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princip, pharm, phys, regional > pharm- local anesthetics > Flashcards

pharm- local anesthetics Flashcards

1
Q

what chemicals and situations cause anesthesia

A

pressure on nerve endings, amines, alcohols, also toxins

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2
Q

how do local anesthetics work

A

produce a reversible, dose dependent blockade of sodium ion influx into the nerve cytoplasm (preventing the nerve from firing). portal of entry is at the nodes on Ranvier (which are the un-myelinated portion between myelinated Schwann cells or thru the highly lipid nerve sheath into the nerve membrane.

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3
Q

what is the role of ionization and pKa on local anesthetics.

A

local anesthetics have an equal amount of ionized and non-ionized parts in solution. once in the body, the non ionized molecules move thru membranes easier, thus moving into the nerve cell. once inside, the non-ionized part is ionized (since only ionized LAs actually work on cells)

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4
Q
  1. what is the pKa range of Local anesthetics?
  2. How much of the LA is unionized at that range?
  3. how does pKa represent the ratio of ionized to non-ionized molecules of LA?
A
  1. LAs are weak bases and have a pKa of 7.6-9
  2. therefore less than 50% is the non ionized (usable) form.
  3. for every number (unit) the pKa is from the pH, add 1 zero to the ratio of ionized to non ionized.
    ex: pH=6.4, pKa=7.4 then ratio=1:10 (1 non ionized:10 ionized)
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5
Q
  1. what is the chemical structure of local anesthetics?
  2. How do local anesthetics exist in the body, and are they water soluble?
  3. how are they packaged? Why?
A
  1. Local Anesthetics consist of a lipophilic end and a hydrophilic end that surrounds an aromatic ring with either an ester or an amide bond.
  2. LAs exist as weak bases in the body and are poorly water soluble and
  3. they are packaged in hydrochloric salts because they are unstable
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6
Q
  1. how do local anesthetics behave in an acidic environment?

2. how do they behave in a basic environment?

A
  1. they are more ionized and therefore less able to pass into nerve cells where they function.
  2. In a basic environment, the unionized portion is increased and absorption is enhanced.
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7
Q

define; 1.axon-

                 2. axolema
                 3. axoplasm-
                 4. schwann cell-
                 5. fascicle-
A

axon-functional unit of the nerve (transmits the impulse)
axolema- nerve cell membrane
axoplasm-cytoplasm of the nerve
schwann cells-surround, insulate and support the axon
fascicle- a bundle of axons

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8
Q

define:

  1. endoneurium
  2. perineurium
  3. epineurium
A
  1. endoneurium- layer of delicate collagen SURROUNDING THE AXON and embedding it in the fascicle
  2. perineurium-overlapping group of cells surrounding EACH FASSICLE & BINDING THE FASCICLES
  3. epineurium- layers of connective tissue SURROUNDING THE GROUP of FASCICLES
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9
Q

DEFINE:

  1. Myelin-

2. Nodes of Ranvier

A
  1. Myelin-liquid substance containing proteins and lipids, forms an insulating layer around some nerves. Prevents current from leaking out of nerve.
  2. Nodes of Ranvier-small unmyelinated segments between schwann cells, contain lots of sodium channels which allow for intense action potentials which jump from node to node (saltatory conduction).
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10
Q

what aspects of the local anesthetic affect nerve blockade?

A
  1. the concentration of the local anesthetic
  2. the time it takes for the LA to fall below its minimum effective point
  3. requires disruption of several contigious channels
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11
Q
  1. Local anesthetics are weak ____?
  2. They are ____ water soluble?
  3. They are therefore prepared with ____ soluble ______ salts which are more ____ and therefore more stable
  4. epi is broken down in ____ solution, so this ph of the total solution is important (when they are mixed).
A
  1. LAs are WEAK BASES
  2. LAs are POORLY WATER soluble
  3. LAs are prepared with WATER SOLUBLE HYDROCHLORIDE SALTS which are ACIDIC and more stable
  4. epi is broken down in ALKALINE solution
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12
Q
  1. sometimes preservatives such as ___ _____ (very acidic) is added to LAs with epi to further stabilize it (making the pH=4)
  2. _____ prevervatives are sometimes added to multi dose vials. some of these can be ___derivatives which induce __?
A
  1. SODIUM BISULFITE is sometimes added to LAs making them acidic
  2. ANTIMICROBIAL preservatives contain PARABEN derivatives which can induce ALLERGIES.
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13
Q

what are the two classes of Local anesthetics

A

1) AMINES

2) ESTERS

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14
Q
  1. The lipophilic end is ____ soluble, ____ charged, and usually a _____ ring.
  2. What does this Lipophillic end do?
A
  1. Lipophilic end is LIPID soluble, UN-CHARGED/un ionized, and usually a BENZENE RING.
  2. The lipophilic end allows the drug to gain access to the sodium channels through the lipid membrane
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15
Q
  1. the hydrophilic end is the ____ soluble and _____ portion, it is also an _____ (what type of chemical/molecule).
  2. It is the end that does what?
  3. How does this happen?
A
  1. hydrophilic end is the WATER soluble and charged/IONIZED portion and it is also an AMINE.
  2. this is the end of that is more effective in the blocking of the nerves
  3. this is what the lipophilic portion becomes once inside the membrane.
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16
Q

what factor most determines the potency of the different agents?

