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5230 > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

3 structural components of local anesthetics

A 
Lipophilic side (benzene ring)
Hydrophilic side (quarternary amine)
Intermediate chain linkage
-Ester or
-Amide
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2
Q

Ester metabolism

A

Via cholinesterase, rapid

Tend to be shorter acting than amides

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3
Q

Ester allergies

A

Higher potential than amides

If allergic to one ester, all esters should be avoided

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4
Q

Amide metabolism

A

In liver by CYP1A2 and CYP3A4
Longer acting generally because they’re more lipophilic and protein bound and require transport to the liver for metabolism

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5
Q

Amide allergies

A 
Extremely rare
No cross allergy among class or with esters
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6
Q

Nerve Fibers A alpha, A delta, B, and C function

A

A alpha: Motor
A delta: Fast pain
B: Preganglionic SNS
C: Slow pain

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7
Q

Side of chemical structure of local anesthetic that can be ionized or not (Lipophillic or hydrophilic)

A

Hydrophillic side

-Can be ionized (charged) or nonionized (not charged)

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8
Q

Mechanism of action of local anesthetics

A
  • Nonionized portion (lipid soluble) enters the nerve
  • Drug reequilibrates
  • Ionized fraction attaches to receptor on the inside of the sodium channel, blocking it
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9
Q

Protein binding of local anesthetics determines:

A

Duration of action

  • Higher percent protein binding = longer duration of action
  • Binding stronger to proteins ~=binding stronger to tissues/nerves
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10
Q

Lipid solubility of local anesthetics determines:

A

Potency
Lipid solubility means they are nonionized and able to penetrate the myelin/nerve bilayer to get into the nerve to ionize and work

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11
Q

pKa of local anesthetics determines:

A

Onset of action
Lower pKa = faster onset
-Closer to 7.4 means theres a larger fraction that nonionized to enter the nerve
*Exception: Chloroprocaine has a high pKa but its fast because it’s given in such high concentrations

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12
Q

Effects on local anesthetics when epinephrine is added

A
  • Shorter onset time (faster) *Except during spinal anesthesia
  • More depth motor and sensory blockage
  • Longer duration of blockade
  • Larger area of blockade
  • Lower peak plasma concentration (less toxicity)
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13
Q

Ester name

A

1 I

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14
Q

Amide name

A

2 I’s

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15
Q

Ropivacaine characteristics

A

Similar to bupivacaine but doesn’t have the cardiac effects/risks

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16
Q

Bupivacaine problem, max dose

A

Preferentially binds to cardiac cells over others, can cause sudden cardiac arrest

  • .75% no longer allowed in US
  • Max dose = 3mg/kg
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17
Q

Lidocaine max dose

A

With epi: 7mg/kg

18
Q

Cocaine max dose

A

Only topical: 200mg

19
Q

Procaine max dose

20
Q

Chloroprocaine max dose

21
Q

Tetracaine max dose

A

1mg/kg (most toxic)

22
Q

Mepivacaine max dose

23
Q

Prilocaine max dose

24
Q

Ion trapping CNS toxicity

A
  • Local anesthetic overdose -> respiratory depression -> hypoxia, acidosis
  • Increased ionized fraction in cerebral circulation (b/c of acidosis, decreased pH)
  • Unable to cross the blood/brain barrier to exit cerebral circulation and reenter systemic circulation
25
Q

Ion trapping in fetal circulation

A

Fetal pH is lower than maternal pH

-Local anesthetic crosses the placental barrier to fetus, ionizes and is unable to cross back to maternal circulation

26
Q

Local anesthetic use in infected tissues

A

Ineffective because tissue is more acidotic

-Local anesthetic is more ionized, not lipid soluble and cannot be absorbed into the nerve

27
Q

Carbonation of local anesthetics

A

Speeds onset of action and intensity of block

  • CO2 diffuses into the nerve and makes the inside more acidotic
  • LA inside the nerve will ionize more = higher concentration of active form in the neuron at the sodium channel
28
Q

Adding sodium bicarbonate to local anesthetics

A

Speeds onset of action

  • Increases the concentration of the non-ionized (lipid soluble) form of the drug on injection
  • Improved diffusion of local anesthetic through the neuronal membrane
  • Also takes away stinging feeling initially felt by patient on injection
29
Q

LAST (local anesthetic systemic toxicity) is a concern with which class of LA?

