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Pharm II > Test 3: Local Anesthetic Additives and Toxicities > Flashcards

Test 3: Local Anesthetic Additives and Toxicities Flashcards

1
Q

Why is epinephrine added to a local anesthetic?

A

To detect intravascular injection
-Especially with PNB and Epidurals.
-Test dose for epidural. If intravascular, the epi will cause an increase in HR>

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2
Q

What are the effects of epinephrine on the block?

A

-Local vasoconstriction
-↓ rate of vascular absorption
-↓ risk of toxicity
-↑ LA available at site of action

Longer and more profound block.

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3
Q

T/F: Epi prolongs the DOA the same way in all LAs. (Blue Box)

A

False: Epi does not prolong the DOA to the same extent with all LAs.
-Greater benefit with short & intermediate acting agents. Activity is more pronounced with short acting drugs. Ex: Lidocaine.
-Effect on longer acting agents is less well defined.

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4
Q

What is the typical concentration of Epi with LA?

A

1:200,000 (5 mcg/mL)

Test dose: 1.5% Lidocaine + 1:200,000 Epi

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5
Q

Alpha2 adrenergic Agonists have the greatest effect on what fibers? (Blue Box!)

A

Most effective on C-Fibers (sensory), then A-Alpha (motor).

Nagelhout:
-The effect is more pronounced in C fibers (sensory) than A delta (motor). That makes the effects mostly sensory specific.

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6
Q

What receptors do Alpha-2 Agonists act on?

A

Spinal & Supraspinal Receptors.
Can be used in NA or PNBs.

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7
Q

What is Clonidine used for?

A

Epidural: 25-75 mcg
PNB: 25 - 150 mcg/mL
-Used in caudals in peds
-SEs: Hypotension, bradycardia, and sedation.
-Avoid in patients with heart block, hypotension, etc.
-100 mcg = 100 min (prolongs duration by 100 min).

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8
Q

What is the effect of Alpha-2 Agonists?

A

Have intrinsic local anesthetic properties of their own.
-Interrupts the nerve’s ability to achieve resting membrane potential from the inactive state.

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9
Q

When is Sodium Bicarbonate most commonly used?

A

-Widely used in epidural anesthesia
-Speeds onset of sensory and motor blockade

Effects in PNB are unclear.

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10
Q

How does NaHCo3 increase the speed of onset?

A

Theoretically, it increases the pH of the LA solution, driving it towards the more non-ionized form.
-The non-ionized form is able to readily diffuse across cell membranes, speeding the onset.

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11
Q

What is the limitation to the addition of bicarb?

A

Precipitation can occur in the LA solution.

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12
Q

Does Bicarb effect pain/stinging of injection?

A

-Theory is that adding NaHCO3 to solution will help decrease nociceptor responsivity to LA, decreasing the pain signals reported to the brain by speeding the onset of the drug.
-Based on patient report. Everyone has different tolerances for pain.

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13
Q

What is the purpose of adding Hyaluronidase to a LA?

A

-Increases spread of the LA
-Facilitates diffusion into the nerve.
-Hyaluronidase is an enzyme that breaks down Hyaluronic acid to increase the spread of LA through the tissues (Hyaluronic acid is an interstitial component that inhibits the spread of substances through tissues)
-Used in ophthalmic blocks.

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14
Q

What are the adverse effects associated with Hyaluronidase in LAs?

A

-Allergic response to enzyme
-Shortened DOA (as it traverses tissues to get to site of action, it gets absorbed)
-↑ in toxicity (inc vascular uptake)

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15
Q

What receptors does Ketamine work on?

A

-NMDA Receptor Antagonist
-Opioid Receptor Agonist

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16
Q

When is Ketamine added to LAs?

A

5-25 mcg
-Intrathecal
-Epidural (Effect unclear)
-PNBs

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17
Q

Why is Ketamine added to Intrathecal blocks?

A

-Shortens the onset of LA analgesia (faster)
-Shortens the duration of action of LA analgesia (faster off)
-Make sure block doesn’t wear off before surgery is finished
-100 mg/mL. High concentration = least volume for intrathecal.

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18
Q

Why is Ketamine added to PNBs?

