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AS - N929 Pharmacology II > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

LAs MOA

A

Reversibly block conduction/transmission along nerve fibers
Preferentially bind to open & inactive VGNa+ channels
- Binds internally to VGNa+
Also block K+, Ca2+, & GPCRs
Do not alter the resting transmembrane or threshold potential

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2
Q

What surrounds each nerve axon?

A

Schwann cells

Support & insulate each axon

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3
Q

What are the Nodes of Ranvier?

A

Periodic segments b/w Schwann cells along the axon that do not contain myelin
High VGNa+ channels concentration here

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4
Q

Saltatory Conduction

A

APs jump from node to node to increase the transmission speed

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5
Q

How many nodes must be block for LAs to inhibit channels in myelinated fibers?

A

3 successive nodes

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6
Q

Axon bundles are called ______

A

Fasciculi

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7
Q

Fasciculi are covered with 3 connective tissue layers

A
  1. Endoneurium - thin, delicate collagen that embeds the axon in the fascicle (innermost layer)
  2. Perineurium - flattened cells layers that bind fascicle groups together (middle layer)
  3. Epineurium - surrounds the perineurium; composed from connective tissue that holds the fascicles together to form a peripheral nerve
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8
Q

What must occur for LAs to exert effects?

A

Diffuse through all 3 connective tissue layers (endoneurium, perineurium, & epineurium)

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9
Q

What restores the RMP?

A

Na+/K+ pump

3 Na+ ions exit
2 K+ ions enter

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10
Q

Which nerve fibers are most difficult to block?

A

Larger nerves - conduct impulses faster & are harder to block

Smaller nerve lacking myelin enhance the sensitivity to LAs
LAs preferentially bind to smaller & unmyelinated fibers

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11
Q

What indicates a successful LA blockade?

A

Vasodilation ↓BP indicates pre-ganglionic fibers (SNS tone)

Type B light myelination 1st blocked

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12
Q

Nerve Fiber Blockade Onset

A

Type B pre-ganglionic (autonomic vasomotor) →
Type C fibers (sympathetic post-ganglionic vasomotor & dorsal root - pain, warm/cold, & touch) →
Type A β (touch & pressure) λ (muscle tone) Δ (pain, cold, & touch) →
Type A α (proprioception & motor)

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13
Q

LA Chemical Structure

A

Ester -COOCH or amide -N binds the aromatic ring to the Carbon group

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14
Q

Ester LAs

A

Shorter acting LA (Tetracaine longest-acting ester < 90min)
Plasma & tissue cholinesterase metabolism via hydrolysis
Para aminobenzoic acid (PABA)

LA allergies uncommon, but higher potential w/ esters
Ester allergy avoid ALL ester LAs d/t cross-reactivity

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15
Q

Amide LAs

A

Longer acting (more lipophilic & protein bound)
Require transport to the liver for metabolism
Hepatic CYP1A2 & CYP3A4

Amide allergies are extremely rare
No cross-allergy b/w ester & amide LAs

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16
Q

What increases LA onset?

A

Higher concentration injected → faster onset

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17
Q

What terminates LA effects?

A

Systemic absorption results in drug termination

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18
Q

What does lipid solubility correlate with?

A
  • Protein binding
  • ↑potency
  • Longer DOA
  • ↑severe cardiac toxicity

Amides are more lipid soluble

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19
Q

LAs are _____ _____

A

Weak bases

Basic drugs become more ionized when placed in a solution w/ pH < pKa
Drugs w/ pKa closer to physiologic pH → faster onset
Weak bases bind to α acid glycoprotein (lesser extent to albumin)

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20
Q

LA impact on smooth muscle:

A

RELAXATION
Vasodilation ↓DOA ↑plasma concentration & potential toxicity

Exceptions: Lidocaine, ropivacaine, & cocaine

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21
Q

Highest → lowest blood concentrations

A

IV → tracheal → caudal → paracervical → epidural → brachial → sciatic → SQ

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22
Q

Drugs to add to LAs spinal/epidural:

A
  • Clonidine
  • Dexmedetomidine
  • Epinephrine
  • Opioids
  • Na+ bicarb
  • Ketorolac
  • Dexamethasone
  • Hyaluronidase
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23
Q

Epinephrine

A

Vasoconstriction ↓vascular absorption rate
↑duration & block potency
↓systemic toxicity risk

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24
Q

Sodium Bicarbonate

A

Commonly used in epidural anesthesia
Theoretically ↑LA solution pH → more drug in the non-ionized state
↓pain on injection
Limitation = precipitation

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25
Q

What receives the highest LA plasma concentration initially?