A

lipid solubility

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17
Q

How are the properties of LAs modified?

A

by lengthening connecting chains or increasing the number of carbon atoms, the drug properties are changed

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18
Q

increasing molecular weight has what effect on a LA

A

increases potency and duration of action

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19
Q

what are the pros to using the minimum effective dose of LAs

A
  1. less risk of toxicity
  2. decreased risk of nerve damage
  3. lowest effective concentration
  4. lowest effective volume
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20
Q

what is the concentration effect

A

higher concentrations speed onset and intensity of block

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21
Q
  1. what 2 major factors affect duration of LAs

2. what 3 factors affect the uptake of the LA?

A
  1. a. drug specificity of: protein binding, lipid solubility
    - –b. absorption of LAs into system;
  2. which is a direct result of blood flow at the given site which is affected by :
    - –a) patient age
    - –b) location (vascularity of sites differs)
    - –c) vasoconstriction (naturally or with epinephrine)
22
Q 
Differential block is based on fiber diameter and myelination; how are the nerve fibers affected from first affected to last affected:
A delta?
B?
A beta?
C?
A alpha?
A gamma?
A

1: B fibers-most sensitive to blockade.
2: C fibers
3: A delta
4. A gamma
5. A beta
6. A alpha: least sensitive to blockade.

23
Q

characteristics of A fibers?
what are the types of A fibers in order of conduction?
what type of sensory conduction does each transmit?

A

A fibers-myelinated fast fibers, wide diameter:
Delta=2-5 mm: –pain–temperature–touch
Gamma=3-6 mm:–skeletal muscle tone–motor–proprioception
Beta=2-12 mm:–touch–pressure
Alpha=12-20 mm:–skeletal muscles–proprioception

24
Q
  1. B fiber characteristics:

2. what do these nerves service so what symptoms would you see?

A

1: 3mm diameter, myelinated PRE-ganglionic autonomic

2. the first symptoms you see with local anesthetics is (autonomic (sympathetic)) changes i.e. “hypotension”

25
Q

so what is the order of blockage and what you see

A
  1. autonomic (blood pressure)
  2. sensory (numbness)
  3. motor (paralysis)
  4. proprioception (inability to know where limbs are)
    (All-Students-Must-Pass)
26
Q

local anesthetics work along the A and C fibers, but how does the action differ?

A

A-delta fibers carry fast pain, so the LA works at the node of Ranvier. There needs to be multiple nodes affected to stimulate blockade with normal dose, but only 2-3 nodes with high concentration LA.
C-fibers carry slow pain,are un myelinated so LAs work along the whole axon.

27
Q

what is “Minimum Blocking Concentration”?

what is it analogous to in anesthesia?

A

Minimum blocking concentration (Cmin) is the lowest concentration needed to block an impulse.
analogous to MAC for inhaled anesthesia

28
Q
  1. LAs with high tissue diffusibility have a __ ____
  2. This is possibly a product of ___
  3. all LAs ___ except for ______
  4. _____ plays a role in potency
  5. but potency is mainly a product of __ ____
A
  1. high tissue diffusibility=FASTER ONSET
  2. high tissue diffusibility is possibly a product of pKa)
  3. all LAs VASODILATE except COCAINE
  4. VASODILATION PROPERTIES of LAs are involved in potency
  5. Potency mainly d/t LIPID SOLUBILITY
29
Q
  1. what is tachyphylaxis?
  2. what factors in administering LAs contribute to it?
  3. what mechanism in the body may be implicated?
A
  1. tachyphylaxis is when repeated injections have less and less efficacy
  2. seen more when dose intervals are longer and result in more patient pain
  3. may be central spinal mechanism (? NDMA agonist also possibly nitric oxide)
30
Q

The mechanism of action of LAs is not fully known- 3 theoriessss:

  1. One theory has to do with Calcium, what is the mechanism?
  2. what is another theory having to do with the axolemma?
  3. what is the most supported theory?
A
  1. The mechanism of LAs is that calcium is displaced from the sarcolemma (Ca+controls Na+ permeability of axolemma)
  2. LAs enter the axolemma by dissolving into its lipid layer (lipid solubility), expands the membrane and distorting the Na+ channel
  3. The most supported theory is the “Specific Receptor Theory”
31
Q

what is the Specific Receptor Theory?

