Local Anesthetics

Question 1

Neurons maintain a resting membrane potential of?

Answer 1

-60 to -70 mV

Question 2

3 states of Na channels:

Answer 2

1. Resting (non conducting)
2. Open (conducting)
3. Inactivated (non conducting)

Question 3

Voltage-gated Na channels are membrane-associated proteins comprising of one large ___ subunit through which Na ions pass, and one or two smaller ____ subunits

Answer 3

Alpha; beta

Question 4

Ester LA are predominately metabolized by?

Answer 4

Pseudocholinesterase

Question 5

Amide LA are metabolized by?

Answer 5

P-450 metabolites in the liver

Question 6

Binding of which subunit prevents channel activation?

Answer 6

Alpha

Question 7

Local anesthetics have a greater affinity for Na channel when?

Answer 7

Open or inactivated state (not resting)

Question 8

What is the basis of the classification of LA as either esters or amides?

Answer 8

The nature of the intermediate chain

Question 9

LA consist of a _____ group separated from a _____ group by an intermediate chaine

Answer 9

Lipophilic; hydrophilic

Question 10

Factors that affect the minimum concentration of LA that will block impulse conduction:

Answer 10

Fiber size, myelination, pH, stimulation frequency, electrolyte concentration

Question 11

acid + acid & base + base =?

Answer 11

Non-ionized

Question 12

Acid + base = ?

Answer 12

Ionized

Question 13

Lipid solubility correlates with?

Answer 13

Potency of LA

Question 14

M-gate closed

Answer 14

Resting or closed phase

Question 15

M-gate and H-gate are open

Answer 15

Activated or open phase

Question 16

H-gate is closed

Answer 16

Inactivated phase

Question 17

LA interaction with which gate causes the effect? What charge is necessary?

Answer 17

H-gate; a positive charge

Question 18

Lipid soluble. Acid form. Generally hydrophobic. Readilly penetrates BBB/placenta

Answer 18

Non-ionized

Question 19

Water soluble. Charged form. Conjugate base form.

Answer 19

Ionized

Question 20

What drug is the exception to the rule that the closer pKa is to physiologic pH, the faster the onset? Is it protein bound?

Answer 20

Chloroprocaine (pKa 9.1) No protein binding

Question 21

What can be added to LA to prolong duration?

Answer 21

Epinephrine

Question 22

What can be added to LA to gain a quicker onset?

Answer 22

Bicarbonate

Question 23

What dose of bicarb is needed when using bupivacaine?

Answer 23

0.1 mEq per 20 ml of bupivacaine

Question 24

What dose of bicarb is needed when using Lidocaine?

Answer 24

1 mEq bicarb per 10 ml of lidocaine

Question 25

Which drugs will Epi not increase the duration? Why?

Answer 25

Bupivacaine, Etidocaine, & Ropivacaine. They have a long duration naturally

Question 26

Why is speed of onset slower when LA is injected into area of infection?

Answer 26

It increases the extent of ionization which slows diffusion through lipid bilayers

Question 27

The greater the amount of LA that exists in the _____ form, the faster the onset

Answer 27

Unionized

Question 28

Short acting LA

Answer 28

Procaine & Chloroprocaine

Question 29

Intermediate acting LA

Answer 29

Lidocaine, Mepivacaine, Prilocaine

Question 30

Long acting LA

Answer 30

Bupivcavine, Etidocaine, Tetracaine

Question 31

LA with high pKa:

Answer 31

Are highly ionized at physiologic pH

Has to have an open (activated) Na channel for effect

Question 32

The nerves with frequent depolarization have greater susceptibility to LA with high pKa:

Answer 32

Sensory nerves & autonomic nerves

Question 33

Sympathetic block is ___ dermatomes _____ than sensory block

Answer 33

2-6; higher

Question 34

Motor block is ___ dermatomes ____ than sensory block

Answer 34

2; lower

Question 35

How does the LA progress in a blockade?

Answer 35

Autonomic, Temperature, Pain (ATP)
Touch, Pressure (TP)
Motor, Vibratory, Proprioception (MVP)

Question 36

_______ must be blocked to stop nerve conduction myelinated axons

Answer 36

2-3 nodes of Ranvier

Question 37

Weak acids combine with ______ charged ions such as:

Answer 37

Positive; Na, Mg, Ca

Question 38

Weak bases combine with ______ charged ions such as:

Answer 38

Negatively; chloride & sulfate

Question 39

Should a weak acid be stored in a low or high pH solution? Why?

Answer 39

High (base). Ionized form should not precipitate