A

To prolong the post-op analgesia.

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19
Q

What is Duramorph?

A

-Intrathecal Morphine
-0.1-0.2 mg
-Provides great analgesia for 20 hours after C/s
-Pruritis

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20
Q

What is the purpose of adding Fentanyl intrathecally?

A

10-25 mcg
-Improves spread
-Prolongs the block
-Dose dependent
-Shorter DOA compared to morphine.

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21
Q

Why would you add Sufentanil to an intrathecal block?

A

5 mcg
-Similar to 0.2 mg of Morphine.
-Shorter DOA with decreased pruritis.
-Can draw up in a TB syringe (each 0.1 mL is 5 mcg. 50 mcg/mL concentration)
-More potent form of fentanyl

22
Q

Why would you add morphine to an Epidural?

A

Provides effective postop analgesia. Used in ortho and obstetrics.
-Risk for late onset respiratory depression (respiratory depression can outlast the analgesic effects - monitor closely)
-Usually single shot done at the end, right before removing epidural catheter.

23
Q

Why would you add fentanyl to an Epidural?

A

2-10 mcg/mL
-Can be a continuous infusion (epidural drip)
-Analgesic partially from systemic absorption.

24
Q

Why would you add Sufentanil to an Epidural?

A

-0.75 - 1.0 mcg/mL
-Can be a continuous infusion
-More lipophilic than Fentanyl
-Plasma levels are the same
-IV = epidural route. (same amount of pain control is provided if given IV or epidurally)
-More potent, can decrease the dosage.

25
Q

Why would you add Hydromorphone to an Epidural?

A

20 mcg/mL
-Can be a continuous infusion
-Less lipophilic than Fentanyl or Sufentanil.

26
Q

What are the doses of Precedex for adding into LAs?

A

-Spinal = 10 mcg
-Epidural = 0.5 mcg/kg
-PNB = 0.5 - 1 mcg/kg

27
Q

Why is the CNS toxicity prolonged with LA overdose?

A

-CNS toxicity = respiratory depression, hypoxia, and acidosis
-Acidosis means increased ionization of LA within the CNS circulation
-LAs are in the ionized form, which means they can’t diffuse across the BBB out of the brain (get stuck in CNS)
-This prolongs and enhances the CNS toxicity of LAs.

28
Q

Why does local anesthetic accumulate in fetal circulation?

A

-Fetal pH is lower than maternal pH.
-When the LA crosses the placenta, it enters this more acidotic area, and gets stuck in its ionized form.
-This may result in high fetal levels of LAs.

29
Q

What happens when LA is injected into infected tissues?

A

-Infected tissues are acidotic and lack lipid solubility.
-Injection of LA into acidotic environment results in increased concentration of the ionized, water-soluble form of the drug.
-This prevents absorption into the nerve.
-Blocks access to the site of action.
-LA becomes ineffective.

30
Q

Why are LAs stored in acidic preparations?

A

-Improves the stability of the drug by increasing the concentration of the ionized, water-soluble form.
-If the non-ionized form was in storage, it would be subject to photodegradation and forms aldehydes.

31
Q

What are the common causes of Local Anesthetic Systemic Toxicity (LAST)?

A

-Inadvertent IV injection or absorption of large amounts of drugs
-Results from continuous infusions (Accumulation of drug/metabolites over many days)
-High systemic blood levels leads to toxicity (inadvertent injection into the venous system causes plasma concentrations to peak rapidly).

32
Q

Which route of administration is associated with the highest frequency of LAST?

A

-Epidurals

33
Q

Which LA is associated with the highest frequency of LAST?

A

Bupivicaine

34
Q

What are ways to prevent LAST from occurring?

A

-Use of test doses to determine if intravascular
-Incremental dosing (split dose into 3, give slowly)
-Frequent aspiration (frank blood flow - 2% rate of false negatives)
-Pharmacologic markers (Epi to detect IV injection)
-Restrict use of cardiotoxic LAs in OB patients (0.75% Bupivicaine)
-Use the lowest dose of LA possible.
-Use of US technqiues

35
Q

What are the symptoms of LAST?

