Local Anesthetics Flashcards
What local anesthetic class is responsible for more allergic reactions?
Esters (due to PABA metabolite)
What is LAST?
Local Anesthetic Systemic Toxicity
What causes LAST syndrome?
Excess plasma concentration of LA from:
- Accidental IV injection
- Systemic absorption from tissue redistribution and clearance metabolism.
What factors affect the magnitude of systemic absorption of local anesthetic?
- Dose
- Vascularity of site
- Concurrent Epi use
- Properties of the drug itself
Would local anesthetic administered via the trachea have a higher or lower chance of systemic absorption than local anesthetic delivered brachially?
Trachea has higher chance of systemic absorption.
What serum electrolyte condition will exacerbate local anesthetic toxicity?
Why?
Hyperkalemia (lowers seizure threshold)
What s/s would be seen with a plasma lidocaine concentration of 1-5 mcg/ml?
Analgesia
What s/s would be seen with a plasma lidocaine concentration of 5-10 mcg/ml?
- Mouth numbness
- Tinnitus
- Muscle twitching
- ↓BP
- Myocardial depression
What s/s would be seen with a plasma lidocaine concentration of 10-15 mcg/ml?
- Seizures
- Unconsciousness
What s/s would be seen with a plasma lidocaine concentration of 15-25 mcg/ml?
- Apnea
- Coma
What s/s would be seen with a plasma lidocaine concentration of >25 mcg/ml?
Cardiovascular Depression
How does lidocaine affect EKGs?
How does it do this?
- Prolongation of PR interval and QRS widening.
- Blockade of Na⁺ channels
Which three drugs are most responsible for cardiac adverse effects when reaching toxic levels systemically?
Bupivacaine > Ropivacaine > Lidocaine
Protein Binding percentages for Bupivacaine, Lidocaine, and Prilocaine?
Bupivacaine - 95%
Lidocaine - 70%
Prilocaine - 55%
How does Lipid Emulsion rescue work?
Lipids encapsulate the local anesthetic and transport it away from cardiac and CNS tissue.
Also provides fat for myocardial metabolism.
What is the bolus dose of Lipid Emulsion?
1.5 mL/kg of 20% lipid emulsion
What is the infusion dose of lipid emulsion?
How long should it be given?
0.25 mL/kg/minute for at least 10 minutes
What is the max dose for lipid emulsion that should be given?
8 mL/kg
What preservative commonly used for amide local anesthetics can be responsible for allergies?
Methylparaben
Why does pregnancy predispose one to cardiovascular toxicity from LA’s?
Pregnancy = ↓ plasma cholinesterases and also decrease in plasma proteins
Should a local anesthetic toxicity patient be hyperventilated or hypoventilated?
Why?
Hyperventilation = ↓ CO₂ = ↓ acidosis
If cardiac arrest occurs with LAST syndrome, how should our epinephrine dosing change?
Small doses (10mcg - 100mcg boluses) are preferred with LAST ACLS.
How much vasopressin should be given if a patient is suffering from hypotension from LAST syndrome?
Trick question. Vasopression should not be given with LAST syndrome.
54kg so 1.5mLs x 54kg = 81mLs
20% infusion = 200mgs / 1mL
81mLs x 200mgs = 16,200mgs administered
What is Cocaine’s MOA?
Blocks presynaptic re-uptake of NE and Dopamine → Increases postsynaptic levels and ↑SNS.
What drug is best for treating cocaine toxicity?
Nitroprusside
Cocaine
Peak:
Duration:
Elimination:
Peak: 30 to 45 mins
Duration: 60 mins after peak
Elimination - Urine
If Drug V (weak base) has a pKa of 9.1, will the drug be more ionized or nonionized at physiological pH?
Drug V will be more ionized at physiological pH.
If the pKa of LA (a weak base) is at 4.5, will the drug be more ionized or nonionized at physiological pH?
LA will be more non-ionized at physiological pH.
Lidocaine
Metabolism:
Metabolite:
Max Dose:
Metabolism: Oxidative dealkylation in liver
Metabolite: Xylidide
Max Dose: 300 mg alone and 500 mg w/ Epi
Prilocaine
Metabolite:
Max Dose:
Metabolite: Orthotoluidine
Max Dose: 600 mg
Converts hemoglobin to methemoglobin
Methylene Blue
Indication:
Dose:
Indication: Methemoglobinemia
Dose: 1 to 2 mg/kg IV over 5 mins
Total dose not to exceed 7 to 8 mg/kg over 24 hours
Bupivacaine and Ropivacaine bind to which protein?
α1-acid glycoprotein
Benzocaine
Onset:
Duration:
Max Dose:
Onset: Rapid
Duration: 30 to 60 mins
Max Dose: 200 to 300 mg spray
Procaine
Potency?
Maximum Single Dose?
pK?
Protein Binding?
Potency - 1
Maximum Single Dose - 500 mg
pK - 8.9
Protein Binding - 6%
Chloroprocaine
Potency?
Maximum Single Dose?
pK?
Protein Binding?
Potency - 4
Maximum Single Dose - 600 mg
pK - 8.7
Protein Binding… no number was given.
