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OB > Locals > Flashcards

Locals Flashcards

1
Q

What do local anesthetics do?

A

Produce reversible conduction blockade of impulses along the central and peripheral nerve pathways

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2
Q

What are the lipophilic and hydrophilic portion separated by?

A

hydrocarbon

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3
Q

True/False: Lipophilic portion is the Benzene ring and is necessary for activity

A

True

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4
Q

Ester

A

-CO-

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5
Q

Amide

A

-NHC-

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6
Q

S enantiomers

A

Left = sinister

less neuro- and cardio-toxic

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7
Q

R enantiomers

A

Right = rectus

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8
Q

How do they work?

A

Inhibit Na+ ions passage through ion-selective Na+ channels

Slows rate of depolarization
Threshold potential not reached
No action potential propogated

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9
Q

What does locals not alter?

A

Resting membrane potential
Threshold potential

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10
Q

What is Cm?

A

minimum concentration to produce conduction blockade

Analogous to MAC

Fibers that are more easily blocked have a low Cm

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11
Q

Factors affecting Cm?

A

Increases: larger diameter

Decreases: higher frequency stimulation, higher pH

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12
Q

Nodes of Ranvier

A

Must block at least 2, preferably 3

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13
Q

What is conducting velocity increased by?

A

myelination and a wider axon terminal

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14
Q

Order of peripheral nerve block speed

A

B fibers, C fibers, small A fibers (delta, gamma), large A fibers (alpha, beta)

regression occurs in opposite fashion

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15
Q

What is differential blockade?

A

Differential spinal blockade is the clinical phenomenon referring to the temporal blockade of autonomic, sensory, and motor nerve fibers when using neuraxial local anesthetics. Autonomic fibers are blocked first, followed by sensory loss to touch/pinprick, followed by loss of proprioception, and lastly motor loss.

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16
Q

What is an example of a differential blockade?

A

epidural bupivacaine. In lower doses is provides analgesia but spares motor function. In higher doses, it blocks motor function.

17
Q

locals bind to the voltage gated sodium channel when it is in the _____ and _____ states

A

active and inactive

18
Q

What form to cross lipid bilayer?

A

Un-ionized

19
Q

Distribution

A

1st large uptake to lungs

2nd distribution to high perfused tissue
(heart, brain, kidneys)

3rd distribution to low perfused tissue
(muscle and fat)

Amides are more widely distributed

20
Q

Why is placental transfer important?

A

ion trapping

21
Q

Why do we worry about which vasopressor can cause fetal acidosis?

A

Once un-ionized local crosses placenta and hits low fetal pH more drug is ionized and can’t cross back

Build up of trapped local in fetal circulation leads to toxicity in fetus

Not good for new baby to have local anesthetic toxicity

22
Q

Onset determined by _____

A

State of Ionization – most important

Lipid Solubility

23
Q

Potency determined by ____

A

lipid solubility

24
Q

duration determined by____

A

protein binding

25
Q

Metabolism

A

amides: hepatic

esthers: pseudocholinesterase, Rapid hydrolysis

26
Q

Fastest local

A

Prilocaine

27
Q

One exception to hydrolysis?

A

Cocaine – significant metabolism in liver

28
Q

What common local injection site contains little to no cholinesterase enzyme?

A

CSF

Must wait until drug goes into systemic circulation for hydrolysis

29
Q

Which 2 local anesthetics have no vasodilator activity?

A

Cocaine
Ropivacaine (only parenteral with vasoconstrictive activity)

30
Q

Epi

A

1:200,000 or
5 mcg/ml

Limits systemic absorption

Maintains drug concentration around nerves

Can prolong Lidocaine by 1/3

No effect to onset

Helps to decrease toxicity

31
Q

Mixing Locals

A

Combos
Faster onset
Longer Duration

Lido/Bupivicaine
Cholorprocaine/Bupivicaine

Effects additive and not synergistic

32
Q

What is systemic toxicity most common from?

A

Most common from IV injection
Less common from absorption

33
Q

Fastest to Slowest blood flow of tissues

A

IV
Tracheal
Intercostal
Caudal
Paracervical
Epidural
Brachial Plexus
Subarachnoid
Subcutaneous

In Time I Can Please Everyone But Suzi and Sally

34
Q

What do you avoid when treating LAST?

A

AVOID vasopressin, calcium channel blockers, betablockers, or local anesthetic

OB (6 decks)

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