A

Highly perfused tissues - brain, heart, & lungs

Risk → toxic levels

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26
Q

What receives the most secondary LA after re-distribution?

A

Muscles receive the most after 2° distribution

27
Q

What LAs are impacted with severe hepatic disease?

A

Amide LAs

Hepatic metabolism CYP450

28
Q

How does renal dysfunction affect LA clearance?

A

Impacts protein binding to α1 glycoprotein & albumin

Renal dysfunction affects clearance far less than hepatic failure

29
Q

Pregnancy Physiological Changes

A

Engorged epidural veins ↓epidural space

Hormonal changes → progesterone levels affect LA sensitivity

30
Q

Local Anesthetics

SEs & Complications

A

LAST
Cauda equina syndrome
Transient neurologic symptoms

31
Q

LAST

A

Local anesthetic systemic toxicity
Rare, but serious
ALWAYS ASPIRATE

32
Q

What most commonly causes LAST?

A

Inadvertent IV injection

  • Blocks inhibitory neurons thought to cause seizures
  • Blocks cardiac ion channels → bradycardia
33
Q

What the most serious LAST complication?

A

Ventricular fibrillation

34
Q

What LAs are thought to be less cardiotoxic?

A

Shorter acting LAs

- More potent agents higher lipid solubility & protein binding

35
Q

LAST Clinical Presentation

A

Rapid onset usually w/in one minute
S/S: Tinnitus, metallic taste, agitation, blurred vision, & circumoral numbness
Muscle twitching, unconsciousness, & seizures

TOXIC LEVELS → cardiac & respiratory arrest

36
Q

LAST Incident Rate

A

0.4 per 10,000

37
Q

LAST most common following what procedures?

A
  1. Epidural - veins & dura
  2. Interscalene - carotid artery & IJ vein
  3. Axillary less common
38
Q

How to prevent LAST

A

Test dose to ensure in the right spot NOT in the vein or dura
Incremental injection w/ aspiration
Use pharmacologic markers
Ultrasound

39
Q

LAST Treatment

A

Prompt recognition & diagnosis
1° airway management - adequate ventilation & oxygenation
Seizure suppression - benzodiazepines & Succinylcholine
Hyperventilation ↑seizure threshold
Prevent hypoxia & acidosis
Lipid emulsion 20% 1.5mL/kg rapid infusion over 2-3min → 0.25mL/kg/min IBW
NOT propofol
Vasopressors - Epi < 1mg/kg NOT vasopressin

40
Q

Lipid Emulsion Therapy MOA

A
  1. Captures LA in blood → lipid sink
  2. ↑fatty acid uptake by mitochondria
  3. Interferes w/ Na+ channel binding
  4. Promotes Ca2+ entry
  5. Accelerated shunting
41
Q

Methemoglobinemia

A

Ferris (Fe2+) Hgb → Ferric (Fe3+) Hgb
↓oxygen-carrying capacity → tissue hypoxia
↓SpO2 not responsive to therapy

Benzocaine-induced methemoglobinemia

42
Q

Methemoglobinemia Treatment

A

Methylene blue 1-2 mg/kg over 3-10 minutes

High levels may require transfusion or dialysis

43
Q

Cauda Equina Syndrome

A

Cause - LA or nerve compression

Manifests as bowel & bladder dysfunction w/ LE weakness & sensory impairment r/t cord ischemia

44
Q

Transient Neurologic Symptoms

A

Associated w/ intrathecal lidocaine
Presentation - burning, aching, cramping pain in the lower back that radiates down the thighs up to 5 days postop
Risk factors include lithotomy position & outpatient surgery

45
Q

Lidocaine HCl (Xylocaine)