A

Amides

-Won’t happen with esters because they’re metabolized so fast by cholinesterases

30
Q

Signs of LAST (and lidocaine plasma level they will occur at)

A

Lidocaine plasma concentration up to 5mcg/mL is therapeutic
-Lightheaded, tinnitus, circumoral (mouth) and tongue numbness
-Visual disturbances
-Muscular twitching (like fasciculation’s)
-Convulsions
-Unconsciousness, coma
-Respiratory arrest
-CV arrest
Bupivacaine goes strait to cardiac arrest

31
Q

Most common CNS sign of LAST

A

Seizure

  • Self limiting, happening because of disinhibition
  • Inhibitory parts of brain are asleep, seizure happens until pt goes deeper to coma
32
Q

Most common time after injection that LAST occurs

A

<1 minute (~50%)

33
Q

Primary goal in treating LAST (and why)

A

Prevent hypoxia and acidosis: they will potentiate LAST

-Rapidly halt seizures with benzos (succs if that doesn’t stop them)

34
Q

ACLS modifications for LAST

A
  • Use smaller doses of epi (10-100mcg)
  • Vaso isn’t recommended
  • Avoid calcium channel blockers and beta blockers
  • Treat ventricular arrhythmias with amiodarone (not lidocaine or procainamide)
35
Q

Lipid emulsion therapy for LAST, and what to do if it doesn’t work

A

1.5 mL/kg bolus of 20% lipid emulsion
Infusion of 0.25mL/kg/min for at least 10 mins after circulatory stability
If circulatory stability isn’t attained consider another bolus of 0.5mL/kg/min
^If this doesn’t work -> cardiopulmonary bypass

36
Q

Pregnancy affect on local anesthetics

A
  • Pregnancy enhances the effect of local anesthetics = dosage should be reduced
  • Elimination of amides are longer in newborns than their mothers (greater volume of distribution)
  • Fetus/newborn isn’t more vulnerable to toxic effects of local anesthetics than adults
  • Combining neuraxial LA with an opioid increases the block density and allows for administration of lower total dose of LA and side effects
  • Spinal bioavailability of fentanyl/sufentanil (lipophilic) is better than morphine/hydromorphone (hydrophilic)
37
Q

Mixing local anesthetics

A
  • Done to make onset faster but keep duration of action long (can make sure you’re in the right space for a longer block since they’re onset sometimes isn’t for 30-40 minutes)
  • Max doses is additive, not individual
38
Q

Tumescent Anesthesia

A

Technique used by plastic surgeons during liposuction

  • SQ injections of large volumes of dilute local anesthetics combined with epi, saline, and sodium bicarbonate
  • Max safe dose of lidocaine w/ epi = 35-55mg/kg
39
Q

Hyaluronidase

A

“Spreading factor”

  • Breaks down the tissue matrix so things can spread/move around to surrounding tissue
  • Makes onset of action faster but duration shorter
  • Used mostly in opthamology (so once injection in the eye can be done and it’ll spread instead of moving needle in the eye)
40
Q

Cocaine unique properties

A

Blocks reuptake of norepinephrine in the sympathetic nervous system: Has sympathomimetic effects
-Easily toxic, only used topically now

41
Q

EMLA

A 
Mixture of lidocaine and prilocaine
-Topical anesthetic 
-Used primarily in peds for IV starts
Max doses
0-3 months: 1g
3-12 months: 2g
1-6 years: 10g
7-12 years: 20g
-Has potential for mehemoglobinemia

5230 (13 decks)

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