Intro to Regional Anesthesia - PM

Question 1

Local Anesthetics are?

Answer 1

Drugs that reversibly bind to voltage-gated sodium channels (NAv)

Question 2

NAv channels have what three functional states?

Answer 2

resting (closed), open, inactive

Question 3

Symptoms of toxicity can occur from any route of administration, but what is the most prominent method?

Answer 3

Inadvertent intravascular injection

Question 4

What is the antidote for local anesthetics?

Answer 4

Time, there is no reversal agent

Question 5

What are the two intermediate carbon groups?

Answer 5

Esters and amides

Question 6

What is responsible for the classification of Local Anesthetic?

Answer 6

the intermediate linkage

Question 7

What are the 5 Esters?

Answer 7

Procaine, Chloroprocain, Tetracaine, Cocaine, Benzocaine

Question 8

What are the Amides?

Answer 8

Lidocaine, Mepivacaine, Prilocaine, Bupivacaine, Ropivacaine, Articaine. (They all have two i’s)

Question 9

Lipophilic

Answer 9

means fat loving. Wants to bind to lipids.

Question 10

Hydrophobic

Answer 10

means fear of water.

Question 11

In general, duration of action is mostly correlated with?

Answer 11

Protein binding, so the more protein bound a LA is, the longer the duration of action.

Question 12

In general, what correlates most with potency?

Answer 12

Lipid solubility. A LA’s high lipid solubility equals a high level of potency.

Question 13

pKa

Answer 13

expresses relationship between uncharged (non-ionized & lipid soluble) and charged (ionized & water soluble) drug concentrations. The drug specific pKa is the pH at which the concentrations are 50/50.

Question 14

LA’s typically have what kind of base?

Answer 14

Weak (pka’s higher than 7.45) (Lower than 7.35 would be a strong base)

Question 15

What does adding a vasoconstrictor do to a LA?

hint - 5 things

Answer 15

1. Limits spread of agent
2. longer duration of effect
3. Reduces systemic absorption
4. Hemostasis for improved visulization
5. Possibility of using a smaller dose of LA overall

Question 16

What are potential negative effects of using a vasoconstrictor and a LA together?

Answer 16

Tissue ischemia leading to necrosis in end organ

Question 17

Use of Epi with an LA is contraindicated in/on?

Answer 17

nose, fingers, toes, or penis, and should be avoided in avulsed flaps and areas with tenuous blood supply.

Question 18

What is the reversal of epi if injected into contraindicated tissue?

Answer 18

phentolamine (1.5-5mg)

Question 19

LA prepackaged with epi are usually indicated with what?

Answer 19

Red top and red lettering on label

Question 20

What does buffering an unionized drug with Sodium Bicarb do?

Answer 20

Speeds its penetration to the nerve tissue

Question 21

What are the LA’s that possess mild vasoconstrictive properties?

Answer 21

Ropivacaine and Lidocaine

Question 22

Most LA’s produce 1._____ that results in increased 2. _____ which can lead to an increase in LA 3.______ . This in turn shortens the duration of 4._____ and increased the probability of 5. ____ effects.

Answer 22

1. relaxation of vascular smooth muscles
2. vasodilation and increased blood flow
3. absorption
4. action
5. toxic

Question 23

Cocaine (in a clinical setting) is only administered in what way?

Answer 23

topically

Question 24

What tissue receives the greatest amount of LA from distribution?

Answer 24

muscle tissue (acts as a depot due to greater tissue mass)

Question 25

Primary method of metabolism for Esters?

Answer 25

ester hydrolysis - which occurs through the action of esterase in plasma, RBC’s, and liver. Primarily, plasma cholinesterase rapidly metabolizes esters.

Question 26

Primary method of metabolism for amides?

Answer 26

In the Liver by microsomal cytochrome p-450 enzymes. (dependent on hepatic blood flow and p-450)

Question 27

LA’s exert their action by inhibiting what?

Answer 27

The passage of NA ions through nerve membranes.

Question 28

How do LA’s prevent normal function of afferent neurons?

Answer 28

by stabilizing the excitable tissue in the region of application.

Question 29

What does LAST stand for?

Answer 29

Local Anesthetic Systemic Toxicity

Question 30

Most common symptom of LAST (life threatening)

Answer 30

Seizures

Question 31

Most common cause of LAST

Answer 31

inadvertent vascular injection

Question 32

Signs of CNS toxicity

Answer 32

mild effects:
tongue numbess
apprehension
restlessness
peri-oral tingling
tremors
slurred speech, 
drowsiness
cardiorespiratory depression
of course seizures
Coma & Death

Question 33

What concentration of lidocaine plasma would you see circumoral numbness?

Answer 33

5 mcg/ml (from lecture, possible test question)

Question 34

Signs of toxicity Cardiovascular

Answer 34

palpitations, HTN, ventricular dysrhythmia, myocardial depression, bradycardia, hypotension, cardiovascular collapse.

Question 35

Signs of toxicity on Peripheral vascular system (PVS)

hint: Biphasic

Answer 35

Low concentrations, LA produce vasoconstriction and an increase in SVR.
As doses increase, vasodilation begins to occur resulting in significant hypotension

Question 36

If your injecting a patient with LA’s, how long should you be watching them?

Answer 36

Should be watching them for at least 10 minutes, but most s/s of toxicity will occur within the first 5 minutes of administration.

Question 37

True allergies are common or rare?

Answer 37

Rare

Question 38

Which is more likely to cause an allergic reaction, ester or amides?
Why?

Answer 38

Esters

Due to preservative para-aminobenzoic acid (PABA)

Question 39

Toxicity-Methemoglobinemia

Answer 39

Prilocaine (Citanest)
the metabolite o-toluidine oxidies hemoglobin to methemoglobin.
Results in tachypnea, metabolic acidosis, and brownish-gray cyanosis.

Question 40

How is Toxicity-Methemoglobinemia reversed?

Answer 40

Spontaneus reversal over 2 to 3 hours, or by administration of methylene blue (1mg/kg)

Question 41

What is the “vacuum cleaner” drug?

Answer 41

Intrallipid - bolus 20% 1.5ml/kg over 1 minute. Is a reversal agent for signs/symptoms of toxicity.

Question 42

What effect does LA toxicity have on a patients electrical function of the heart?

Answer 42

Increases PR interval and duration of QRS complex. Progresses to sinus bradycardia, complete AV block, and/or cardiac arrest.