Also has a rapid onset
Tetracaine
Potency?
Maximum Single Dose?
pK?
Protein Binding?
Potency - 16
Maximum Single Dose - 100 mg (topical)
pK - 8.5
Protein Binding - 76%
Lidocaine
Potency?
Maximum Single Dose (w and wo epi)?
pK?
Protein Binding?
Potency - 1
Maximum Single Dose - 300 mg
w/ Epi: 500mg
pK - 7.9
Protein Binding - 70%
Prilocaine
Potency?
Maximum Single Dose (w and wo epi)?
pK?
Protein Binding?
Potency - 1
Maximum Single Dose - 400 mg (but a different table in Millers also says 600mg so….🤷)
no epi
pK - 7.9
Protein Binding - 55%
slides 45 and 54 from Castillos LA Part I and II lecture (semester 2)
Mepivacaine
Potency?
Maximum Single Dose (w and wo epi)?
pK?
Protein Binding?
Potency - 1
Maximum Single Dose - 300-400 mg
w epi: 500mg
pK - 7.6
Protein Binding - 77%
slides 45 and 54 from Castillos LA Part I and II lecture (semester 2)
Bupivacaine
Potency?
Maximum Single Dose (w and wo epi)?
pK?
Protein Binding?
Potency - 4
Maximum Single Dose - 175 mg
w epi: 225 mg
pK - 8.1
Protein Binding - 95%
Levobupivacaine
Potency?
Maximum Single Dose (w and wo epi)?
pK?
Protein Binding?
Potency - 4
Maximum Single Dose - 150-175 mg
no epi added
pK - 8.1
Protein Binding - > 97%
slides 45 and 54 from Castillos LA Part I and II lecture (semester 2)
Ropivacaine
Potency?
Maximum Single Dose (w and wo epi)?
pK?
Protein Binding?
Potency - 4
Maximum Single Dose - 200 mg
no epi added
pK - 8.1
Protein Binding - 94%
Eutectic Mixture of LA (EMLA) dose components and dosage?
Lidocaine 2.5% and Prilocaine 2.5%
1 to 2 grams/10 cm2 area
For subarachnoid blocks, dosing for a a 5ft person is ____ of 0.75% Bupivacaine… how much do you increase for each inch above 5ft?
1 ml
Increase by 0.1 mL/inch over 5 ft.
What is epinephrine 1:200,000 mean?
Convert that to mcg/mL.
1:200,000 means 1 gram of epinephrine is dissolved in 200,000 mL of solvent.
- 1g/200,000 mL
- 1000mg/200,000 mL
- 1 mg/200 mL
- 1000 mcg/200 mL
- 10 mcg/2 mL
- 5 mcg/mL
Compute 1:500,000 Epi to mcg/mL
1,000,000/ 500,000=2
2 mcg/mL
Compute 1:10,000 Epi to mcg/mL
1,000,000/ 10,000 = 100
100 mcg/mL
0.5% equates to how many milligrams per milliliter?
5 mg/mL
2% equates to how many milligrams per mL ?
20 mg/mL
2% lidocaine is the most common concentration used in the OR
112.5 mg of Bupivacaine with Epi and 250 mg of Lidocaine with Epi were given during surgery.
What are the percentages of each LA based on the recommended max single dose in mg?
Max single dose of Bupivacaine with Epi: 225 mg
112.5/225 = 50%
Max single dose of Lidocaine with Epi: 500 mg
250/500 = 50%
When the peripheral nerve block is wearing off, what comes back first? Proximal or Distal?
Proximal comes back first & then distal.
Peripheral Nerve Block onset of action is dependent on the local anesthetic’s ____.
pK
The duration of a peripheral nerve block depends on the ____ of the local anesthetic.
dose (the duation of action is proportional to the time the drug is in contact with nerve fibers)
What is the sequence of blockades for a segmental block in Neuraxial Anesthesia?
- SNS (Myelinated preganglionic B fibers)
- Sensory (Myelinated A, B fibers, unmyelinated C fibers)
- Motor (Myelinated A-δ and unmyelinated C fibers)
For SAB, the ____ effect is 2 spinal segments cephalad of the sensory block.
For SAB, the ____ effect is 2 spinal segments caudal the sensory block.
SNS
Motor
When the following are added to the LA, what is the result?
- dexmetatomadine
- magnesium
- clonidine and ketamine
- dexamethasone
- dexmetatomadine: increases the duration of both sensory and motor - first analgesic request after spinal anesthesia
- magnesium: increased duration with SAB with or without opioids
- clonidine and ketamine: pediatric regional prolonged duration
- dexamethasone: increased duration
What vasoconstricotrs and dose would you use for a LAB?
Epinephrine 0.2mg
Phenylephrine 2mg
What areas are contraindicated to add a vasoconstrictor to your LA for infiltration?
- Do not add a vasoconstrictor during an intracutaneous injection
- Do not add to end artery sites (fingers, toes, ears, nose and penis)
Tumescent local for liposuction: What is it? how to make the solution? dose?
- SQ infiltration at large volumes (5L or more)
- Solution: diluted lidocaine (0.05% or 0.10%) with epi 1:100,000
- Dose: 7mg/kg