A
  1. LAs do not work at the external sodium channel, but the internal.
  2. once the non-ionized portion is in the neuron and is ionized, it heads to the sodium channel in its ACTIVATED-OPEN position.
  3. The LA then attaches to the sodium channel in the INACTIVATED-CLOSED state, preventing it from opening again and generating an action potential
32
Q

what are the 3 states of a sodium channel

A
  1. Activated-open
  2. Inactivated-closed
  3. Rested-closed
33
Q
  1. LAs may affect what other channels (to a lesser degree)?
  2. What affects does this possibly cause?
  3. what secondary messenger may also be involved?
A
  1. LAs may affect Calcium and Potassium channels
  2. this may explain the cardiac effects (of lidocaine etc).
  3. G-protein (secondary messenger) may be involved as well.
34
Q

what don’t LAs do in regards to threshold & membrane potential?

A

LAs do not change membrane potential or threshold, the decrease in permeability of sodium slows the rate of depolarization such that threshold potential is not reached and an action potential is not propagated.

35
Q
  1. what do absorption and distribution do to LAs and what does it determine?
  2. What happens if you have a high concentration with quick offset (absorption and distribution)?
A
  1. absorption and distribution don’t determine onset like they do with volatile gasses; it determines duration of action and offset (blood takes the anesthetic away from the site of injection (where you want it) to the rest of the body (where you DON’T need it).
  2. This offset to the body can cause toxicity with high concentrations.
36
Q

what determines plasma concentration?

A

the rate of tissue distribution, the rate of drug clearance and tissue absorption.

37
Q

since blood takes the LA away from the site, the more vascular the site, the faster the maximum blood concentration (of the LA) is reached.
what is the order from highest to lowest for :brachial plexus, caudal, epidural, intercostals

A

first (most absorbed) to last

  1. intercostals
  2. caudal
  3. epidural
  4. brachial plexus
38
Q
  1. how do vasoconstrictors help local anesthetics?
  2. What LAs benefit the most from the vasoconstriction of epi? Name 3 of them.
  3. which LA has its own vasoconstriction properties
A
  1. vasoconstrictors reduce systemic absorption by decreasing blood flow to that area.
  2. This is especially true for short and intermediate acting LAs such as Procaine, Lidocaine & Mepivicaine.
  3. cocaine is a vasoconstrictor on its own (but is usually only used nasally)
39
Q

how much does epi prolong the effects of LAs

A

epi prolongs the effects of LAs by 50% (by decreasing distribution to the body, the LA has prolonged contact with neuronal tissue)

40
Q

In the spine epi does what (besides acting directly on the blood vessles)

A

it acts on alpha receptors which inhibit the release of substance P

41
Q
  1. what other medication can be added to LAs to decrease systemic absorption?
  2. what else does this medication do?
A
  1. clonidine (central acting alpha 2 agonist (alot less alpha 1)
  2. which prevents release of substance P and prolongs local anesthetic in spine).
42
Q

which LA has more chance of having high levels systemically:
amides or esters?
Why?

A

Amides have more of a chance of being and even going toxic

d/t the fact that esters are metabolized quickly by tissue plasmaesterases

43
Q
  1. excretion of LAs- what form are they excreted in?

2 If you acidify the urine, what happens (what would this be good for)?

A
  1. LAs are excreted as water soluble metabolites (converted by liver or plasma).
  2. acidifying the urine will create more of the ionized version of the tertiary amine base form to form a water soluble/charged form.
44
Q
  1. how are amides metabolized?

2. what organ issues can lead to Amide toxicity, can prolong duration by how many “times/X”?

A
  1. Amides links are metabolized in the liver by CP450 microsomal enzymes.
  2. toxicity is more common with amides in patients with liver failure (can prolong LAs presence in blood stream up to 3X longer).
45
Q

if you are giving a brachial block which direction will the block go (proximal to distal or distal to proximal)?

A

block goes from proximal to distal because mantle fibers are on the outside of the nerve and these service the proximal limb.

46
Q

if bupivicaine is given inadvertently for a Bier block, what would be your next step

A
  1. get interlipids ready
  2. get pacer and atropine ready
  3. release cuff slowly in increments of minutes
47
Q
  1. If your spinal level (sensory) is at L4, then your sympathetic block is at what level?
  2. What level is your motor block?
A
  1. your sympathetic level is L2 when your sensory is L4; sympathetic blocks are about 2 levels above your sensory block (blood pressure effects,? heart rate)
  2. Your motor block would be L6 (motor is 2 levels below your sensory block).
48
Q

name the short acting LAs

A

Procaine, Chloroprocaine

49
Q

name the medium acting LAs

A

Lidocaine, Mepivicaine, Prilocaine

50
Q

name the long acting LAs

A

Bupivicaine, Etidocaine, Ropivicaine, Tetracaine

51
Q
  1. how are esters metabolized?

2. which one is different?

A
  1. mainly in plasma and to some degree in liver

2. cocaine (which is metabloized in liver)

52
Q
  1. what are some conditions that could lead to issues with esters?
  2. what does this cause?
A
  1. a) liver disease (increased BUN)
    - -b) pregnancy
    - -c)chemotheraputics
  2. systemic toxicity

princip, pharm, phys, regional (18 decks)

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