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Anesthesia Pharm > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

Mechanism of Action of Local Anesthetics

A

Local Anesthetics (LA) produce reversible blockade of conduction of electrical impulses along nerve fibers

Reversibly block voltage-gated sodium channels in neurons (primary site of action)

  1. Penetrate/enter inner cell membrane of neuron
  2. Bind receptors within/near site of action
  3. Preventing influx of sodium ions
  4. Blocking propagation of the action potential
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2
Q

The mechanism of local anesthetics depend on what factors?

A

Nerves being blocked

Chemical structure of local anesthetic

Properties of local anesthetic

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3
Q

Local anesthetics cause reversible and transient loss of sensation (analgesia) in a portion of the body without _____

A

loss of consciousness

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4
Q

What is the sequence of sensory function blockade?

A

Pain → Temperature → Touch → Pressure → Motor

*recovery occurs in reverse order

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5
Q

Differential blockade is dependent on ___ and determined by ___.

A

Dependent on nerve sensitivity to local anesthetics

Determined by nerve fiber

oType

oDiameter

oMyelination

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6
Q

Lipid solubility is determined by ___

A

Aromatic ring and its substitutions

Tertiary amine substitutions

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7
Q

Greater lipid solubility equals ____

A

Increased potency (concentrations range 0.5-4%)

Increased protein binding

Longer duration of action

Slower onset of action

Higher tendency for cardiac toxicity

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8
Q

Greater protein binding for LAs equals _____

A

Longer duration of action

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9
Q

Higher pKa equals _______

A

Slower onset of action

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10
Q

Greater inherent vasodilation equals _____

A

Increases systemic absorption

Increases chances of toxicity

Decreases duration of action

Decreases onset of action

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11
Q

Systemic absorption/distribution dependent on ______

A

Site of injection

Dose

Addition of vasoconstrictor

Patient related factors

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12
Q

What are the two phases of diffusion?

A

Rapid disappearance phase – uptake by rapidly equilibrating tissue with high vascular perfusion

Slow phase of disappearance – individual local anesthetic distribution, biotransformation and excretion

Called the two compartment model

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13
Q

Metabolism/Excretion of Amide-Type LAs

A

Metabolized in the liver by CYP1A2 and CYP3A4 à can result in significant systemic levels with rapid absorption, increases potential for toxicity

Excreted by the kidneys

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14
Q

Metabolism/Excretion of Ester-Type LAs

A

Metabolism catalyzed by plasma and tissue cholinesterase via hydrolysis à rapid and occurs throughout body, reduces potential for toxicity

Results in water soluble metabolites that are excreted in urine

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15
Q

Mixture of local anesthetics are used to ____

A

achieve quick onset and long duration

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16
Q

Potency, spread/depth of epidural anesthesia is increased during ____

A

pregnancy

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17
Q

Newborn and elderly patients exhibit ____

A

prolonged half lives (decreased metabolism)

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18
Q

Hepatic dysfunction reduces metabolism of ____ LAs

A

amide type

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19
Q

Addition of sodium bicarbonate increases _____ resulting in _____.

A

increases pH

resulting in more drug in nonionized state and accelerated onset of action

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20
Q

What is the most commonly used vasocontrictor added agent to LAs?

A

Epinephrine

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21
Q

How does adding epinephrine to a LA decrease the chance of toxicity?

A

It decreases vascular absorption which results in reduced blood concentrations and reduced risk of toxicity

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22
Q

Epinephrine concentration 1:100,000 = ___

A

10 mcg/mL

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23
Q

Epinephrine concentration 1:200,000 = ____

A

5 mcg/mL

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24
Q

LAs that have a low potency and a short duration of action include ____

A

Procaine

  • Slow onset
  • DOA: 60-90 minutes

Chloroprocaine

  • Fast onset
  • DOA 30-60 minutes
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25
Q

LAs that have an intermediate potency and duration include ___

A

Mepivacaine

  • Fast onset
  • DOA 120-240 minutes

Lidocaine

  • Fast onset
  • DOA 90-120 minutes
26
Q

LAs that have a high potency and long duration include ____

A

Bupivacaine

  • Slow onset DOA 180-600 minutes

Ropivacaine

  • Slow onset DOA 180-600 minutes
27
Q

For site of injection, areas with high vascularity result in ___

A

greater uptake and higher blood concentrations

28
Q

Drugs that alter/compete for plasma cholinesterase activity ____

A

Decrease hydrolysis of ester type

Examples: succinylcholine, neostigmine, pyridostigmine

29
Q

Drugs that inhibit hepatic enzymes/decrease hepatic blood flow ____

A

Result in increased accumulation of amide type (such as lidocaine)

Examples: cimetidine, propranolol

30
Q

What interaction do opioids/alpha adrenergic agonists have on LAs?

A

Potentiate analgesic effects

31
Q

Which type of local is associated with increased allergic response?

A

Ester-type

Derivatives of and metabolized to PABA (para-aminobenzoic acid)

Cross reactivity within class

32
Q

Treatment of LA allergy

A

Mild reactions: PO/IV diphenhydramine, famotidine

Severe: epinephrine, corticosteroids

33
Q

What causes Local Anesthetic System Toxicity (LAST)?

A

Increased systemic concentrations of local anesthetic

oIntravascular injections

oHigher doses

oHigher absorption

oDecreased metabolism and elimination

34
Q

Which LAs are at higher risk for causing LAST?

