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Week 1 Flashcards

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1
Q

How many nodes of Ranvier do you have to block to say you have a Block? And what type of conduction have you blocked?

A

3, Saltutory Conduction

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2
Q

If you breach the endoneurium for how long can you have numbness for?

A

4-6 months

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3
Q

Local Anesthetics are what?

A

Drugs that REVERSIBLY block the conduction of electrical impulses along nerve fibers

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4
Q

What influence their ability to produce systemic effects and possibly toxicity?

A

The intrinsic potency and fate of the drugs after absorption

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5
Q

Symptoms of toxicity can occur if administered how?

A

Local infiltration, intravenously or regionally. Pretty much any mode of administration may cause toxicity

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6
Q

Axon?

A

an extension of a centrally located neuron, it is the functional unit of peripheral nerves

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7
Q

Axolemma?

A

also known as Axoplasm, are the intracellular contents and are the major components of the axon

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8
Q

Schwann Cells?

A

It surrounds each axon and functions as support and insulation

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9
Q

Myelin

A

concentric layers of liquid substance in Schwann cells

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10
Q

Nodes of Ranvier

A

Small segments of nerve between Schwann Cells that do not contain myelin

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11
Q

On the Nerve which is the primary site at which LA exert their Action? and why?

A

Nodes of Ranvier; they have limited diffusion barriers for drugs to penetrate, they also contain large numbers of NA+ Channels

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12
Q

What is Saltatory Conduction?

A

Between Nodes of Ranvier where there are large numbers of sodium Channels and are able to generate an action potential so intense that it can jump from node to node; SIGNIFICANTLY FACILITATES CONDUCTION SPEED ALONG THE AXON

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13
Q

Which is harder to block myelinated nerves or unmyelenated nerves? and why?

A

Myelinated Nerves because they are better insulated and are larger, they conduct impulses faster

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14
Q

Fasciculi

A

Bundles of axons

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15
Q

LA must diffuse into what 3 connective tissue layers of the nerve for it to exert their pharmacologic action?

A

Endoneurium, Perineurium, and Epineurium

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16
Q

What is the Resting Membrane potential for neuronal membrane?

A

-70 to -90mV

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17
Q

Where is the Sodium Potassium pump located? and what does it do for membrane potential?

A

It is an active energy dependent process that create the resting Membrane Potential. It keeps a higher concentration of sodium ions outside the cell and a higher concentration of potassium ions inside the cell creating the voltage difference.

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18
Q

Name the 3 functional states of Sodium channels

A

Resting (closed), Open, and inactive

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19
Q

Which channel does the LA bind to?

A

Fast voltage-gated sodium channels within the axon. It prevents the sodium from rushing into the axon.

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20
Q

What does the ionized vs. unionized parts do on the nerve?

A

ionized form binds to the gated sodium channel while in the inactivated state and unionized form crossess the lipid bilayer to enter the neuron.

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21
Q

Cmin is what?

A

Minimum Blocking Concentration; its the lowest concentration of drug that is needed for blocking impulse propagation

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22
Q

what factors determine Cmin?

A

Temp, pH, Ca++ concentration of bathing solution, type of nerve being studied, site of action, dilution, systemic absorption, and degredation

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23
Q

Cmin is analogous to what other anesthetic parameter?

A

Minimal Alveolar Concentration (MAC)

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24
Q

What structure of LA is interchangeable with Ester or Amide?