A

-CV: HTN and tachydysrhythmias initially, progress to decreased contractility, arrhythmias (bradycardia), and hypotension.
-CNS: agitation, tinnitus, circomoral numbness, blurred vision, and a metallic taste followed by muscle twitching, unconsciousness, seizures, and finally cardiac and respiratory arrest.

36
Q

When should you suspect LAST? (Blue Box!)

A

Consider LAST in any patient with altered mental status, neurologic symptoms or CV instability after a regional anesthetic.

37
Q

What is the treatment for LAST?

A

-Call for help
-Infuse 20% Lipid Emulsion
-Airway management (prevent hypoxia and acidosis, 100% O2)
-Seizure suppression (Benzos)
-BLS/ACLS

Possible CP bypass needed

38
Q

What are the adjustments to BLS/ACLS with LAST?

A

-Keep Epi doses to <1 mg/kg
-Avoid vasopressin, CCBs, Beta Blockers, Local Anesthetics (no IV Lidocaine), and Propofol (if hypotensive).

39
Q

T/F: Propofol can be substituted for lipid emulsion therapy. (Blue Box)

A

False: Propofol is not a substitute for lipid emulsion therapy.

40
Q

What is the MOA for Lipid Emulsions?

A

1) Lipid Sink: Captures the LA in the blood
2) Metabolic Effect: Increased fatty acid uptake (mitochondrial action)
3) Membrane Effect: Interference with LA binding to Nav
4) Cytoprotection: Activation of the Akt cascade (protects cytoplasm inside of the cell)
5) Inotropic Effect: Promotion of Ca++ entry via Voltage Gated Calcium Channels
6) Pharmacokinetic Effect: Accelerated shunting (moving blood out to get LA out)

41
Q

What is the dosing for Lipid Emulsion?

A

Based on LBW
-Bolus of 1.5 mL/kg
-Continuous infusion at 0.25 mL/Kg/min for at least 10 minutes after the return of HD stability
-If instability continues, can repeat bolus and increase infusion to 0.5 mL/kg/min.
-Make dose 10 mL/kg over 30 minutes

42
Q

What is Methemoglobinemia?

A

-High concentrations of metHb in the blood. Doesn’t carry O2
-Fe2+ (ferrous form of Hgb) is oxidized to form Fe3+ (ferric form of hemoglobin)
-Causes tissue hypoxia.
-Left shift in the Oxy/Hgb Dissociation Curve
-

43
Q

What are the S/Sx of Methemoglobinemia?

A

-Decreased O2 sat via pulse ox that is unresponsive to O2 supplementation. (SpO2 hovers at 85%)
-Cyanosis
-Chocolate colored blood
-Tachypnea/tachycardia
-Confusion
-HA
-Dizziness
-Coma/death

44
Q

What causes Methemoglobinemia? (Blue Box!)

A

-Benzocaine
-Prilocaine

45
Q

What is the treatment for Methemoglobinemia (Blue Box!)

A

Methylene Blue 1-2 mg/kg IV.

46
Q

What is the most common cause of Cauda Equina Syndrome?

A

-Accidental intrathecal injection of Chloroprocaine.
-Large dose & preparation containing Sodium Metabisulfite (preservative)
-Low pH

Incidence has disappeared with preservative free solutions.

Also associated with 5% Lidocaine if given continuously.

47
Q

What are the symptoms of Cauda Equina Syndrome?

A

Acute loss of function of the lumbar plexus.
-Saddle Anesthesia: S3-S5 dermatomes.
-Numbness or pins & needles of perineum, genitals, and/or anus.
-Bowel/bladder dysfunction.
-Bilateral lower extremity weakness/sensory impairment.
-May be permanent.

48
Q

What is the most common cause of Transient Neurologic Syndrome (TNS)?

A

-Single dose spinal administration of Lidocaine 5%.

49
Q

What are the symptoms of TNS?

A

-Back & lower extremity pain
-Burning, aching, cramp-like, radiating pain in the anterior/posterior thigh.
-Low back pain is common.

Lasts up to 5 days post-op. Not permanent.

50
Q

What is the Treatment for TNS?

A

-Supportive
-NSAIDs

Pharm II (24 decks)

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