A

Long acting and potent LAs

35
Q

S/S of LAST

A

Neurological Symptoms

  • lightheadedness, visual disturbances, muscle twitching, convulsions, unconsciousness, coma, respirartoy arrest, CVS depression

Cardiac Symptoms

  • Ventricular fibrillation
  • Ventricular tachycardia
  • ST changes
  • Wide complex
  • Hypotension
  • Tachycardia
  • Bradycardia/asystole
36
Q

Prevention of LAST

A

Ensure appropriate access

Adhere to maximum dose recommendations

Be aware of concentration calculations

Choose agent that is suitable with least necessary potency and toxicity profile

Addition of vasoconstrictor

Careful patient observation following injection

Immediate discontinuation upon recognition of toxic symptoms

37
Q

Treatment of LAST

A

Immediately stop injection/aspirate if possible and do not administer any additional local anesthetics

Supportive care to treat signs and symptoms

Airway management: 100% oxygen

Seizure suppression: benzodiazepines

BLS/ACLS algorithms

Avoid vasopressin, CCBs, beta-blockers, propofol

Lipid emulsion 20% infusion

38
Q

For treatment of LAST with lipid emulsion 20% infusion, what is the dosing guidelines?

A

Bolus 1.5 mL/kg (lean body mass) IV over 1 minute

Continuous infusion 0.25 mL/kg/min

Repeat bolus once/twice after 5 minutes for persistent cardiovascular effects

Double infusion rate if blood pressure remains low

Continue infusion for at least 10 minutes after attaining stability

Upper limit: 10 mL/kg over first 30 minutes

39
Q

What causes aquired methemoglobinemia?

A

LA metabolites include o-toluidine derivatives, which are responsible for inducing hemoglobin oxidation

Metabolite causes iron atom in hemoglobin to be oxidized from a ferrous form (Fe2+) ferric form (Fe3+) (conversion of hemoglobin to methemoglobin)

Methemoglobin is incapable of binding and transporting oxygen

Methemoglobin accumulation leads to tissue hypoxia

40
Q

What agents can cause methemoglobinemia?

A

Prilocaine

Lidocaine

Tetracaine

Benzocaine

41
Q

What pre-existing factors place a patient at higher risk for development of methemoglobinemia?

A

G6PD deficiency

Congenital or idiopathic methemoglobinemia

Cardiac or pulmonary compromise

Exposure to oxidizing agents or their metabolites

Infants < 6 months

42
Q

Signs/Symptoms of Methemoglobinemia?

A

Onset: Immediate or delayed

Cyanotic skin discoloration, lightheadedness, headache, tachycardia, fatigue, confusion, tachypnea, seizures, arrhythmias, acidosis, death, chocolate-brown discoloration of blood

43
Q

Treatment of Acquired Methemoglobinemia

A

Immediate discontinuation of LA and other oxidizing agents

Methylene blue 1-2 mg/kg administered over 5 minutes

oAt lower doses, increases conversion of methemoglobin to hemoglobin

oMay repeat dose in 1 hour if needed

oMaximum dose 7-8 mg/kg

44
Q

Maximum dose of Bupivacaine and Levobupivacaine

A

Plain: 2mg/kg

With epinephrine: 3mg/kg

Total max dose Bupivicaine Plain: 175mg

Total max dose Bupivicaine with epinephrine: 225mg

45
Q

Maximum dose of Lidocaine

A

Plain: 5mg/kg

With epinephrine: 7mg/kg

Total max dose Plain: 350mg

Total max dose with epi: 500mg

46
Q

Maximum dose of Mepivacaine

A

Plain: 5mg/kg

With epinephrine: 7mg/kg

47
Q

Maximum dose of Ropivacaine

A

Plain: 3mg/kg

With epinephrine: 3mg/kg

Total max dose Plain: 200mg

Total max dose with Epi: 250mg

48
Q

Maximum dose of Prilocaine

A

Plain: 6mg/kg

With epinephrine: 8mg/kg

Total max dose Plain: 400mg

Total max dose with Epi: 600mg

49
Q

Maximum dose of Procaine

A

7mg/kg

Total max dose: 350-600mg

50
Q

Maximum dose of Chloroprocaine

A

Plain: 11mg/kg

With epinephrine: 14mg/kg

Total max dose Plain: 800mg

Total max dose with Epi: 1000mg

51
Q

Class of Procaine = ____.

Potency, Onset, Duration

A

Ester

Low Potency

Slow Onset

Short DOA

52
Q

Class of Tetracaine = ____.

Potency, Onset, Duration

A

Ester

High Potency

Slow Onset

Intermediate/Long DOA

53
Q

Class of Lidocaine = ____.

Potency, Onset, Duration

A

Amide

Intermediate potency

fast onset

intermediate DOA (long with epi)

54
Q

Class of Bupivacaine = ____.

Potency, Onset, Duration

A

Amide

High potency

Slow onset

Long DOA (longer with epi)

55
Q

Class of Ropivacaine = ____.

Potency, Onset, Duration

A

Amide

High potency

Slow Onset

Long DOA

56
Q

1G = ___mg = ___mcg

1mg = ___mcg

A

1G = 1,000mg = 1,000,000 mcg

1mg = 1,000mcg

57
Q

Which LAs are administered topically?

A

lidocaine (both IV and topical)

Benzocaine

Cocaine

58
Q

Increased CNS concentrations of LAs will lead to what symptoms?

A
  • Lightheadedness, tinnitus, tongue numbness
  • visual disturbances
  • muscular twitching
  • convulsions
  • unconsciousness
  • coma
  • respiratory arrest
  • cardiovascular system depression
59
Q

The larger, myelinated, nerve fibers for motor, proprioception are how sensitive to LAs?

A

Not very sensitive (AKA it takes a lot of medication to penetrate those fibers)

60
Q

The smaller unmyelinated nerve fibers are how sensitive to LAs?

A

very sensitive, it takes less of the drug to penetrate them

Anesthesia Pharm (18 decks)

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