A

Intermediate bond

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25
What are the 2 Types of LA?
Esters and Amide
26
What correlates with LA POTENCY?
Lipid solubility
27
What correlates with LA DURATION?
Protein binding
28
LA Onset of Action is INDIRECTLY correlated to what?
ionization of the LA
29
Which LA has a faster onset? a more ionized or unionized LA?
unionized; it crosses the lipid bilayer to produce LA effect.
30
3 LA that produces vasoconstriction?
Cocaine, Ropivacaine, and Lidocaine
31
Which 2 vasoconstrictive LA can be administered parentarally?
Lidocaine and Ropivacaine
32
How does Cocaine produce vasoconstrictive properties?
it blocks the reuptake of norepinephrine
33
What determines the peak plasma concentration?
Total dose NOT volume or Concentration
34
2 reasons Epinephrine is used with LA as an additive? What Epi concentration is normally used with LA?
Constricts vessels to reduce rate of vascular absorption and serves as marker for intravscular injections. 1:200,000 or 5mcg/ml
35
What are other additives other then Epinephrine that can be used in LA?
opioids, NaHCO3, ketorlac, hyaluronidase
36
Why are LA combined with NaHCO3?
LA are stored more acidic environment making the drug more ionized when administered into a patient acid + base= ionized. But by adding the bicarb it makes the LA more unionized when administered because base + base= unionized
37
In general what increases absorption of LA?
Tissue sites with increased Blood flow increase absorption.
38
Order of highest uptake to lowest uptake of LA
IV, Tracheal, Intercostal, Caudal, Paracervical, Epidural, Brachial plexus, Subarachnoid, Sciatc, Femoral, Subcutaneous In Time I Can Please Everyone But Susie and Sally
39
How does Ion trapping Occur?
LA overdose leads to Acidosis which increases ionization of the LA that prevents LA from crossing BBB trapping LA in Cerebral Cirulation
40
Ion Trapping in pregnancy
LA in maternal circulation and enters the fetus and equilibriates. Because fetus has a lower pH than mom LA becomes more ionized and unable to cross the placenta causing ion trapping
41
why is LA prepared slightly acidic?
improves the stability of the drug by increasing the concentration of the ionizedform of drug; when drugs sit unionized for a long period of time it will cause precipitate.
42
Weak acids want to unite with what ions?
positively charged ions: Na+ Mg++ or Ca++
43
Weak Bases unite with what ions?
Negatively charged ion; Cl- or SO4--
44
What drugs are weak acids?
Thiopental and other Barbiturate
45
Acid+Acid=
unionized
46
The more unionized a drug is it is easier? or harder? to cross the BBB and the Placenta?
easier
47
weak acids give up what?
Hydrogen ions
48
Will induction with sodium thiopental be faster if the patient is acidotic or alkalotic?
acidotic
49
Should you mix thiopental with a low pH solution?
No it may precipitate
50
Why is thiopental mixed and stored in a solution with pH=10-11?
Because it is a weak acid and by storing it in a basic solution it makes the drug more ionized decreasing the risk of precipitation of the drug
51
Arm to brain time is how long?
28-32 Sec
52
Base+Base=
more unionized
53
Acid+Baes
more ioniozed
54
Drugs that are weak bases?
Ketamine, opioids, and benzodiazepines
55
How are Ester LA metabolized?
By ester hydrolysis, Occurs through acions of esterase in plasma, red blood cells, and the liver. *PRIMARY- plasma choinesterase (rapidly metabolizes ester LA)
56
Other names for plasma Cholinesterase
Pseudocholinesterase and Butyrlcholinesterase
57
How are Amide LA metabolized?
Primarily by the liver by microsomal cytochrome P-450
58
Which is the least toxic amide LA? but what adverse effect can it cause?
Prilocaine clearance is 2.84L/min but it can cause methemoglobinemia
59
What main factors determine rate of elimination for amide metabolism?
Hepatic enzyme activity and blood flow
60
What is the most common cause of Local Anesthetic systemic Toxicity (LAST)?
The inadvertent intravascular injection and adminstration of excessive dose
61
What effect does LA have on the brain?
depression of neuronal function
62
Stimulatory activity in the CNS results from overdose of LA because?
LA selectively depresses inhibitory functions in the cerebral cortex letting the facilitory neurons functions go unopposed
63
If you have significant increase of LA in the Plasma what happens to the inhibitory and facilitory pathways?
They both get depressed causing generalized CNS depression
64
At what plasma level Concentration do you start seeing toxicity from LA?
5mcg/mL ; light headedness, tinnitus, cicumoral and tongue numbness
65
at 5 - 10mcg/mL what toxicity effects do you see from LA?
visual disturbance and Muscular twitching
66
at 10-15mcg/mL what toxicity effects do you see from LA?
convulsion and unconsiousness
67
at 15 -20mcg/ml what toxicity effects do you see from LA?
Coma
68
at 20-25mcg/mL what toxicity effects do you see with LA?
Respiratory arrest then CVS depression
69
What happens to PVS in low plasma toxic concentrations LA?
vasocontriction
70
What happens to SVR @ high plasma toxic concentrations of LA?
Vasodilation leading to hypotension
71
What happens to EKG with CV toxicity from LA?
Prolonged conduction time causing AV block, sinus brady, or cardiac arrest
72
Conductivity, automaticity, and pacing of the heart are affected in LA toxicity because?
Sodium Channels are blocked
73
Which is more cardio toxic? Bupivacaine or Ropivacaine?
Bupivacaine
74
What is the preservative in Amide?
Methylparaben
75
What is the preservative in Esters?
Para-Aminobenzoic Acid (PABA)
76
Which LA is more likely to have allergic reactions? and why?
Esters because of the PABA
77
Why does MetHgb happen when prilocaine or cetacaine is used?
they metabolize into O-toluidine which oxidizes Hgb and MetHgb
78
S/S of MetHgb?
brownish gray cyanosis, tachypnea and acidosis
79
How do you treat MetHgb?
Spontaneous reversal occurs within 2-3hrs. Or can administer Methylene Blue 1mg/kg it immediately reverses the MetHgb.
80
What pt population should you be vigilant in detecting Met Hgb and why?
Pt with sever anemia or heart failure because they can't tolerate decrease O2 carrying capacity
81
What pt population should you avoid MetHgb causing agents?
OB patients because 10%conversion of | FHgb to MetHgb leades to fetal cyanosis
82
How to prevent LAST
- ID patients at high risk - Pretreat with benzodiazepine 5-10min prior to LA - Know Toxic LA limits - Monitoring and having resuscitative drugs ready - Equipment - Aspirate frequently - Don't burn bridge of Communication
83
Treatment of LAST
- Bolus 20% intralipid 1.5ml/kg over 1min then continuous infusion 0.25ml/kg/min. - Double the infusion rate if BP returns but remains low - Continue the infusion for a minimum of 30min
84
EMLA cream should not be used in what pts?
<12 mos age
85
What is EMLA 5% cream composed of?
Lidocaine 25mg and Priolocaine 25mg
86
Where should you not inject Epinephrine?
fingers, nose, toes, and hose
87
Remember Lidocaine 2345678
234g/mol 56% Protein Bound pKa: 7.8
88
Esters LA are derivatives of what acid?
carboxylic acid
89
Is normal Hgb Fe++ or Fe+++?
Fe++
90
Fe+++ is what?
It is methemoglobin and can't bind to oxygen
91
Bupivacaine pKa and toxic dose?
pKa: 8.1 2. 5mg/kg w/o epi 3. 2mg/kg w/epi
92
Lidocaine pKa and toxic dose
pKa: 7.8 4mg/kg w/o epi 7mg/kg w/ epi
93
Mepivacaine pKa and toxic dose
pKa:7.6 4mg/kg w/o epi 7mg/kg w/ epi
94
Ropivacaine pKa and toxic dose
pKa: 8.1 3mg/kg w/o epi 3.5mg/kg w/ epi
95
What can you do when pt is allergic to and ester? when pt is unresponsive to epi and steroids?
Can give Methylene Blue

Regional 1 (2 decks)

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