A

Weak base amide LA
Rapid onset
Protein binding 64-70%
↓DOA

46
Q

Lidocaine Uses

A
  • Antiarrhythmic
  • Topical
  • Induction to blunt SNS
  • Nebulized
  • Multimodal pain management
  • Regional anesthetic
47
Q

Lidocaine

Antiarrhythmic

A 
ACLS algorithm
Class IB 
Depress myocardial automaticity
Vtach or Vfib 1-1.5 mg/kg IV
Refractory 0.5-0.75 mg/kg
Total dose 3 mg/kg
Maintenance infusion 1-4 mg/min (30-50 mcg/kg/min)
48
Q

Lidocaine

Topical

A

Eutectic mixture of LA (EMLA)
Lidocaine:Prilocaine 1:1 mixture

Contraindicated use on mucous membranes, broken skin, infants < 1mos old, methemoglobinemia history

49
Q

Lidocaine

Induction

A

1-1.5 mg/kg IBW
↓pain associated w/ Propofol
Admin 1-3 min prior to laryngoscopy attenuate HTN
Blunt CV sympathetic response to intubation
↓CBF → attenuates ↑ICP in patients w/ ↓compliance
Block reflex bronchoconstriction

50
Q

What causes the pain associated with Propofol on injection?

A

Phenol

51
Q

How best to prevent the pain associated with Propofol?

A

Large bore IV
AC vein
Tourniquet 60 second veno occlusion
Opioid dose

52
Q

Lidocaine LTA

A

Laryngotracheal topicalization anesthesia
Decrease emergence phenomenon - coughing, sore throat, & dysphonia
Lidocaine 4% pre-filled 4mL syringe (remove excess → easier to inject exact dose)
DL then insert LTA holding the catheter at the end near the syringe
Place LTA w/ black marking at the vocal cord level then inject

53
Q

Lidocaine

Airway Block

A

Nebulized lidocaine 4% direct to the oropharynx
Swish & spit or swallow lidocaine
Tongue depressor w/ lidocaine gel
Spray as you go
Transtracheal block inject 4% through the cricothyroid membrane

54
Q

Lidocaine

Multimodal

A

Pain management
Infusion 2 mg/kg/hr
↓narcotic requirements
MOA unknown
Reduces postop pain w/ open & laparoscopic GI surgeries
↓pain associated w/ improved functional outcomes in prostatectomy, thoracic, & spine procedures

55
Q

Lidocaine

Regional

A

Peripheral nerve blocks
- Bier block

Neuraxial anesthesia - spinal & epidural

56
Q

Bier Block

A

Short procedures
Lidocaine 0.5% 25-50mL
Onset 5-10 minutes
Tourniquet pain at 20 minutes

57
Q

Lidocaine Dose-Dependent Effects

Plasma Concentration 1-5 μ/mL

A

Analgesia

58
Q

Lidocaine Dose-Dependent Effects

Plasma Concentration 5-10 μ/mL

A

Tinnitus, circumoral numbness, skeletal muscle twitching, systemic HoTN, & myocardial depression

59
Q

Lidocaine Dose-Dependent Effects

Plasma Concentration 10-15 μ/mL

A

Seizures

Unconsciousness

60
Q

Lidocaine Dose-Dependent Effects

Plasma Concentration 15-25 μ/mL

A

Apnea & coma

61
Q

Lidocaine Dose-Dependent Effects

Plasma Concentration > 25 μ/mL

A

Cardiovascular depression

62
Q

Exparel

A

Liposomal bupivacaine
*Only mix w/ NS 0.9% or bupivacaine
Lidocaine breaks down the capsule → bupivacaine bolus ↑toxicity risk
Caution in patients w/ hepatic disease

63
Q

Exparel SEs

A

N/V

Dizziness, headache, bradycardia, tachycardia, somnolence, hypoesthesia, & lethargy

64
Q

Cocaine

A

Original LA derived from the cocoa plant
Only naturally occurring
Blocks the monoamine transporter in the adrenergic system
Unable to reuptake catecholamines → vasoconstriction
1° topical nose & throat
Max dose 5mL 5%
Caution w/ other epi containing solutions, MAOIs, & tricyclics

AS - N929 Pharmacology II (10 decks)

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