Neuraxial Anesthesia Pharmacology Flashcards by Claire Edwards

What are the 3 parts that make up a LA structure

Aromatic Ring (lipophilic)
Intermediate chain
Tertiary amine (hydrophilic)

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Which part of the LA structure determines the drug class, metabolism, and allergic potential?

Intermediate chain

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Esters (-COO-) contain which drugs and are metabolized by___?

Those with one “i”

metabolized by the plamsa EXCEPT cocaine is metabolized by the liver

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Amides (-NHCO-) contain which drugs and are metabolized by____?

Those with two “i”s

metabolized by the liver

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Which drug class has more common allergies and why?

Esters because of para-aminobenzoic acid
*there is cross sensitivity between them, but not with amides

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What factor determines the onset of action?

pKa except with chloroprocaine

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What determines the potency?

lipid solubility

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What determines the duration?

protein binding (a1-acid-glycoprotein)

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local anesthetic agents are weak ______, compounds with a pKa close to physiologic pH will have a faster onset of blockade as more molecules remain in the nonionized state.

Bases

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What factors affect Vascular uptake and plasma concentration of LA?

Site
Tissue blood flow
Physiochemical properties
Metabolism
Addition of vasoconstrictor

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List the sites with the highest to lowest uptake of LA based on blood concentration

Intravenous
Tracheal
Intercostal
Caudal
Paracervical
Epidural
Brachial
Sciatic
Subcutanoues

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LA block receptors from___?

inside of the cell

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Baracity

The density of a LA compared to the CSF

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Isobaric

Density is equal to the CSF
Equal to 1
Tends to stay in the place it is injected

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Hyperbaric

Density >CSF/1
Sinks within the CSF; moves downward from point of injection

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Hypobaric

Density<CSF/1
Floats/ Rises within the CSF; moves upward from point of injection

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List Hyperbaric LA

Bupvicaine 0.75% in 8.25% dextrose
Lidocaine 5% in 7.5% dextrose
Tetracaine 0.5% in 5% dextrose
Procaine 10% in water
***Dextrose diluent= hyperbaric except procaine 10%

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Isobaric LA

Bupvicaine 0.5% in saline
Bupvicaine 0.75% in saline
Lidocaine 2% in saline
Tetracaine 0.5% in saline

** all are in saline

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Hypobaric LA

Bupivicaine .3% in water
Lidocaine .5% in water
Tetracaine .2% in water

**all in water

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What type of LA do we typically use?

Hyperbaric

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Significance of hyperbaric LA and spinal low points in supine position

The furthest a hyperbaric LA can travel is T6 in the supine position, so expect bradycardia and hypotension since the cardiac accelerators are T1-T4

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How are LA eliminated?

Reuptake through vascular reabsorption of the vessels in the pia mater
*NO metabolism happens in CSF

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Which LA does epi increase the DOA of spinal blocks and by how much?

Bupivicaine 0.5-.75% and tetracaine 0.5-1% by 20-50%

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List spinal LA from shortest to longest DOA

2-chlorprocaine 3%
Tetracaine 0.5-1%
Ropivicaine 0.5-1%
Bupivicaine 0.5-0.75%
Levobupivicaine 0.5%

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Bupivicaine and levobupivicaine spinal dose

T10: 10-15mg T4: 12-20mg *need more to go higher

Ropivicaine spinal dose

T10: 12-18mg T4: 18-25mg

2-chloroprocaine spinal dose

T10: 30-40mg T4: 40-60mg

Tetracaine spinal dose

T10: 6-10 mg T4: 12-16mg

True or False: You don't have to aspirate before injecting epidural dose if you confirmed placement initially

False ALWAYS ASPIRATE FIRST

What does incremental dosing of 5mL in an epidural avoid?

1. Accidental high spinal 2. Hypotension from rapid autonomic blockade 3. LAST

What is the fastest and most basic LA? Where is it commonly used?

2-Chloroprocaine In outpatient surgery because it wears off so fast

Alkalinization of epidural LA and its effects

Adding NaHCO3 makes it more basic (increases pH) - Increases concentration of nonionized free base - Increases rate of diffusion of drug - Increases speed of onset of block

What is the epidural dose of LA? Top-up dose?

Initial: 1-2mL per segment of spine Top-up dose: 50% of initial dose

When do you give the top-up dose?

Before the block decreases more than 2 dermatomes

True or false: the epidural space varies depending on the region of the spine and since the thoracic region has smaller epidural space than the lumbar region, there is greater spread in the the thoracic.

True

What determines how strong or dense the epidural block is?

Concentration

List epidural LA from shortest DOA and fastest onset to longest and slowest

2-Chloroprocaine Lidocaine Ropivicaine Bupivicaine Levobupivicaine

What effect do vasopressors have as adjuncts to neuraxial blocks?

Extend duration

What effect do opioids have as adjuncts to neuraxial blocks?

Improves Analgesia and density

What adjunct improves analgesia, duration, and density?

Alpha 2 agonists (precedex, clonidine)

What is the target of opioids when used in neuraxial anesthesia?

substantia gelatinosa of the dorsal horn (lamina 2)

How do neuraxial opioids provider broader pain relief?

