCB, ß blockers, lidocaine
  • Intralipid 20% 1.5 mL/kg rapid bolus immediately; follow with infusion 0.25 mL/kg/min x 10 min
  • Cardio-pulmonary bypass
25
Q

Local anesthetics MOA?

A

LAs bind to the Na+ channel alpha subunit when it is in the inactivated closed state

(in the inner portion of the channel)

Impulse conduction blockade is caused by inhibition of the influx of Na+ ions (during depolarization phase of action potential)

26
Q

List max doses of LAs Bupivacaine, ropivacaine, etidocaine, lidocaine, mepivacaine, choroprocaine, cocaine, tetracaine

A

Bupivacaine 2.5 mg/kg Cocaine 3 mg/kg Tetracaine 3 mg/kg Ropivacaine 3 mg/kg (3.5 w epi) Etidocaine 4 mg/kg Lidocaine 4 mg/kg (7 w epi) Mepivacaine 4 mg/kg (7 w epi) Chloroprocaine 12 mg/kg

27
Q

LA drug interactions?

A

Pseudocholinesterase inhibitors may prolong the duration of ester anesthetics

Cimetidine and propranolol decrease hepatic blood flow, decrease clearance of amide LA and cocaine

Analgesia promoted by opioids, clonidine, and epinephrine added to LA

28
Q

what drug is the exception to the pKa-onset rule

A

Chloroprocaine

although the pKA is high (8.7) it has the fastest onset because it’s given in higher concentrations (has more molecules crossing the membrane)

29
Q

List each fiber from fastest to slowest and list what it senses.

(A: alpha, beta, delta, gamma; B; C)

A

A-alpha: motor and proprioception

A-beta: motor, touch, pressure

A-gamma: motor/muscle tone (fine motor modulation)

A-delta: pain, temp, touch

B: PREganglionic autonomic

C: dull pain, temp, touch, POSTganglionic autonomic

30
Q

Large fibers have the

_____ conduction velocity,

_____ capacitance, and

_____ threshold for excitability (highest/lowest)

A

Highest conduction velocity

Highest capacitance

Lowest threshold for excitability

31
Q

LA toxicity s/s?

A

CNS

circumoral numbness, tinnitus, vision changes, dizzy, slurred speech, restless, muscle twitching (especially in the face), seizures (which cause CNS depression, apnea, hypotension)

CV

hypotension, myocardial depression, AV block

Note: bupivacaine is most CV toxic

32
Q

which nerve roots has the motor neurons?

A

ventral = efferent = motor

33
Q

When looking at % non-ionized and onset, which LA doesn’t follow the rule?

A

Rule: higher % non-ionized = faster onset

Chloroprocaine is the exception to the rule because it is only 2 % non-ionized and has a fast onset (we give it in higher concentrations to have this effect)

34
Q

Do ionized or non-ionized drugs cross a lipid membrane?

A

NON-ionized

35
Q

What factor of an LA is most important in determining potency? Which drugs are highly potent?

A

Lipid solubility

Highly potent: etidocaine, bupivacaine, tetracine

36
Q

pKa - effects on onset

A

the closer the pKa is to 7.4 (closer to physiological pH) will be FASTER ONSET than a drug with pKa of 9

37
Q

Describe the typical structure of a LA

A

Lipophilic head (aromatic ring)

Intermediate chain containing an amide (NH) or an ester (COO-)

Hydrophilic tail (tertiary amine)

38
Q

What does adding bicarb do to the LA effect?

A

Increases onset

Enhances block depth

Increases spread of block

39
Q

What is TNS (transient neurologic symptoms), aka transient radicular irritation?

A

Neuro-Inflammatory process causes pain in lower back, butt, posterior thigh, 6-36h after full recover from SAB, lasts about a week

Associated more with lidocaine

40
Q

what impact does the intermediate chain have on potency and toxicity

A

↑ in the length of the intermediate chain (↑ number of carbon atoms) → ↑ potency & ↑ toxicity

41
Q

LA lipid solubility & potency, toxicity, DOA

A

highly lipid soluble = More potent, higher risk of toxicity, longer DOA

42
Q

Which ion establishes and maintains resting membrane potential?

A

K+

43
Q

when do you redose chloroprocaine (epidural)?

A

chloroprocaine lasts about an hour before you have to redose

44
Q

Allergy to LA is usually due to what?

A

Allergy to PABA, esters

Other: preservative reaction (ex: Methylparaben additive)

45
Q

Spinals are dosed based on what?

A

DOSES.

Just know them. :’(

46
Q

how does temp affect onset

A

↓ temperature = ↓ drug absorption across the nerve membrane = ↓ onset

47
Q

hwat do you do if your pt has seizures r/t LA toxicity

A
  1. airway
    • seizure = lots of metabolism → they need more O2
    • get CO2 normalized
  2. benzos - anticonvulsant properties
48
Q

What characteristics govern LA systemic absorption?

A

Physiochemical factors

  • pKa, pH, and lipid solubility
    • ​ex: water soluble will be removed faster from site
  • blood flow

Physiologic conditions:

  • tissue pH
  • pCO2
  • temp
  • characteristics
    • ​Note: elderly and pregnant are more at risk for toxicity

volume of solution or vehicle used (ex: epi)

concentration of local anesthetic

49
Q

Conditions that increase the risk for LA toxicity

A
  1. Pregnancy
  2. hypoxia
  3. pH abnormalities
  4. CV modulating drugs (ex: β-blockers)
50
Q

action potential - absolute refractory period

when? why is it important?

A

when the voltage gated Na+ channels are in inactivated state

regardless of how strong the stimuli, no action potential can be generated

51
Q

LA absorption by type of block from high to low?

A

I Think I Can Place Epidural Blocks So Smoothly

  1. Intravenous
  2. Tracheal
  3. Intercostal
  4. Caudal
  5. Paracervical
  6. Epidural
  7. Brachial plexus
  8. Subarachnoid
  9. Subcutaneous
52
Q

Local anesthetics are strong/weak acids/bases

A

Weak bases

Packaged in acidic formulations (to make them water soluble & not precipitate) but basic upon injection

53
Q

concept of frequency or use dependent blockade

A

the more frequently the nerve cycles through actio potential, the more readily the Na++ channels are found in ianctive state, the more rapidly the blockade occurs

resting nerves are less sensitive than repetitively stimulated nerves

54
Q

How are esters vs. amides metabolized?

A

Esters: hydrolyzed by non-specific esterase’s in the plasma and tissues (mostly liver)

  • metabolized faster w/ low chance of toxicity
  • metabolite = PABA (para-aminobenzoic acid), except for cocaine

Amides: metabolized in the liver, CP450

  • slower than esters
  • aromatic hydroxylation
  • N-dealkylation
  • amide hydrolysis
55
Q

in a neuron, where are the voltage gated Na+ channels found?

A

in the axon

concentrated in the nodes of Ranvier

56
Q

What is Exparel?

A

Bupivacaine extended release liposome injection, only approved for bunionectomy and hemorrhoidectomy

When mixed with another local, it will change the effects and increase chance of toxicity

57
Q

More specifically, what is the clinical sequence of local anesthesia blockade (5 steps), what is blocked?

A

1- sympathetic block (autonomic block: vasodilation, warm skin)

2- loss of pain and temp

3- loss of proprioception

4- loss of touch and pressure (pressure is difficult to block)

5- motor blockade

Summer Pharm (2016) ** (17 decks)

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