They diffuse into the general circulation and affect opioid receptors throughout the body

Neuraxial opioid MOA

Neurotransmission reduced by decreased cAMP, decreased Ca++ conductance and increased K+ conductance

List hydrophilic neuraxial opioids

Morphine Hydromorphone Meperidine

List lipophilic neuraxial opioids

Fentanyl Sufentanil

Compare DOA between lipophilic and hydrophilic opioids

Hydrophilic have a longer DOA (6-24 hrs) vs. (2-4 hrs)

Compare CSF spread between lipophilic and hydrophilic opioids

Hydrophilic have a wider spread (larger area of pain relief) More rostral spread

Compare onset between lipophilic and hydrophilic opioids

Hydrophilic take longer to start (30-60min) vs. (5-10 min)

Compare systemic absorption between lipophilic and hydrophilic opioids

Hydrophilic

Compare respiratory depression between lipophilic and hydrophilic opioids

Hydrophilic occurs late which is a problem..need to tell recovery nurse

Sufentanil doses for: Intrathecal: Epidural: Epidural infusion:

Intrathecal: 5-10mcg Epidural: 25-50mcg Epidural infusion: 10-20 mcg/hr

Fentanyl doses Intrathecal: Epidural: Epidural infusion:

Intrathecal: 10-20 mcg Epidural: 50-100mcg Epidural infusion: 25-100 mcg/hr

Hydromorphone doses Epidural: Epidural infusion:

Epidural: 0.5-1mg Epidural infusion: 0.1-0.2 mg/hr

Meperidine Doses Intrathecal: Epidural: Epidural infusion:

Intrathecal: 10mg Epidural: 25-50mg Epidural infusion: 10-60mg/hr

Morphine Doses Intrathecal: Epidural: Epidural infusion:

Intrathecal: 0.25-0.3 mg Epidural: 2-5 mg Epidural infusion: 0.1-1mg * use lower end dose for outpatient

Why does epidural administration of opioids require higher dosing than intrathecal?

It has farther to get to the spinal cord. Some is absorbed in the fatty tissue and the bloodstream.

What is a very common cause of pruritis? Prophylaxis? Treatment?

Opioids Prophylaxis: morphine dose <300mcg ondansetron 4mg Nubain: 2.5-5 mg Treatment: Benadryl 25-50mg IV Naloxone 0.1mg IV Buprenex

What is the best treatment for opioid induced pruritis and what is the disadvantage of it?

Naloxone - it also reverse analgesia

What monitoring equipment is required for intrathecal opioid use?

Capnography Pulse oximetry Alarms

What opioids cause worse respiratory depression effects?

Hydrophilics because don't show up until later and take longer to wear off. *hydrophilics cause cephalad spread

Opioid reversal

Naloxone 0.1-0.2mg

Treatment for opioid induced nausea/urinary retention

Ondansetron Naloxone Phenergan

What combo has high incidence of opioid induced nausea/urinary rentention?

Fentanyl/sufentanil + Morphine

Morphine doses that decrease nausea/urinary retention

<300mcg <100mcg almost absent

How long do alpha 2 agonists prolong sensory and motor blockade by?

1 hour

Side Effects of alpha 2 agonists

Hypotension, bradycardia, sedation *very short lived, give boluses

Alpha 2 agonist doses for neuraxial anesthesia

Dexmedetomidine: 3 mcg Clonidine: 15-45 mcg

What LA do vasoconstrictors have a profound increase in DOA?

Tetracaine

Vasoconstrictor neuraxial doses

Epi: 0.2-0.3mg Phenylephrine: 2-5mg

Symptoms of epidural hematoma

Lower extremity weakness, numbness Low back pain Bowel/bladder dysfunction

Who does Tubog say to refer to for antiplatelet considerations?

American Society for Regional Anesthesia and Pain Medicine

Differentiate the primary and secondary uses of aspirin

Primary: Preventing first event Secondary: Preventing recurrent event

Holding guidelines for aspirin

High and intermediate Risk procedures: hold 4-6 days Low Risk: generally don't need to hold *Central neuraxial block don't have any additional precautions

How long do hold NSAIDs for with high risk surgeries?

5 half lives

What intermediate risk procedures should you hold NSAIDs for?

cervical ESI and stellate ganglion block

How long should Tirofiban (aggrastat) and eptifibatide (integrilin) be held for?

4-8 hours

How long should Abciximab (Reopro) be held for?

24-48 hours

List thienopyridine derivatives and how long they should be held for

Clopidogrel (plavix): 5-7 days Prasugrel(Effient): 7-10 days Ticlopidine (Ticlid) : 10 days

What is the therapeutic dose for unfractionated heparin and how long does it need to be held for?

>20,000 U daily "Remember 24 hours and you'll be safe"

How long does LMWH need to be held prior to a block or catheter placement?

Therapeutic: 24 hrs Prophylactic: 12 hrs

What labs need to be checked when a patient is on LMWH?

PTT, ACT, Plt, AntiXa

Regional anesthesia consideration for vitamin K antagonist

Hold for 5 days ensure INR<1.5

Which antiplatelet therapy is an absolute contraindication to neuraxial anesthesia?

Thrombolytic agents (T-PA, streptokinase, alteplase, urokinase)

When should DOACs be discontinued?

72 hours *check drug level or antiplatelet if <72 hours

Herbal therapy considerations

No precautions if not on other blood-thinning agents

Neuraxial Anesthesia Pharmacology Flashcards

(85 cards)